Dissolution, Solubility, and Stability of the Basic Ferric Sulfate-Arsenates [Fe(SO₄)_x(AsO₄)_y(OH)_z·nH₂O] at 25–45°C and pH 2–10

Table 3

Experimental data and solubility determination for the basic ferric sulfate-arsenate FeSAsOH-2 [Fe(SO₄)_0.37(AsO₄)_0.59(OH)_0.49·0.28H₂O].

Temp (°C)	Initial pH	Time (h)	Dissolution data (mmol/L)				log_IAP	Mean log_IAP	ΔGf^o (kJ/mol)	Mean ΔGf^o (kJ/mol)
			pH	Fe	SO4	AsO4
25^a	2	5760	2.08	1.466507	1.233705	0.077881	−22.03	−22.01	−931.40	−931.31
		6480	2.09	1.469193	1.222011	0.078749	−22.00	±0.02	−931.28	±0.09
		7200	2.09	1.468476	1.222011	0.078682	−22.00		−931.28
		7920	2.09	1.469551	1.220452	0.078349	−22.00		−931.29
25	6	5760	3.00	0.065984	0.634473	0.000728	−23.46	−23.45	−939.59	−939.56
		6480	3.00	0.066342	0.642113	0.000745	−23.45	±0.01	−939.54	±0.03
		7200	3.00	0.066432	0.641022	0.000730	−23.46		−939.57
		7920	3.00	0.066342	0.646479	0.000735	−23.45		−939.55
25	10	5760	3.05	0.052823	0.601104	0.000611	−23.59	−23.59	−940.35	−940.33
		6480	3.04	0.053987	0.604534	0.000604	−23.59	±0.00	−940.33	±0.02
		7200	3.04	0.054076	0.602195	0.000606	−23.59		−940.32
		7920	3.04	0.054041	0.601572	0.000608	−23.59		−940.32
25^b	2	5760	2.06	1.463821	1.244932	0.073477	−22.08	−22.06	−931.70	−931.62
		6480	2.07	1.462030	1.235109	0.074745	−22.06	±0.02	−931.58	±0.08
		7200	2.07	1.461672	1.226377	0.074011	−22.06		−931.59
		7920	2.07	1.462925	1.228872	0.073677	−22.06		−931.60
35	2	5760	2.02	1.420846	1.403979	0.060930	−22.11	−22.10
		6480	2.02	1.423532	1.405071	0.060797	−22.11	±0.01
		7200	2.03	1.426218	1.396495	0.060130	−22.09
		7920	2.02	1.425144	1.401173	0.060730	−22.11
45	2	5760	1.97	1.292818	1.598266	0.057994	−22.17	−22.19
		6480	1.96	1.283865	1.626333	0.058461	−22.19	±0.02
		7200	1.96	1.277598	1.615886	0.058261	−22.19
		7920	1.96	1.282970	1.611676	0.058394	−22.19

^a,b Dissolution tests in duplicate.