Assessing the Effects of Biochar on the Immobilization of Trace Elements and Plant Development in a Naturally Contaminated Soil

Soil contamination with trace elements is an important and global environmental concern. This study examined the potential of biochars derived from rice husk (RHB), olive pit (OPB), and a certified biochar produced from wood chips (CWB) to immobilize copper (Cu²⁺) and lead (Pb²⁺) in aqueous solution to avoid its leaching and in a pot experiment with acidic Xerofluvent soils multicontaminated with trace elements. After assessing the adsorption potential of Cu²⁺ and Pb²⁺ from an aqueous solution of the three studied biochars, the development of Brassica rapa pekinensis plants was monitored on polluted soils amended with the same biochars, to determine their capability to boost plant growth in a soil contaminated with several trace elements. RHB and CWB removed the maximum amounts of Cu²⁺ and Pb²⁺ from aqueous solution in the adsorption experiment. The adsorption capacity increased with initial metal concentrations for all biochars. The efficiency in the adsorption of cationic metals by biochars was clearly affected by biochar chemical properties, whereas total specific surface area seemed to not correlate with the adsorption capacity. Among the isotherm models, the Langmuir model was in the best agreement with the experimental data for both cations for CWB and RHB. The maximum adsorption capacity of Cu²⁺ was 30.77 and 58.82 mg g⁻¹ for RHB and CWB, respectively, and of Pb²⁺ was 19.34 and 77.52 mg g⁻¹ for RHB and CWB, respectively. The application of 5% of RHB and CWB to the acidic polluted soils improved soil physico-chemical properties, which permitted the development of Brassica rapa pekinensis plants. RHB and CWB have been shown to be effective for the removal of Cu²⁺ and Pb²⁺, and the results obtained regarding plant development in the soils contaminated with trace elements indicated that the soil amendments have promising potential for the recovery of land polluted with heavy metals.