Document MJORGwD8YNvRR02pK0pqkkaRL

Patented Jan. 20, 1942 2,270,783 > * t * iK A UNITED STATES PATENT OFFICE 2,270,783 ELECTROCHEMICAL METHOD OF PRODUCING WHITE LEAD Guimard E. Johnson, Hammond, Reginald G. Bowman, Gary, and William J. Knox, Jr., Ham mond, Ind., assignors to International Smelt ing and Refining Company, East Chicago,. Ind., a corporation of Montana No Drawing. Application December 6, 1937, Serial No. 178,352 4 Claims. (Cl. 204--88) This invention relates to the production of into the catholyte which is also acted upon by white lead and has for an object the provision of the current, the acetate ions replacing a part certain improvements in processes for producing of the hydroxide and carbonate ions that migrate white lead. More particularly, the invention con to the anolyte. This is compensated for by per- templates the provision of certain improvements 5 mitting a certain amount of seepage of catholyte in processes for producing white lead by elec into anolyte through the diaphragm. The seep trolysis. age is controlled by selecting a diaphragm fabric The present-day commercial process for pro of the desired porosity for a given hydrostatic ducing white lead electrolytically is carried out in solution head of catholyte of a selected composi- a so-called bi-fluid cell having a lead anode and 10 tion in the cathode compartment. The addition an iron cathode separated by a porous dia of relatively small amounts of anolyte to catho phragm. The anode is surrounded by an elec lyte and catholyte to anolyte permits adjusting trolyte (the anolyte) containing sodium acetate the sodium concentration of the two electrolytes and a very small amount of sodium carbonate. and the conservation of chemicals, since all The cathode is surrounded by an electrolyte (the 13 make-up solution can then be added to the catholyte) containing sodium acetate and a rela anolyte in the form of filtrate from the filters. tively large amount of sodium carbonate. Each All anolyte in the filter cakes is replaced by electrolyte is maintained in rapid circulation water by a counter current washing operation about its electrode. The circulation systems of and returned to the anolyte circulation system. the two electrolytes are entirely Independent 20 In addition, wash water filtrate Is also returned and no communication .exists between the cath as required to replenish the losses enumerated olyte and anolyte in the cell except through the above. As the volume of solutions transferred diaphragni in the cell. between the two electrolytes is very small the In practice, a small amount of N&2CO3, not ex anolyte as previously stated is essentially free ceeding about .05%, is added to the anolyte be 25 of the reacting salts and they are only brought fore placing the electrolytic cells in operation. into the zone where the white lead Is precipitated When the current is turned on, the lead dis in electro-chemical equivalent amounts, there is solves from the surface of the anode and is im never an excess present to alter the reaction or mediately precipitated as white lead at a slight influence the size of the particle. distance from the anode surface. The precipitate 30 The white lead which is removed continuously is carried down through the cell by the descend from the cell by the circulation of the anolyte, ing current of anolyte in a thick cloud without is removed from the anolyte by settling and depositing on the anode surface. Hydrogen and filtering. The filter pulp is washed, dried, ground the hydroxide ions are liberated at the cathode. and air floated, and is then barrelled in a dry The hydroxide and carbonate ions of the hy 35 pulverulent form. The clear anolyte is recircu drolyzed sodium carbonate (NasCOa) . of the lated through the cell. catholyte migrate through the diaphragm to The composition of the anolyte during its pas ward the anode, replenishing the anions removed sage through the cell remains unchanged except z from the anolyte by precipitation of the lead Ions. for a small increase in the acetate concentration. By this electrolytic migration, the electro-chemi 40 This is controlled by dilution with wash water cal equivalent amount of anions required to pre from the filter. The catholyte is depleted in car cipitate the lead cations as they are dissolved at bonate ions and a small percent of acetate ions, the anode are transported to the anolyte. Slight and enriched in hydroxide ions during its passage traces of carbonate can be detected in the anolyte through the cathode compartment of the cell. but it is entirely free of dissolved lead salts. 45 The excess of hydrate ions is neutralized and the However, {.here is no sodium carbonate (NasCOs) loss in carbonate ions restored by passing the present in the solution film in contact with the catholyte through carbonation towers, in which anode. The foregoing outlines the major reaction. In a stream of descending solution passes through a rising stream of COa gas from a coke burning practice,, in order to replenish and conserve 60 boiler. The acetate loss is replenished as noted chemicals and to restore the loss In volume of by running a small stream of anolyte Into the catholyte due to decomposition of water at the catholyte after it is discharged from the cells. cathode, evaporation and mechanical losses, In the United States patent to Ralph M. Har anolyte is added to the catholyte in a small con rington. No. 1,308,948, it is recognized that the tinuous stream. This introduces sodium acetate 69 character and quality of the white lead product *;. z$k PNY C00G06 3d1 ' 2 2,270,783 may be controlled by regulating the amount of ide. "Excess carbonation," as used herein and carbon dioxide supplied to the catholyte, and it as understood in the art, means carbonation In Is further recognized that in order to obtain excess of that required to maintain the bicar rapid carbon dioxide absorption and at the same bonate ion concentration of the anolyte at the time avoid precipitation of white lead on the 5 value necessary for the production of a white anode, it is necessary to maintain the catholyte lead product of desired composition. The alkali as compared with the anolyte relatively strongly metal hydroxide may be added to the anolyte alkaline. in any suitable manner as, for example, by dis We discovered that the composition of the solving the hydroxide in the anolyte outside the white lead produced varies directly with the 10 cell, by adding a preformed solution of the hy HCO3 ion or bicarbonate content of the anolyte. droxide to the anolyte outside the cell, or by add Our investigations have indicated that the white ing catholyte high in hydroxide (after electroly lead formation is represented by the following sis and prior to carbonation) to the anolyte out reaction equation: side the cell. Each of these procedures effects 3Pb(CaH302) 2+4Na2C03+2H20= 2PbC03'Pb(0H)3+2NaHC03-f6NaC3H30a 16 the desired control of the bicarbonate ion con centration in the anolyte, and hence the compo sition of the precipitated white lead, in a man The composition of the basic lead salt precipi ner such that tl.,, Edition of ions not entering tated varies with the pH value of the solution in into the composition of the precipitated white which it Is formed. It will be apparent, there 20 lead is not substantially greater than the loss of fore, that if only sodium carbonate (NaaCCh) such ions in the course of normal operation of and lead acetate (Pb(C2H3C>3)3> were supplied to the cell. The solution of hydroxide for addition the solution, the sodium bicarbonate (NaHC03) to the anolyte may be formed by employing as content would progressively increase and the solvent the filtrate normally employed as make- ratio of HCO3 to OH ions in the resulting pre 26 up solution. The invention permits simplifica cipitated lead salt would increase until finally tion of the carbonation operation and provides only PbC03 would be produced. In other words a simple method of maintaining a supply of the carbon dioxide (COa) content of the precipi anolyte of the proper concentration with respect tated white lead bears a direct relation to the to bicarbonate. Instead of controlling the car- sodium bicarbonate (NaHC03) concentration of 80 bonation operation to completely or partially the anolyte. This has been found to be true in neutralize the catholyte solution from the cell actual operation. In order to control the com (depleted in carbonate Ion and high in hydrox position of the white lead produced, therefore, ide) and, in the case of the partially neutralized it is necessary to control the NaHCCh content of catholyte, adding an acid or bicarbonate to the the anolyte. 