Precipitation of Basic Lead Acetate Effect of Small Amounts of Bismuth as Inhibitor DUDLEY HAINES HASKELL of insoluble lead salts due to sulfates, carbonates, silicates, lead acetate are used in W. P. Fuller & Company, San Francisco, Calif. etc., present as impurities. the production of many Numerous tests showed that lead salts. It is customary to all grades of litharge tested produce these acetates by disThe addition of measured amounts of bisreacted consistently in one solving various amounts of muth to solutions of acetic acid prior to the of these two categories. The litharge in dilute solutions of cause for the varying beacetic acid. addition of litharge show in a quantitative havior was not immediately Manufacturers of lead acemanner how the naturally occurring bisapparent until complete analytate recognize that different muth content of commercial lead affects ses of all brands tested inbrands of litharge exhibit the precipitation of basic lead acetate as dicated that the presence and varying behaviors when going practiced in color-making plants. amount of bismuth as an iminto solution. These variapurity in the litharge were tions are generally attributed Tests carried out with normal litharges responsible. to the impurities present in which have been analyzed for bismuth fit I n Figure 1 the contents of most commercial lead oxides in well with the values recorded here. A the flasks were made up accordand also t o the crystal problem still to be solved is: By what ing to the test cited above. s t r u c t u r e of t h e o x i d e s mechanism does bismuth act to prevent The litharge used contained (tetragonal a n d ortho0.01 per cent bismuth as an imrhombic). the precipitation of basic lead acetate? purity. The ingredients and I n considering the suitability the manner of treatment of A of a certain made and brand of litharge for-a given process, it is customary for the manuand B were identical except that, prior to dissolving the facturer to submit the material to an empirical test. One litharge in A , 0.0136 gram of bismuth trioxide was added to the acetic acid solution. This gave sample A the equivalent such test characteristic of those found to be popular among manufacturers of lead chromate pigments and lead naphof an impurity of 0.02 per cent bismuth, which was sufficient thenate driers is as follows: 25 ml. of glacial acetic acid are to prevent the precipitation of basic lead acetate a t this diluted to 500 ml., and 122 grams of the litharge sample are concentration:
I
EAD acetate and basic
Flask Sp. gr. of liquid phase W t .of Pb in 2 ml. of soln., gram
B
A 1.2312 0.4490
1.1678 0.3274
Pig lead is produced in this country under three standard grades (1): Grade I I1
I11
Type of Lead Corroding Chemioal Common
Max. Bi Content, % 0.05 0.005 0.25
Further investigation showed that the larger the amount of bismuth present, the greater the concentration of basic lead acetate before precipitation occurred.
Quantitative Tests on the Effect of Small Amounts of Bismuth To demonstrate the statement of the last paragraph, further small amounts of bismuth trioxide were added to the acetic acid solution before the addition of litharge. For convenience a litharge containing 0.010 per cent bismuth by analysis was selected for all the tests conducted as follows: I n every case 25 ml. of glacial acetic acid and 122 grams of litharge were used. The concentration of the solution was changed by varying the amount of water. The figures in Table I indicate the volume of dilute acetic acid before the addition of litharge. Prior to the addition of the litharge, bismuth trioxide was added in steps to give artificially contaminated samples of 0.01,0.02 per cent,0.03 per cent bismuth,
FIGURE 1. EFFECT OF BISMUTH TRIOXIDE IN PREVENTING PRECIPITATION OF BASIC LEADACETATE
gradually added and stirred until reaction is completed. The temperature is maintained a t 50" C. A satisfactory litharge is considered one which goes into solution and precipitates out in a voluminous mass of microscopic needles of basic lead acetate. A litharge considered unsatisfactory goes into solution but fails t o precipitate out, except for small amounts 873
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Vol. 33, No. 7
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLE I. PRECIPITATION IN DILUTEACETIC ACID SOLUTIONS Sample 2
Bi content % Biz08 addeh, gram MI. of water in B MI. of water in A
0.0063
Sample 1
,--
None
0.01
None
0.02 0 0136
0.03 0.0272
0.04 0.0408
0.0644
535(+) 545(-)
520(i) 525(-)
45O(f)
430(+)
400(+) 430(-)
390(+)
% BISMUTH
FIGURE 2.
