Fig. 2. Effect of initial solution pH on the adsorption of Cu(ii), Zn(ii) and Pb(ii) onto prepared adsorbent PEI-RCSA (conditions: 25 ± 1 °C; adsorbent dosage: 1 g L⁻¹; shaking speed: 130 rpm; contact time: 8 h; C₀: 200 mg Cu per L, 200 mg Zn per L and 200 mg Pb per L).