86 anolyte to compensate for the incomplete neu Our discovery of the effect of the HCO3 ion or tralization. the carbonation operation may be bicarbonate content of the anolyte on the com permitted to proceed to the point at which ex position of the white lead produced Is described cess carbonation is effected without the necessity in our United States Patent No. 1,845.713, dated for exercising extreme caution to secure exact February 16, 1932, which covers control of the 40 neutralization or accurate deficient carbonation. bicarbonate content of the anolyte by maintain The invention simplifies the process also by elim ing a uniform and deficient carbonation of the inating the necessity for exact control of addi catholyte and adding an acid or a bicarbonate tion of catholyte to anolyte by electrolysis and by to the anolyte. seepage through the diaphragm to meet changes Our aforementioned patent also points out that 45 in operating conditions. The composition of it is desirable that the carbonate salt content of anolyte thus harmfully altered can be adjusted the anolyte be kept low--much lower than is re readily by the method of the invention. In the quired in order to avoid formation of white lead preferred method of the invention, the carbona incrustations on the anode--in order to permit tion operation is so controlled as to effect sub- washing the white lead free of these salts in the 50 stantlally uniform and excess carbonation of the finishing of the white lead separated from the catholyte for each particular set of operating anolyte. This is important in the commercial conditions designed to produce a product of par production of white lead by the electrolytic ticular composition. method, since the presence of any considerable In accordance with our invention, using a bi- amount of alkali metal carbonate in the white 55 fluid cell with a lead anode suspended in an lead product renders it unfit for use as paint pig anolyte capable of yielding a solvent for the lead, ment. We have found that the difficulty in e. g., sodium acetate, and a suitable inert cath washing the white lead sufficiently free of ad ode suspended In a catholyte containing sodium sorbed salts increases with Increasing concentra carbonate and separated from the anolyte by a tion of carbonate salt in the anolyte to a point at which it is practically impossible to eliminate suitable diaphragm, and to which an excess of carbon dioxide (CO2) is supplied in the carbona them. This may be explained by adsorption of tion operation, the anolyte solution is sampled the salts in the white lead particles, but It seems and analyzed at regular Intervals, say every hour, more probable that a reaction may occur as fol and Its bicarbonate content adjusted to and lows: 55 maintained at the desired figure by the addition of an alkali metal hydroxide, as pointed out 2(2PbC03.Pb(0H)a) +Na3C03-f-NaHC03= above. 3NftPba(C03) aOH+HaO For example, in a cell operated at a current whereby the carbonate salt becomes chemically density of 30 amperes per square foot of cathode combined and therefore very difficult or impos 70 area and producing approximately .011 pound of sible to remove. Our present invention provides for control of white lead per ampere hour and operating at an anolyte displacement rate of 18 gallons per min the bicarbonate content of the anolyte by means of excess carbonation of the catholyte and the ute while maintaining uniform and excess car bonation of the catholyte, the sodium bicarbon- addition to the anolyte of an alkali metal hydrox 75 ate content of the anolyte is maintained at l PNYC000083Q2 * * u 2,270,783 3 0.0561% through adjustment by the addition of re-use of the regenerated cathoiyte. the compo sodium hydroxide thereto to produce a white lead sition of the precipitated white lead being con containing 11.60% of carbon dioxide (COa). To trolled by reference to the bicarbonate ion con produce white lead of greater or smaller COa centration in the anolyte, the improvement which content the acid carbonate content of the anolyte a comprises adjusting the bicarbonate ion concen may be increased or decreased by the addition of tration in the anolyte by subjecting the cathoiyte lesser or greater amounts, respectively, of sodium to excess carbonation and adding to the anolyte hydroxide. The exact acid carbonate content re a sufficient amount of uncarbonated cathoiyte quired for the production of a particular white containing hydroxyl ions to establish in the lead product should be determined in each In- io anolyte bicarbonate tons in the desired concen stance by experiment. The carbonate salt con tration. whereby addition of ions not entering tent of the analyte U maintained at not ex -V TZjfz into the composition of the prec.ipita*a/% whit* Ut sc*. rcic. *iz sgr *1.25*"^- . h u l TTS5ma> less. `tnrrr. srx ro>?- sainr. `wss- n\ 'rwr K 'turrmC. * hundredths of one percent (0.06%). The signifi 15 the cell. cance of the limited carbonate salt content of the 3. In the process of producing white lead of anolyte specified may be appreciated by com constant particular composition by electrolysis in parison with the limitation of the carbonate salt - ^ifluld cell in which the Ua.d is precis* content of the anolyte necessary to avoid trouble tated in an anolyte capable under electrolysis of some precipitation of white lead on the anode in 20 yielding a lead solvent and containing bicarbon accordance with the Harrington patent. In this ate salt, the steps which consist in determining case the carbonate salt content of the anolyte the bicarbonate ion concentration In the anolyte may run as high as six tenths of one percent corresponding to the precipitation of white lead (0.60%), which content, however, will produce of the particular composition, and maintaining white lead containing so much carbonate salt 23 said bicarbonate ion content in the anolyte by that it is not feasible in commercial operation to maintaining a uniform and excess carbonation wash It sufficiently free of such salt as to pro of the cathoiyte and by adding an alkali metal duce a first grade white lead paint pigment. hydroxide to the anolyte in such an amount that We claim: the amount of added alkali metal ions is not sub- 1. In a process of producing white lead of con sn stantially In excess of the amount of alkali metal stant particular composition by electrolysis in a blfiuid cell Involving the use of an anolyte ca ions lost in the course of normal operation of the cell but sufficient to establish In the anolyte pable under electrolysis of yielding a lead solvent bicarbonate ions in the desired concentration for and containing a bicarbonate and of a cathoiyte precipitation of white lead of the particular com- containing a carbonate which is altered during 35 position. the course of the process by removal of carbon 4. In a process of producing white lead of con ate ions, and involving carbonation of the cath stant particular composition by electrolysis in a oiyte to restore carbonate Ions thereto and re-use bifluid cell involving the use of (1) an anolyte of the regenerated cathoiyte, the composition of capable under electrolysis of yielding a lead sol the precipitated white lead being controlled by id vent and containing & carbonate and a bicar reference to the bicarbonate ion concentration in bonate and (2) a cathoiyte containing a car the anolyte, the improvement which comprises bonate which is altered during the course of the adjusting the bicarbonate ion concentration in process by removal of carbonate ions, and in the anolyte by subjecting the cathoiyte to ex volving carbonation of the cathoiyte to restore. cess carbonation and by incorporating hydroxyl 43 carbonate Ions thereto and re-use of the regen Ions in the anolyte in the form of a soluble metal erated cathoiyte, the composition of the precipi hydroxide in such an amount that the amount tated white lead being controlled by reference to of added metal ions of said hydroxide is not sub the bicarbonate ion concentration in the anolyte. stantially in excess of the amount of metal ions the improvement which comprises maintaining lost in the course of normal operation of the cell, 50 the carbonate concentration in the anolyte at or the amount of metal hydroxide incorporated in below a predetermined maximum which is sub the anolyte being sufficient to establish therein stantially less than the concentration resulting In bicarbonate ions in the desired concentration, objectionable deposition of white lead on the whereby the addition of ions not entering Into anode, and adjusting the bicarbonate ion con- the composition of the precipitated white lead is 55 centration in the anolyte by subjecting a portion not substantially greater than the loss of such of the cathoiyte to excess carbonation and by ions in the course of normal operation of the adding to the anolyte the remaining portion of cell. uncarbonated cathoiyte containing sodium hy 2. In a process of producing white lead of con droxide to establish In the anolyte bicarbonate stant particular composition by electrolysis in a <j u Ions in the desired concentration, whereby the blfiuid cell involving the use of an anolyte ca concentration of ions not entering into the com pable under electrolysis of yielding a lead sol position of the precipitated white lead is not in vent and containing a bicarbonate and a cath creased in the course of normal operation of the oiyte containing a carbonate which is altered cell. during the course of the process by removal of u j GUNNARD E. JOHNSON. carbonate Ions, and involving carbonation of the REGINALD G. BOWMAN. cathoiyte to restore carbonate Ions thereto and WILLIAM J. KNOX, Jr . ! I Ps^o00 Patented Jan. 20, 1942 2,270,783 UNITED STATES PATENT OFFICE 2,270,783 ELECTROCHEMICAL METHOD OF PRODUCING WHITE LEAD Gunaard E. Johnson, Hammond, Reginald G. Bowman, Gary, and