Mechanistic Study of Ni(II) Sorption by Green Rust Sulfate

Mechanisms for thallium(I) adsorption by zinc sulfide minerals under aerobic and anaerobic conditions

The highly toxic heavy metal thallium is widely distributed in sulfide ores and released into the environment by sulfide mining. However, the interface between the sulfide minerals and Tl(I) is unclear. In this study, the capacity for adsorption of thallium(I) by a common sulfide mineral (zinc sulfide) was investigated in aerobic and anaerobic environments, which revealed three mechanisms for adsorption on the ZnS surface (surface complexation, electrostatic action and oxidation promotion). Batch experiments indicated that the Tl(I) adsorption capacity of ZnS in an aerobic environment was approximately 9.3% higher than that in an anaerobic environment and was positively correlated with the pH. The adsorption kinetic data showed good fits with the pseudosecond-order model and the Freundlich isotherm model. The Tl(I) adsorption mechanism varied in different oxidative and pH environments. XPS, FTIR, and EDS results implied that complexation with surface hydroxyl groups was involved in the adsorption process. pH experiments and zeta analyses suggested that electrostatic attraction was also involved. Surface complexation and electrostatic attraction were the dominant mechanisms at pH values above 6. Furthermore, oxidative dissolution of ZnS and hydrolysis of Zn2+ enhanced the complexation with hydroxyl groups on the mineral surface and facilitated Tl adsorption. In this study, this interface mechanism provided new insights into thallium migration in sulfurized mineral environments in aerobic and anaerobic transition regions.

Effect of Ni2+, Zn2+, and Co2+ on green rust transformation to magnetite

In this study, we investigated Ni²⁺, Zn²⁺, and Co²⁺ mineralogical incorporation and its effect on green rust transformation to magnetite. Mineral transformation experiments were conducted by heating green rust suspensions at 85 °C in the presence of Ni²⁺, Zn²⁺, or Co²⁺ under strict anoxic conditions. Transmission electron microscopy and powder X-ray diffraction showed the conversion of hexagonal green rust platelets to fine grained cubic magnetite crystals. The addition of Ni²⁺, Zn²⁺, and Co²⁺ resulted in faster rates of mineral transformation. The conversion of green rust to magnetite was concurrent to significant increases in metal uptake, demonstrating a strong affinity for metal sorption/co-precipitation by magnetite. Dissolution ratio curves showed that Ni²⁺, Zn²⁺, and Co²⁺ cations were incorporated into the mineral structure during magnetite crystal growth. The results indicate that the transformation of green rust to magnetite is accelerated by metal impurities, and that magnetite is a highly effective scavenger of trace metals during mineral transformation. The implications for using diagenetic magnetite from green rust precursors as paleo-proxies of Precambrian ocean chemistry are discussed.

Mineralization of tribromophenol under anoxic/oxic conditions in the presence of copper(II) doped green rust: Importance of sequential reduction-oxidation process

The groundwater environment often undergoes the transition from anoxic to oxic due to natural processes or human activities, but the influence of this transition on the fate of groundwater contaminates are not entirely understood. In this work, the degradation of tribromophenol (TBP) in the presence of environmentally relevant iron (oxyhydr)oxides (green rust, GR) and trace metal ions Cu(II) under anoxic/oxic-alternating conditions was investigated. Under anoxic conditions, GR-Cu(II) reduced TBP to 4-BP completely within 7 h while GR only had an adsorption effect on TBP. Under oxic conditions, GR-Cu(II) could generate •OH via dioxygen activation, which resulted in the oxidative transformation of TBP. Sixty-five percentage of TBP mineralization was achieved via a sequential reduction-oxidation process, which was not achieved through single reduction or oxidation process. The produced Cu(I) in GR-Cu(II) enhanced not only the reductive dehalogenation under anoxic conditions, but also the O₂ activation under oxic conditions. Thus, the fate of TBP in anoxic/oxic-alternating groundwater environment is greatly influenced by the presence of GR-Cu(II). The sequential reduction-oxidation degradation of TBP by GR-Cu(II) is promising for future remediation of TBP-contaminated groundwater.

Synthesis, characterization and performances of green rusts for water decontamination: A review

In recent years, the application of green rusts (GRs) for water purification has received significant attention, but its full understanding has not been well achieved. Then, the comprehension about the synthesis and characteristics of GRs can highly favor their decontamination performances for the site-specific conditions. This review comprehensively summarized the synthesis, characteristics and performances of GRs including the GR (Cl^-), GR (CO₃^2-) and GR (SO₄^2-) for sequestration of various aqueous pollutants (e.g., tetrachloride, Cr(VI), Se(VI), and U(VI), etc.). Generally, the different reactivity of GRs toward contaminants is strongly dependent on the GRs' characteristics (e.g., interlayer distance, specific surface area, and Fe(II) content) and solution chemistry (e.g., pH, background electrolytes, dissolved oxygen, and contaminant concentration, etc.). In addition, the reaction mechanisms of GRs with the contaminants involve the redox reactions, adsorption, catalytic oxidation, interlayer and octahedral incorporation, which can mutually or singly contribute to the decontamination to varying degrees. Particularly, this review addressed the transformation pathways of GRs under various solution chemistry conditions and clarified that the stability of GRs should be the key challenge for the real application. Finally, how to effectively use the GRs for water decontamination was proposed, which will significantly benefit the rational control of environmental pollution.