Nutrient optimization in bioleaching: are we overdosing?

The general trend in biomining (i.e., bioleaching and biooxidation) is the use of media with high concentrations of the nutrients (nitrogen as ammonium, phosphorous as phosphate, and K), which are considered to be essential for microbial growth. The depletion of any of the nutrients would affect negatively the bioleaching (and biooxidation) capacity of the microorganisms, so the formulation of the different media ensures that there is a surplus of nutrients. However, some of these nutrients (e.g., phosphate, K) may be already present in the ore and are made available to the microorganisms when the ore is exposed to the low-pH media used during bioleaching. The effect of phosphate addition (109 mg/L) and depletion on the bioleaching of low-grade sulfidic ore alongside the determination of ammonium (i.e., 25 mg/L, 50 mg/L, 109 mg/L, 409 mg/L, and 874 g/L) requirements were studied. The results of the experiments presented showed that the addition of phosphate did not have any effect on the bioleaching of the low-grade sulfidic ore while the addition of ammonium was necessary to obtain higher redox potentials (>650 mV vs. Ag/AgCl) and higher metal (Co, Cu, Ni, and Zn) dissolutions. Temperature was the factor that shaped the microbial communities, at 30°C, the microbial community at the end of all the experiments was dominated by Acidithiobacillus sp. as well as at 42°C, except when nutrients were not added and Sulfobacillus sp. was the dominant microorganism. At 55°C, DNA recovery was unsuccessful, and at 60°C, the microbial communities were dominated by Sulfolobus sp. In conclusion, the amount of nutrients in bioleaching could be reduced significantly to achieve the redox potentials and metal dissolution desired in bioleaching without affecting the microbial communities and bioleaching efficiencies.

Natural carbon mineralization and its control on the geochemical evolution of coal-based aquifers in the Salt Range, Punjab, Pakistan.

Hydrochemical analysis of the Salt Range was conducted to understand carbon weathering and its impact on groundwater evolution within the complex geological framework of Punjab. Our results showed that groundwater samples were alkaline with a pH range of 7.0-8.6 and 7.8-8.8 for the eastern Salt Range (ESR) and Trans-Indus Salt Range (TSR), respectively, while that of the Central Salt Range (CSR) was acidic to moderately alkaline ranging between 5.7 and 7.5. The water types of Ca-Mg-HCO3, Ca-Mg-Cl, and Ca-Cl2 were the dominant hydro-chemical facies in ESR and CSR sites. However, groundwater of the TSR site falls under Ca-Mg-Cl, Ca-Cl2, and mixed types of Ca-Mg-SO4. Our new findings suggest that groundwater chemistry is primarily controlled by rock dominance and reverse ion exchange reaction, followed by evapotranspiration processes. The wells of ESR, CSR, and TSR were reported with higher levels of Fe and Zn. Regarding the suitability for irrigation, sodium adsorption ratio (SAR), magnesium adsorption ratio (MAR), sodium percentage (Na%), Kelley's ratio (KR), and potential salinity (PS) at all three sites (ESR, TSR, and CSR) had the potential to become a salinity hazard. The conceptual model of geochemical evolution shows that both local and regional salinization is driven by local geology and intensive coal mining activities. The neutralization capacity of the parent geological formation buffers the acidity and lowers the overall trace element enrichment. The potential of natural weathering could be further explored as a solution to coal mining's impact on the environment.

Groundwater nitrate and fluoride profiles, sources and health risk assessment in the coal mining areas of Salt Range, Punjab Pakistan.

