Geo-environmental and mechanical behaviors of As(V) and Cd(II) co-contaminated soils stabilized by goethite nanoparticles modified biochar

Goethite nanoparticles modified biochar (FBC) could address the weak effectiveness of conventional biochar commonly to process heavy metal(loids) (HMs) co-contamination with different charges. However, few studies have focused on the change of soil mechanical properties after stabilization. In this study, FBC was synthesized to stabilize simultaneously arsenic (As (V)) (anions) and cadmium (Cd (II)) (cations) in co-contaminated soils. Batch adsorption, leaching toxicity, geotechnical properties and micro-spectroscopic tests were comprehensively adopted to investigate the stabilization mechanism. The results showed that FBC could immobilize As (V) mainly through redox and surface precipitation while stabilizing Cd (II) by electrostatic attraction and complexation, causing soil agglomeration and ultimately making rougher surface and stronger sliding friction of contaminated soils. The maximum adsorption capacity of FBC for As (V) and Cd (II) was 31.96 mg g-1 and 129.31 mg g-1, respectively. Besides, the dosages of FBC required in contaminated soils generally were approximately 57% higher than those in contaminated water. FBC promoted the formation of small macroaggregates (0.25-2 mm) and the shear strengths of co-contaminated soils by 21.40% and 8.34%, respectively. Furthermore, the soil reutilization level was significantly improved from 0.14-0.46 to 0.76-0.83 after FBC stabilization according to TOPSIS method (i.e., technique for order preference by similarity to an ideal solution). These findings confirm the potential of FBC in immobilizing As (V) and Cd (II) of co-contaminated soils and provide a useful reference for green stabilization and remediation of HMs co-contaminated sites. Goethite nanoparticles modified biochar (FBC) can make up the shortcoming of conventional biochar to immobilize simultaneously arsenic (As (V)) and cadmium (Cd (II)) in co-contaminated soils.FBC is conducive to the formation of the soil small macroaggregates (i.e., 0.25-2 mm).FBC promotes soil shear strengths of As (V) and Cd (II) co-contaminated soils by increasing internal friction.