Document qdNGzb3ZvRDjpenLj5ZxYo08E

Patented Oct. 22, 1940 2,218,940 UNITED STATES PATENT OFFICE 2,218,940 WHITE LEAD Gustave W. Thompson, Brooklyn, N. Y., and Alex ander Stewart, Roselle, N. J,, assignors to Na tional Lead Company, New York, N. Y., a cor poration of New Jersey Application March 26,1937, Serial No. 133,244 13 Claims. (Cl. 23--70) The invention relates to a novel basic carbon ate white lead and the process of its manufac ture. While the conventional formula for white lead 5 is 2PbC03.Fb(0H)2, the commercial product is found to contain varying chemical combinations of lead carbonate (PbCCb), lead hydroxide <Pb(OH)2) and uncombined normal lead car bonate (PbCCb). The variation is due to diffih! cutties in the control of the carbonating reaction and has been mere or less unavoidable in the processes heretofore followed, correspondingly affecting the uniformity of the pigment as to its chemical and physical characteristics. This inl.'i venfion provides a new system whereby the car bonating reaction can easily be carried on to give a product not only of consistently uniform pro perties, chemical and otherwise, but also with notable manufacturing economy, and more es20 pecially, in its preferred form, to give a new white lead product definitely superior to the white leads heretofore available to the trade. Among the desirable physical attributes in a pigment are tinting value and hiding power, 25 fineness and uniformity of particle size, color, ana oil-taking power. According to the pre ferred procedure under this invention, white lead can be made with a tinting value of approxi mately 220-240 as compared to a tinting value 30 of 100-11C for the product of the standard Dutch process and with a particle distribution, determined by the Thompson cone classifier, in dicated as an average diameter by surface mean of 3 microns and finer, approximately 99% as 35 against 65% for the Dutch process, and also be ing substantially free from coarse particles or hard agglomerates, i. e,, gritty particles which may be felt when the dry powder is rubbed be tween the fingers and known in the industry as ,ir, "sandy lead". This new product has satisfac tory oil absorption properties and unusually high paint thickening properties which is specially de sirable. For example, by the Gardner mobilometer test, a paint containing 68% of this new white lead as the pigment has a mobility factor of 0.122, a gram yield value of 92, and a consis tency value in seconds for a 120 gram plunger drop of 83, as compared to Dutch process white lead with a mobility factor of 0.202, a gram yield value of 24 and a consistency value in seconds of 0.5 for a 120 gram plunger drop, the drop being in all cases through or employing the middle 10 centimeters of the plunger stroke. The new process can be carried out on the batch or continuous system and Fig. 1 repre sents in diagram suitable apparatus for the batch system, though without limitation thereto; Fig. 2 shows a modification thereof; and Fig. 3, an extension of the same apparatus adapted for continuous treatment. t> According to this invention, a suspension or slurry is prepared of finely divided metallic lead or powdered lead oxide (PbO), or both, in water containing a relatively small amount of proper catalyst, such, for example, as lead acetate which 10 is preferred, pr some catalyst-forming agent, such as acetic acid. If the slurry is constituted of or contains metallic lead particles, it may be first blown with air or other oxidizing agent, ac cording to known processes, until such particles )5 are oxidized. This and the subsequent reactions can be satisfactorily conducted within the tem perature range of 20-70 C. If pure lead oxide (PbO), i. e., free from metallic lead, is used to make the slurry, the oxidation step may be 20 omitted. Fumed or sublimed litharge may be used but that degree of fineness is not required for the successful operation of this process. In Fig. 1, ( marks the slurry tank and 2 its air blowing connection. A power stirrer, 3, keeps 26 the slurry constantly agitated and in the condi tion of a suspension, reasonably homogeneous. In this state it is subjected to the effect of be ing forced or circulated in the form of a stream or current through one or more treating systems, 30 at the same time being charged with a carbonat ing gas CO2 injected or introduced into it as or just after it enters the pumping or forcing mech anism of the system and so that the slurry and gas pass through the system together in close 35 mechanical mixture. Whether it be due to the pump-created turbulence, the high velocity, the abrupt pressure changes within the system, the attrition effects, or to some other cause or causes, the effect of thus pumping the mixed gas and 40 slurry has been found to exercise an important influence on the carbonating reaction and on the quality of the product. The result is quite dif ferent from that ordinarily obtainable from car bonating methods heretofore employed, 1. e., 45 blowing the gas into the slurry or spraying the slurry into an atmosphere of the gas. Aside from chemical considerations mentioned later, it gives an unusually high absorption and reac tion efficiency and accounts for the substantially 50 complete elimination of "sandy lead," In the product. It obviates the subsequent use of classification apparatus and the heavy expense attendant thereon. 