# Preparation and Modification of Biochar Materials and their Application in Soil Remediation
## 4 Application of Biochar in Soil Remediation
### Removal of Heavy Metals
The modification methods of surface structure characteristics are generally divided into physical method, chemical method, and combined method [65]. In the early stage, [PERSON] et al. [114] modified activated carbon with sodium dodecyl sulfonate to reduce the heavy metal content in phosphoric acid and reduce the content of cadmium and chromium. Scholars have modified biochar similarly to activated carbon, mainly by chemical modification, through adding acid, alkali, oxidants, and supporting various metal oxides to aminated, acidify, and alkalinize biochar. Oxidation, etc., increase the surface oxygen-containing functional groups, thereby achieving a good repair effect. Studies on the adsorption effect of modified biochar are dominated by heavy metals, followed by organics, and most of them are adsorption of heavy metals in aqueous solution. Table 5 provides a summary of studies on soil pollution remediation by various types of modified biochar in recent years. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Raw Material** & **Modification** & **Pollutant** & **Tested Soil** & **Remediation Effect** & **Reference** \\ \hline \multirow{4}{*}{Bamboo hardwoods} & \multirow{4}{*}{sulfur-iron} & \multirow{4}{*}{Cr} & \multirow{4}{*}{plant farmland} & \multirow{4}{*}{Sulfur-modified biochar (S-BC) and sulfur-iron modified biochar (SF-BC) addition increased the content of soil organic matter, alpha diversity indices, and changed soil bacterial community structure. The exchangeable Cd in soil was decreased by 12.5\%, 29.7\%, 18.53\% under the treatments of \multirow{4}{*}{Poultry, cow, sheep manure} & \multirow{4}{*}{Chitosan, ZVI} & \multirow{4}{*}{Cr} & \multirow{4}{*}{uncontaminated surface soil} & \multirow{4}{*}{Motified sheep manure biochar reduced Cr(VI) by 55\%, and poultry manure modified Dichar reduced Cr(VI) by 48\%.} & \multirow{4}{*}{[113]} \\  & & & & Modified biochar decreased the content of available As, \multirow{4}{*}{Fe-Mn} & \multirow{4}{*}{As} & \multirow{4}{*}{paddy soil} & \multirow{4}{*}{increased the residual, amorphous hydrots oxide-bound, and crystalline hydrots oxide-bound A= forms.} & \multirow{4}{*}{[115]} \\  & & & & Acid-soluble Cd, Zn, Cu in soils embedded with poultry litter & \\ \multirow{4}{*}{Eucalyptus wood and poultry litter} & \multirow{4}{*}{iron} & \multirow{4}{*}{Cd, Cu, Zn, Pb} & \multirow{4}{*}{paddy soil near Zn and Pb mines} & \multirow{4}{*}{paddy soil near Zn and Pb mines} & \multirow{4}{*}{paddy soil near Zn to 10\%, \% in soils embedded soil. Plant biomass increased by 32\% in the treatments containing magnetic PLB magnetic PLB} & \multirow{4}{*}{[109]} \\  & & & & & & \\ \multirow{4}{*}{Coconnut shell} & \multirow{4}{*}{HCI + ultrasonication} & \multirow{4}{*}{Cd, Ni, and Zn} & \multirow{4}{*}{topssoil of paddy fields} & \multirow{4}{*}{In groups with \% MCSB addition, the acid soluble Cd, Ni and ZnO 2\% decreased by 30\%, 15\%, 57\%, and 12.7\%, respectively.} & \multirow{4}{*}{[78]} \\  & & & & Modification increased the Hg\({}^{2}\) absorptive capacity of biochar by 73\%, to 67.11 mg = 51.1 and freely available Hg in TCLP & \\ \multirow{4}{*}{Rice husk} & \multirow{4}{*}{Sulfur} & \multirow{4}{*}{Hg} & \multirow{4}{*}{Hg contaminated soil} & \multirow{4}{*}{(toxicity characterization leaching procedure) headaches by 95\%, 97.4\%, and 99.3\%, respectively, compared to untreated soil.} & \multirow{4}{*}{[116]} \\ \cline{1-1} \cline{5-5} \cline{5-5} \cl