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 2

Experimental data and solubility determination for the basic ferric sulfate-arsenate FeSAsOH-1 [Fe(SO₄)_0.27(AsO₄)_0.73(OH)_0.27·0.26H₂O].

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	1.98	0.122388	0.099170	0.060330	−23.04	−23.04	−914.05	−914.06
		6480	1.98	0.122030	0.096832	0.059796	−23.05	±0.01	−914.09	±0.03
		7200	1.98	0.123373	0.099482	0.059996	−23.04		−914.04
		7920	1.98	0.122746	0.099170	0.059863	−23.04		−914.06
25	6	5760	3.68	0.000252	0.069076	0.007664	−25.19	−25.22	−926.33	−926.47
		6480	3.68	0.000253	0.068764	0.006838	−25.23	±0.03	−926.53	±0.14
		7200	3.68	0.000257	0.069232	0.006851	−25.22		−926.49
		7920	3.68	0.000254	0.068453	0.006837	−25.22		−926.52
25	10	5760	4.03	0.000217	0.072195	0.010698	−25.22	−25.24	−926.50	−926.59
		6480	4.04	0.000203	0.072195	0.010925	−25.25	±0.02	−926.64	±0.09
		7200	4.04	0.000207	0.072663	0.010887	−25.24		−926.59
		7920	4.04	0.000203	0.072351	0.010961	−25.24		−926.63
25^b	2	5760	1.98	0.130983	0.079056	0.068739	−22.99	−22.97	−913.76	−913.64
		6480	1.99	0.132236	0.078588	0.069339	−22.96	±0.02	−913.60	±0.12
		7200	1.99	0.132594	0.079991	0.068538	−22.96		−913.61
		7920	1.99	0.133669	0.079523	0.068605	−22.96		−913.59
35	2	5760	1.94	0.152202	0.135814	0.041910	−23.06	−23.04
		6480	1.95	0.153634	0.138153	0.042044	−23.03	±0.02
		7200	1.95	0.153813	0.136593	0.041510	−23.04
		7920	1.95	0.153545	0.136749	0.041910	−23.04
45	2	5760	1.91	0.267427	0.244496	0.036772	−22.86	−22.86
		6480	1.92	0.272351	0.246679	0.035837	−22.84	±0.02
		7200	1.91	0.270829	0.247302	0.035103	−22.87
		7920	1.91	0.271187	0.246211	0.035771	−22.86

^a,bDissolution tests in duplicate.