Evaluating the effectiveness of thiourea-modified biochar derived from wheat straw for Cd, Ni, and Zn adsorption in...

In recent years, researchers have focused on developing innovative biochar modification techniques to enhance adsorption efficiency and reduce the mobility and bioavailability of heavy metals. However, few studies have investigated the application of modified biochar in heavy metals-contaminated soils, with most research focusing on aqueous solutions. In Iran, the potential of biochar as an effective adsorbent for removing heavy metals from contaminated soils, especially acidic soils, has been largely overlooked. The effectiveness of biochar is influenced by both the type of biomass used and the method of modification. Additionally, there is a significant gap in current literature regarding the research on thiourea as a potential modification agent for biochar. This study focused on the characteristics of thiourea-modified wheat straw biochar (TWB) and its effects on the adsorption isotherms and kinetics of heavy metals (Cd, Ni, and Zn) in acidic soil. The biochar was produced from wheat straw in an oxygen-free furnace at a temperature of 550 °C for 3 h, with a heating rate of 25 °C per min. To enhance the adsorption efficiency, thiourea was used to modify the wheat straw biochar (WB). The findings revealed that the thiourea modification reduced the carbon content but increased the nitrogen, hydrogen, sulfur, oxygen levels, specific surface area, cation exchange capacity (CEC), and pH compared to unmodified biochar. Adsorption isotherms and kinetics analyses indicated that the Langmuir model best described the adsorption of heavy metals in soil treated with both TWB and WB, while the pseudo-second-order model more accurately represented the adsorption kinetics. The results indicated that the adsorption of Cd, Ni, and Zn in soil treated with 8% TWB was significantly higher than in the control, achieving levels of 6164.45, 4684.47, and 4233.58 mg kg^-1, respectively. This study demonstrated that TWB enhances the adsorption of heavy metals due to its advantageous properties, which include an optimal pH, high CEC, a variety of functional groups, a large specific surface area, and a porous structure. Therefore, thiourea-modified wheat straw biochar serves as an effective, economical, and environmentally friendly adsorbent for immobilizing heavy metals and reducing their bioavailability in acidic contaminated soils.