William J. Knox, Jr., Ham mond, Ind., assignors to International Smelt ing and Refining Company, East Chicago, Ind., a corporation of Montana No Drawing. Application December 6,1937, Serial No. 178,352 4 Claims. '(CL 204--88) This invention relates to the production of into the catholyte which is also acted upon by white lead and has for an object the provision of the current, the acetate ions replacing a part certain improvements in processes for producing of the hydroxide and carbonate ions that migrate white lead. More particularly, the invention con to the anolyte. This is compensated for by per- templates the provision of certain improvements g mitting a certain amount of seepage of catholyte in processes for producing white lead by elec into anolyte through the diaphragm. The seep trolysis. age is controlled by selecting a diaphragm fabric The present-day commercial process for pro of the desired porosity for a given hydrostatic ducing white lead electrolytically is carried out in solution head of catholyte of a selected composi- a so-called bi-fiuid cell having a lead anode and 10 tion tn the cathode compartment. The addition an iron cathode separated by a porous dia of relatively small amounts of anolyte to catho phragm. The anode is surrounded by an elec lyte and catholyte to anolyte permits adjusting trolyte (the anolyte) containing sodium acetate and a very small amount of sodium carbonate. the sodium concentration of the two electrolytes and the conservation of chemicals, since all The cathode is surrounded by an electrolyte (the 15 make-up solution can then be added to the catholyte) containing sodium acetate and a rela anolyte in the form of filtrate from the filters. tively large amount of sodium carbonate. Each All anolyte in the filter cakes Is replaced by electrolyte is maintained in rapid circulation water by a counter current washing operation about its electrode. The circulation systems of and returned to the anolyte circulation system. the two electrolytes are entirely independent 20 In addition, wash water filtrate is also returned and no communication exists between the cath as required to replenish the losses enumerated olyte and anolyte in the cell except through the above. As the volume of solutions transferred diaphragm in the cell. between the two electrolytes is very small the In practice, a small amount of NaaCOs, not ex anolyte as previously stated is essentially free ceeding about .05%, is added to the anolyte be 25 of the reacting salts and they are only brought fore placing the electrolytic cells in operation. into the zone where the white lead is precipitated When the current is turned on, the lead dis in electro-chemical equivalent amounts, there is solves from the surface of the anode and is im never an excess present to alter the reaction or mediately precipitated as white lead at a slight influence the size of the particle. distance from the anode surface. The precipitate 30 The white lead which is removed continuously is carried down through the ceil by the descend from the cell by the circulation of the anolyte. ing current of anolyte in a thick cloud without is removed from the anolyte by settling and depositing on the anode surface. Hydrogen and filtering. The filter pulp is washed, dried, ground the hydroxide ions are liberated at the cathode. and air floated, and is then barrelled in a dry The hydroxide and carbonate ions of the hy 35 pulverulent form. The clear anolyte is recircu drolyzed sodium carbonate (NaaCO:) of the lated through the cell. catholyte migrate through the diaphragm to The composition of the anolyte during Its pas ward the anode, replenishing the anions removed sage through the cell remains unchanged except from the anolyte by precipitation of the lead Ions. for a small increase in the acetate concentration. By this electrolytic migration, the electro-chemi 40 This is controlled by dilution with wash water cal equivalent amount of anions required to pre from the filter. The catholyte Is depleted in car cipitate the lead cations as they are dissolved at bonate ions and a small percent of acetate ions, the anode are transported to the anolyte. Slight and enriched in hydroxide ions during its passage traces of carbonate can be detected In the anolyte through the cathode compartment of the cell. but it is entirely free of dissolved lead salts. 45 The excess of hydrate ions is neutralized and the However, there is no sodium carbonate (NaaCOs) loss in carbonate ions restored by passing the present In the solution film in contact with the catholyte through carbonation towers, in which anode. a stream of descending solution passes through a The foregoing outlines the major reaction. In rising stream of COa gas from a coke burning practice, in order to replenish and conserve 50 boiler. The acetate loss is replenished as noted chemicals and to restore the loss in volume of by running a small stream of anolyte into the catholyte due to decomposition of water at the catholyte after it is discharged from the cells. cathode, evaporation and mechanical losses, In the United States patent to Ralph M. Har anolyte is added to the catholyte in a small con rington, No. 1,308,948, it is recognized that the tinuous stream. This Introduces sodium acetate 55 character and quality of the white lead product PNYC0C008384 2 2,270,783 may be controlled by regulating the amount of ide. "Excess carbonation," as used herein and carbon dioxide supplied to the catholyte, and it as understood in the art, means carbonation In is further recognized that in order to obtain excess of that required to maintain the bicar rapid carbon dioxide absorption and at the same bonate ion concentration of the anolyte at the time avoid precipitation of white lead on the 5 value necessary for the production of a white anode, it is necessary to maintain the catholyte lead product of desired composition. The alkali as compared with the anolyte relatively strongly metal hydroxide may be added to the anolyte alkaline. in any suitable manner as. for example, by dis We discovered that the composition of the solving the hydroxide in the anolyte outside the white lead produced varies directly with the 10 cell, by adding a preformed solution of the hy HCOa Ion or bicarbonate content of the anolyte. droxide to the anolyte outside the cell, or by add Our Investigations have indicated that the white ing catholyte high In hydroxide (after electroly lead formation is represented by the following sis and prior to carbonation) to the anolyte out reaction equation: side the cell. Each of these procedures effects 3Pb(CiHb0j)j+4NaiC03+2H20= 2PbCOj-Pb(OH)a+2NaHCOj+6NaCittiOi 18 the desired control of the bicarbonate ion con centration in the anolyte. and hence the compo sition of the precipitated lead, in a man The composition oi u.e basic lead salt precipi- ner such that uie audition ui uns not entering tated varies with the pH value of the solution in into the composition of the precipitated white which It is formed. It will be apparent, there- 20 lead is not substantially greater than the loss of fore, that if only sodium carbonate (N&aCOs) such ions in the course of normal operation of and lead acetate (P^CsHbOala) were supplied to the cell. The solution of hydroxide for addition the solution, the sodium bicarbonate (NaHCOa) to the anolyte may be formed by employing as content would progressively increase and the solvent the filtrate normally employed as make ratio of HCO3 to OH ions in the resulting pre- jg up solution. The invention permits simplifica cipitated lead salt would increase until finally tion of the carbonation operation and provides only PbCOa would be produced. In other words a simple method of maintaining a supply of the carbon dioxide (COa) content of the precipi anolyte of the proper concentration with respect tated white lead bears a direct relation to the to bicarbonate. Instead of controlling the car sodium bicarbonate (NaHCOi) concentration of 30 bonation operation to completely or partially the anolyte. This has been found to be true in neutralize the catholyte solution from the cell actual operation. In order to control the com (depleted in carbonate ion and high in hydrox position of the white lead produced, therefore, ide) and, in the case of the partially neutralized it Is necessary to control the NaHC03 content of catholyte. adding an acid or bicarbonate to the the anolyte. 