To reveal the engineering properties of Zn-contaminated soil solidified with a new cementitious material, namely phosphate rock powder-MgO-cement (PMC), several series of solidified soil characterization tests including moisture content, dry density, pH value, unconfined compressive strength, and stress-strain curve were conducted. The traditional Portland cement was selected for a comparison purpose. The effects of curing time and Zn2 + concentration on these property indexes were investigated to explore the inhibition mechanism of heavy metal Zn2+ on the stabilization process. In addition, the correlations of unconfined compressive strength with three physical property indexes were analyzed. The results indicated that the PMC stabilizer was far superior to the cement for stabilizing Zn-contaminated soil in terms of mechanical properties and environmental impacts. The normalized moisture content of PMC stabilized soil was greater than the cement stabilized soil, indicating a more complete hydration reaction. A small amount of Zn2+ can promote the hydration reaction, but when the Zn2+ concentration exceeded 0.5 %, the hydration reaction was significantly hindered. The dry density of PMC stabilized soil was about 6 % more than cement stabilized soil under the same conditions. The pH values of PMC stabilized samples were much lower than the cement stabilized soil samples and distributed in 8.0-9.5. The stress-strain characteristic of PMC stabilized soil was softening type and the heavy metal Zn2+ was solidified by adsorption, which could make the stress-strain curve of cement stabilized sample change from brittle type to ductile type.

Soil Pb contamination is inevitable, as a result of phosphate mining. It is essential to explore more effective Pb remediation approaches in phosphate mining wasteland soil to ensure their viability for a gradual return of soil quality for cultivation. In this study, a Pb-resistant urease-producing bacterium, Serratia marcescens W1Z1, was screened for remediation using microbially induced carbonate precipitation (MICP). Magnesium polypeptide (MP) was prepared from soybean meal residue, and the combined remediation of Pb contamination with MP and MICP in phosphate mining wasteland soil was studied. Remediation of Pb using a combination of MP with MICP strain W1Z1 (WM treatment) was the most effective, with the least exchangeable Pb at 30.37% and the most carbonate-bound Pb at 40.82%, compared to the other treatments, with a pH increase of 8.38. According to the community analysis, MP moderated the damage to microbial abundance and diversity caused by MICP. Total nitrogen (TN) was positively correlated with Firmicutes, pH, and carbonate-bound Pb. Serratia inoculated with strain W1Z1 were positively correlated with bacteria belonging to the Firmicutes phylum and negatively correlated with bacteria belonging to Proteobacteria. The available phosphate (AP) in the phosphate mining wasteland soil could encapsulate the precipitated Pb by ion exchange with carbonate, making it more stable. Combined MPMICP remediation of Pb contamination in phosphate mining wasteland soil was effective and improved the soil microenvironment.

To overcome large deformation of deep phosphate rock roadways and pillar damage, a new type of constant-resistance large-deformation negative Poisson's ratio (NPR) bolt that can withstand a high pre-stress of at least 130 KN was developed. In the conducted tests, the amount of deformation was 200-2000 mm, the breaking force reached 350 KN, and a high constant-resistance pre-stress was maintained during the deformation process. A stress compensation theory of phosphate rock excavation based on NPR bolts is proposed together with a balance system for bolt compensation of the time-space effect and high NPR pre-stress. Traditional split-set rock bolts are unable to maintain the stability of roadway roofs and pillars. To verify the support effect of the proposed bolt, field tests were conducted using both the proposed NPR bolts and split-set rock bolts as support systems on the same mining face. In addition, the stress compensation mechanism of roadway mining was simulated using the particle flow code in three dimensions (PFC3D)-fast Lagrangian analysis of continua (FLAC(3D)) particle-flow coupling numerical model. On-site monitoring and numerical simulations showed that the NPR excavation compensation support scheme effectively improves the stress state of the bolts and reduces the deformation of the surrounding rock. Compared to the original support scheme, the final deformation of the surrounding rock was reduced by approximately 70%. These results significantly contribute to domestic and foreign research on phosphate-rock NPR compensation support technology, theoretical systems, and engineering practices, and further promote technological innovation in the phosphate rock mining industry. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).