Reinforcement and remediation of Ni contaminated sludge by EDTA grouting vacuum preloading with varying loading model

The reinforcement and remediation of contaminated sludge is consistently a key research point. This paper proposes a grouting vacuum preloading method to enhance the soil with high water content and to remove heavy metal contaminants of Ni in the soil. Ethylenediaminetetraacetic acid (EDTA) is injected to leach the Ni-contaminated soil under step loading vacuum pressure. Various indicators, including soil settlement, discharged water, water content, penetration resistance, Ni²⁺ content, and Ni²⁺ removal rate, are analyzed. Test results show that both EDTA grouting and step loading have significant positive effects on the soil reinforcement and remediation. When the soil initial water content is below 100%, the soil water content is reduced by 67.5% and the Ni²⁺ removal rate reaches 97.34% using vacuum preloading combined with EDTA grouting and one-time loading. For soil with an initial water content of up to 120%, applying a step loading of 40-80 kPa increases the Ni²⁺ removal rate to 97.9% from 91.6% corresponding to one-time loading, ultimately restoring the soil to an unpolluted state. These findings can serve as a valuable reference for in-situ reinforcement and remediation of Ni-contaminated soil with high water content.