35 anolyte to compensate for the incomplete neu Our discovery of the effect of the HCO3 Ion or tralization. the carbonation operation may be bicarbonate content of the anolyte on the com permitted to proceed to the point at which ex position of the white lead produced is described cess carbonation is effected without the necessity in our United States Patent No. 1.845,713, dated for exercising extreme caution to secure exact February 16, 1932, which covers control of the 40 neutralization or accurate deficient carbonation. bicarbonate content of the anolyte by maintain The Invention simplifies the process also by elim ing a uniform and deficient carbonation of the inating the necessity for exact control of addi catholyte and adding an acid or a bicarbonate tion of catholyte to anolyte by electrolysis and by to the anolyte. seepage through the diaphragm to meet changes Our aforementioned patent also points out that 43 In operating conditions. The composition of it is desirable that the carbonate salt content of anolyte thus harmfully altered can be adjusted the anolyte be kept low--much lower than is re readily by the method of the-invention. In the quired in order to avoid formation of white lead preferred method of the invention, the carbona incrustations on the anode--in order to permit tion operation is so controlled as to effect sub washing the white lead free of these salts in the 60 stantially uniform and excess carbonation of the finishing of the white lead separated from the catholyte for each particular set of operating anolyte. This is important in the commercial conditions designed to produce a product of par production of white lead by the electrolytic ticular composition. method, since the presence of any considerable In accordance with our invention, using a bi- amount of alkali metal carbonate in the white 55 fluid cell with a lead anode suspended in an lead product renders it unfit for use as paint pig anolyte capable of yielding a solvent for the lead, ment. We have found that the difficulty in e. g.. sodium acetate, and a suitable inert cath washing the white lead sufficiently free of ad ode suspended in a catholyte containing sodium sorbed salts increases with increasing concentra carbonate and separated from the anolyte by a tion of carbonate salt in the anolyte to a point fto suitable diaphragm, and to which an excess of at which it is practically impossible to eliminate carbon dioxide (COa> is supplied in the carbona them.' This may be explained by adsorption of the salts in the white lead particles, but It seems more probable that a reaction may occur as fol lows : 2(2PbCOjJPb(OH> 7) +NaaC03+NaHC03= 3NaPb*<COj ) aOH-I-HaO tion operation, the anolyte solution is sampled and analyzed at regular intervals, say every hour, and its bicarbonate content adjusted to and maintained at the desired figure by the addition of an alkali metal hydroxide, as pointed out above. For example, in a cell operated at a current whereby the carbonate salt becomes chemically density of 30 amperes per square foot of cathode combined and therefore very difficult or impos- 70 area and producing approximately .011 pound of sible to remove. white lead per ampere hour and-operating at an Our present invention provides for control of anolyte displacement rate of 18 gallons per min the bicarbonate content of the anolyte by means ute while maintaining uniform and excess car of excess carbonation of the catholyte and the bonation of the catholyte, the sodium bicarbon addition to the anolyte of an alkali metal hydros- 7# ate content of the anolyte is maintained at d w- PNYCCC008365 2,270,783 3 0.0561% through adjustment by the addition of re-use of the regenerated catholyte, the compo sodium hydroxide thereto to produce a white lead sition of the precipitated white lead being con containing 11.60% of carbon dioxide <COa). To trolled by reference to the bicarbonate ion con produce white lead of greater or smaller COa centration in the anolyte, the improvement which content the acid carbonate content of the anolyte 6 comprises adjusting the bicarbonate ion concen may be increased or decreased by the addition of tration in the anolyte by subjecting the catholyte lesser or greater amounts, respectively, of sodium to excess carbonation and adding to the anolyte hydroxide. The exact acid carbonate content re a sufficient amount of uncarbonated catholyte quired for the production of a particular white containing hydroxyl ions to establish In the lead product should be determined in each in- 10 anolyte bicarbonate ions in the desired concen stance by experiment. The carbonate salt con tration, whereby addition of ions not entering tent of the anolyte Is maintained at not exceed into the composition of the precipitated white ing about twenty-five one-hundredths of one per lead is not substantially greater than the loss of cent (0.25%), and preferably less than six one- such ions in the course of normal operation of hundredths of one percent (0.06%). The signifi- 15 the cell. cance of the limited carbonate salt content of the 3. In the process of producing white lead of anolyte specified may be appreciated by com constant particular composition by electrolysis in parison with th^mitation of the carbon.^ salt a bif!' ;j, ir. . white lead is precipi content of the anolyte necessary to avoid trouble tated in an anolyte capable under electrolysis of some precipitation of white lead on the anode In id yielding a lead solvent and containing bicarbon-, accordance with the Harrington patent. In this ate salt, the steps which consist in determining case the carbonate salt content of the anolyte the bicarbonate ion concentration in the anolyte may run as high as six tenths of one percent corresponding to the precipitation of white lead (0.60%), which content, however, will produce of the particular composition, and maintaining white lead containing so much carbonate salt 23 said bicarbonate ion content in the anolyte by that It is not feasible in commercial operation to maintaining a uniform and excess carbonation wash it sufficiently free of such salt as to pro of the catholyte and by adding an alkali metal duce a first grade white lead paint pigment. hydroxide to the anolyte in such an amount that We claim: the amount of added alkali metal ions is not sub 1. In a process of producing white lead of con- so stantially in excess of the amount of alkali metal stant particular composition by electrolysis in a ions lost in the course of normal operation of bifluid cell involving the use of an anolyte ca the cell but sufficient to establish in the anolyte pable under electrolysis of yielding a lead solvent bicarbonate ions in the desired concentration for and containing a bicarbonate and of a catholyte precipitation of white lead of the particular com containing a carbonate which is altered during S3 position. the course of the process by removal of carbon 4. In a process of producing white lead of con ate ions, and involving carbonation of the cath stant particular composition by electrolysis in a olyte to restore carbonate Ions thereto and re-use bifluld cell involving the use of U) an anolyte of the regenerated catholyte, the composition of capable under electrolysis of yielding a lead sol the precipitated white lead being controlled by *> vent and containing a carbonate and a bicar reference to the bicarbonate ion concentration In bonate and (2) a catholyte containing a car the anolyte, the improvement which comprises bonate which is altered during the course of the adjusting the bicarbonate ion concentration in process by removal of carbonate ions, and in the anolyte by subjecting the catholyte to ex volving carbonation of the catholyte to restore cess carbonation and by incorporating hydroxyl -id carbonate ions thereto and re-use of the regen ions in the anolyte in the form of a soluble metal erated catholyte, the composition of the precipi hydroxide in such an amount that the amount of added metal Ions of said hydroxide Is not sub stantially in excess of the amount of metal Ions tated white lead being controlled by reference to the bicarbonate ion concentration in the anolyte. the improvement which comprises maintaining lost in the course of normal operation of the cell, 50 the carbonate concentration in the anolyte at or the amount of metal hydroxide Incorporated in below a predetermined maximum which is sub the anolyte being sufficient to establish therein stantially less than the concentration resulting In bicarbonate ions in the desired concentration, objectionable deposition of white lead on the whereby the addition of ions not entering into anode, and adjusting the bicarbonate ion con 'the composition of the precipitated white lead is 55 centration in the anolyte by subjecting a portion not substantially greater than the loss of such of the catholyte to excess carbonation and by ions in the course of normal operation of the adding to the anolyte the remaining portion of cell. 2. In a process of producing white lead of con stant particular composition by electrolysis in a uo uncarbonated catholyte containing sodium hy droxide to establish In the anolyte bicarbonate ions in the desired concentration, whereby the bifluid cell involving the use of an anolyte ca concentration of ions not entering into the com pable under electrolysis of yielding a lead sol position of the precipitated white lead is not in vent and containing a bicarbonate and a cath creased in the course of normal operation of the olyte containing a carbonate which Is altered cell. during the course of the process by removal of w carbonate ions, and involving carbonation of the catholyte to restore carbonate ions thereto and GUNNARD E. JOHNSON. REGINALD G. BOWMAN. WILLIAM J. KNOX, Jr . PNYC00006386 Patented Jan. 20, 1942 2,270,783 UNITED STATES PATENT OFFICE 2,270,783 ELECTROCHEMICAL- METHOD OF PRODUCING WHITE LEAD Gunnard E. Johnson, Hammond, Reginald G. Bowman, Gary, and William J. Knox, Jr., Ham mond, IndM assignors to International Smelt ing and Refining Company, East Chicago, IncL, a corporation of Montana No Drawing. A^Ucatio- *'--->mber 6, 1937, serial