Manganese removal processes and geochemical behavior in residues from passive treatment of mine drainage.

Efficiency of Mn passive treatment from mine drainage (MD) is limited, in the presence of Fe, because of the wide stability field of dissolved Mn(II) species. Physicochemical and mineralogical characterization, as well as static leaching tests at pH 7 (CTEU-9) of four samples were performed to assess Mn immobilization processes from MD and post-treatment stability of residues. Samples consisted of half-calcined dolomite, from three column reactors that treated Mn in MD. The first residue originated from real acid mine drainage treatment (R-AMD; pH 2.4; 623 mg/L Fe; 22 mg/L Mn), the second from real contaminated neutral drainage (R-CND; pH 6.7; 0.6 mg/L Mn) and the third from synthetic CND (S-CND; pH 6.8; 47 mg/L Mn). A sample of calcite (CAL) was also collected in a field oxic limestone drain that treats AMD (pH 4.1; 10.2 mg/L Fe; 12.4 mg/L Mn) on a closed mine site. Mineralogical analyses showed Mn immobilization in the form of MnOx. In R-AMD residues, Fe and Al concentrations almost doubled relative to half calcined dolomite before MD treatment, while Mn removal was inefficient. In S-CND residues, high concentrations of Mn were immobilized (>6.6 g/kg). The mineralogy of R-AMD residues showed that Fe precipitates coated the dolomite, in the form of Fe-(oxy)hydroxysulfates. Half-calcined dolomite is effective for Mn removal in S-CND, but Fe inhibits Mn treatment in AMD. Metal(loid)s in eluates were below the threshold limits, but the pH of R-CND (11.1) and S-CND (10.5) residues no longer met the discharge criteria (pH 6.0 to 9.5).

Le Bourre B ，Neculita CM ，Coudert L ，Rosa E ... -  《-》

Stability of metal-rich residues from laboratory multi-step treatment system for ferriferous acid mine drainage.

Jouini M ，Rakotonimaro TV ，Neculita CM ，Genty T ，Benzaazoua M ... -  《-》

Manganese and limestone interactions during mine water treatment.

Manganese removal from mining-affected waters is an important challenge for the mining industry. Addressed herein is this issue in both batch and continuous conditions. Batch experiments were carried out with synthetic solutions, at 23+/-2 degrees C, initial pH 5.5 and 8.3 g limestone/L. Similarly, continuous tests were performed with a 16.5 mg/L Mn(2+) mine water, at 23 degrees C, initial pH 8.0 and 20.8 g limestone/L. Calcite limestone gave the best results and its fine grinding proved to the most effective parameter for manganese removal. In either synthetic solutions or industrial effluents, the final manganese concentration was below 1 mg/L. A change in limestone surface zeta potential is observed after manganese removal and manganese carbonate formation was suggested by IR spectroscopy. The conclusion is that limestone can remove manganese from industrial effluents for values that comply with environmental regulations.

Silva AM ，Cruz FL ，Lima RM ，Teixeira MC ，Leão VA ... -  《-》

Environmental behavior of metal-rich residues from the passive treatment of acid mine drainage.

In closed or abandoned mine sites, passive systems are often used for acid mine drainage (AMD) treatment. They generate metal-rich residues with variable chemical stability, which is rarely reported. The objective of the present study was to evaluate the potential mobility of contaminants (metals and sulfates) from AMD post-treatment residues to better anticipate their fate and enable their proper management. Sampling of a field tri-step passive system, consisting of two passive biochemical reactors (PBR1 and PBR2), separated by a wood ash reactor (WA), implemented in the reclaimed Lorraine mine site, QC, Canada, was carried out. Samples were collected from the inlet (In) and the outlet (Out) of each treatment unit. Physicochemical and mineralogical characterization was performed. The potential mobility of the metals was then assessed via static and kinetic leaching tests. Results showed that all residues had high metal contents (e.g. Fe content >29 g/kg in PBR1-In, > 76 g/kg in WA-In and > 80 g/kg in PBR2-Out). A high residual neutralizing potential was also found in the WA residues (inorganic carbon 6.5%). Native and organic sulfur were found in the PBR2 residues, while Fe-oxyhydroxide (hematite, goethite and magnetite), carbonate and sulfate minerals were present in all residues. According to USEPA regulations, all residues were considered non-hazardous, but Quebec's provincial regulation relative on mining effluents classifies these residues as leachable for some metals, such as Fe, Al, Ni, Zn and Mn. A potential generation of contaminated neutral mine drainage (Al, Ni, Mn and Zn concentrations exceeding criteria) could occur from PBR1 (In & Out) and WA (In & Out) residues. Moreover, the PBR2 residues (In & Out) regenerated AMD rich in Fe and sulfates, especially for PBR2-Out (1 g/L Fe and 6 g/L sulfates). Therefore, all residues were proven to require stabilization prior to their landfill (co-)disposal with municipal waste.

Jouini M ，Neculita CM ，Genty T ，Benzaazoua M ... -  《-》

Characterization of iron and manganese minerals and their associated microbiota in different mine sites to reveal the potential interactions of microbiota with mineral formation.

Different environmental conditions such as pH and dissolved elements of mine stream induce precipitation of different minerals and their associated microbial community may vary. Therefore, mine precipitates from various environmental conditions were collected and their associated microbiota were analyzed through metagenomic DNA sequencing. Various Fe and Mn minerals including ferrihydrite, schwertmannite, goethite, birnessite, and Mn-substituted δ-FeOOH (δ-(Fe1-x, Mnx)OOH) were found in the different environmental conditions. The Fe and Mn minerals were enriched with toxic metal(loid)s including As, Cd, Ni and Zn, indicating they can act as scavengers of toxic metal(loid)s in mine streams. Under acidic conditions, Acidobacteria was dominant phylum and Gallionella (Fe oxidizing bacteria) was the predominant genus in these Fe rich environments. Manganese oxidizing bacteria, Hyphomicrobium, was found in birnessite forming environments. Leptolyngbya within Cyanobacteria was found in Fe and Mn oxidizing environments, and might contribute to Fe and Mn oxidation through the production of molecular oxygen. The potential interaction of microbial community with minerals in mine sites can be traced by analysis of microbial community in different Fe and Mn mineral forming environments. Iron and Mn minerals contribute to the removal of toxic metal(loid)s from mine water. Therefore, the understanding characteristics of mine precipitates and their associated microbes helps to develop strategies for the management of contaminated mine water.

Park JH ，Kim BS ，Chon CM 《-》