Investigation On Stabilization/Solidification Characteristics of Lead Contaminated Soil Using Innovative Composite Model of Cement And Soda Residue

Abstract

The cement solidification/stabilization method of heavy metal contaminated soils has been promoted in engineering practice and applied on a large scale for site remediation, but it still reveals some scientific problems in the current complex and variable global extreme climate. To solve these problems and explore cement-based soil remediation technology, this study used the waste soda residue produced in large quantities in the "ammonia-soda process" as a composite additive, and established an innovative composite model of cement and soda residue by adding different ratios, which was applied to the remediation experiments of lead-contaminated soil. The innovative composite model solidification/stabilization of cement and soda residue for unconfined compressive strength and toxic leaching properties under different soil environmental conditions were investigated. Moreover, curing and leaching mechanisms are discussed, and future industrial practice was evaluated. The results showed that the addition of soda residue improved the early (20 days) unconfined compressive strength (UCS) of the composite curing agent for lead-contaminated soil by an average of 23.1% Mpa. When the percentage of soda residue composite was 40%, the UCS strength was 0.96 Mpa, which reached the maximum. The concentration of Pb2+ in the leachate of the cement-soda residue composite curing agent was greatly reduced (average 3.28 times) compared with that of a single cement in the same situation, with an average leached Pb2+ concentration of 1.87 mg·L-1. This indicates that the addition of alkali residue improved the curing effect. The curing mechanism was divided into four steps, mainly a complex physicochemical reaction between the cement-soda residue composite and soil particles. The leaching mechanism of cement-soda residue to aqueous solution is mainly the consumption of acid ions by alkaline substances. This study will provide scientific data to support potential lead-containing soil in site remediation technologies and future large-scale engineering applications.