Table 3.

Parameters determined for Zn(II) sorption on mineral-organic sorbent.

Model	Parameter	System
		Zn	Zn/Cu/Sr	Zn/Ni/Cu	Zn/Cu/Sr/Ba
Kinetic studies
PSO	qe,cal, mg/g	1.1	0.93	1.3	1.2
	k2, g/mg·min	0.05	0.06	0.04	0.02
	R 2	0.99	0.99	0.98	0.98
Equilibrium Studies
Langmuir	qm, mg/g	6.5	3.4	3.7	3.4
	b, L/mg	0.02	0.04	0.03	0.03
	RL	0.3–0.8	0.1–0.6	0.3–0.8	0.2–0.8
	R 2	0.99	0.95	0.98	0.99
Thermodynamic Studies
∆G°, kJ/mol	293 K	−9.7	−10.4	−9.9	−9.8
	303 K	−10.4	−10.6	−10.4	−10.6
	313 K	−11.1	−11.3	−11	−11.2
	323 K	−11.8	−12.1	−11.6	−11.8
	∆H°, kJ/mol	11	11.6	7.4	8.1
	∆S°, J/mol·K	70	33	59	61.5
	R 2	0.93	0.88	0.98	0.78

q_{e, cal} is the quantities of metal (mg/g) sorbed from the solution at equilibrium time, respectively, k₂ (g/mg·min) is the second-order rate constant, q_m is maximum adsorption capacity (mg/g), b is Langmuir adsorption constant (L/mg), R² is coefficient of determination, ΔG° is Gibbs free energy change, ΔH° is enthalpy change, and ΔS° is entropy change.