No. i 4 Claims. (CL 204--88) This invention relates to the production of into the catholyte which is also acted upon by white lead and has for an object the provision of the current, the acetate ions replacing a part certain improvements in processes for producing of the hydroxide and carbonate ions that migrate white lead. More particularly, the invention con to the anolyte. This is compensated for by per- templates the provision of certain improvements 5 mitting a certain amount of seepage of catholyte in processes for producing white lead by elec into anolyte through the diaphragm. The seep trolysis. age is controlled by selecting a diaphragm fabric liie present-day commercial process for pro of the desired porosity for a given hydrostatic ducing white lead electrolytlcally is carried out in solution head of catholyte of a selected composi- a so-called bi-fluid cell having a lead anode and 10 tion in the cathode compartment. The addition an iron cathode separated by a porous dia of relatively small amounts of anolyte to catho phragm. The anode is surrounded by an elec lyte and catholyte to anolyte permits adjusting trolyte (the anolyte) containing sodium acetate the sodium concentration of the two electrolytes and a very small amount of sodium carbonate. and the conservation of chemicals, since all The cathode is surrounded by an electrolyte (the 15 make-up solution can then be added to the c&tholyte) containing sodium acetate and a rela anolyte in the form of filtrate from the filters. tively large amount of sodium carbonate. Each All anolyte in the filter cakes is replaced by electrolyte is maintained in rapid circulation water by a counter current washing operation about its electrode. The circulation systems of and returned to the anolyte circulation system. the two electrolytes are entirely independent 20 In addition, wash water filtrate is also returned and no communication exists between the cath- as required to replenish the losses enumerated olyte and anolyte in the cell except through the above. As the volume of solutions transferred diaphragm in the cell. between the two electrolytes is very small the In practice, a small amount of NasCOs, not ex anolyte as previously stated is essentially free ceeding about .05%, is added to the anolyte be 26 of the reacting salts and they are only brought fore placing the electrolytic cells in operation. into the zone where the white lead Is precipitated When the current is turned on, the lead dis in electro-chemical equivalent amounts, there is solves from the surface of the anode and is Im never an excess present to alter the reaction or mediately precipitated as white lead at a slight influence the size of the particle. distance from the anode surface. The precipitate 30 The white lead which is removed continuously is carried down through the cell by the descend from the cell by the circulation of the anolyte, ing current of anolyte in a thick; cloud without is removed from the anolyte by settling and depositing on the anode surface. Hydrogen and filtering. The filter pulp is washed, dried, ground the hydroxide ions are liberated at the cathode. and air floated, and is then barrelled in a dry The hydroxide and carbonate Ions of the hy 35 pulverulent form. The clear anolyte is recircu drolyzed sodium carbonate (NaaCOa) of the lated through the cell. c&tholyte migrate through the diaphragm to The composition of the anolyte during its pas ward the anode, replenishing the anions removed sage through the cell remains unchanged except from the anolyte by precipitation of the lead ions. for a small Increase in the acetate concentration. By this electrolytic migration, the electro-chemi 40 This is controlled by dilution with wash water cal equivalent amount of anions required to pre from the filter. The catholyte is depleted in car cipitate the lead cations as they are dissolved at bonate ions and a small percent of acetate ions, the anode are transported to the anolyte. Slight and enriched in hydroxide Ions during its passage traces of carbonate can be detected In the.&noiyte through the cathode compartment of the cell. but it is entirely free of dissolved lead salts. 45 The excess of hydrate ions is neutralized and the However, there is no sodium carbonate (NasCOj) loss in carbonate ions restored by passing the present in the solution film in contact with the catholyte through carbonation towers, in which anode. a stream of descending solution passes through a The foregoing outlines the major reaction. In rising stream of COa gas from a coke burning practice, in order to replenish and conserve 50 boiler. The acetate loss is replenished as noted chemicals and to restore the loss in volume of by running a small stream of anolyte into the catholyte due to decomposition of water at the catholyte after it is discharged from the cells. cathode, evaporation and mechanical losses, In the United States patent to Ralph M. Har anolyte Is added to the catholyte In a small con rington, No. 1,308,948, it is recognized that the tinuous stream. This introduces sodium acetate 66 character and quality of the white lead product pnrcoo,0S38 2 2,270,783 may be controlled by regulating the amount of carbon dioxide supplied to the catholyte, and It is further recognized that In order to obtain ide. "Excess carbonation," as used herein and as understood in the art, means carbonation in excess of that required to maintain the bicar rapid carbon dioxide absorption and at the same bonate ion concentration of the anolyte at the time avoid precipitation of white lead on the 5 value necessary for the production of a white anode, it is necessary to maintain the catholyte lead product of desired composition. The alkali as compared with the anolyte relatively strongly metal hydroxide may be added to the anolyte alkaline. In any suitable manner as, for example, by dis We discovered that the composition of the solving the hydroxide in the anolyte outside the white lead produced varies directly with the 10 cell, by adding a preformed solution of the hy HCOa ion or bicarbonate content of the anolyte. droxide to the anolyte outside the cell, or by add Our investigations have indicated that the white ing catholyte high in hydroxide (after electroly lead formation is represented by the following sis and prior to carbonation) to the anolyte out reaction equation: side the cell. Each of these procedures effects 3Pb(C2H302)j+4Na2C034'2H30= 2PbCOs Pb (OH) a+2NaHC03 +6NaCaH30a the desired control of the bicarbonate ion con centration in the anolyte, and hence the compo sition of the precipitated white lead, in a man The composition of tn uasio leau capi ner such that the addition of Ions not entering tated varies with the pH value of the solution in into the composition of the precipitated white which it is formed. It will be apparent, there- 20 lead is not substantially greater than the loss of fore, that if only sodium carbonate (NaaCCb) such Ions in the course of normal operation of and lead acetate (PbCCaHsOa^) were supplied to the cell. The solution of hydroxide for addition the solution, the sodium bicarbonate <NaHC03) to the anolyte may be formed by employing as content would progressively increase and the solvent the filtrate normally employed as make ratio of HCO3 to OH tons in the resulting pre- up solution. The invention permits simplifica cipitated lead salt would increase until finally tion of the carbonation operation and provides only PbC03 would be produced. In other words a simple method of maintaining a supply of the carbon dioxide (COa) content of the precipi anolyte of the proper concentration with respect tated white lead bears a direct relation to the to bicarbonate. Instead of controlling the car sodium bicarbonate (NaHC03> concentration of bonation operation to completely or partially the anolyte, This has been found to be true in neutralize the catholyte solution from the cell actual operation. In order to control the com (depleted in carbonate ion and high in hydrox position of the white lead produced, therefore, ide) and, in the case of the partially neutralized it is necessary to control the NaHC03 content of catholyte, adding an acid or bicarbonate to the the anolyte. 