Document 4vaLNrnD9M0xQw5n85e44yOKj

Patented July 15, 1941 ftWOMAi HAD C;I . utr^S;:.(tT hkt 2,249,330 UNITED STATES PATENT OFFICE 2,249,330 LEAD SULPHATE Alexander Stewart, Roselle, N. J., assignor to National Lead Company, New York, N. Y,, a corporation of New Jersey No Drawing. Application December 6, 1937, Serial No. 178,349 13 Claims. (CL 23--127) This invention relates to a new form of lead the bottom of the container for the purpose of sulphate pigment having a particular crystal oxidizing any metallic lead that may be present formation, and unusual covering power as well and thereafter maintaining a vigorous agitation. as other useful properties, and to the process of The agitation by air is desirably supplemented by making such product. The new process falls In 5 a mechanical agitator such as motor-driven pad the known class of wet or precipitation lead sul dle wheel of the turbine type submerged in the phate processes wherein lead oxide is brought container. into solution by the effect of an acetic or nitric With the slurry between 60 and 95 C. and ion and the lead sulphate is precipitated by the preferably at about 80 C. sulphuric acid is added introduction of sulphuric acid. It differs from 10 in three stages, which stages may however fol prior proposals in respect to the manner of ef low the one directly after the other without in fecting the sulphation of the lead slurry, this terruption. In the first stage it is added at such being so carried on as to produce an orderly suc rate or in such quantity as to convert all of the cession of chemical reactions, resulting in a pre solid phase of the slurry into the form of hydrated cipitated sulphate which contains a large pro- 15 trlbaslc lead sulphate (PbS04.3Pb0.Hj0) as de portion of aclcular or needle-11ke crystals, quite termined after filtering, washing and drying at distinct from the crystal formation of lead sul 105 C. And no more add is added or allowed phates heretofore known to the art. to be present during this stage than will be suf By virtue of this crystal formation the pigment ficient to accomplish that result, which will be is much superior to present commercial forms, 20 obtained in about one and one-half hours. notwithstanding that its chemical composition After this stage has been reached and during may be tile same. Its particular points of su the second stage the add is introduced slowly periority are, first, its hiding power, of greatest and preferably at a uniform rate and until the importance in the paint Industry, which is equiv whole of the solid phase (trlbaslc sulphate) of alent per pound to at least 1.25 to 1.33 pounds 25 the first stage has been converted to the form of of ordinary basic lead sulphate now available to anhydrous monobasic sulphate (PbSQtJPbO), no the trade. Next, its paint thickening property more add being admitted or allowed to be pres which is a measure of its keeping and brushing ent at any time than will suffice to carry this quality and is shown in the following table com second stage conversion to completion, 1. e. all to paring paint consistencies at different pigment 30 monobasic form. The amount of add introduced concentrations (as determined by the Gardner is however sufficient to carry the liquid phase of mobilometer, using a 120 gram plunger at 70 the slurry over to the add side so that at the F.): end of the second stage the solution is acid in character turning litmus paper red. Percent pigment by weight linseed oil point Time in seconds for plunger drop: middle 10 cm. New product 8ubUmed product (commercial) After all of the solid phase has thus been, con verted to monobasic form the latter will be found to consist of aclcular crystals and has certain practical value as a pigment and can be sold as such, but for some purposes is less desirable than the product of the third stage which preferably immediately follows but which must not begin 55.0................................................................ 00.0................................................................ 62.5................................................................ 00.0................................................... 14 23 23 05 5 8 9 until all of the solid phase of the second stage has become completely monobasic. During the 13 third stage acid addition is continued slowly and preferably at a uniform rate until such an amount In the foregoing it will be seen that the new has been added as, by previous calculation, will product requires only 55% by weight, as com pared to 66% by weight of the commercial prod suffice to produce a product approximately of equimolecular proportions of monobasic lead sul uct, to produce the same consistency value. phate and normal lead sulphate and represented Again, ordinary basic lead sulphate, packed in 50 empirically by the formula ZPbSOtPbO, the slur ordinary tin cans in the form of a paste with ry during the whole of this third stage contin linseed oil, hardened and livered in approximate uing to remain on the acid side. This product ly three to four months, whereas the new product will be 63.5% monobasic and 36.5% normal but has not hardened or livered in a test of over one the reaction can be continued to produce a pro year. 55 portion of as little as 40% monobasic and 60% According to this invention a slurry Is made of normal sulphate within this invention. In any lead oxide PbO or finely divided lead or a mix event the product will contain a relatively large ture of both in water containing a small amount and generally predominating proportion of adcu- 0000-NLI-00001897 2,240,380 33%) Is slowly dropped Into a slurry containing basic lead sulphate, on drying at 105 C. as fol- lead oxide (PbO) and a small amount of the lows: acetate ion at a constant temperature, the liquid Percent Penjent phase being saturated with respect to the oxide, Total lead oxide (PbO)... 