2 2,218,940 nary type, centrifugal preferred, and it, or they, are of relatively small capacity and high speed. The reaction takes place, mainly, inside the pump intake or in the pump chamber or equivalent 5 space wherein the reagents are momentarily con fined in contact and violent agitation, and by the appropriate regulation of the gas admission, the reaction thus occurs in such space between fixed though regulable proportions of slurry and car lo bon dioxide. The slurry-gas mixture is passed either repeatedly through one or two pumps or spaces, comprised in a circulating system, or successively through a long series of them, being in any event kept agitated so that the solids are 1 kept homogeneously distributed in the liquid during the treatment. In the batch system as shown by Pig. 1, the slurry passes through the pump intake pipe 4 to the pump 5, and is delivered by the latter 20 back to the tank I. The supply of the car bonating gas which may be CO2 or a mixture of such gas and air, is admitted by way of the pipe connection 6 under regulation of the valve indicated. The pump 5 which may be assumed 25 to be an ordinary centrifugal type pump with a capacity approximating say, 450 gallons per min ute at about 1750 R. P. M,, circulates the slurrygas mixture continuously from and to the tank while the power stirrer keeps the solids suspend30 ed. This circulation is continued until a pre determined and sufficient quantity of CO: has been absorbed, as later pointed out. With a single pump, care is required that the gas admission does not render it gas-bound or otherwise interfere with the uniformity of the gas and slurry proportions. Greater precision can be secured by using two pumps in tandem as indicated in Pig. 2, where the second pump is marked 7, and the gas entrance located be40 tween the two is marked 6. The first pump feeds the slurry to the second under a pressure tend ing to balance that of the gas, also admitted un der pressure, so that their relative admissions are more easily kept uniform. 45 By the use of two pumps, or with care by the use of only one, the rate of gas admission can be such that substantially all that admitted to the pump intake can be absorbed by the slurry before it reaches the slurry tank and this reg50 ulation, being the most economical, is preferred though not indispensable. There need be no waste of carbon dioxide, the gas is proportion ately admitted and at a rate not substantially exceeding that at which it can be taken up by 55 the slurry stream. The final slurry is discharged through pipe 3, Pig. 2, and the white-lead water-pulp, with or without filtering or settling and siphoning, is transferred to a conventional oil incorporating 00 system, where linseed oil is incorporated with the pigment, directly forming what is known as white-lead-in-oil, or the original pulp may be filtered without washing and then dried and packed as a dry product. The slurry liquor or 65 filtrate can be re-used. Figure 3 illustrates a form of the same ap paratus suited for operation on a continuous basis. Instead of returning the slurry back to the original tank I, it is delivered by the tandem 70 pumps 5 and 7, via pipe line 9, to a second tank 10, and from the latter it is drawn or taken by another pair of tandem pumps II and 12, and delivered to another tank 13, and so on until, in the last tank, the reaction is complete and 75 the slurry discharged and treated as before. The CO2 admission is between the pairs of pumps as in Pig. 2, by the pipe connections marked 14. and each tank has its power stirrer to maintain the suspension. Return or by-pass pipes 15, aie desirably provided for each container so that 5 as necessity arises the partially reacted slurry of one tank may be returned back to the same tank, thus to prolong the treatment. In any case, the air for oxidizing metallic lead, if any, may be blown into the slurry either pre 10 viously to the pumping treatment or coincidently with it and air may be admitted along with the CO2, the important consideration being that the metallic lead be entirely oxidized and reacted with the CO2 before discharge so that it will not 15 appear in the final white-lead water-pulp. As will now be understood, any desired calcu lated amount of carbon dioxide may be admitted to the slurry by the means above described, and since the various mechanical conditions, such as 0 pump speed, velocity of slurry, rate of gas ad mission and temperature, etc., are easily kept uniform, any calculated amount can be combined with a calculated amount of lead and the treat ment can accordingly be depended upon to pro 25 duce a white lead product consistently uniform in both chemical and physical properties. This is of special commercial importance. The further part of this invention involves and depends upon a particular control of the gas ad 30 mission and carbonating reaction which is easily performed according to the process above de scribed. We have found that the initial