3$ anolyte to compensate for the incomplete neu Our discovery of the effect of the HCOa ion or tralization, the carbonation operation may be bicarbonate content of the anolyte on the com permitted to proceed to the point at which ex position of the white lead produced is described cess carbonation is effected without the necessity in our United States Patent No. 1,845,713, dated for exercising extreme caution to secure exact February 16, 1932, which covers control of the 4t> neutralization or accurate deficient carbonation. bicarbonate content of the anolyte by maintain The invention simplifies the process also by elim ing a uniform and deficient carbonation of the inating the necessity for exact control of addi catholyte and adding an acid or a bicarbonate tion of catholyte to anolyte by electrolysis and by to the anolyte. seepage through the diaphragm to meet changes Our aforementioned patent also points out that 45 in operating conditions. The composition of it is desirable that the carbonate salt content of anolyte thus harmfully altered can be adjusted the anolyte be kept low--much lower than is re readily by the method of the*, invention. In the quired in order to avoid formation of white lead preferred method of the invention, the carbona incrustations on the anode--in order to permit tion operation is so controlled as to effect sub washing the white lead free of these salts in the so stantially uniform and excess carbonation of the finishing of the white lead separated from the catholyte for each particular set of operating anolyte. This is important in the commercial conditions designed to produce a product of par production of white lead by the electrolytic ticular composition. method, since the presence of any considerable In accordance with our invention, using a bi amount of alkali metal carbonate in the white 55 fluid cell with a lead anode suspended in an lead product renders it unfit for use as paint pig anolyte capable of yielding a solvent for the lead, ment. We have found that the difficulty in e. g., sodium acetate, and a suitable inert cath washing the white lead sufficiently free of ad ode suspended in a catholyte containing sodium sorbed salts increases with increasing concentra carbonate and separated from the anolyte by & tion of carbonate salt in the anolyte to a point so suitable diaphragm, and to which an excess of at which it is practically impossible to eliminate carbon dioxide (COa) is supplied in the carbona them/ This may be explained by adsorption of tion operation, the anolyte solution is sampled the salts in the white lead particles, but it seems and analyzed at regular intervals, say every hour, more probable that a reaction may occur as fol and its bicarbonate content adjusted to and lows: 2(2PbC03.Pb(0H)a) -{-NaaCOj-f-NaHCCb^ w maintained at the desired figure by the addition of an alkali metal hydroxide, as pointed out above. 3NaPba(COj ) aOH+HaO For example, in a cell operated at a current whereby the carbonate salt becomes chemically density of 30 amperes per square foot of cathode combined and therefore very difficult or impos- 70 area and producing approximately .011 pound of sible to remove. Our present Invention provides for control of white lead per ampere hour and-operating at an anolyte displacement rate of 18 gallons per min the bicarbonate content of the anolyte by means ute while maintaining uniform and excess car of excess carbonation of the catholyte and the bonation of the catholyte, the sodium bicarbon addition to the anolyte of an alkali metal hydrox- 7ft ate content of the anolyte is maintained at x 38 00 co 2,370,783 3 0.0561% through adjustment by the addition of re-use of the regenerated catholyte. the compo- sodium hydroxide thereto to produce a white lead sitlon of the precipitated white lead being con- containing 11.60% of carbon dioxide (COa). To trolled by reference to the bicarbonate ion con- produce white lead of greater or smaller CCh centratlon in the anolyte. the improvement which content the acid carbonate content of the anolyte 5 comprises adjusting the bicarbonate ion concen- may be increased or decreased by the addition of tration in the anolyte by subjecting the catholyte lesser or greater amounts, respectively, of sodium to excess carbonation and adding to the anolyte hydroxide. The exact acid carbonate content re- a sufficient amount of uncarbonated catholyte quired for the production of a particular white containing hydroxyl ions to establish in the lead product should be determined in each in- io anolyte bicarbonate ions in the desired concen- stance by experiment. The carbonate salt con- tration. whereby addition of ions not entering tent of the anolyte is maintained at not exceed- into the composition of the precipitated white lng about twenty-five one-hundredths of one per- lead is not substantially greater than the loss of cent (0.25%), and preferably less than six one- such Ions in the course of normal operation of hundredths of one percent (0.06%), Thesignifl- 15 the cell. cance of the limited carbonate salt content of the 3. In the process of producing white lead of anolyte specified may be appreciated by com- constant particular composition by electrolysis in parison wltl* lianii*____ .. carbonate salt a bifiuld cell in which the white lead is precipi- content of the anolyte necessary to avoid trouble- tated in an anolyte capable under electrolysis of some precipitation of white lead on the anode in 20 yielding a lead solvent and containing bicarbon- accordance with the Harrington patent. In this a^e salt, the steps which consist in determining case the carbonate salt content of the anolyte the bicarbonate ion concentration in the anolyte may run as high as six tenths of one percent corresponding to the precipitation of white lead (0.60%), which content, however, will produce of the particular composition, and maintaining white lead containing so much carbonate salt 25 salt? bicarbonate ion content in the anolyte by that it is not feasible in commercial operation to maintaining a uniform and excess carbonation wash it sufficiently free of such salt as to pro- of the catholyte and by adding sin alkali metal duce a first grade white lead paint pigment. hydroxide to the anolyte in such an amount that We claim: the amount of added alkali metal ions is not sub- 1. In a process of producing white lead of con- so stantlally in excess of the amount of alkali metal stant particular composition by electrolysis in a ions lost in the course of normal operation of bifiuld cell Involving the use of an anolyte ca the cell but sufficient to establish in the anolyte pable under electrolysis of yielding a lead solvent bicarbonate ions in the desired concentration for and containing a bicarbonate and of a catholyte precipitation of white lead of the particular com- containing a carbonate which is altered during 35 position. the course of the process by removal of carbon 4. In a process of producing white lead of con ate ions, and involving carbonation of the cath stant particular composition by electrolysis in a olyte to restore carbonate ions thereto and re-use bifluid cell involving the use of (1) an anolyte of the regenerated catholyte, the composition of capable under electrolysis of yielding a lead sol- the precipitated white lead being controlled by to vent and containing a carbonate and a bicar reference to the bicarbonate ion concentration in bonate and (2) a catholyte containing a car the anolyte, the improvement which comprises bonate which is altered during the course of the adjusting the bicarbonate ion concentration in process by removal of carbonate Ions, and in the anolyte by subjecting the catholyte to ex volving carbonation of the catholyte to restore cess carbonation and by incorporating hydroxyl Ions in the anolyte in the form of a soluble metal carbonate ions thereto and re-use of the regen erated catholyte, the composition of the precipi hydroxide in such an amount that the amount of added metal ions of said hydroxide Is not sub stantially in excess of the amount of metal ions tated white lead being controlled by reference to the bicarbonate ion concentration In the anolyte, the improvement which comprises maintaining lost in the course of normal operation of the cell, the amount of metal hydroxide Incorporated in 50 the carbonate concentration in the anolyte at or below a predetermined maximum which is sub the anolyte being sufficient to establish therein stantially less than the concentration resulting in bicarbonate ions in the desired concentration, objectionable deposition of white lead on the whereby the addition of ions not entering into anode, and adjusting the bicarbonate ion con- the composition of the precipitated white lead Is 55 centratlon in the anolyte by subjecting a portion not substantially greater than the loss of such of the catholyte to excess carbonation and by ions in the course of normal operation of the adding to the anolyte the remaining portion of cell. 2. In a process of producing white lead of con uncarbonated catholyte containing sodium hy droxide to establish in the anolyte bicarbonate stant particular composition by electrolysis in a ions In the desired concentration, whereby the bifiuld cell involving the use of an anolyte ca concentration of ions not entering into the com pable under electrolysis of yielding a lead sol position of the precipitated white lead is not in vent and containing a bicarbonate and a cath creased in the course of normal operation of the olyte containing a carbonate which is altered cell. during the course of the process by removal of GUNNARD E. JOHNSON. carbonate ions, and involving carbonation of the REGINALD G. BOWMAN. catholyte to restore carbonate ions thereto and WILLIAM J. KNOX, Jr . pNrcooooa3a9 Patented Jan. 20, 1942 2,270,783 UNITED STATES PATENT OFFICE 2,270,783 ELECTROCHEMICAL METHOD OF PRODUCING WHITE LEAD Gunnard E. Johnson, Hammond, Reginald G. Bowman, Gan , and William J. Knox, Jr., Ham* roond, Ind., assignors to International Smelt* ing and Refining Company* Fast Chicago, Ind., a corporation of Montana No Drawing. Application December 6, 1937, Serial No. 178,352 4 Claims. i(CL 204--88) This invention relates to the production of into the catholyte which is also acted upon by white lead and has for an object the provision of the