84.8 Lead sulphate (PbSOs)... 67.6 there occurs a transformation or precipitation Total sulptmr trioxide Lead oxide (PbO)............ 42.4 (SOj)................................ 15.2 of a portion of the dissolved lead oxide into the 100.0 insoluble compound above referred to as hy 100.0 drated trlbaslc lead sulphate. Due to the pres This resulting solid phase is constituted of ence of the acetate ions and the relatively slow long, well-defined acicular monocllnlc crystals rate of addition of the sulphuric acid, the liquid xo which have eventuated from the large lamellar phase is rapidly restored to Its saturation value crystals of the first stage product and which at the particular operating temperature. Fur condition appears to govern the crystal charac ther addition of sulphuric add increases the teristics of the subsequent ultimate product of amount of this hydrated trlbaslc lead sulphate, this invention. the liquid being constantly resaturated with lead 15 The third stage of the process performs the oxide PbO as the process continues until all of function of so uniting or assembling the said the uncomblned lead has been converted to the monobasic and normal lead sulphate molecules trlbaslc form. At the point where this has oc as to produce crystals which represent either a curred and the lead oxide is completely trans coalescence of the two substances, a solid solu- formed, which point may be recognized, without 2Q tion of one in the other, or a product of adsorp analysis, by an increase in the electrical resist tion, this being the result of the partial neu ance of the slurry over Its Initial value, the solid tralization of the acicular monobasic sulphate phase turns from the yellow color of litharge of the second stage occurring In a normal lead to a snow white and then consists substantially acetate solution having a pH value approxlmat- of the above mentioned hydrated trlbaslc lead 25 25 C. and within the temperature su-lp-hate. T--his product, which Is the most basic range above stated viz. 60-95* C. sulphate produced under these conditions, shows The distinctly crystalline, white, substantially the following chemical composition after drying Insoluble product of the third stage, conform at 105* C. ing to the proximate empirical composition M 2PbSOi.BbO, cannot be regarded as a definite Percent Total lead oxide (PbO)... 00.1 Lead sulphate (PbSO,) --ero3a0n. fl chemical compound, as may be proved by the Total eolpbor trioxkle (80*).............................. 8.1 Combined water (HiO).. 1.8 Hydrated lead oxide (3PbOJasO)................... 00.4 phase relations involved In its formation as well as by X-ray analysis, refractive index, specific 100.0 gravity, and microscopic examination. Nor can 100.0 55 it be regarded as an ordinary mechanical mix This product consists of large well-defined, ture. X-ray analysis by the powder method lamellar, elongated crystals and Is produced In using a cylindrical vacuum camera, rotating the a basic lead acetate solution containing lead ox specimen continuously during exposure to a nar ide and the acetate ion substantially In the molar row beam of X-rays coming from a high Inten ratio of 7:4. This solution has a pH value of about 9.3 as measured at 25 C. The reaction 40 sity copper target X-ray tube, shows a spectro gram indicative of a true compound for the com may be written position, monobasic lead sulphate, PbSO<.PbO. 4PbO+H2S04=PbSO4.3Ph0H3O The lnterplanar spaclngs, particularly six of these While the rate of acid introduction during the first stage Is of no particular consequence, provided more than necessary to produce the trl baslc sulphate is not Introduced and the basicity of the solution phase Is maintained. It Is de sirable In the second and third stages that the acid be Introduced slowly and over a period, for 45 60 spacings, are definitely characteristic of this materlal. The diffraction pattern for the product of this Invention shows a displacement In the spectral lines indicative of solid solution, which Is or characterizes a mixed crystal. Not only Is there microscopic evidence of homogeneous crys tals acicular lnstructure, but diffraction pattern reveals a definite shift In the lnterplanar spac both stages, approximating three and one-half to four and one-half hours, the total time for the process being around five to six hours, de