To assess the loading profiles of groundwater nitrate (NO3-) and fluoride (F-), their spatial distributions, geochemistry and associated health risks were determined for 131 groundwater samples from eastern (ESR), central (CSR) and Trans-Indus Salt Ranges (TSR) in Pakistan. Groundwater NO3- concentrations were 0.2-308 mg/L (mean 59 mg/L) in ESR, 2.7-203 mg/L (mean 73 mg/L) in CSR and 1.1-259 mg/L (mean 69 mg/L) in the TSR. Forty-one %, 57% and 36% of the ESR, CSR and TSR samples, respectively, exceeded the WHO and Pak-NEQs permissible limit of 50 mg/L NO3-. Likewise, groundwater F- concentrations ranged from 0.1-1.8 mg/L (mean 0.6 mg/L), 0.1-2.7 mg/L (mean 0.9 mg/L) and 0.3-2.5 mg/L (mean 1.6 mg/L) mg/L in the ESR, CSR and TSR sites, respectively. In this case, 3%, 17% and 27% of the ESR, CSR and TSR samples, respectively, exceeded the WHO and Pak-NEQs permissible limit of 1.5 mg/L F. Oxidation of coal and coal waste resulted in the release of NO3- to groundwater. By contrast, enrichment of F- in groundwater was due to dissolution and cation exchange processes. Elevated values of the Higher Pollution Index (PI) and Health Risk Index (HRI) reflect a non-acceptable carcinogenic risk for drinking water NO3- and F- which should be addressed on a priority basis to protect human health.

Potentially toxic elements contamination in surface sediment and indigenous aquatic macrophytes of the Bahmanshir River, Iran: Appraisal of phytoremediation capability.

To determine the status and sources of contamination and phytoremediation capability of Typha latifolia L. in the Bahmanshir River of Iran, the concentration of eight potentially toxic elements (As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn) in sediment and plant tissues from ten sampling sites were measured. Mean concentrations of Cd, Cr, Cu, Pb, and Zn in the sediment exceeded those of local background. PCA-MLR receptor analysis suggested that the sediment contamination was due to municipal wastewater/vehicular pollution and weathering/industrial/agricultural activities, with contributions of 66% and 34%, respectively. Average enrichment factor (EF) and modified hazard quotient (mHQ) for Pb and Cu were categorized as moderate. Modified pollution index (MPI) and modified ecological risk index (MRI) values suggested moderate to heavy pollution and low ecological risk, respectively. The values of sediment quality guidelines (SQGs), ecological contamination index (ECI), contamination severity index (CSI), and toxic risk index (TRI) were all similar, reflecting low to moderate contamination and toxicity. Typha latifolia L. showed good phytostabilization capability for Cd, Cu, and Pb, and phytoextraction capacity for Zn. Using the metal accumulation index (MAI) and the comprehensive bioconcentration index (CBCI), Typha latifolia L. was shown to have acceptable performance in the accumulation of Cd, Cu, Pb, and Zn and thus, can be considered a good candidate for bioaccumulation of these elements in the study area. Overall, this study suggests that phytoremediation using Typha latifolia L. could be a practical method for uptake and remove of potentially toxic elements from aquatic environments.

Characteristics and mechanisms of Pb(II) sorption onto Fe-rich waste water treatment residue (WTR): A potential sustainable Pb immobilisation technology for soils.

Pb contamination of soils is a global problem. This paper discusses the ability of an Fe-rich waste, water treatment residual (WTR), to adsorb Pb(II). This was investigated using batch sorption experiments, X-ray diffraction, electron microprobe microanalysis, PHREEQC modeling and Extended X-ray Absorption Fine Structure (EXAFS) analysis. The WTR is composed of approximately 23 wt. % natural organic matter (NOM), 70 wt. % ferrihydrite and <10 wt. % silicate material. Pb(II) sorption to WTR was dependent on initial Pb(II) load, particle size, time and pH, but not on ionic strength. EXAFS analysis at the Pb LIII-edge confirmed that Pb(II) sorbed to WTR by co-existing bidentate edge-sharing and monodentate or corner-sharing complexes, with 2 O at ∼2.31-2.34 Å, 1 Fe at ∼3.32-3.34 Å, 2 Fe at ∼3.97-3.99 Å and 1 Pb at ∼3.82-3.85 Å. Linear combination showed that the Pb(II)-sorbed spectra were best fit with a ∼0.9 ± 0.1 and 0.1 ± 0.1 contribution from Pb(II)-sorbed ferrihydrite and Pb(II)-sorbed humic acid end members, respectively. Overall, we show that Pb(II) sorbs via strong inner-sphere complexation of Pb(II) to the ferrihydrite component of the WTR, which itself is stable over a wide pH range. Therefore, we suggest that Fe-rich WTR wastes could be used as effective adsorbents in Pb(II)-contaminated soils to help ensure sustainable terrestrial ecosystems.

