Thermodynamic Properties of Ga(III)-Hydroxysalt in Sulfate Aqueous Solution

• Published in: Transactions of the Japan Institute of Metals 1988, Vol.29(2), pp.160-169
• Main Authors: Yamauchi, Chikabumi, Sakao, Hiroshi
• Format: Article
• Language: English
• Subjects: gallium; gallium-hydroxysalt; hydrolysis; neutralization; solubility; sulfate aqueous solution; titration curve
• ISSN: 0021-4434; 2432-4701
• DOI: 10.2320/matertrans1960.29.160

The present investigation was carried out to examine the chemical composition of precipitates produced during a titration of aqueous solution containing gallium sulfate with sodium hydroxide, to obtain the standard free energy of formation of Ga(III)-hydroxysalt, and to determine the pH-dependence of its solubility at 333 K. The results obtained are summarized as follows. (1) The hydrolysis proceeds via two steps. The precipitates produced in the first and second step hydrolyses were identified to be {Nax, (H3O)1−x}Ga3(SO4)2(OH)6, where the value of x varies with the composition of the solution, and GaOOH, respectively. These Hydrolysis reactions are represented by xNa++3Ga3++αSO42−+βHSO4−+(7−x)H2O={Nax, (H3O)1−x}Ga3(SO4)2(OH)6+(5+x+β)H+, where α+β=2, and {Nax, (H3O)1−x}Ga3(SO4)2(OH)6+(x−1)H2O=3GaOOH+(x⁄2)Na2SO4+{(4−x)/2}H2SO4. (2) The standard free energies of formation of {Nax, (H3O)1−x}Ga3(SO4)2(OH)6 were obtained for the x-values of 0.13, 0.22, 0.38 and 0.66 at 333 K. (3) The pH-dependence of the solubility of {Nax, (H3O)1−x}Ga3(SO4)2(OH)6 was determined for various choices of the parameter, which can be calculated from the initial composition of solutions.