pending upon plant operation. For the second stage, a calculated amount of acid Is admitted sufficient to convert the solid phase of the first stage (trlbaslc lead sulphate) Into monobasic 65 lngs of the components, monobasic lead sulphate, PbS04J*b0, and normal lead sulphate, PbS04, which is all Indicative of solid solution. The relation of the refractive indices of the products of the several stages above discussed, to normal sulphate, is Indicated as follows: lead sulphate as represented by the following Average equation -efractlve PbS04.3PbO.HjOrfHaS04=2(PbS04FbO) -j-2HaO 60 Trlbaslc lead sulphate Index (PbSO4.3PbO.H3O) -- 2.1 The progress of this reaction which tabes place Monobasic lead sulphate (PbSOFbO)___ 2.02 in a basic lead acetate solution containing PbO (Equlmolecular proportions of monobasic and the acetate ion substantially In the molar and normal lead sulphate (PbSCh-PbO-- ratio of 4:3 (corresponding to the pH value of 65 PbS04) 2.0) about 7.8 at 25* C- but dropping to about 6.3 Normal lead sulphate (PbSO)--------------------1.89 at the conclusion of this stage) Is attended by The above Indicates that the normal, mono constant thickening of the slurry. Indicating a basic, and trlbaslc lead sulphates are entirely dif constant change In the physical structure of the ferent compounds. The monobasic and equi- solld phases. The end point of this second stage 70 molecular proportions of monobasic and normal reaction Is manifested by a second Increase of lead sulphate have refractive Indices that are about 30% of the previous electrical resistance very close together, suggesting that the mono of the slurry. The resulting solid phase which basic has formed or grown Into a mixed crystal Is Insoluble under the prevailing conditions, shows or solid solution with normal lead sulphate, In a composition equivalent to anhydrous mono. 75 the proportions described. The microscope yields 0000-NLI-000018977 2,340,330 3 sufficient evidence that the equlmolecular pro priate type of dryer and without any necessary portions of monobasic and normal lead sulphate, grinding or classification treatment is at once or the product of the third stage of this process, ready for the market. is not a mechanical mixture. Moreover, the ap While the foregoing example gives a product proximate equlmolecular proportion of mono s Indicating a proximate composition of 73% lead basic and normal lead sulphate shows a strong sulphate and 27% lead oxide (PbO), I do not birefringence of the particles that could not be of course confine myself to this proportion, my normal lead sulphate and establishes the product Investigations having shown that the total lead as not a mechanical mixture. This condition sulphate content of the product may vary be- persisted to a composition approximating 70% 10 tween 57% and 83% without impairing the val normal lead sulphate and 30% monobasic lead uable pigmentary properties due to the large sulphate, indicating that the monobasic lead sul proportion of acicular crystals. phate crystal tends to control the crystal form When the total lead sulphate is 57.6% the of the third stage product and must pick up nor product is wholly monobasic acicular lead sul- mal lead sulphate. 15 phate, the product of the second stage; when it Microscopically, the percentage by weight of is 73.1%, which is the equlmolecular proportion, acicular crystals present, In varying proportions. the acicular product is approximately 63% In the several products, is approximately as fol monobasic lead sulphate and 37% normal lead lows: sulphate; when it is 83%. the product is 40% 20 monobasic lead sulphate and 60% normal lead Percent sulphate, and when it is 66% the product is 80% Approximate composition acicular crystals monobasic lead sulphate and 20% normal lead sulphate. The exceptional pigmentary proper Monobasic lead sulphate, 80%--normal lead sulphate* 20% ......................................... Monobasic lead sulphate, 63%--normal lead sulphate, 37% .............................................................................. - Monobasic lead sulphate, 5S%--normal lead sulphate, 4l% ........................................................................... Monobasic lead sulphate, 40%--normal lead sulphate, 60%.......................................................................................... Monobasic lead sulphate, 20%--normal lead sulphate, 80%................... ..................................................................... Substantially none, 0%--normal lead sulphate, 100%-- ties resulting from the crystal coalescence of the 96 25 third stage are particularly manifested in the 80 equlmolecular product, but also to an advanta 80 geous degree in other third stage products in the range between 66% and 83% total lead sulphate. 