Table 3.

Second order kinetic model and Hill sorption model parameters for the adsorption of Cd(II), Pb(II) and Zn(II) onto biochars. Kinetics conducted at initial concentration 5 mg.L⁻¹ and pH 7. Sorption isotherms with concentrations starting at 0.05 mg.L⁻¹ to 50 mg.L⁻¹ (Zn with pH 7.5 and Cd with pH of 6.5) and up to 85 mg.L⁻¹ for Pb (pH 5), contact time = 24 h, t = 22 ± 2 °C. Values are parameters means ± standard deviation; different letters indicate significant differences in parameters between biochars grouped by element (p < 0.05; pairwise ONE-WAY ANOVA).

		Second order kinetic model		Hill sorption model
Element	Biochar	k2 (g.mg−1.min−1)	Qe (mg.g−1)	n	qm (mg.g−1)	KH (mg.L−1)
Pb	MSP550	0.8 ± 0.2 a	0.345 ± 0.003 a	0.7 ± 0.2 a	41 ± 8 a	1 ± 1 a
	OSR550	0.27 ± 0.03 b	0.348 ± 0.002 a	2.7 ± 0.7 b	46 ± 4 a	0.22 ± 0.03 b
	OSR700	0.19 ± 0.03 c	0.368 ± 0.005 c	3.2 ± 0.3 b	56 ± 1 b	0.137 ± 0.005 c
	SWP550	0.10 ± 0.02 bc	0.344 ± 0.007 b	-	0.44∗	-
	WSP550	0.53 ± 0.06 d	0.346 ± 0.001 a	2.1 ± 0.5 b	42 ± 3 a	0.19 ± 0.02 b
Cd	MSP550	0.079 ± 0.008 a	0.877 ± 0.007 a	1.4 ± 0.3 a	8.0 ± 0.7 a	2.6 ± 0.6 a
	OSR550	0.16 ± 0.01 b	0.882 ± 0.004 a	3.0 ± 0.8 b	19 ± 1 b	0.71 ± 0.06 b
	OSR700	0.068 ± 0.007 a	0.883 ± 0.008 a	6.4 ± 0.6 c	20.5 ± 0.5 b	0.335 ± 0.005 c
	SWP550	0.5 ± 0.4 d	0.089 ± 0.006 a	-	10.31∗	-
	WSP550	0.13 ± 0.02 c	0.875 ± 0.007 a	6 ± 1 bc	18 ± 1 b	1.53 ± 0.06 a
Zn	MSP550	0.28 ± 0.05 a	1.070 ± 0.005 a	1.0 ± 0.5 a	3.3 ± 0.3 a	0.10 ± 0.06 a
	OSR550	0.36 ± 0.05 a	1.081 ± 0.003 a	1.6 ± 0.2 a	8.6 ± 0.3 b	0.068 ± 0.009 a
	OSR700	0.38 ± 0.07 a	1.046 ± 0.004 b	4.0 ± 0.6 b	10.7 ± 0.4 c	0.045 ± 0.002 b
	SWP550	0.06 ± 0.04 b	0.27 ± 0.03 ab	-	0.67∗	-
	WSP550	0.4 ± 0.1 a	1.075 ± 0.006 a	4 ± 1 a	6.2 ± 0.6 a	0.034 ± 0.004 c

^∗Highest sorption capacity determined experimentally.