Efficient removal of multiple low-level heavy metals by microcrystalline cellulose-based calcium carbonate/L-cysteine doped polyethyleneimine composite MCC@CaCO3/LPEI: Performance and mechanisms

Multiple low-concentration heavy metals (HMs) often coexist in the wastewater discharged after pretreatment, which also pose a potential threat to the aquatic ecological environment. However, few of reported adsorbents are capable of simultaneously and effectively removing multiple HMs from wastewater. In this study, a novel microcrystalline cellulose-based adsorbent MCC@CaCO 3 /LPEI was synthesized via a facile precipitation reaction, and used for the separate and simultaneous removal of Cd(II), Pb(II), Cr(VI), Cu(II), and Zn(II) from aqueous solution. Results showed that MCC@CaCO 3 /LPEI could remove 99.2 %-99.9 % of low-level HMs (1–2 mg·L −1 ) in the mono-component system, and the remaining concentrations of HMs met the standards for drinking water quality of China (GB5749–2022). The electrostatic attraction, ion exchange, chemical precipitation, and the surface complexation of functional groups were the main removal mechanisms. HMs adsorption data of MCC@CaCO 3 /LPEI was well fitted to the Pseudo-second-order and Langmuir models. MCC@CaCO 3 /LPEI remained high HMs removal rate (above 95 %) after seven adsorption-desorption cycles. In the HMs multi-component system, MCC@CaCO 3 /LPEI also exhibited excellent adsorption for all HMs, and the equilibrium adsorption capacities of Cd(II), Pb(II), Cr(VI), Cu(II), and Zn(II) were 1.15, 1.30, 0.91, 0.78, and 0.73 mg·g −1 , respectively. All five HM ions were completely removed after five adsorption-desorption cycles in the HM multi-component system. Meanwhile, the high removal rate (>99 %) of HMs in the simulated wastewater demonstrated the excellent environmental stability of MCC@CaCO 3 /LPEI. Conclusively, MCC@CaCO 3 /LPEI can be used as an adsorbent with promising applications for removing multiple low-concentration HMs from wastewater.