Comparative Study on the Leaching Characteristics of Cd Passivated in Soils under Continuous Simulated Acid Rain

Abstract

The in situ passivation is considered a feasible and effective remediation for moderately and lowly heavy-metal-polluted soil. Under natural precipitation, the continuous leaching characteristics of heavy metals with the immobilizers are unclear and require more study for practical applications. In this work, calcium superphosphate (CS) and activated carbon (AC) were added as stabilizers to passivate Cd in hydromorphic paddy (HP) and gray fluvo-aqvic (GF) soils. Simulated acid precipitation at different pH and salt concentrations were used as eluents. The leachate and soil were collected to analyze the stability and fraction changes of Cd. The results showed that with the eluents from 120–200 mL to 200–250 mL, the leached Cd increased and reached the highest concentration and then gradually decreased. Comparative analysis showed that the two passivators in GF soil had higher application values than those in HP soil, while AC showed 3–77 times the capacity of CS in multiple conditions. The addition of AC conversed the exchangeable and oxidized states of Cd to the residual and reduced states, while the addition of CS conversed the exchangeable and reduced states of Cd to the residual and oxidized states. The above results can provide important references for the immobilization of heavy metal cations in soil and the sustainable utilization of soil.