Seasonal variations in arsenic mobility and bacterial diversity: The case study of Huangshui Creek, Shimen Realgar Mine, Hunan Province, China.

Rivers throughout the world have been contaminated by arsenic dispersed from mining activities. The biogeochemical cycling of this arsenic has been shown to be due to factors such as pH, Eh, ionic strength and microbial activity, but few studies have examined the effects of both seasonal changes and microbial community structure on arsenic speciation and flux in mining-affected river systems. To address this research gap, a study was carried out in Huangshui Creek, Hunan province, China, which has been severely impacted by long-term historic realgar (α-As4S4) mining. Water and sediment sampling, and batch experiments at different temperatures using creek sediment, were used to determine the form, source and mobility of arsenic. Pentavalent (AsO43) and trivalent arsenic (AsO33-) were the dominant aqueous species (70-89% and 30-11%, respectively) in the creek, and the maximum concentration of inorganic arsenic in surface water was 10,400 µg/L. Dry season aqueous arsenic concentrations were lower than those in the wet season samples. The sediments contained both arsenate and arsenite, and relative proportions of these varied with season. 8.3 tons arsenic per annum were estimated to be exported from Huangshui Creek. Arsenic release from sediment increased by 3 to 5 times in high water temperature batch experiments (25 and 37 °C) compared to those carried out at low temperature (8 °C). Our data suggest that the arsenic-containing sediments were the main source of arsenic contamination in Huangshui Creek. Microbial community structured varied at the different sample sites along the creek. Redundancy analysis (RDA) showed that both temperature and arsenic concentrations were the main controlling factors on the structure of the microbial community. Protecbacteria, Bacteroidetes, Cyanobacteria, Firmicutes, Verrucomicrobia, and Planctomycetes were the stable dominant phyla in both dry and wet seasons. The genera Flavobacterium, Hydrogenophaga and Sphingomonas occurred in the most highly arsenic contaminated sites, which removed arsenic by related metabolism.Our findings indicate that seasonal variations profoundly control arsenic flux and species, microbial community structure and ultimately, the biogeochemical fate of arsenic.

Characterization of Mining-Related Aromatic Contaminants in Active and Abandoned Metal(loid) Tailings Ponds.

This study reports on the compositional diversity of organic compounds in metal(loid)-bearing tailings samples from both active and abandoned tailings ponds. Tailings samples were qualitatively analyzed by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOFMS). In addition, the priority PAHs (16), PAEs (6), and phenols (2) were quantitatively analyzed using gas chromatography-mass spectrometry (GC-MS). We attribute the presence of some of aromatic organics in studied tailings ponds to particular sources. Mineral floatation reagents are likely the major sources of small-ring aromatics in tailings ponds, and products from metallurgical processing and burning of fossil fuels in the mining area or further afield are also possible contributors and might be the main source of large-ring aromatics. We found that tailings ponds abandoned for decades can still have organics concentrations at levels of concern. Large-ring aromatics are generally more toxic than other contaminants, and these were more abundant in abandoned tailings ponds. This suggests that these large-ring organics do not readily decompose or biodegrade into less toxic byproducts, as do volatiles and many other organic compounds. Our aromatic contaminants database provides an important starting point for researchers to investigate and compare similar contaminants that might be also present in other tailings ponds and emphasizes the necessity of considering their transformations over time.

Metagenomic exploration of multi-resistance genes linked to microbial attributes in active nonferrous metal(loid) tailings.

