Modeling the geochemical evolution of mine waters during mixing.

This study focuses on assessing the hydrogeochemical processes influencing the mobility of dissolved metal and metalloid species during mine effluent mixing. Field samples were collected to characterize effluents at an active gold mine located in the Abitibi Greenstone belt in western Québec, Canada. Controlled laboratory mixing experiments were further performed with real effluents. In situ physicochemical parameters, concentrations of major dissolved ions and trace elements were analyzed. Mineralogical analyses were also performed on precipitates from the laboratory mixtures. The data were used for statistical analyses and for modeling the geochemical evolution of effluents using PHREEQC with the wateq4f.dat database (with modifications). The results suggest that the formation of secondary minerals such as schwertmannite, Fe(OH)3, and jarosite could significantly affect the concentrations of trace elements in effluents. The precipitation of secondary minerals immobilized trace elements through coprecipitation and sorption processes. The main limitations of the modeling approach used here include the evaluation of the ion balance for low pH samples with high Fe and Al concentrations and the omission of biological processes. The approach provides insights into the geochemical evolution of mine effluents and could be adapted to several mining sites as a tool for improving water management.

Influence of ozone microbubble enhanced oxidation on mine effluent mixes and Daphnia magna toxicity.

The mining industry often must mix different kinds of water on the mine site during pre-treatment or post-treatment before the final discharge of the treated water to the environment. Microbubble ozonation has proven to be efficient in the removal of contaminants of concern from mine water, such as metals, metalloids, and nitrogen compounds, which can persist in the environment and entail toxicity issues. This study evaluated the efficiency of ozone microbubbles combined with lime precipitation on contaminant removal and its impact on toxicity for Daphnia magna with five different mine effluent mixes from an active mine site located in Abitibi-Témiscamingue, QC, Canada. For the non-acidic mixes, two scenarios were tested: first, pre-treatment of metals using lime precipitation and a flocculant was conducted prior to ozonation; and second, ozonation was conducted prior to metals post-treatment using the same precipitation and flocculation technique. Results showed that the NH3-N removal efficiency ranged from 90% for the lower initial concentrations (1.1 mg/L) to more than 99% for the higher initial concentrations (58.4 mg/L). Moreover, ozonation without metals pre-treatment improved NH3-N treatment efficiency in terms of kinetics but entailed abnormal toxicity issues. Results of bioassays conducted on water with metals pre-treatment did not show any toxicity events but showed abnormal toxicity patterns on the mixes treated without metals pre-treatment (diluted effluents were toxic, while undiluted were not). At 50% dilution, the water was toxic, probably due to the potential presence of metal oxide nanoparticles. The confirmation of the source of toxicity requires further investigation.

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).

Effect of the electrocoagulation process on the toxicity of gold mine effluents: A comparative assessment of Daphnia magna and Daphnia pulex.

Mine effluents must meet discharge criteria for both physicochemical parameters and toxicity. While chemical precipitation is efficient for the treatment of metallic elements in mine effluents, the removal of sulfates, as a source of salinity and potential toxicity, is limited by gypsum solubility. This study evaluated the efficiency of electrocoagulation (EC), an emerging process to treat mine water, in removing sulfates and acute toxicity in two gold mine effluents (E1 and E2), before and after treatment (Fe-electrodes, 30 min at 20 mA/cm2, and pH near neutrality). Standard toxicity tests were conducted on two daphnia species, Daphnia magna (standard test species) and Daphnia pulex (more common in cold climate). Four uncontaminated surface waters (S#1 to S#4), which originated from different watershed lithologies, were also used as dilution media with E1 to assess water quality effect on toxicity response. Statistical analyses using the Student's t-test showed no significant difference in immobility or mortality caused by surface waters on either D. magna or D. pulex species (p > 0.05). However, higher toxicity was observed with both daphnia when reconstituted hard water was used for testing of the treated effluent E2. The present study highlights the toxicity effect added by EC despite a sulfates-related salinity decrease of >7.5%. Further research should identify and confirm the potential sources of observed toxicity.

A review of the implications and challenges of manganese removal from mine drainage.

Manganese (Mn) is the third most abundant transition metal in the Earth's crust. Decades of increasing worldwide mining activities have inevitably led to the release of large amounts of this metal into the environment. Mine drainage, either acidic or neutral, often contains high levels of Mn, which have potentially detrimental effects on ecosystems and receiving water bodies. This review provides a comprehensive assessment of the main implications and challenges of Mn treatment in mine drainage. With this aim, the beneficial and adverse effects of Mn on ecosystems and human health are presented first. A comparison of background and mine effluents Mn contents is also provided, further stressing the need for Mn removal from mine drainage. Several technical options to address Mn contamination in acid and neutral mine drainage, and the challenges associated with Mn removal, are subsequently discussed. Thus, this paper presents up-to-date knowledge on the available physicochemical and biological processes deemed operative in Mn removal during mine drainage treatment and their limitations considering the distinctive behavior of Mn. The discussion is further extended to passive treatment systems, which are the most commonly implemented systems for mine drainage treatment on abandoned or closed mine sites, and highlights both their design criteria and operation requirements, as well as the factors that influence Mn removal efficiency. Finally, new perspectives on future research and development needs are identified to address the challenges in Mn removal during mine drainage treatment.