current, the acetate Ions replacing a part certain improvements In processes for producing of the hydroxide and carbonate ions that migrate white lead. More particularly, the invention con to the anolyte. This is compensated for by per templates the provision of certain improvements 5 mitting a certain amount of seepage of catholyte In processes for producing white lead by elec into anolyte through the diaphragm. The seep trolysis. age is controlled by selecting a diaphragm fabric The present-day commercial process for pro of the desired porosity for a given hydrostatic ducing white lead electrolytically is carried out in solution head of catholyte of a selected composi a so-called bi-fluid cell having a lead anode and 10 tion in the cathode compartment. The addition an iron cathode separated by a porous dia of relatively small amounts of anolyte to catho phragm. The anode is surrounded by an elec lyte and catholyte to anolyte permits adjusting trolyte (the anolyte) containing sodium acetate the sodium concentration of the two electrolytes and a very small amount of sodium carbonate. and the conservation of chemicals, since all The cathode is surrounded by an electrolyte (the 15 make-up solution can then be added to the catholyte) containing sodium acetate and a rela anolyte in the form of filtrate from the filters. tively large amount of sodium carbonate. Each All anolyte in the filter cakes is replaced by electrolyte is maintained in rapid circulation water by a counter current washing operation about its electrode. The circulation systems of and returned to the anolyte circulation system. the two electrolytes are entirely independent 20 In addition, wash water filtrate is also returned and no communication exists between the cath as required to replenish the losses enumerated olyte and anolyte in the cell except through the above. As the volume of solutions transferred diaphragm in the cell. between the two electrolytes is very small the In practice, a small amount of NajCOs, not ex anolyte as previously stated is essentially free ceeding about .05%, is added to the anolyte be- 25 of the reacting salts and they are only brought fore placing the' electrolytic cells in operation. into the zone where the white lead is precipitated When the current is turned on, the lead dis in electro-chemical equivalent amounts, there is solves from the surface of the anode and is im never an excess present to alter the reaction or mediately precipitated as white lead at a slight influence the size of the particle. distance from the anode surface. The precipitate 30 The white lead which Is removed continuously is carried down through the cell by the descend from the cell by the circulation of the anolyte. ing current of anolyte In a thick cloud without Is removed from the anolyte by settling and depositing on the anode surface. Hydrogen and filtering. The filter pulp is washed, dried, ground the hydroxide ions are liberated at the cathode. and air floated, and is then barrelled in a dry The hydroxide and carbonate ions of the hy- 35 pulverulent form. The dear anolyte Is recircu drolyzed sodium carbonate (N&2CO3) of the lated through the cell. catholyte migrate through the diaphragm to The composition of the anolyte during its pas ward the anode, replenishing the anions removed sage through the cell remains unchanged except from the anolyte by precipitation of the lead Ions, for a small increase in the acetate concentration. By this electrolytic migration, the electro-chemi- 40 This is controlled by dilution with wash water cal equivalent amount of anions required to pre cipitate the lead cations as they are dissolved at from the filter. The catholyte is depleted in car bonate ions and a small percent of acetate ions, the anode are transported to the anolyte. Slight and enriched in hydroxide ions during its passage traces of carbonate can be detected In the anolyte through the cathode compartment of the cell. but it is entirely free of dissolved lead salts. 45 The excess of hydrate ions is neutralized and the However, there is no sodium carbonate (NaaC03) loss in carbonate ions restored by passing the present in the solution film in contact with the anode. The foregoing outlines the major reaction. In catholyte through carbonation towers, in which a stream of descending solution passes through a rising stream of COa gas from a coke burning practice, in order to replenish and conserve 50 boiler. The acetate loss is replenished as noted chemicals and to restore the loss in volume of by running a small stream of anolyte into the catholyte due to decomposition of water at the catholyte after it is discharged from the cells, cathode, evaporation and mechanical losses, anolyte Is added to the catholyte in a small con In the United States patent to Ralph M. Har rington, No. 1,308,948, it is recognized that the tinuous stream. This introduces sodium acetate 06 character and quality of the white lead product c0, 0, 2 2,270,783 may be controlled by regulating the amount of ide. "Excess carbonatlon," as used herein and carbon dioxide supplied to the catholyte, and it as understood in the art. means carbonatlon in is further recognized that In order to obtain rapid carbon dioxide absorption and at the same excess of that required to maintain the bicar bonate ion concentration of the anolyte at the time avoid precipitation of white lead on the. 5 value necessary for the production of a white anode, it is necessary to maintain the catholyte as compared with the anolyte relatively strongly lead product of desired composition. The alkali metal hydroxide may be added to the analyte alkaline. in any suitable manner as. for example, by dis We discovered that the composition of the solving the hydroxide in the anolyte outside the white lead produced varies directly with the 10 cell, by adding a preformed solution of the hy HCO3 ion or bicarbonate content of the anolyte. Our investigations have indicated that the white lead formation is represented by the following droxide to the anolyte outside the cell, or by add ing catholyte high in hydroxide (after electroly sis and prior to carbonation) to the anolyte out reaction equation: side the cell. Each of these procedures effects 3Pb(CiH303)i+4Na2C03+2Hi0= 18 the desired control of the bicarbonate ion con 2PbCOj Pb (OH) a+2NaHCOj+6NaCiHaCh centration in the anolyte, and hence the compo sition of the precipitated white lead, In a man The composition of the basic lead salt precipi ner such that the addition of ions not entering tated varies with the pH value of the solution in into the composition of the precipitated white which it is formed. It will be apparent, there- go lead is not substantially greater than the loss of fore, that if only sodium carbonate (NasC03> such ions in the course of normal operation of and lead acetate (Pb<C3H302)3> were supplied to the cell. The solution of hydroxide for addition the solution, the sodium bicarbonate (NaHCCh) to the anolyte may be formed by employing as content would progressively increase and the solvent the filtrate normally employed as make ratio of HCO3 to OH ions in the resulting pre- 35 up solution. The invention permits simplifica cipitated lead salt would Increase until finally tion of the carbonation operation, and provides only PbC03 would be produced. In other words a simple method of maintaining a supply of the carbon dioxide (CO3) content of the precipi anolyte of the proper concentration with respect tated white lead bears a direct relation to the to bicarbonate. Instead of controlling the car sodium bicarbonate (NaHCCh) concentration of.30 bonation operation to completely or partially the anolyte. This has been found to be true in neutralize the catholyte solution from the cell actual operation. In order to control the com (depleted in carbonate ion and high in hydrox position of the white lead produced, therefore, ide) and, in the case of the partially neutralized it is necessary to control the NaHCCh content of catholyte. adding an acid or bicarbonate to the the anolyte. 