Optimization of Preparation of Activated Carbon from Ricinus communis Leaves by Microwave-Assisted Zinc Chloride Chemical Activation: Competitive Adsorption of Ni²⁺ Ions from Aqueous Solution

Table 1

Design factors and levels.

Independent variables	Symbol	Range and levels
		1	2	3	4
Radiation power (W)	A	100	200	400	600
Radiation time (min)	B	4	6	8	10
Concentration of ZnCl2 (vol%)	C	30	40	50	60
Impregnation time (h)	D	16	20	24	28