Effect of physicochemical properties of biochar from different feedstock on remediation of heavy metal contaminated soil in mining area

The feedstock used to prepare biochar plays a leading role in its physicochemical properties, and the physicochemical properties of biochar determine the remediation potential for heavy metal. Therefore, it is of great theoretical and practical value to systematically compare the physicochemical properties of biochar from different feedstocks and analyze its remediation behaviors on heavy metal contaminated soil. In this study, three typical feedstock biochar, straw biochar (SB), coconut shell biochar (CSB) and sludge-derived biochar (SSDB) are mixed with heavy metal contaminated soil at a ratio of 0.5%, 2.5% and 5% respectively, and incubation at 25 °C and 70% field water holding capacity for 30 days. The results showed that the three biochar could significantly reduce the leaching concentration and acid soluble fraction of heavy metals, and the remediation effect of biochar on heavy metals improved with the increase of dosage and the extension of incubation time. Among them, 5% dosage of SSDB obtains the optimal remediation effect. Redundancy analysis shows that the pore diameter and C contents of biochar are negatively correlated with short-term leaching of heavy metals; the electrical conductivity, available phosphorus and anion content are negatively correlated with the long-term leaching of heavy metals. The SB has higher available phosphorus and manifests a microporous structure with vascular bundles, making it have a larger specific surface area, and suitable for heavy metal remediation through complexation, adsorption and precipitation. The CSB has a higher pH value, a large pore diameter, and a high H/C atomic ratio and hydrophobicity, and is suitable for heavy metal remediation through complexation, electrostatic attraction and adsorption. The SSDB has a higher electrical conductivity anion content, but a lower degree of aromatization, and is suitable for heavy metal remediation by precipitation.