T H E SOLUBILITY OF LEAD SULFATE I N AQUEOUS SOLUTIONS OF SULFURIC ACID AT HIGH CONCENTRATIONS H. D. CROCKFORD Department of Chemistry, University of North Carolina, Chapel Hill, N . C . AND
J. A. ADDLESTONE Department o j Chemistry, Virginia Polytechnic Institute, Blacksburg, Virginia Received August 20, 1996
Crockford and Brawley (1) have determined the solubility of lead sulfate in aqueous sulfuric acid solution up to 80 per cent acid at 0", 25", 35", and 50°C. Donk (2) has made a systematic study of the same system up to approximately 100 per cent acid at 0", 50°, loo", 150", and 200°C. His work was concerned principally with the composition of the solid phases and his actual solubility data are quite meager, in some cases being completely lacking. A complete discussion of the relationships in the binary system sulfuric acid-water is given by Mellor (3). The purpose of the work reported in this paper was to add to the data of the ternary system, particularly at the higher acid concentrations. To this end solubility data have been determined a t acid concentrations up to approximately 104 per cent sulfuric acid, corresponding to 80.5 per cent sulfur trioxide, at 0", 25", 35") and 50°C. The eutectic temperature in the binary system lead sulfate-sulfuric acid has also been determined. EXPERIMENTAL
The usual procedure employed for solubility measurements was followed. Various mixtures were allowed to come to equilibrium in glassstoppered bottles, properly agitated in constant temperature baths. The temperatures were constant to f0.02'C. at the three higher temperatures. For the 0°C. isotherm the temperature was never over 0.1"C. Equilibrium was rapidly attained in those cases in which lead sulfate was the only solid phase. When sulfuric acid or one of its hydrates was a solid phase, considerable trouble from supercooling was experienced. The materials employed were prepared and purified according to the methods used by Crockford and Brawley (1). The analytical procedures were likewise the same. The compositions of the solid phases were obtained by the method of 303
304
H. D. CROCKFORD AKD J. A . ADDLESTOKE
intersecting tie-lines. For the determination of the lead sulfate-sulfuric acid eutectic temperature, the usual cooling curve method was used. DATA A K D CONCLUSIONS
The data obtained for the 25", 35", and 50°C. isotherms were plotted on large coordinate paper and the best curve drawn through the points. The concentrations given in table 1 are taken from these curves. I t was TABLE 1 Solubility of lead sulfate i n aqueous s u l j u k aczd at 25", S5', and 50'C. LEAD SULFATE,
CONCENTRATION O F ACID IN P EIGET PER CENT
I
25°C.
80 85 90 95 100 101 102 103
1s MILLIGRAMS
PER
1000
35°C
11.5 60.0 200 800 18,000 31,000 47,000 63 ,OOO
24.0 100 318 1,060 22,000 36,000 52,000 68,000
G . OF SOLCTIOK, AT
I
50'C
42.0 130. 380 1,260 27,600 42,000 56,000 72,000
TABLE 2 Data )r the 0°C. isotherm ACID CONCENTRANO.
TION I N WEIGHT P E R CENT
LEAD SVLFATE I N MG. P E R 1000 G . OF SOLUTION
SOLID P H A S E S ~
77.48 79.10
4.2 8.6
89.44
42 0
91.69 94 03 96.52 97.08
272 680 2200 3000
Lead sulfate Lead sulfate and sulfuric acid monohydrate Lead sulfate and sulfuric acid monohydrate Lead sulfate Lead sulfate Lead sulfate Lead sulfate and sulfuric acid
not thought worthwhile to give the data for the met residues. The results agree with those of Donk, in that lead sulfate is the only solid phase at these temperatures. I n table 2 are given the data for the 0°C. isotherm as actually determined. No solutions exist above 97.08 per cent. The lead sulfatesulfuric acid eutectic temperature was found to be 5.4"C. If all the data available on the ternary system are plotted it is found that
SOLUBILITY OF LEAD SULFATE
305
lead sulfate exists as the only solid phase over the major part of the diagram. On the lead sulfate-water side of the diagram the binary eutectic is of course a t practically 0°C. On the lead sulfate-sulfuric acid side is the one eutectic whose temperature is given above. On the sulfuric acidwater side are found three hydrates of sulfuric acid. Two of these have definite melting points. Only the monohydrate exists above 0°C. Within the diagram will be four ternary eutectics, all of which will occur very close to the sides of the diagram. The 0°C. isotherm shows the existence of five solubility curves. On two of these the solid phase is lead sulfate; on two others it is the monohydrate of sulfuric acid; on the other it is anhydrous sulfuric acid. The values of the acid concentrations at the intersections of these curves (solutions 2, 3, and 7), are essentially the same as the values given by Donk. SUMMARY
The solubility of lead sulfate in various solutions of sulfuric acid at concentrations above 80 per cent and a t O", 25", 35O, and 50°C. has been determined. The solid phase at 85", 35", and 5OoC. is always lead sulfate. At 0°C. sulfuric acid and sulfuric acid monohydrate also exist as solids REFERENCES (1) CROCKFORD AND BRAWLEY: J. Am. Chem. Soc. 66, 2600 (1934). (2) DONK:Chem. Weekblad 13, 92 (1916). (3) MELLOR:A Comprehensive Treatise on Inorganic and Theoretical Chemistry, Vol. X, p. 352. Longmans, Green and Co., London and New York (1930).
