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April 7, 2026Separations0 citationsOpen Access

Upcycling Coal Gangue and Phosphate Tailings into Layered Double Hydroxides for Simultaneous Remediation of Cr (VI), Cd (II) and Ni (II) in Contaminated Soils

QYQ. YeWuhan Institute of Technology PZPei ZhaoWuhan Institute of Technology XXXuan XiaWuhan Institute of Technology

Key Points

The aim is to explore the potential of upcycling coal gangue and phosphate tailings into layered double hydroxides for remediating contaminated soils.
Utilized coal gangue and phosphate tailings as feedstocks for layered double hydroxide synthesis.
Performed calcination, acid leaching, and hydrothermal coprecipitation at 700 °C.
Conducted a 7-day mung bean bioassay to assess plant growth and heavy metal uptake.
Used 16S rRNA sequencing to analyze microbial diversity post-treatment.
Achieved immobilization efficiencies of 76.28% for Cr (VI), 99.96% for Cd (II), and 99.95% for Ni (II) within 24 hours.
Confirmed long-term stability with leached concentrations of metals below 0.3 mg L−1 after freeze-thaw cycles.
Increased mung bean seed germination from 50% to 73%, with enhanced biomass and over 80% reduction in metal uptake.
Restored microbial diversity and functionality, highlighting ecological benefits.

Abstract

Two mineral-based solid residues, namely coal gangue (CG) and phosphorus tailings (PT), two of the largest solid waste streams in the mining industry, were used as the sole metal feedstocks to fabricate a novel MgCaFeAl layered double hydroxide (LDH-GT) via a 700 °C calcination, acid leaching and hydrothermal coprecipitation route, with simultaneous synthesis of white carbon black from the reaction byproducts. Under optimized conditions (total metal load is 150 mg kg−1, LDH-GT dose is 0.09 g, pH from 6 to 7), the synthesized material achieved concurrent immobilization efficiencies of 76.28%, 99.96%, and 99.95% for Cr (VI), Cd (II) and Ni (II), respectively, within a 24 h reaction period. TCLP leachability decreased by 82 to 91% relative to the untreated soil. After three wetting, drying and freeze–thaw cycles, the leached concentrations of all three metals remained below 0.3 mg L−1, confirming excellent long-term stability. Mechanistic analyses revealed that Cr (VI) was mainly sequestered through interlayer anion exchange and surface complexation, whereas Cd (II) and Ni (II) were immobilized via isomorphic substitution into the LDH lattice, precipitation as carbonates, and incorporation into Fe/Mn oxides. A 7-day mung bean bioassay showed that LDH-GT amendment increased seed germination from 50% to 73%, enhanced root and shoot biomass by 1.1- to 1.6-fold, and decreased plant Cr, Cd, and Ni contents by over 80%. The 16S rRNA sequencing further demonstrated that LDH-GT reversed the decline in microbial α diversity induced by heavy metal stress, restored aerobic chemoheterotrophic and sulfur cycling functional guilds, and reduced pathogenic signatures. This study provides the demonstration of a waste-to-resource LDH that achieves efficient, durable remediation of multi-metal-contaminated soils, offering a scalable route for coupling solid waste valorization with in situ site restoration.

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