T H E SYSTEM :LITHIUM SULPHATE-ALUMIPI'CM SULPHATEWATER J. P. SASDERS AND J. T. DOBBINS
Introduction The alkali elements cesium, rubidium, potassium and sodium form alums with aluminum. Cesium forms the most stable alum, the stability decreasing with increase in atomic weight from cesium down to sodium. Since lithium has a lower atomic weight than sodium and is also a type element, it is of interest to know if this element forms an alum under any conditions. Previous investigators seem uncertain as to the formation of an alum by lithium and aluminum. The system, lithium sulphate-aluminum sulphate-water has not been studied to any great extent. Kralovanskyl stated that lithium aluminum sulphate-Li~S04.Al~(S04)~.2~H~0,-is formed on evaporation of a mixed solution of lithium sulphate and aluminum sulphate below 11.' Rammelsberg2 was not able to prepare the double sulphate and states that it does not exist. Schreinemakers and de WaaP made a more systematic study of the system and found that only the solid phases, LizSO4.HzO and A12(S04)3.~8H20 They found that when an unsaturated solution containing are present at 30'. equivalent quantities of lithium sulphate and aluminum sulphate was evaporated a t constant temperature crystals of A ~ z ( S O ~ ) ~ . I ~alooe H . Z separated. O As Kralovansky claimed to have obtained a lithium alum at 11' it was thought that possibly it might become a stable phase a t a temperature below that a t which Schreinemakers and de Kaal worked. Therefore, the isotherm at zero centigrade, was determined. Experimental Procedure
A series of solutions was prepared from lithium sulphate and aluminum sulphate by adding solid lithium sulphate to solutions of varying concentrations of aluminum sulphate in some cases and solid aluminum sulphate to solutions of lithium sulphate in others until a solid phase remalned in contact with solution. These solutions were kept immersed in an ice box containing crushed ice and water for six months. During this time the solutions were shaken several times each day. sampling The solutions u.ce sampled by pipetting and weighing small quantities of the clear solution from the bottles and making up to a known volume. The residues were sampled by dipping the solid from the bottles, draining the liquid, weighing the wet solids, dissolving and making to a known volume as in the case of the liquids. 1 Schweigger's J., 54,349 (1928). a
Sitzungsber. Akad. Wiss. Berlin, 1848, 385. Chem.Weekblad, 3, 539 (1906).
LITHIUM SULPHATE-ALUXINUM SULPHATE-WATER
3087
Methods of Analysis Sulphates-The sulphates were determined by precipitating with excess lead nitrate in solution and titrating the excess lead nitrate with sodium molybdate according to the method used by \Gley4 for the volumetric determination of lead. This method was tested satisfactorily before the analysis of this system was undertaken. Aluminum-The aluminum was determined by the precipitation of aluminum with lithium chloride and igniting the precipitate to 2Li20.5A1203. The procedure consists in adding an excess of lithium chloride solution to the sample of aluminum and making the solution just alkaline with ammonium hydroxide. The precipitate is washed, ignited and weighed as 2Li20.jA1203. Lithium-The lithium was calculated from the sulphate in excess of that equivalent to aluminum. The composition of the solid phase was determined from analysis of the wet residue, by use of tie-lines. Experimental Results
TABLE I Composition of Solutions and Corresponding Residues in the System : Lithium Sulphate-Aluminum Sulphate-Kater at Zero Solution Residue *~l2(S04), Li2S04 hlz(SO4)3 Li2S04 per cent
per cent
per cent
IO.IO
4 0 . IO
I O .61
36.51
3.53 5.09
11.40 12.80 14.65 1j.90
38.01 30.81
17.05
11.55
per cent
2j.02
0
26.30
0.99
23.30 20.15
4.51
19.31 19.00 18.14 17.80
16.60 16.I O 13.35 11.43 9.09 7.49 6.39 4.73 2.31 0
8.63
18.52
19.59 20.09 20.67 21.96 23.39 23.43
Ind. Eng. Chem., Anal. Ed., 2, 124 (1930).
5.48 2 . j6
5.79 1 3 .I O 26.j 5 54,OI 61.03
3088
J . P. SANDERS AND J. T. DOBBINS
Discussion of Results The results are plotted in Fig. I. The values are plotted as a three-component system : lithium sulphate-aluminum sulphate-water. The curve represented by continuous lines and points represented by circles indicate the results obtained a t zero degrees. The curve of Schreinemakers and deWaal is represented by broken lines and points by X. Curve aPs shows the various concentrations of lithium sulphate and aluminum sulphate in contact with Alz(S04).18HzO as solid phase and curve P8b the concentrations with Li&30a. HzO as solid phase. There is no indication of the existence of a lithium alum a t this temperature.
FIG.I Mutual Solubilities of Lithium Sulphate and Aluminum Sulphate in Kater a t Zero and 30 and j o Degrees.
The results indicate th:rt the solubility of each salt decreases with the increase in concentration of the other. On comparing the results with those found by Schreinemakers and de \Tad at 3 0 ° , it will be seen that a change of temperature does not have very much effect on the solubility of lithium sulphate in the presence of aluminum sulphate, whereas, the lowering of the temperature decreases materially the solubility of aluminum sulphate in the presence of lithium sulphate. Lithium sulphate is slightly more soluble at zero degrees than at 30'. After the completion of the investigation of the system a t zero degrees and comparing the results with those obtained by Schreinemakers and de JTaal at 30°, it was decided to determine the transition point for the A t this point the solution was found to contain 24.74 per system at 50'.
LITHICM SULPHATE-ALUMIXCM SULPHATE-WATER
3089
cent of aluminum sulphate and 11.93 per cent of lithium sulphate. The transition point at j o o is represented by PI; that a t 30 degrees by PZand that a t zero degrees by P3 in Fig. I . When the concentrations at the transition points at the three temperatures are compared, it is seen that as the temperature rises the lithium sulphate becomes less soluble and the aluminum sulphate more soluble. The transition point was determined at 2 5 degrees, the point is represented by P4. The solution contained 19.75$ &(so4)3 and 13.j jq LipSOI. Conclusions I . I n the system lithium sulphate-aluminum sulphate-water no lithium aluminum alum exists as a stable solid between zero and fifty degrees. 2. Lithium sulphate mono-hydrate and aluminum sulphate octodecahydrate are alone stable solid phases in contact with aqueous solutions between zero and fifty degrees. 3. The salts depress mutually the solubility of each other. 4. Change of temperature does not have much effect on the solubility of lithium sulphate in presence of aluminum sulphate. The lowering of the temperature decreases the solubility of aluminum sulphate in the presence of lithium sulphate. j. The increase in temperature displaces the transition point in the direction of higher concentration of aluminum sulphate and lower concentration of sodium sulphate. l'nzverszly of Sorth Carolzna, Chapel Hall, Sorth Carolzna.