basicity and also the initial electrical resistance of the liquid phase of the slurry remain practically con 35 stant and unaffected for a considerable period after the gas injection has been started. For example, if the process is being conducted at 30 C., the initial pH value of the slurry which ordinarily approximates 9.5, and its initial spe 40 cific resistance which may, with an operating temperature of 60 C,, approximate 790 ohms, continue constant at these values for several hours and then with continued gas injection show a sharp change, the pH dropping abruptly to ap 45 proximately 7.5 (at 30 C.), and the specific re sistance abruptly increasing to approximately 1060 ohms (at 60 C.). These values, which are to some extent dependent upon temperature, quantity of catalyst, etc., are presented as exam 60 ples and not as defining absolute properties of a slurry under the best conditions. We have found that if the gas admission be stopped just at the beginning of this drop in pH value, or the increase in resistance, the solid 65 phase of the slurry, after filtering and drying, at that moment will have a chemical composition, which may be expressed by the formula 4PbCCh.2Pb (OH) 2.PbO, 00 and with little or no uncombined lead carbonate (PbCCb) or lead hydroxide (Pb(OH)2) present, and our further invention consists in continuing the gas admission or the carbonating reaction only up to or about this critical point. The white 05 lead pulp obtaining at this moment is then sep arated from the liquor and transferred to the regular oil-incorporating system to make whitelead-in-oil, or to the dryer to make dry white lead. The composition above indicated charac 70 terizes the new white lead product first above re ferred to. It has a total CO2 content of between 9.92 and 10.3%, a total combined water content of between 1.9 and 2.1% and a total PbO con tent of about 88%, being partially or wholly hy- 75 0000-NLI-000018971 2,218,940 3 dfated and being, as we believe, the most basic carbonate of lead. Several specific chemical analyses of this prod uct after drying at 105 C., are as follows: and the CO2 content of the white lead will have risen to about 11.3% and the combined water to about 2.3%. Still further admission will even tually convert the pulp to normal carbonate, CO2 Example n #3 #4 ffi Carbon dioxide (CO?).......... .............. ................. Combined water (HjO).................................. ........ Total lead oxide tPbO) ............................ ........... Percent 9. 92 2.03 88. 06 100.00 Percent 10.00 2. (X) *8. 00 100.00 Percent 10.10 2. 07 87.83 100. CO Percent 10.20 2. 10 S7. 70 100.00 Percent 10. 30 2. 10 87.60 100.00 Percent 10.3 1.9 87.8 100.00 While we have assigned to it the empirical formula of 4PbC03.2Pb(0H)2.Pb0, as above stated, the product may be partially or wholly hydrated, and if wholly hydrated the empirical 20 formula might be 'iPbCO3.3Pb.2K2O or, i:i aque ous suspension, might properly be considered as a hydrated lead oxide-lead hydroxide-lead carbo nate combination whereof the formula might be expre.v-ed as 4PbC03.2Pbi0H) s-PbO.HiO. The 25 hydrated mole of PbO, being unstable, loses its water of hydration when the ratio of free water to total solids is lowered by filtering drying, or other de-watering. The composition can also be properly identified 30 by the molar ratio of its component ingredients as follows: Fb0:C02:Ki0=3.36 to 3.74:2 to 2.22:1 or 35 Total FbO:total basic PbO=2.33 to 2.48:1 The basic PbO content of basic lead carbonate white lead, it may be said, is the PbO content represented in the formula as not being in direct combination with CO2. The lead carbonate con40 tent of white lead made in accordance with the preferred form of this invention ordinarily ap proximates 60.2% to 62.5%, equivalent to a PbO content of 50.3% to 52.2% and therefore the PbO content comprising the basic portion of the white 45 lead approximates 35.3% to 37.7% and with a total PbO content of 87.6% to 88.1%. If the gas admission is stopped prematurely, i. e,, before reaching the critical point, more or less uncombined PbO will be certain to be found 50 in the pulp and the color and tinting value of the final product will be poor and low. The critical point Indicates the disappearance of one of the constituents of the solid phase of the slurry and results from the changed degree of basicity 55 of the dissolved catalyst-forming agent when in equilibrium with the single solid phase repre sented by the aforementioned composition. If the gas admission is continued beyond the critical point, an additional solid phase develops 60 in the slurry which may be represented by the formula 2PbCCbPb(OH) 2, and which by itself would be ordinary white lead. The resulting pulp then becomes a mixture of this common white lead with the new white lead of the formula 05 4PbC03.2Fb(OH)2PbO or otherwise, as explained p.b<we. The presence of 2PbC03.Pb(0H)3. \1 not in too great proportion does no harm beyond some what reducing the tinting value and hiding power, and we do not intend to limit our product inven70 tion by its complete exclusion or by the exclusion of any normal carbonate. Continued gas admis sion will