450(-)
ZOO(-)
0.05
400(-)
ACETIC
~01,UI'IOVS
etc. The (+) sign indicates that precipitation takes place, as in sample B. The (-) sign indicates that precipitation does not take place, as in sample A . The relatively slight precipitate which does occur in A (Figure 1) is not basic lead acetate but mainly lead J carbonate. Litharge rapidly absorbs carbon dioxide from the air. Although this lead carbonate appears somewhat bulky in Figure IA, in most cases i t amounts to less than 0.5 gram and is consequently of slight significance in the equilibrium. I n cases of doubtful precipitation the classification can be positively established by a microscopic examination of the precipitate. If no needles occur, i t is safe to assume that the normal precipitation of basic lead acetate has been inhibited by the presence of bismuth. Figure 2 is constructed from the data of Table I. Below the dashed line precipitation occurs. Above
0.07 0.081
0.0952
0.09 0.1088
0.1224
365(+) 3SO(-)
357(+)
350(+) 357(-)
340(+) 350(--)
0.08 365(-)
0.10
graphed after 6 months of standing at 25" C. In heavier concentrations (when precipitation was not quickly obtained) a slow precipitation of basic lead acetate gradually occurred, but only after several Tveeks or months of standing. 6. When bismuth is present with amounts greater than 0.25 per cent litharge in concent,rations within the above range, precipitation does occur against the rule. This led to confusion in discovering the characteristics of the limited range presented above. The peculiarity is mentioned, but its investigation has not yet been attempted. In commercial litharge bismuth will seldom be out of the range of 0.002 to 0.15 per cent.
!N 122 GMS. LlTHARGE
PRECIPITATIOK I S D I L U T E
0.06 0 068 380(+) 3YO(-)
PRECIPITATE
'
260-
'
'
'
.02 .04 .OB .08
0
'
'
.!O
,I2
./ 4
.I 6
.I8
.20 . 2 Z
BISMUTH, GRAMS PER
FIGURE
3.
PLOT O F DAl.4 IN
.2 4 .26
2 8 3 0 .32 3 4 3 6
LITER
TABLE 11
Experimenters have recorded in detail the equilibrium reactions (4) of the system lithargelead acetate-water. Yet the literature on lead Bismuth, contains only meager references to the importance G./L. of bismuth as an impurity on the reactions of lead 0.182 0.186 compounds (9, 6). Small amounts and traces of bismuth are known to affect the purity of color 0.258 of leadpigments (8) and also to have a deleterious 0.264 0.297 effect on the performance of st,orage batt,eries using lead oxide grids (7). The difficulty of 0.346 bismuth removal (6) as an impurity from lead ensures its presence in practically all commercial grades of litharge. It would therefore seem that the present findings could serve as the foundation for a practical appraisal of litharges by pigment manufacturers and also for more extended investigations of this phenomenon.
OF BISMUTH ON PRECIPITATIOX TABLE 11. EFFECT
y Bi in
LTtharpe 0.01 0.01 0.02 0.02 0.03 0.03
0.04 0.04 0.05 0.05
Precipitation None Ppt. None Ppt. None P t. &ne Ppt. None Ppt.
Basic Lead Acetate, G./L.
Bismuth, GJL.
Bi in Lltharge
319.3 319.3 337.7 337.7
0,0476 0.0527 0.0790 0.0826 0.110
0.06 0.06 0.07 0.07 0.08 0.08 0.09
357.8
0,118 0.148
0.1 0.09
274.7 277.3
288.1
357.8
366.8
0,0227
0.022~
0.151
0.1
Precipitation None Ppt. None P t &,de Ppt. None
p ;ie Ppt.
Basic Lead Acetate, G./L. 366.8 376.1 391.0 399.5 399.5
2:;:;
431.0
the solid line basic lead acetate remains in solution. The area between the lines represents conditions where precipitation is indefinite. Figure 3 represents the data of Table 11, obtained by converting the figures of Table I to grams per liter. I n making these tests the following precautions were observed: 1. The litharge mas as free as possible from carbon dioxide or 2.
3. 4.
5.
other impurities. The glacial acetic acid was redistilled prior to use, with only the middle fraction retained. The temperature of the solution was kept between 50" and 55' C. during the addition of the litharge. The bismuth trioxide was completely dispersed in solution before addition of litharge. The material was stirred for a t least 30 minutes. In the more dilute concentrations the inhibiting action of bismuth seemed to be permanent. Samples A and B were photo-
::;::
Acknowledgment The author wishes to thank P. Van Rysselberghe of Stanford University for his assistance.
Literature Cited (1) A. S. T. M. Staylards, P a r t I. p. 594 (1930). (2) Hofman, H. O., Metallurgy of Lead", 1st ed., p. 18, New York, McGraw-Hill Book Co., 1918. (3) Ibid., p. 240. (4) Jackson, R. F., U. 5. Bur. Standards, Sci. Paper 232 (1914). ( 5 ) Smythe, J. A., "Lead". p. 147, New York, Longmans, Green & Co., 1923. (6)Ibjd., p. 255. (7) Vinal, G. W., "Storage Batteries", 2nd ed., pp. 112-14, New York, John Wiley & Sons, 1930.
