Chromium desorption kinetics influenced by the rice husk and almond soft husk modified biochar in a calcareous soil

Abstract

This study introduced modified biochar to enhance the adesorption isotherms of hexavalent chromium in a calcareous soil. Almond soft husk and rice husk biochars as precursor reagents were applied to prepare the modified biochars with abundant amino groups for heavy metal removal. For this purpose, biochars included levels zero (without biochar or control) and 4 wt% (unmodified biochar and modified biochar). Biochars were modified separately with Fe3O4, NaOH, KOH, H2SO4, and HNO3 and four levels of potassium dichromate (0–150 mg/kg soil) were used. Sampling from the treated soil was carried out 5 months after the contamination of soil with chromium. All treatments (5 g) were extracted with 25 mL of a 0.01 M EDTA solutions. The suspensions were shaken for different time periods (5 to 2880 min) at 150 rpm. Concentration of Cr was analyzed in each extract by atomic absorption spectrophotometer. The results indicated that adding rice husk and almond soft husk biochars to the soil resulted in a decrease in Cr uptake at all extraction times compared to control, whereas the rice husk biochar showed a lower reduction in Cr removal than the control compared to the almond soft husk biochar. Based on the determination coefficient and standard error, the best two-constant rate equations are considered the best predictor of the chromium release kinetics trend in the studied soil.