Table 5. Rate constants k and correlation coefficients R² for the leaching of Ni at different temperatures for the chemical reaction controlled model and the diffusion through the product layer model.

	Saprolite laterite				Limonite laterite
	Diffusion through the product layer		Chemical reaction		Diffusion through the product layer		Chemical reaction
	1 − 2/3x−(1 − x)2/3		1 − (1 − x)1/3		1 − 2/3x−(1 − x)2/3		1 − (1 − x)1/3
	k	R 2	k	R 2	k	R 2	k	R 2
100	0.000876	0.99036	0.003119	0.95677	0.000812	0.99038	0.097538	0.95461
120	0.001035	0.99684	0.003451	0.96923	0.000959	0.99694	0.006491	0.96684
140	0.001225	0.99632	0.003838	0.98212	0.001134	0.99661	0.006858	0.98007
160	0.001494	0.9903	0.004378	0.98267	0.001361	0.9926	0.00725	0.98002
180	0.001851	0.99607	0.005108	0.98953	0.001751	0.99652	0.00775	0.97907