Deep insight on mechanism and contribution of arsenic removal and heavy metals remediation by mechanical activation phosphogypsum.

Arsenic-containing wastewater and arsenic-contaminated soil can cause serious environmental pollution. In this study, phosphogypsum with partial mechanical activation of calcium oxide was used to prepare a new phosphogypsum-based passivate (Ca-mPG), and its remediation performance on arsenic-contaminated soil was evaluated in terms of both effectiveness and microbial response. The results showed that the optimum conditions for the preparation of the passivate were optimized in terms of single factor and response surface with a ball milling speed of 200 r/min, a material ratio of 6:4 and a ball milling time of 4 h. Under these conditions, the adsorption capacity was 37.75 mg/g. The leaching concentration of arsenic (As) in the contaminated soil after Ca-mPG modification decreased from 25.75 µg/L to 5.88 µg/L, which was lower than the Chinese national standard (GB/T 5085.3-2007); Ca-mPG also showed excellent passivation effect on other heavy Metals (copper, nickel, cadmium, zinc). In addition, As-resistant bacteria and passivators work together to promote the stabilization effect of contaminants during the remediation of As-contaminated soil. The mechanisms of Cu, As(III)/As(V), Zn, Cd, and Ni removal were related to ion exchange, electrostatic adsorption of substances on heavy metals, calcium binding to other substances to produce precipitation; and microbially induced stabilization of HMs, oxidized. Overall, this study demonstrates an eco-friendly "waste-soil remediation" strategy to solve problems associated with solid waste reuse and remediation of HM-contaminated soils.

Remediation of arsenic contaminated water and soil using mechanically (ball milling) activated and pyrite-amended electrolytic manganese slag.

With the development of industry, heavy metal (HM) pollution of soil has become an increasingly serious problem. Using passivators made of industrial by-products to immobilize HMs in contaminated soil is a promising in-situ remediation technology. In this study, the electrolytic manganese slag (EMS) was modified into a passivator (named M-EMS) by ball milling, and the effects of M-EMS on adsorption of As(V) in aquatic samples and on immobilization of As(V) and other HMs in soil samples were investigated under different conditions. Results demonstrated that M-EMS had a maximum As(V) adsorption capacity of 65.3 mg/g in the aquatic samples. Adding M-EMS to the soil reduced the leaching of As (from 657.2 to 319.8 µg/L) and other HMs after 30 d of incubation, reduced the bioavailability of As(V) and improved the quality and microbial activity of the soil. The mechanism for M-EMS to immobilize As in the soil are complex reactions, ion exchange reaction with As and electrostatic adsorption. This work provides new ideas of using waste residue matrix composites for sustainable remediation of Arsenic in the aquatic environment and soil.

Simultaneous immobilization of multiple heavy metals in polluted soils amended with mechanical activation waste slag.

Heavy metal soil contamination has become an increasingly serious problem in industrial development. However, industrial byproducts used for remediation are one aspect of green remediation that can contribute to sustainable practices in waste recycling. In this study, electrolytic manganese slags (EMS) were mechanically activated and modified into a passivator (M-EMS), and the heavy metal adsorption performance of M-EMS, heavy metal passivation ability in soil, dissolved organic matter (DOM) change and its effect on the microbial community structure of soil were investigated. The findings revealed that the maximum adsorption capacities of As(V), Cd2+, Cu2+ and Pb2+ were 76.32 mg/g, 301.41 mg/g, 306.83 mg/g and 826.81 mg/g, respectively, indicating that M-EMS demonstrated remarkable removal performance for different heavy metals. The Langmuir model fits Cd2+, Cu2+ and Pb2+ better than the Freundlich model, and monolayer adsorption is the main process. Surface complexation played a major role in the As(V) adsorption's on the surface of metal oxides in M-EMS. The passivation effect was ranked as Pb > Cr > As>Ni > Cd > Cu, with the highest passivation rate of 97.59 % for Pb, followed by Cr (94.76 %), then As (71.99 %), Ni (65.17 %), Cd (61.44 %), and the worst one was Cu (25.17 %). In conclusion, the passivator has the effect of passivation for each heavy metal. The addition of passivating agent can enhance the diversity of microorganisms. Then it can change the dominant flora and induce the passivation of heavy metals through microorganisms. XRD, FTIR, XPS and the microbial community structure of soil indicated that M-EMS can stabilize heavy metals in contaminated soils through four main mechanisms: ion exchange, electrostatic adsorption, complex precipitation and the microbially induced stabilization. The results of this study may provide new insights into the ecological remediation of multiple heavy-metal-contaminated soils and water bodies and research on the strategy of waste reduction and harmlessness by using EMS-based composites in combination with heavy metals in soil.