Synergistic solidification of heavy metal tailings by polyethylene glycol (PEG) and microorganisms

Abstract

A significant amount of tailings rich in heavy metals is left behind after mining, causing environmental pollution due to long-term storage. In recent years, microbial-induced carbonate precipitation (MICP) has shown potential to solidify and stabilize heavy metal-contaminated soils. However, high concentrations and complex mixtures of heavy metals have toxic effects on microorganisms, resulting in decreased carbonate yield. Additionally, tailings sand often has a small particle size and poor permeability, which significantly reduces the solidification uniformity when using traditional grouting methods. To address these challenges, a low pH treatment method using PEG-MICP was proposed. This method increased the unconfined compressive strength (UCS) of tailings sand by 2.5 times and significantly improved soil uniformity while substantially reducing exchangeable heavy metal ions. Microscopic analysis showed that the introduction of PEG modifies the morphology of calcium carbonate, transforming calcite from a mineral to sheet-like and faceted forms, thus enhancing solidification efficiency. This study suggests that PEG-MICP has broad application prospects for solidifying heavy metal-contaminated tailings sand. • A low one-phase-low-pH grouting method was proposed to improve the uniformity of the soil. • After introducing PEG-MICP for synergistic solidification of heavy metal tailings, the carbonate minerals transformed from blocky to lamellar, enhancing the strength of the solidified soil. • The efficiency of heavy metal solidification increased to 80 % after the introduction of PEG-MICP, with Pb 2+ reaching 96 % and meeting international standards for polluted sites. • The biochemical mechanism of PEG-MICP synergistic solidification of heavy metal tailings was revealed, providing a new perspective and effective method for the remediation of heavy metal contaminated sites.

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