Multicomponent adsorption of heavy metals onto biogenic hydroxyapatite: Surface functional groups and inorganic mineral facilitating stable adsorption of Pb(Ⅱ)

Due to the coexistence of various heavy metals in the contaminated environment, it is essential to comprehensively study the multicomponent adsorption of heavy metals in order to tackle these combined pollutants. Herein, the adsorption processes of Pb(Ⅱ), Cu(Ⅱ) and Cd(Ⅱ) by biogenic hydroxyapatite (BHAp) were investigated in single and multicomponent systems. The maximum adsorption capacity for Pb(Ⅱ), Cu(Ⅱ) and Cd(Ⅱ) by BHAp in single system reached 311.16, 82.05 and 92.54 mg g-1, respectively, while adsorption capacity for Cu(Ⅱ) and Cd(Ⅱ) in multicomponent system decreased more obviously than that of Pb(Ⅱ). Furthermore, the stability of Cu(Ⅱ) and Cd(Ⅱ) adsorbed on BHAp was indeed influenced in multicomponent system. By means of the characterization analysis, it was found that ion exchange was more instrumental in the adsorption processes of Cu(Ⅱ) and Cd(Ⅱ) in single system than in multicomponent system. Significantly, it was observed that the proportion of generally stable Pb(II) adsorbed on BHAp exceeded 95% in both single and multicomponent systems. This result might be due to the in-site growth of stable crystals of PbxCa10-x(PO4)6(OH)2, which was synergistically induced by surface functional groups and inorganic mineral of BHAp, and was unaffected by the coexistence of Cu(Ⅱ) and Cd(Ⅱ).