70 In all cases the particle size, as measured by sur- 60 30 face mean, may be assumed to be not particular 10 ly different from the commercial (sublimed) sul 3 phate. The superior properties of this product are positively Indicated to be the result of the Investigation of the specific gravity of prod acicular formation of the particles, which ap- ucts resulting from the partial neutralization of 35 proximate an average diameter, by surface- monobasic lead sulphate with sulphuric acid mean, of 12 microns. revealed a direct proportion between the per I claim: centage of normal lead sulphate and specific 1. In the method of making basic lead sul gravity, i. e., a decrease in specific gravity with phate by reacting with sulphuric acid on a slurry increased normal lead sulphate content. I have 40 of lead oxide, containing a sulphation-promot- found that the products of the second and third lng catalyst, the improvement which consists in stages have a specific gravity within the range regulating the admission of the acid so that all 6.54 to 6.91. of the solid phase of the slurry is successively The process according to this invention is con converted to trtbasic lead sulphate and mono- ducted in its preferred embodiment over a five 45 basic sulphate, under a reaction temperature of to six hour period within the temperature range between 60* and about 95* C. of 60-95 C. The acetate ion--lead oxide (PbO), 2. The process of making basic lead sulphate or finely divided lead (Pb), and water ratios may of high pigmentary value which comprises pre vary over wide limits, depending on the character paring a slurry of lead oxide containing a sul- of the lead oxide or the finely divided lead used. 50 Phation-promoting catalyst, subjecting, the I have found, however, that the proportion, slurry to agitation and a temperature of not sub 1:60:520, is generally satisfactory, although I stantially less than 60* C. nor more than 95 C,, do not confine myself thereto. As an example admitting sulphuric acid thereinto in such of commercial procedure, there is added to a amount and rate that the solid phase becomes wooden tank containing about 2,000 gallons of 65 substantially wholly converted into and consti water, approximately 1920 pounds of finely di tuted of trlbasic lead sulphate, then feeding fur vided lead oxide PbO or metal Pb, or both, and ther sulphuric acid until such solid phase be approximately 40 pounds of 70% acetic acid. Air comes substantially wholly converted into and is blown through the slurry via port holes in the constituted of monobasic lead sulphate, there- tank bottom and the aerated slurry is agitated 55 after continuing said acid feeding under agita also by a stirrer at a temperature of 70-80* C. tion and heat, and ceasing this feeding when The sulphuric acid needed for the first stage will more than about 20% and less than about 60% be 61.5 gallons, for the second 61.5 gallons, and of normal lead sulphate has been produced in for the third 41 gallons, total 164 gallons of said solid phase. 33% acid. It is run in slowly and uniformly 65 3* The Process of making improved basic lead from stage to stage and over a total period ap sulphate which comprises preparing a slurry of proximating. as stated, about six hours. The lead oxide containing a sulphation-promoting amount for the first stage is ordinarily admitted catalyst, subjecting the slurry to agitation and relatively quickly and through a larger orifice, a temperature of not substantially less than 60" which is partially closed or substituted by a 70 C. nor more than 95* C., admitting sulphuric acid smaller one for the next following stages. The thereinto in such amount that the solid phn pulp is desirably agitated a short time before fil becomes substantially wholly converted into and tration. The filtrate will contain substantially constituted of trlbasic lead sulphate, then feeding all of the acetate radical charged and may be re further sulphuric acid until such solid phase be- cycled. The filter cake is dried in any appro 75 comes substantially wholly converted into and 0000-NLI-000018978 4 2,249,330 constituted of monobasic lead sulphate, there slurry in amount enough to convert all the oxide after continuing said acid feeding under agita Into hydrated tribaslc lead sulphate and continu tion and heat, and ceasing such admission when ing the agitation and heat until a first Increase about 37% or normal lead sulphate has been in electrical resistance of the liquid phase h produced in said solid phase. 5 occurred, then introducing more sulphuric acid 4. The process of mating Improved basic lead in amount not more than will convert all said sulphate which comprises preparing a slurry of tribaslc sulphate to monobasic sulphate and con lead oxide containing a sulphatlon-promotlng tinuing this Introduction over a period of about catalyst, subjecting the slurry to agitation by two hours under the same condition of agitation, air-blowing and to a temperature of not less 10 the temperature being at least about 60 C., until than 60 C. nor more than 95 C., admitting sul a second Increase in electrical resistance of the phuric acid thereinto in such amount that the liquid phase has occurred, the pH value then solid phase becomes substantially wholly con dropping to about 6.3. verted Into and constituted of tribaslc lead sul 9. The process of the preceding claim In which phate, then admitting further sulphuric add 15 following the second Increase of electrical re until such solid phase becomes substantially sistance, further sulphuric acid Is Introduced un wholly converted Into and constituted of mono der the same conditions of heat and agitation basic lead sulphate, thereafter continuing said until some normal lead sulphate has been acid admission, air blowing and heat, and ceas formed, not exceeding about .37%, and has co- ing the acid admission when more than about 20 alesced with the monobasic sulphate forming a 20% and less than about 60% of normal lead product composed mainly of acicular crystals. sulphate has been produced in said solid phase. 