Comparative study of layered double hydroxides intercalated by MoS42− and Mo3S132− on removal of Cu(II) and Pb(II): Adsorption mechanism and environmental stability

Mg Al layered double hydroxides (LDHs) intercalated by Mo 3 S 13 2− and MoS 4 2− (Mo 3 S 13 -LDHs/MoS 4 -LDHs) were prepared through the ion exchange method and compared their removing ability of Cu(II), Pb(II) from wastewater. When the batch experiment conducted at dosage 0.3 g/L, pH neutral, contact time 360 min, concentration 6 mmol/L and temperature 298 K, the adsorption capacity of Cu(II)/Pb(II) onto Mo 3 S 13 -LDHs and MoS 4 -LDHs was 2.76, 4.85 and 2.15, 4.66 mmol/g, Mo 3 S 13 -LDHs showed a higher adsorption capacity, which was because the larger amount of adsorption sites on Mo 3 S 13 2− . In mixed systems, Mo 3 S 13 -LDHs/MoS 4 -LDHs exhibited the preferential selectivity of Pb(II). When Mo 3 S 13 -LDHs/MoS 4 -LDHs adsorbed the low concentrations of Cu(II)/Pb(II), Mo 3 S 13 2− /MoS 4 2− first captured heavy metals and fixed into the interlayer. With the increase of concentration, Cu(II)/Pb(II) were still captured by the interlayered Mo 3 S 13 2− unlike MoS 4 -LDHs that hydroxyl groups onto LDHs began to capture Cu(II)/Pb(II). In the dynamic adsorption experiment, Mo 3 S 13 -LDHs could treat a larger volume of sewage than MoS 4 -LDHs. Mo 3 S 13 -LDHs exhibited better selectivity for Cu(II)/Pb(II) under the interference of organic and other metal ions in wastewater, and heavy metals after the treatment by Mo 3 S 13 -LDHs were more stable in the environment. Therefore, Mo 3 S 13 -LDHs could be considered as an environmentally stable adsorbent to remove heavy metals from wastewater compared to MoS 4 -LDHs.