Effective removal of Cu(II), Pb(II) and Cd(II) by sodium alginate intercalated MgAl-layered double hydroxide: adsorption properties and mechanistic studies

To improve the adsorption efficiency of layered double hydroxides (LDHs) for heavy metals, a novel sodium alginate (SA) intercalated MgAl-LDH (SA-LDH) was synthesized in this work. SA-LDH was characterized by XRD, FTIR, XPS and employed as adsorbent for Cd(II), Pb(II), Cu(II) elimination. Adsorbent dosage, initial pH and contact time, which are regarded as several key parameters, were optimized. The results showed that SA-LDH exhibited better adsorption performance compared with the pristine MgAl-LDH. The maximum adsorption capacities of SA-LDH for Cu(II), Pb(II) and Cd(II) reached 0.945, 1.176 and 0.850 mmol/g, respectively. The possible mechanisms were analyzed by XPS, XRD and FTIR. The results showed that Cd(II), Pb(II) and Cu(II) may be removed by SA-LDH via (i) bonding or complexation with Sur-OH or Sur-O- of SA-LDH, (ii) precipitation of metal hydroxides or carbonates, (iii) isomorphic substitution, and (iv) chelation with -COO- in the interlayers. This work provides an effective method for the development of LDH-based adsorbent and the treatment of wastewater containing heavy metals.

Automated summary

A novel sodium alginate intercalated MgAl-LDH was synthesized for improved heavy metal adsorption efficiency. The SA-LDH exhibited better adsorption performance compared to pristine MgAl-LDH, with maximum adsorption capacities of 0.945 mmol/g for Cu(II), 1.176 mmol/g for Pb(II), and 0.850 mmol/g for Cd(II). Possible mechanisms of heavy metal removal by SA-LDH were analyzed via XPS, XRD, and FTIR, showing various pathways including bonding with surface functional groups, precipitation, isomorphic substitution, and chelation. This work provides an effective method for developing LDH-based adsorbents for wastewater treatment.