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 6

Experimental data and solubility determination for the basic ferric sulfate-arsenate FeSAsOH-5 [Fe(SO₄)_0.24(AsO₄)_0.70(OH)_0.42·0.16H₂O].

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	1.96	0.156678	0.120377	0.028163	−24.29	−24.27	−879.30	−879.20
		6480	1.97	0.157752	0.121780	0.028096	−24.27	±0.02	−879.16	±0.10
		7200	1.97	0.157842	0.122092	0.027896	−24.27		−879.17
		7920	1.97	0.157484	0.123651	0.028163	−24.27		−879.16
25	6	5760	3.90	0.000913	0.079679	0.001860	−26.01	−26.01	−889.09	−889.12
		6480	3.89	0.000902	0.081083	0.001853	−26.01	±0.00	−889.11	±0.03
		7200	3.89	0.000894	0.081083	0.001844	−26.01		−889.14
		7920	3.89	0.000897	0.081239	0.001849	−26.01		−889.12
25	10	5760	4.16	0.000584	0.093557	0.002324	−26.16	−26.17	−889.95	−890.05
		6480	4.15	0.000573	0.090750	0.002227	−26.18	±0.01	−890.08	±0.10
		7200	4.15	0.000570	0.090594	0.002232	−26.18		−890.09
		7920	4.15	0.000572	0.091374	0.002228	−26.18		−890.08
25^b	2	5760	1.96	0.160080	0.125211	0.027562	−24.29	−24.26	−879.28	−879.15
		6480	1.97	0.163393	0.127238	0.027095	−24.26	±0.03	−879.13	±0.13
		7200	1.97	0.163751	0.125834	0.027762	−24.25		−879.08
		7920	1.97	0.163482	0.127082	0.027562	−24.25		−879.10
35	2	5760	1.94	0.240299	0.208788	0.006020	−24.49	−24.48
		6480	1.94	0.247909	0.212998	0.005877	−24.48	±0.01
		7200	1.94	0.246925	0.208320	0.005908	−24.48
		7920	1.94	0.247014	0.212842	0.005897	−24.48
45	2	5760	1.88	0.373162	0.342887	0.004635	−24.42	−24.40
		6480	1.89	0.373700	0.345070	0.004664	−24.39	±0.02
		7200	1.89	0.373521	0.344290	0.004661	−24.39
		7920	1.89	0.374147	0.345849	0.004678	−24.39

^a,bDissolution tests in duplicate.