L-Cysteine/Hydrotalcite Hybrid for Collaborative Removal of Cu(II), Hg(II) and Pb(II) Ions from Aqueous Solutions: Different Metal Ions Require Different Mechanisms

The L-cysteine/hydrotalcite hybrid has been synthesized by incorporating L-cysteine anion into the interlayer of hydrotalcite. The sample is purposed for the removal of Cu2+, Pb2+ and Hg2+ from aqueous solutions. The structure and morphology of L-cysteine/hydrotalcite are characterized by XRD, FTIR, SEM and BET. The effects of various physic-chemical factors such as pH, adsorbent dosage and contact time are investigated. The maximum adsorption capacities of L-cysteine/ hydrotalcite for Cu2+, Pb2+ and Hg2+ are 157.99, 81.24 and 215.90 mg/g, respectively, which are obviously higher than those of the pristine hydrotalcite. The adsorption kinetics are fitted by the pseudo-second order model. The adsorption isotherms are well described by the Langmuir equation. As confirmed by XRD and XPS analysis, a mechanism for adsorbed Cu2+ in the form of coordinated complexes and isomorphous substitution is proposed. In contrast, a precipitation mechanism is suggested for adsorbed Hg2+ and Pb2+. The results demonstrate that L-cysteine/hydrotalcite is a promising adsorbents for efficient elimination toxic metal ions from wastewater.