Mine drainage: Remediation technology and resource recovery

Experimental study on the treatment of AMD by SRB immobilized particles containing "active iron" system

The inhibition and toxicity of high acidity and heavy metals on sulfate-reducing bacteria in acid mine drainage (AMD) were targeted. Highly active SRB immobilized particles were prepared using SRB, warm sticker wastes (iron powders), corncobs, and Maifan stones as the main matrix materials, employing microbial immobilization technology. The repair ability and reusability of highly active immobilized particles for AMD were explored. The results indicate that the adaptability of immobilized particles to AMD varied under different initial conditions, such as pH, Mn2+, and SO42-. The adsorption process of immobilized particles on Mn2+ follows the quasi-second-order kinetic model, suggesting that it involves both physical and chemical adsorption. The maximum adsorption capacity of immobilized particles for Mn2+ is 3.878 mg/g at a concentration of 2.0 mg/L and pH 6. On the other hand, the reduction process of immobilized particles on SO42- adheres to the first-order reaction kinetics, indicating that the reduction of SO42- is primarily driven by the dissimilation reduction of SRB. The maximum reduction rate of SO42- by immobilized particles is 94.23% at a concentration of 800 mg/L and pH 6. A layered structure with a flocculent appearance formed on the surface of the immobilized particles. The structure's characteristics were found to be consistent with sulfate green rust (FeII4FeIII2(OH)12SO4·8H2O). The chemisorption, ion exchange, dissimilation reduction, and surface complexation occurring between the matrices in the immobilized particles can enhance the alkalinity of AMD and decrease the concentration of heavy metals and sulfates. These results are expected to offer novel insights and materials for the treatment of AMD using biological immobilization technology, as well as improve our understanding of the mechanisms behind biological and abiotic enhanced synergistic decontamination.

Environmental contamination and health risk assessment of potentially toxic trace metal elements in soils near gold mines - A global meta-analysis

Gold mining is the most important anthropogenic source of heavy metal emissions into the environment. Researchers have been aware of the environmental impacts of gold mining activities and have conducted studies in recent years, but they have only selected one gold mining site and collected soil samples in its vicinity for analysis, which does not reflect the combined impact of all gold mining activities on the concentration of potentially toxic trace elements (PTES) in nearby soils at a global scale. In this study, 77 research papers from 24 countries were collected from 2001 to 2022, and a new dataset was developed to provide a comprehensive study of the distribution characteristics, contamination characteristics, and risk assessment of 10 PTEs (As, Cd, Cr, Co, Cu, Hg, Mn, Ni, Pb, and Zn) in soils near the deposits. The results show that the average levels of all 10 elements are higher than the global background values and are at different levels of contamination, with As, Cd, and Hg at strong contamination levels and serious ecological risks. As and Hg contribute to a greater non-carcinogenic risk to both children and adults in the vicinity of the gold mine, and the carcinogenic risks of As, Cd, and Cu are beyond the acceptable range. Gold mining on a global scale has already caused serious impacts on nearby soils and should be given adequate attention. Timely heavy metal treatment and landscape restoration of extracted gold mines and environmentally friendly approaches such as bio-mining of unexplored gold mines where adequate protection is available are of great significance.

Removal of Iron, Manganese, Cadmium, and Nickel Ions Using Brewers’ Spent Grain

The human-made pollution of surface and ground waters is becoming an inevitable and persistently urgent problem for humankind and life in general, as these pollutants are also distributed by their natural circulation. For example, from mining activities and metallurgy, toxic heavy metals pollute the environment and present material risk for human health and the environment. Bioadsorbers are an intriguing way to efficiently capture and eliminate these hazards, as they are environmentally friendly, cheap, abundant, and efficient. In this study, we present brewers’ spent grain (BSG) as an efficient adsorber for toxic heavy metal ions, based on the examples of iron, manganese, cadmium, and nickel ions. We uncover the adsorption properties of two different BSGs and investigate thoroughly their chemical and physical properties as well as their efficiency as adsorbers for simulated and real surface waters. As a result, we found that the adsorption behavior of BSG types differs despite almost identical chemistry. Elemental mapping reveals that all components of BSG contribute to the adsorption. Further, both types are not only able to purify water to reach acceptable levels of cleanness, but also yield outstanding adsorption performance for iron ions of 0.2 mmol/g and for manganese, cadmium, and nickel ions of 0.1 mmol/g.

A Multidisciplinary Approach for the Assessment of Origin, Fate and Ecotoxicity of Metal(loid)s from Legacy Coal Mine Tailings

Over the course of history, the development of human societies implied the exploitation of mineral resources which generated huge amounts of mining wastes leading to substantial environmental contamination by various metal(loid)s. This is especially the case of coal mine tailings which, subjected to weathering reactions, produce acid mine drainage (AMD), a recurring ecological issue related to current and past mining activities. In this study, we aimed to determine the origin, the fate and the ecotoxicity of metal(loid)s leached from a historical coal tailing heap to the Beuveroux river (Franche-Comté, France) using a combination of mineralogical, chemical and biological approaches. In the constitutive materials of the tailings, we identified galena, tetrahedrite and bournonite as metal-rich minerals and their weathering has led to massive contamination of the water and suspended particles of the river bordering the heap. The ecotoxicity of the AMD has been assessed using Chironomus riparius larvae encaged in the field during a one-month biomonitoring campaign. The larvae showed lethal and sub-lethal (growth and emergence inhibition and delay) impairments at the AMD tributary and near downstream stations. Metal bioaccumulation and subcellular fractionation in the larvae tissues revealed a strong bioavailability of, notably, As, Pb and Tl explaining the observed biological responses. Thus, more than 70 years after the end of mining operations, the coal tailings remain a chronic source of contamination and environmental risks in AMD effluent receiving waters.