Fig. 6

a Effect of the initial pH [initial concentration of Pb(II) and Cr(VI): 100 mg L^− 1; adsorbent dose: 0.06 g; T = 25 °C; contact time: 135 min], b point of zero charge, c contact time [initial concentration of Pb(II) and Cr(VI): 100 mg L^− 1; adsorbent dose: 0.06 g; T = 25 °C; initial pH for Pb(II) and Cr(VI); 3.0 and 5.2], d adsorbent dose [initial concentration of Pb(II) and Cr(VI): 100 mg L^− 1; T = 25 °C; initial pH for Pb(II) and Cr(VI); 3.0 and 5.2; contact time: 250 min], e initial metal concentration [T = 25 °C; initial pH for Pb(II) and Cr(VI); 3.0 and 5.2; contact time: 250 min; adsorbent dose: 0.06 g] and f temperature [initial concentration of Pb(II) and Cr(VI): 100 mg L^− 1; adsorbent dose: 0.06 g; contact time: 135 min; adsorbent dose: 0.06 g] for the adsorption of Pb(II) and Cr(VI) onto CSM/SA hybrid beads