Dissolution and Solubility of the (B a x S r 1 - X)HAsO4· h2O Solid Solution in Aqueous Solution at 25°C and pH 2

Six different members of the (ba x sr 1 - x)haso4·h 2o solid solution were prepared and characterized,and then dissolution of the synthetic solids was studied at 25°c and ph 2 in a series of batch experiments for 4320 h. with the increase in the ba/(ba + sr) mole fraction of the solids,the aqueous ph decreased and the aqueous barium concentration increased. the aqueous strontium and arsenic concentrations had the highest values at ba / (ba + sr) = 0.21. the solubility products for bahaso4·h2o and srhaso4·h 2o were calculated to be 10 - 5.52 and 10 - 4.62,respectively. the corresponding free energies of formation were determined to be - 1543.99 ± 0.18 kj/mol and - 1537.94 ± 0.02 kj/mol. the solid solution had a minimum solubility product of 10 - 5.61 at ba / (ba + sr) = 0.82. the guggenheim coefficients were determined to be a o = 1.55 and a 1 = - 4.35. the lippmann diagram was a typical lippmann diagram for a nonideal solid solution with a negative enthalpy of mixing. the system shows an alyotropic minimum at the aqueous ba / (ba + sr) activity fraction of 0.87 where the solutus and solidus curves meet. at the end of the dissolution experiment,the dissolution followed the saturation curve for the pure endmember bahaso 4 ·h2o and approached the intersection with the minimum stoichiometric saturation curve on the lippmann diagram. © 2014 xuehong zhang et al.