In this study, there is presented a thorough investigation of the effect of biochar produced via pyrolysis of carrot pulp with pre and post-modification by thiourea (CH4N2S) at three rates (0, 4%, and 8%) on fractionation of Cu and Zn in acidic soil. The sequential extraction procedure of BCR was utilized for the determination of heavy metals fractionation. According to the FTIR analysis, the thiourea-modified biochar (TMB) had more surface functional groups in comparison with the carrot pulp biochar (CB). The 8% TMB application, was more effective in increasing the CEC, pH, EC, and SOC of the soil than the 8% CB treatment. The BCR test revealed that after the addition of CB and TMB, the acid extractable Cu and Zn decreased considerably. Thioureamodified biochar was more effective than pristine biochar in decreasing the acid extractable metals fraction. The addition of TMB induced the conversion of the acid extractable fraction of Cu to residual and organic matter bound fractions, and the acid extractable fraction of Zn to residual, organic matter bound and oxides bound fractions. This work suggests that thioureamodified biochar can be a low-cost and effective amendment for immobilizing Cu and Zn in contaminated acidic soils.
