Table 4.

Intra-particle diffusion constants for Cu (II) removal using ZnO as adsorbent.

Sample	10−2 ki1 (mg g−1 min−0.5)	Ci1 (mg g−1)	$r_{\mathrm{\text{i1}}}^2$	10−2 ki2 (mgg−1 min−0.5)	Ci2 (mg g−1)	$r_{\mathrm{\text{i2}}}^2$
Zn-AL	0.918	0.292	0.9906	0.120	7.989	0.9996
Zn-ST	1.160	0.006	1.0000	0.065	8.482	1.0000