In this study, the effect of biochar produced via pyrolysis of potato peel before and after modification by thiourea (CH4N2S) at three rates (0, 4%, and 8%) on the adsorption of lead (Pb), and nickel (Ni) in contaminated acidic soil was investigated. The results showed that the thioureamodified potato peel biochar (TMPB) has a higher pH, cation exchange capacity (CEC), surface functional groups, O/C, and H/C ratios than the potato peel biochar (PB). The addition of thioureamodified biochar to soil, especially at the application rate of 8%, increased soil pH, CEC, and organic carbon (OC). The pseudo-second-order kinetic model with lower SE and higher R2 was introduced as the best model of adsorption kinetics. The adsorption of Pb, and Ni by soil amended with TMPB reached equilibrium at 16, and 16 h, respectively. The results of fitting the obtained data with the adsorption isotherm models showed that the adsorption of heavy metals in the control soil and the soil amended with TMPB is consistent with the Langmuir isotherm model. The maximum adsorption capacity values of Pb increased from 846.71 mg kg−1 in control soil to 5067.23 and 6149.75 mg kg−1 in soil amended with 4% TMPB and 8% TMPB, respectively. Similarly, the maximum adsorption capacity values of Ni increased from 591.63 mg kg−1 in control soil to 3792.1 and 4311.98 mg kg−1 in soil amended with 4% TMPB and 8% TMPB, respectively. The results of this 3 rd IYFSWC study showed that thiourea-modified potato peel biochar can be used as a low-cost and eco-friendly amendment to the adsorption of heavy metals in contaminated acidic soils.
