Intra-particle diffusion parameters for Cu(ii), Zn(ii), Cd(ii), and Pb(ii) adsorption onto SiPy.

Metal ions	K p1	C 1	R 2	K p2	C 2	R 2
Cu(ii)	3.941	71.755	0.875	−0.011	90.3	0.728
Zn(ii)	3.367	59.635	0.960	0.011	75.251	0.861
Cd(ii)	1.779	46.345	0.935	0.054	54.906	0.980
Pb(ii)	0.777	31.097	0.716	0.01	35.054	0.728