Mobility and speciation of geogenic arsenic in bedrock groundwater from the Canadian Shield in western Quebec, Canada.

High arsenic concentrations occur in groundwater collected from a fractured crystalline bedrock aquifer in western Quebec (Canada). Sampling and analysis of water from 59 private wells reveal that more than half of the bedrock wells exceed the Canadian guideline value of 10µg/l for arsenic, whereas shallow wells in unconsolidated surficial deposits are not affected by the contamination. The weathering of arsenic-bearing sulfides present along the mineralized fault zone is considered to be the primary source of arsenic in groundwater. High-arsenic wells are generally characterized by mildly reducing conditions (Eh<250mV), weak alkaline conditions (pH>7.4), low Ca/Na ratios, elevated dissolved Fe and Mn concentrations and high proportions of As(III). Private bedrock wells are open boreholes that likely receive groundwater from multiple contributing fractures. Hence, it is proposed that dissolved arsenic is mainly derived from the contribution to the well discharge of reducing and alkaline geochemically evolved groundwater that contains arsenic as As(III). Geochemically evolved groundwater provides favorable conditions to release arsenic by reductive dissolution of iron and manganese oxyhydroxides and alkaline desorption from mineral surfaces. Thus, high-arsenic wells would contain a high proportion of geochemically evolved groundwater, while oxidizing low-pH recharge water causes dilution and sequestration of arsenic. In relation with the chemical evolution of groundwater along the flow path, most contaminated wells are located in confined areas whereas most of the wells located in unconfined recharge areas are not contaminated. The occurrence of boreholes with high dissolved arsenic as As(V) and oxidizing conditions is attributed to extensive sulfide oxidation and alkaline desorption. This work shows that the determination of arsenic speciation provides a valuable tool to investigate the behavior of arsenic in bedrock groundwater.

Processes governing the stable isotope composition of water in the St. Lawrence river system, Canada.

Linkages between δ(18)O-δ(2)H and hydrological processes have been investigated from isotopic time series recorded in the St. Lawrence River basin. Three stations were monitored from 1997 to 2008. They include the Ottawa River, the St. Lawrence River main channel at Montreal and the fluvial estuary. All sites depict seasonal isotopic cycles characterized by heavy isotope depletions during the snowmelt period and heavy isotope enrichments throughout the ice-free period. The data define δ(2)H-δ(18)O regression lines falling below the meteoric water line. In the Ottawa River, calculations suggest that approximately 8 % of the total inflow to the basin is lost through evaporation. In the St. Lawrence River main channel, seasonal isotopic fluctuations most likely reflect hydrological processes occurring within the Great Lakes and mixing with tributaries located downstream. In the St. Lawrence River fluvial estuary, isotopic data allow partitioning streamflow components and suggest that the recorded seasonal variations mainly respond to mixing processes.

Serological profile of Toxoplasma gondii and Neospora caninum infection in commercial sheep from São Paulo State, Brazil.

Neosporosis and toxoplasmosis are two important infections in young and adult sheep, leading to low production and abortion. This study aimed to determine the frequency of antibodies to Toxoplasma gondii and Neospora caninum in sheep from the eastern region of São Paulo State, Brazil. Serum samples (382) were collected from the sheep and assayed for T. gondii through modified agglutination test (MAT) and indirect fluorescent antibody test (IFAT), and for N. caninum antibodies, through IFAT, with cut-off titers equal to 16 (T. gondii) and 25 (N. caninum). All frozen samples were sent to the Center for Zoonoses Research (NUPEZO), Department of Veterinary Hygiene and Public Health (DHSVP), FMVZ, UNESP, for serological tests. A total of 71/382 (18.6%) samples reacted to T. gondii, especially at titers 16 (28; 39.4%), 64 (15; 21.1%), 256 (21; 29.6%) and 1024 (6; 8.5%) by MAT, and 16 (34; 47.9%), 64 (18; 25.4%), 256 (14; 19.7%) and 1024 (5; 7%) by IFAT. As regards N. caninum, 49/382 (12.8%) samples reacted at titers 25 (17; 34.7%), 50 (11; 22.5%), 100 (11; 22.5%), and ≥ 200 (10; 20.4%). These animals presented infection but no clinical signs. Six and ten animals had high titers for toxoplasmosis and neosporosis. No significant association was observed between antibodies for both parasites (P=0.535) according to Fisher's exact test, and no correlation was found between T. gondii (MAT) and N. caninum antibody titers (r=-0.0068; P=0.895), T. gondii (IFAT) and N. caninum antibody titers (r=-0.0025; P=0.961). Thus, T. gondii and N. caninum infections were observed in farms located in São Paulo State, where sheep play an important economical role for the national and regional business.