Silica-magnesium coupling in lignin-based biochar: A promising remediation for composite heavy metal pollution in...

Lignin hydrothermal silica-carbon material served as a backbone for MgCl₂ activation to prepare lignin-based silicon/magnesia biochar (ALB/Si-Mg) for Cd²⁺, Pb²⁺, Cu²⁺, and Zn²⁺ removal from water and soil environment. Characterization studies revealed a 1017.71-fold increase in the specific surface area of ALB/Si-Mg compared to the original lignin biochar (ALB), producing abundant oxygen functional groups (OC-O, Si-O, Mg-O), and mineral matter (Mg₂SiO₄ and MgO). Crucially, batch adsorption experiments demonstrated that the adsorption capacity of ALB/Si-Mg for Cd²⁺, Pb²⁺, Cu²⁺, and Zn²⁺ was 848.17, 665.07, 151.84, and 245.78 mg/g, which were 29.09-140.45 times of the ALB. Soil remediation experiments showed that applying ALB/Si-Mg increased soil effective silicon (109.04%-450.2%) and soil exchangeable magnesium (276.41%-878.66%), enhanced plant photosynthesis, and notably reduced the bioavailability of heavy metals in soil as well as the content of heavy metals in Pakchoi, thereby promoting Pakchoi growth and development. The presence of oxygen-containing functional groups on ALB/Si-Mg, along with Mg₂SiO₄ and MgO nanoparticles, enhanced the adsorption capacity for heavy metals through the promotion of heavy metal precipitation, ion exchange, and complexation mechanisms. This study establishes the groundwork for the coupling of silica and magnesium elements in biochar and the remediation of composite heavy metal environmental pollution.