35 anolyte to compensate for the incomplete neu Our discovery of the effect of the HCO3 ion or tralization, the carbonation operation may be bicarbonate content of the anolyte on the com permitted to proceed to the point at which ex position of the white lead produced is described cess carbonatlon is effected without the necessity in our United States Patent No. 1,845.713, dated for exercising extreme caution to secure exact February 16, 1932, which covers control of the 40 neutralization or accurate deficient carbonation. bicarbonate content of the anolyte by maintain The invention simplifies the process also by elim ing a uniform and deficient carbonatlon of the inating the necessity for exact control of addi catholyte and adding an acid or a bicarbonate tion of catholyte to anolyte by electrolysis and by to the anolyte. seepage through the diaphragm to meet changes Our aforementioned patent also points out that 45 in operating conditions. The composition of it is desirable that the carbonate salt content of anolyte thus harmfully altered can be adjusted the anolyte be kept low--much lower, than is re readily by the method of the invention. In the quired in order to avoid formation of white lead preferred method of the invention, the carbona incrustations on the anode--in order to permit tion operation is so controlled as to effect sub washing the white lead free of these salts in the 60 stantially uniform and excess carbonation of the finishing of the white lead separated from the catholyte for each particular set of operating anolyte. This is important in the commercial conditions designed to produce a product of par production of white lead by the electrolytic ticular composition. method, since the presence of any considerable In accordance with our invention, using a bl- amount of alkali metal carbonate in the white 55 fluid cell with a lead anode suspended in an lead product renders It unfit for use as paint pig anoiyte capable of yielding a solvent for the lead, ment. We have found that the difficulty in e. g., sodium acetate, and a suitable inert cath washing the white lead sufficiently free of ad ode suspended in a catholyte containing sodium sorbed salts increases with increasing concentra carbonate and separated from the anolyte by a tion of carbonate salt in the anolyte to a point 60 suitable diaphragm, and to which an excess of at which it is practically Impossible to eliminate carbon dioxide (COa) is supplied in the carbona them.- This may be explained by adsorption of tion operation, the anolyte solution is sampled the salts in the white lead particles, but It seems and analyzed at regular intervals, say every hour, more probable that a reaction may occur as fol and its bicarbonate content adjusted to and lows: w 2 (2PbC03JPb( OH) a) +NajCOj+NaHCCh=: 3NaPba( COs) 3OH+H3O maintained at the desired figure by the addition of an alkali metal hydroxide, as pointed out above. For example, in a cell operated at a current whereby the carbonate salt becomes chemically density of 30 amperes per square foot of cathode combined and therefore very difficult or Impos- 70 area and producing approximately .011 pound of sibie to remove. Our present Invention provides for control of white lead per ampere hour and-operating at an anolyte displacement rate of 18 gallons per min the bicarbonate content of the anolyte by means of excess carbonatlon of the catholyte and the ute while maintaining uniform and excess car bonation of the catholyte, the sodium bicarbon addition to the anolyte of an alkatl metal hydro*- t ate content of the anolyte Is maintained at 1 PNYCQ0008391 2,270,783 3 0.0561% through adjustment by the addition of re-use of the regenerated catholyte, the compo sodium hydroxide thereto to produce a white lead sition of the precipitated white lead being con containing 11.60% of carbon dioxide (COj ). To trolled by reference to the bicarbonate ion con produce white lead of greater or smaller COj centration in the anolyte. the improvement which content the acid carbonate content of the anolyte 5 comprises adjusting the bicarbonate ion concen may be increased or decreased by the addition of tration in the anolyte by subjecting the catholyte lesser or greater amounts, respectively, of sodium to excess carbonation and adding to the anolyte hydroxide. The exact acid carbonate content re a sufficient amount of uncarbonated catholyte quired for the production of a particular white containing hydroxyl ions to establish in the lead product should be determined in each in 10 anolyte bicarbonate ions in the desired concen stance by experiment. The carbonate salt con tration. whereby addition of ions not entering tent of the anolyte is maintained at not exceed into i,ne composition of the precipitated white ing about twenty-five one-hundredths of one per lead is not substantially greater than the loss of cent (0.25%), and preferably less than six one- such ions in the course of normal operation of hundredths of one percent (0.06%). The signifi 15 the cell. cance of the limited carbonate salt content of the 3. In the process of producing white lead of anolyte specified may be appreciated by com constant particular composition by electrolysis in parison with the limitation of the carbonate salt a bifiuid cell in which the white lead is precipi content of the anolyte necessary to avoid trouble tated in an anolyte capable under electrolysis of some precipitation of white lead on the anode in 20 yielding a lead solvent and containing bicarbon accordance with the Harrington patent. In this ate salt, the steps which consist in determining case the carbonate salt content of the anolyte the bicarbonate ion concentration in the anolyte may run as high as six tenths of one percent corresponding to the precipitation of white lead (0.60%), which content, however, will produce of the particular composition, and maintaining white lead containing so much carbonate salt 25 said bicarbonate ion content in the anolyte by that it is not feasible in commercial operation to maintaining a uniform and excess carbonation wash it sufficiently free of such salt as to pro of the catholyte and by adding an alkali metal duce a first grade white lead paint pigment. hydroxide to the anolyte In such an amount that We claim: the amount of added alkali metal ions Is not sub 1. In a process of producing white lead of con 30 stantially in excess of the amount of alkali metal stant particular composition by electrolysis In a ions lost In the course of normal operation of bifluid cell involving the use of an anolyte ca the cell but sufficient to establish in the anolyte pable under electrolysis of yielding a lead solvent bicarbonate ions in the desired concentration for and containing a bicarbonate and of a catholyte precipitation of white lead of the particular com containing a carbonate which is altered during 33 position. the course of the process by removal of carbon 4. In a process of producing white lead of con ate Ions, and involving carbonatlon of the cath stant particular composition by electrolysis in a olyte to restore carbonate ions thereto and re-use bifluid cell involving the use of (I) an anolyte of the regenerated catholyte, the composition of capable under electrolysis of yielding a lead sol the precipitated white lead being controlled by 40 vent and containing a carbonate and a bicar reference to the bicarbonate ion concentration in bonate and <2> a catholyte containing a car the anolyte, the improvement which comprises bonate which is altered during the course of the adjusting the bicarbonate ion concentration in process by removal of carbonate Ions, and In the anolyte by subjecting the catholyte to ex volving carbonation of the catholyte to restore cess carbonatlon and by incorporating hydroxyl **5 carbonate ions thereto and re-use of the regen ions in the anolyte in the form of a soluble metal erated catholyte. the composition of the precipi hydroxide in such an amount that the amount tated white lead being controlled, by reference to of added metal ions of said hydroxide is not sub the bicarbonate ion concentration in the anolyte, stantially in excess of the amount of metal ions the improvement which comprises maintaining lost in the course of normal operation of the cell, 50 the carbonate concentration in the anolyte at or the amount of metal hydroxide Incorporated in below a predetermined maximum which is sub the anolyte being sufficient to establish therein stantially less than the concentration resulting in bicarbonate ions in the desired concentration, objectionable deposition of white lead on the whereby the addition of ions not entering into anode, and adjusting the bicarbonate ion con the composition of the precipitated white lead Is 55 centration in the anolyte by subjecting a portion not substantially greater than the loss of such of the catholyte to excess carbonation and by ions in the course of normal operation of the cell. 2. In a process of producing white lead of con adding to the anolyte the remaining portion of uncarbonated catholyte containing sodium hy droxide to establish in the anolyte bicarbonate stant particular composition by electrolysis in a 00 ions in the desired concentration, whereby the btfluid cell involving the use of an anolyte ca concentration of ions not entering into the com pable under electrolysis of yielding a lead sol position of the precipitated white lead is not in vent and containing a bicarbonate and a cath creased in the course of normal operation of the olyte containing a carbonate which is altered cell. during the course of the process by removal of 05 carbonate ions, and involving carbonation of the catholyte to restore carbonate ions thereto and GUNNARD E. JOHNSON. REGINALD G. BOWMAN. WILLIAM J. KNOX, Jr . PNYC000093 92 In t e r n a t io n a l Sme l t in g a n d Re f in in g Co mp a n y 20 North Wacker Drive, Chicago, 111. F. O. CASE M*n4er of MidweC Di<rief February 2nd, 1942 Mr. Frederick Laist Vice-President International Smelting and Refining Gompany Broadway New York City Res Johnson et al. Application Serial No. 178,352, for: Electro- _ _ j i_ Dear fclr. Laist: Chemical Method of Producing White lead - New patent Ho. 2.270.783 This will acknowledge receipt of Mr. James W. Laist's letter of January 29th concerning the above patent. One copy of this patent is being forwarded to Mr. Johnson for his files and the other is being retained in this office. Very truly yo FOCvlc cc: Mr. James W. Laist C< PNYC0000Q393 N11205.01