quickly convert all of the solids into 2PbCChPb(OH) 2, or ordinary white lead, at which time the pH value of the liquid phase will 73 have dropped to about 6.2 as measured at 30 C. content about 16.4%. It is important, therefore, when the highest tinting value is desired, to stop gas admission promptly at the very beginning of the change from the initial and previously constant pH value or the specific resistance value. The change of hydrogen ion concentration occurs abruptly and care is needed to guard against exceeding the critical point fur ther than will produce the quality of product desired. While the white lead product of this invention consists primarily of the chemical compound to which we have assigned the empiri cal formula 20 27 4FbC03.2Pb (OH) 2.PbO, or 4PbCO3.3PbO.2H2O it includes also mixtures or blends in which this compound is present in sufficient qualtity to im part its superior attributes to the mixture. A specific example of the practice of the in vention in the production of the new product is 2.". as follows: To 1,000 gallons of water, 1,760 pounds of finely divided metallic lead or litharge or a mixture of litharge and finely divided metallic lead are added together with between 2% to 5 Vi pounds of lead acetate or catalyst-forming agent, 40 for example, 1 !4 to 2V2 pounds of 70% acetic acid. Agitation is started in the main tank, passing air into the slurry continuously. The pump or pumps are started and the carbon dioxide flow is also started, the admission rate being adjusted 4.-, to the size of the equipment which in the par ticular instance under description, was at the rate of 20 lbs. of carbon dioxide, or about 1900 cubic feet of 10% by volume of carbon dioxide gas in air per hour. Cost permitting, pure dry carbon dioxide gas could be used. The tempera ture of the reaction is maintained within limits of 20-70 C., by injecting live steam as needed or otherwise, although this may vary considerably without affecting efficiency or the quality of the r>5 product. The critical point above disclosed will ordinarily be reached in about ten hours at which times gas admission is stopped and the pumps are then used to deliver the pulp to the storage department. It will be appreciated that the ab- 60 sence of "sandy lead" and also free metallic lead, as already stated, eliminates the need and ex pense of the classifying operations, which ordi narily next succeed after the carbonatlon. It will be appreciated further that within the principles 65 above explained various departures are possible and will be resorted to according to particular circumstances, and within the scope of the claims appended hereto. We claim: 70 1. The process of making basic carbonate white lead which comprises maintaining a slurry of lead oxide with a carbonation-promoting catalyst, re acting on such slurry with carbon dioxide until the liquid phase of the slurry shows an abrupt 75 0000-NLI-000018972 4 2.218.940 drop in pH value and the solid phase of the slurry level value and the solid phase is largely consti attains the formula 4PbCC)3.2Pb(OH)2.PbO, ceas tuted of white lead having the empirical farmula ing such reaction when this condition has been of 4PbC03.2Pb(OH)2PbO, then ceasing such reached and separating out the solid phase while treatment and separating out the solid matter. r, it consists mainly of basic carbonate of the com 7. White lead comprised essentially of basic S position indicated by said formula. lead carbonate obtained by the process of claim 2. The process of making basic carbonate white 1 and corresponding to the empirical formula lead which comprises maintaining in a suitable 4PbC03.2Pb(OH>2PbO characterized by substan tank, a slurry of lead oxide in water containing tial freedom from particles exceeding 3 microns : 1 a carbonation-promoting catalyst, passing a cru- diameter by surface mean and by tinting and 10 rent of the slurry from the tank through a sepa paint thickening properties substantially in ex rate treating chamber under conditions of violent cess of those of standard Dutch process white turbulence mechanically imposed upon it in such lead. chamber, simultaneously admitting carbon diox- 8. White lead comprising basic lead carbonate ' ide into said chamber, and repeating such treat formed by reaction of gaseous CO2 on lead hy- 15 ment until the liquid phase of the slurry shows drate according to claim 1 and corresponding to an abrupt drop in pH value and the solid phase the empirical formula 4PbC03.2Pb(0H) 2PbO of the slurry has attained a composition repre sented by the formula 4PbCC>3.2Pb(OH)2.PbO. and characterized by its pure white color without yellow component, its substantial freedom from -"1 3. The process of making white lead contain ing as its principal component basic lead car bonate of the formula 4PbCC>3.2Pb(OH)2PbO, which comprises maintaining a suspension, of particles in excess of 3 microns diameter and 20 paint thickening properties greatly in excess of those of standard Dutch process white lead. 9. The process of making white lead which lead oxide in water containing a carbonation' promoting catalyst, in a suitable tank, passing a current of such suspension from the tank through a separate treating chamber under con comprises subjecting a carbonatable lead oxide slurry to a succession of partial carbonating 25 treatments, each such treatment consisting in passing the slurry from a tank through a small ditions of violent turbulence while admitting car treating chamber under conditions of violent bon dioxide into such chamber, repeating such agitation mechanically imposed upon it within 1 treatment under the same conditions of turbu the chamber, while admitting carbon dioxide to 30 lence and gas admission until the pH value of the liquid phase of the suspension manifests an abrupt drop following an initial level period of ... substantially no variation, and then ceasing gas admission and filtering out the solid phase. 