INFLUENCE OF TOBACCO STRAW BIOCHAR, HUMIC ACID AND SUPERPHOSPHATE ON THE IMMOBILIZATION OF Cd AND Pb IN CONTAMINATED SOIL

To explore the effect of tobacco straw biochar on the remediation and improvement of soil mildly polluted with heavy metals, and to find remediation materials suitable for alkaline composite heavy metal soils in northern China. Biochar (5%,w/w), humic acid (3%,w/w), and superphosphate (2 A,w/w) were used as passivation materials to remedy soils in plots slightly polluted with Cd and Pb. After 60 days, the repair effects of the various treatments applied herein were compared by measuring the pH, cation exchange capacity (CEC), and heavy metal BCR (community bureau of reference) extraction state contents of the soils. After culturing for 60 days, the pH value of the soil subjected to the compound treatment was closer to that of the original alkaline soil, and the soil CEC increased to a certain extent under all of the three passivation schemes applied herein. In the BCR extraction state of the slightly polluted plot subjected to the compound biochar treatment, the proportion of the oxidation state of Cd increased by 70.26%, while the proportion of the weak acid extraction state of Cd decreased by 39.7%. The proportion of Pb in the residue state increased by 60.44 A, while the proportion of Pb in the weak acid extraction state decreased by 53.89%, which effectively reduced the migration and transformation of heavy metals in the soil. This study showed that the three passivation schemes were more effective for treating Pb than Cd in the tested plots, and the addition of biochar compounded with humic acid and superphosphate did not have a significantly superior synergistic effect than the addition of a single passivation material. However, the compounding scheme had a more positive effect in terms of compensating for phosphate fertilizer in contaminated soil and regulating the soil pH.