Improving soil properties and microbial communities in copper tailings using montmorillonite-based Chlorella gel beads.

Copper tailings are the waste left over from copper ore dressing, and their massive pose severe challenges to the ecosystem. In this study, sodium alginate-Chlorella-montmorillonite (SCM) gel beads were prepared by combining sodium alginate, Chlorella, and montmorillonite. The laboratory pot and in-situ field experiment results indicated that the input of SCM gel beads facilitated the formation of larger particle-size soil aggregates and enhanced soil water retention and cation exchange capacities. The pot experiment demonstrated that the application of MMT and Chlorella significantly increased organic carbon content in the tailing soil. The field experiment showed that the application of SCM gel beads at the optimal dosage of 700 g/m increased the plant height and fresh weight by 1.77 and 1.22 times, respectively, as well as the chlorophyll content. Furthermore, in SCM group, the proportion of large soil aggregates(particle size >0.25 mm) was increased by 6.66 %, and the R, mean weight diameter (MWD), and geometric mean diameter (GWD) values were also significantly increased, and the increase in large soil aggregates and aggregate stability indicated the improvement of soil structure. Additionally, the dominant microorganisms at the phylum level were Proteobacteria, Acidobacteriota, and Bacteroidota, while they were Sphingomonas, Vicinamibacteraceae, and Candidatus at genus level. These dominant microorganisms were indigenous species to copper tailing. The alpha diversity determination results indicated that SCM gel bead input increased the microbial community richness, but had little effect on their diversity. Our results demonstrated that as soil amendment, SCM gel beads stimulated the growth of tailing native microorganisms, increasing their richness. Overall, the combination of Chlorella, and montmorillonite, as an amendment, improved soil properties of copper tailing and soil microbial community structure. Our findings provide valuable references for developing effective and sustainable soil remediation strategies in tailing areas.