52 / 2021-06-30 05:06:03

Influence of biochar addition on the adsorption behaviour of cadmium and nickel onto the soil

biochar, cadmium, nickel, soil, adsorption forms

Influences of the addition of rice straw biochars prepared at 400 °C (RB400) and 700 °C (RB700) on the adsorption behaviour of cadmium and nickel onto the clay soil were investigated in this study. Based on the Langmuir model, the maximum adsorption capacities (Q_m) of Cd²⁺ and Ni²⁺ on the soil with different biochar addition ratios were in the order of Ni²⁺ > Cd²⁺ in the both single- and binary- metals adsorption isotherms and the Q_m values of Cd²⁺ and Ni²⁺ were larger in the single-metal system than that in the binary-metals system. The maximum adsorption capacities of Cd²⁺ and Ni²⁺ onto the soil increased with the addition ratios of RB400 and RB700 and the increase amplitude of RB700 were larger than that of RB400. Compared with the pseudo-first-order equation, the adsorption kinetics of Cd²⁺ and Ni²⁺ of the soil with different biochars addition were better fitted by the pseudo-second-order equation (R² > 0.97). The adsorption of Cd²⁺ and Ni²⁺ onto the soils reached equilibrium earlier in the binary-metals system than in the single-metal system. The acid soluble and reducible fractions were the dominant parts of Cd²⁺ and Ni²⁺ adsorption onto the soil, accounting for approximately 50-70% and 20-30% of the adsorption amounts. For Cd²⁺ adsorption onto the soil, the application of biochars dramatically decreased the proportion of acid soluble fraction but increased that of reducible and residual fractions. Competence between Cd²⁺ and Ni²⁺ decreased the proportion of acid soluble fraction but increased that of reducible fraction. Results from this study suggest that application rates of biochars and types of metal ions should be taken into account when removing metal contaminants from soil using biochars.