10. The process of making basic lead sulphate 5. The process of making Improved basic lead pigment which consists In Introducing sulphuric sulphate which comprises preparing a slurry of acid. In such amount and rate, into a slurry of lead oxide In the relative proportions of 60 lbs. 25 lead oxide containing sulphatlon-promotlng Ions, lead oxide to about 520 pounds of water and con while such slurry is being vigorously agitated, taining a sulphation-promoting catalyst, sub until the whole of the solid phase thereof Is con jecting such slurry to air-blast agitation and verted to hydrated tribaslc lead sulphate at one mechanical stirring and to a temperature of not time, said phase then containing no free lead less than about 60 C., admitting sulphuric add 30 oxide nor ^any other form of lead sulphate, and thereinto at such rate and amount that the solid phase becomes substantially wholly converted when this condition has been ascertained to ex ist, continuing the add introduction under like into and constituted of tribaslc lead sulphate, condition of agitation until the whole of the solid then admitting further sulphuric acid until such phase is converted into monobasic lead sulphate solid phase becomes substantially wholly con 35 at one time, containing no free lead oxide or verted into and constituted of coalesced crystals other form of lead sulphate, and separating such of monobasic and normal lead sulphate. solid phase as the product. 6. The process of making tribaslc lead sulphate which comprises preparing a slurry of lead oxide containing a sulphatlon-promotlng catalyst, and subjecting It to agitation and a temperature of 60 C. to 95 C., and admitting sulphuric acid thereto in amount not exceeding the ratio of about 61.5 gallons of approximately 33% acid to 1920 pounds of lead oxide. 7. The process of making monobasic lead sul phate which comprises preparing a slurry of lead oxide containing a sulphation-promoting catalyst, agitating it and beating it to a temperature of about 60 C. to 95 C., introducing sulphuric acid into such slurry In amount not exceeding the proportion of about 65.5 gallons of approximately 33% acid to 1920 pounds of lead oxide and con tinuing the agitation until the solid phase be comes wholly constituted of tribaslc lead sulphate and then Introducing more sulphuric acid not exceeding the same proportion until the whole of the solid phase becomes converted to mono basic lead sulphate. 43 60 55 11. The process of the preceding claim in which the add introduction Is continued further and until said wholly monobasic phase becomes partially converted to normal lead sulphate and contains not more than about 37% of such nor mal sulphate. 12. The process of making basic lead sulphate pigment which consists in agitating a slurry of lead oxide containing sulphatlon-promotlng ions by blowing air Into It and colnddently Introduc ing sulphuric acid Into such slurry In such amount and rate to convert the whole of the solid phase thereof Into hydrated tribaslc lead sulphate at one time, said solid phase then con taining no free lead oxide nor any other form of lead sulphate and, when this condition has been ascertained to exist, continuing the add introduction under like conditions of agitation until the whole of the solid phase is converted into monobasic lead sulphate at one time, con taining no free lead oxide or other form of lead 8. The process of making improved basic lead sulphate, and separating such solid phase as the sulphate pigment which comprises preparing a 60 product. slurry of lead oxide In water containing a sul 13. Basic lead sulphate produced by the proc phation-promoting catalyzer and maintaining ess set forth In claim 2, having the formula such slurry at a temperature above room tem perature and in constant agitation, introducing 2PbSOPbO and characterized by its pure white color and freedom from tribaslc lead sulphate. sulphuric acid into such heated and agitated 86 ALEXANDER STEWART. 0000-NU-000018979 CERTIFICATE OF CORRECTION. 5 Patent No. 2,214-9,330. ALEXANDER STEWART. July 15, I9J4I. It Is hereby certified that error appears In the printed specification of the above numbered patent requiring correction as follows: Page I4., first column, line I4., claim 3, for the word "or" read --of--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case In the Patent Office. Signed and sealed this 7th day of October, A. D. 19^1. (Seal) Henry Van Arsdale, Coranlssloner of Patents. 0000-NLI-000018980