Lead adsorption by silica-immobilized humin under flow and batch conditions: Assessment of flow rate and calcium and magnesium interference

Batch and column experiments were performed to determine the Pb(II) binding ability of silica-immobilized humin biomass under different conditions. Batch experiments were performed to determine the interference of Ca(II) and Mg(II) and column experiments were used to determine the effect of flow rate and the presence of Ca(II) and Mg(II) on the Pb(II) adsorption by the humin biopolymer. The results from the batch experiments showed that Pb binding decreased as the concentrations of Ca and Mg increased. At a concentration of 100 mM, the interference of Ca alone was 36%, while for Mg it was 26%; however, when both cations were present, the interference increased up to 42%. Column experiments were performed at flow rates of 1, 1.5, 2, and 3 mL min−1 using a 0.1 mM Pb(II) solution. The results showed that the highest Pb adsorption was obtained at the flow rates of 1 and 1.5 mL min−1. The average Pb binding capacity at these two flow rates was 182.3 ± 0.7 μM Pb g−1. In addition, a recovery of 99.5 ±0.3% was obtained. Immobilized humin exposed under flow conditions to Pb-Ca, Pb-Mg or Pb-[Ca + Mg] solutions (Pb used at 0.1 mM and Ca and Mg at 1 mM) showed a Pb binding capacity of 161 ± 5, 175 ± 5, and 171 ± 1 μM g−1, respectively. In mixtures containing Pb-Ca, Pb-Mg and Pb-Ca-Mg, the Pb recovery was 89.8% ± 0.35, 90.3% ± 0.43, and 88.1% ± 0.5, respectively. Pb recovery was performed using 30 bed volumes of 0.1 M HCl as stripping agent. The results of these experiments demonstrated that silica-immobilized humin biomass has the potential for Pb removal from aqueous solution even in the presence of 20 mM of calcium and magnesium.