MgO-loaded nitrogen and phosphorus self-doped biochar: High-efficient adsorption of aquatic Cu2+, Cd2+, and Pb2+ and its remediation efficiency on heavy metal contaminated soil

Abstract

In this study, the MgO-loaded fish scale biochar (MgO-FB) was synthesized by impregnation of MgCl₂ using fish scales as precursor, and the modified biochar was applied for the adsorption of aquatic Cu²⁺, Cd²⁺, and Pb²⁺, and the immobilization of heavy metals in soils. The maximum adsorption capacities of MgO-FB for Cu²⁺, Cd²⁺, and Pb²⁺ were 505.8, 327.2, and 661.2 mg/g, respectively. In addition, MgO-FB can keep the excellent adsorption capacity under various environmental disturbances including pH, humic acid, and high ionic strength. Multiple characterizations and comparative experiments have demonstrated that the hydroxyapatite components and the MgO micro-nanoparticles on MgO-FB enhanced the adsorption capacity for Cu²⁺, Cd²⁺, and Pb²⁺ through ion-exchange and precipitation process. The metal-π electron coordination and complexation with oxygen-, nitrogen-, and phosphorus-containing groups were also responsible for the removal of heavy metal ions. Besides, MgO-FB also performed excellently for the immobilization of Cu, Cd, and Pb in soils, and the contents of available Cu, Cd, and Pb were reduced by 84.2%, 74.2%, and 53.7% respectively with the addition of MgO-FB. In general, these results show that waste fish scales co-pyrolysis with MgCl₂ impregnation can be considered as a promising and efficient material for the remediation of heavy metal contaminated waters and soils.

Keywords: Adsorption; Fish scales biochar; Heavy metal; Hydroxyapatite; Magnesium oxide.