4. The process of making white lead contain ing as its principal component basic lead car bonate of the formula 4PbC03.2Pb(0H)2.Pb0, which comprises reacting on a slurry of lead ' oxide in water containing a carbonation-promot ing catalyst, with carbon dioxide until the pH value of the liquid phase of the slurry manifests an abrupt drop to about 7.5, following an initial such chamber at a rate no greater than can be absorbed by the slurry during its passage through the chamber and such treatment being repeated on said slurry until it is free of uncombined lead oxide. 3 10. The process of making white lead which comprises subjecting a carbonatable lead oxide slurry to a succession of partial carbonating treatments, each such treatment consisting in passing the slurry from a tank through two se- 40 ries-ccnnected pumps wherein it is subject to violent agitation, while admitting carbon dioxide to the second pump at a rate no greater than can level value of about 9.5, and ceasing the reaction and removing the solids while the pH indication remains at said lower value. be absorbed by the slurry during its passage therethrough, such treatment being repeated on 45 said slurry until it is free of uncombined lead 5. The process of making white lead contain ing as its principal component basic lead car bonate of the formula 4PbCC>3.2Pb(OH)2PbO, 1 which comprises maintaining a suspension of lead oxide in water containing a carbonationpromoting catalyst, in a suitable tank, passing a current of such suspension through a separate treating chamber under high turbulence, while oxide. 11. White lead comprised essentially of basic lead carbonate corresponding to the empirical formula 4PbC03.2Pb(0H) 2TbO, characterized by 50 having over 90% of its particles of diameter smaller than 3 microns by surface mean, by hay ing a lead carbonate content between about 60.2% and about 62.5%, a tinting value in the ' admitting carbon dioxide into such chamber and general order of 200, and a mobility factor in the 55 regulating the rate of such admission so as to be order of .122 by Gardner mobilometer test for substantially completely absorbed by the sus paint composed of 68% of said white lead as the pension, repeating such treatment under like pigment. conditions of turbulence and gas admission until 12. The process of making basic white lead the pH value manifests an abrupt drop follow which comprises maintaining a carbonatable 60 ing an initial level period of substantially no slurry of lead oxide, passing a current of such variation, and ceasing gas admission and separat slurry through a treating chamber under condi ing out the solids before the pH value manifests tions of violent agitation, while admitting carbon a further drop. dioxide gas into such chamber and continuing !| ' 6. The process of making basic carbonate such treatment until the pH value of the liquid 65 white lead which comprises maintaining in agi phase manifests an abrupt drop following an tation in a suitable tank a slurry of lead oxide, initial level period of substantially no variation water and a carbonation-promoting catalyst, cir and ceasing gas admission and separating out the culating such slurry through a separate treating solid phase before the pH value manifests a 1 chamber and back to the tank, mechanically further drop. 70 and violently agitating the slurry in its passage 13. The process of making white lead which through said treating chamber and coincidental comprises maintaining a carbonatable lead oxide ly admitting CO2 into said chamber until the pH slurry in a state of agitation in a suitable tank value of the liquid phase in said tank manifests in part at least by blowing air into it, subjecting 75 an abrupt drop following an initial substantially such slurry to a succession of partial carbonating 75 0000-NLI-000018973 2,2X8,940 5 treatments, each such treatment consisting In passing slurry from said tank through a small treating chamber under conditions of violent agi tation mechanically imposed upon it within the 8 chamber, while admitting carbon dioxide to such chamber at a rate no greater than can be ab sorbed by the slurry during its passage through the chamber and such treatment being repeated on said slurry until it Is free of uncombined lead oxide. GUSTAVE W. THOMPSON. ALEXANDER STEWART. 0000-NLI-000018974 Oct 22, 1940. G. W. THOMPSON ETT AL WHITS LEAD Filed March 26, 1937 2,218,940 0000-NLI-000018975