Odiel River (SW Spain), a Singular Scenario Affected by Acid Mine Drainage (AMD): Graphical and Statistical Models to Assess Diatoms and Water Hydrogeochemistry Interactions

Sensitivity of Pathogenic Bacteria Strains to Treated Mine Water

Mine water as a result of meteoric and/or underground water's contact with tailings and underground workings could have an elevated content of metals associated with sulfate, often acidic, due to the bio-oxidation of sulfides. When entering aquatic ecosystems, the mine water can cause significant changes in the species' trophic levels, therefore a treatment is required to adjust the alkalinity and to remove the heavy metals and metalloids. The conventional mine water treatment removes metals, but in many cases it does not reduce the sulfate content. This paper aimed to predict the impact of conventionally treated mine water on the receiving river by assessing the genotoxic activity on an engineered Escherichia coli and by evaluating the toxic effects generated on two Gram-negative bacterial strains, Pseudomonas aeruginosa and Escherichia coli. Although the main chemical impact is the severe increases of calcium and sulfate concentrations, no significant genotoxic characteristics were detected on the Escherichia coli strain and on the cell-viability with a positive survival rate higher than 80%. Pseudomonas aeruginosa was more resistant than Escherichia coli in the presence of 1890 mg SO₄^2-/L. This paper reveals different sensitivities and adaptabilities of pathogenic bacteria to high concentrations of sulfates in mine waters.

Red mud-biochar composites (co-pyrolyzed red mud-plant materials): Characteristics and improved efficacy on the treatment of acidic mine water and trace element-contaminated soils

The use of commercially sourced dopants for synthesizing biochar-based composites could be economically undesirable. The current work aimed to explore the possibility of making low-cost biochar-based composites using red mud (an industrial waste from alumina production) as dopants. Two types of red mud were used: one from a Bayer process and another from a sintering process. Different techniques (wet chemical, magnetic, SEM-EDS, FTIR, XPS and XRD analyses) were adopted to characterize the synthesized red mud-biochar composites, along with the pristine biochar. The composites were superior to the pristine biochar in terms of acid neutralizing capacity, specific surface area, and degree of magnetization. Two laboratory simulation experiments were conducted to assess the improved efficacy of the composites on the treatment of acidic mine water and mine water-contaminated soils. In general, application of the composites resulted in a significantly higher removal rate of mine water-borne trace elements compared to the pristine biochar treatment. The composites also had better effects on immobilizing the soil-borne trace elements and weakening the uptake of trace elements by the test vegetable plant species grown in the composite-treated soils, as compared to the pristine biochar-treated soil. By comparison, the sintering red mud-biochar composite had a generally better performance compared to the Bayer red mud-biochar composite.

Acid Mine Drainage Effects in the Hydrobiology of Freshwater Streams from Three Mining Areas (SW Portugal): A Statistical Approach

Aljustrel, Lousal and S. Domingos mines are located in the Iberian Pyrite Belt (IPB), one of the greatest massive sulfide ore deposits worldwide. These mines' surrounding streams are affected by Acid Mine Drainage (AMD). The main purpose of this study was to understand AMD influence in the water quality and diatom behavior. Thus, waters and diatoms were sampled in 6 sites from the 3 selected mines on winter and summer of 2016. The highest concentrations were found in acidic sites: A3 (Aljustrel-Al, Cd, Cu, Fe and Zn (and lowest pH)) and L1 (Lousal-As, Mn, Ca, Mg, SO₄^2- and conductivity). The most abundant diatom species was Pinnularia aljustrelica with 100% of dominance in A3 and S1 acidic sites, which puts in evidence this species adaptation to AMD harsh conditions. Multivariate cluster analysis allowed us to reinforce results from previous studies, where spatial differences were more relevant than seasonal ones. In 12 years (2004-2016), and with many transformations undertaken (re-opening and rehabilitation), there is a conservative behavior in the biological species (diatoms) and physicochemical concentrations (metals, pH and sulfates) from these three mining sites. This type of biogeochemical diagnosis is necessary for the sustainable use of these waters and the prevention of the polluting process, aimed to protect the water ecosystem and its biodiversity.