Mine tailings sites are considered as a continuous source of discharged metal(loid)s and residual organic flotation reagents. They are extremely toxic environments representing unique ecological niches for microbial communities. Mine tailings as a source of multi-resistance genes have been poorly investigated. Metagenomic analysis for four active nonferrous metal(loid) tailings sites with different environmental parameters was conducted. The abundance of Thiobacillus, able to tolerate acidity and showing iron- and sulfur/sulfide oxidation capacities, was significantly different (p < 0.05) between acid and neutral tailings sites. Correlation analyses showed that Zn, Pb, TP, Cd, and Cu were the main drivers influencing the bacterial compositions. Multi-metal resistance genes (MRGs) and antibiotic resistance genes (ARGs), such as baca and copA, were found to be co-selected by high concentrations of metal(loid)s tailings. The main contributors to different distributions of MRGs were Thiobacillus and Nocardioides genus, while genera with low abundance (<0.1%) were the main contributors for ARGs. Functional metabolic pathways related to Fe-S metabolism, polycyclic aromatic hydrocarbons (PAHs) degradation and acid stress were largely from Altererythrobacter, Lysobacter, and Thiobacillus, respectively. Such information provides new insights on active tailings with highly toxic contaminants. Short-term metal(loid) exposure of microorganism in active nonferrous metal(loid) tailings contribute to the co-occurrence of ARGs and MRGs, and aggravation of tailings acidification. Our results recommend that the management of microorganisms involved in acid tolerance and metal/antibiotic resistance is of key importance for in-suit treatment of the continuous discharge of tailings with multiple metal(loid) contaminants into impoundments.

Bacterial shifts during in-situ mineralization bio-treatment to non-ferrous metal(loid) tailings.

Nonferrous mine tailings have caused serious problems of co-contamination with metal(loid)s. It is still a global challenge to cost-effectively manage and mitigate the effect of the mining wastes. We conducted an in-situ bio-treatment of non-ferrous metal(loid) tailings using a microbial consortium of sulfate reducing bacteria (SRB). During the bio-treatment, the transformation of metal(loid)s (such as Cu, Fe, Mn, Pb, Sb, and Zn) into oxidizable and residual fractions in the subsurface tended to be higher than that observed in the surface. As well the mineral compositions changed becoming more complex, indicating that the sulfur reducing process of bio-treatment shaped the bio-transformation of metal(loid)s. The added SRB genera, especially Desulfotomaculum genus, colonized the tailings suggesting the coalescence of SRB consortia with indigenous communities of tailings. Such observation provides new insights for understanding the functional microbial community coalescence applied to bio-treatment. PICRUSt analysis revealed presence of genes involved in sulfate reduction, both assimilatory and dissimilatory. The potential for the utilization of both inorganic and organic sulfur compounds as S source, as well as the presence of sulfite oxidation genes indicated that SRB play an important role in the transformation of metal(loid)s. We advocate that the management of microorganisms involved in S-cycle is of paramount importance for the in situ bio-treatment of tailings, which provide new insights for the implementation of bio-treatments for mitigating the effect of tailings.

Origin and Fate of Vanadium in the Hazeltine Creek Catchment following the 2014 Mount Polley Mine Tailings Spill in British Columbia, Canada.

Results from the analysis of aqueous and solid-phase V speciation within samples collected from the Hazeltine Creek catchment affected by the August 2014 Mount Polley mine tailings dam failure in British Columbia, Canada, are presented. Electron microprobe and X-ray absorption near-edge structure (XANES) analysis found that V is present as V3+ substituted into magnetite and V3+ and V4+ substituted into titanite, both of which occur in the spilled Mount Polley tailings. Secondary Fe oxyhydroxides forming in inflow waters and on creek beds have V K-edge XANES spectra exhibiting E1/2 positions and pre-edge features consistent with the presence of V5+ species, suggesting sorption of this species on these secondary phases. PHREEQC modeling suggests that the stream waters mostly contain V5+ and the inflow and pore waters contain a mixture of V3+ and V5+. These data, and stream, inflow, and pore water chemical data, suggest that dissolution of V(III)-bearing magnetite, V(III)- and V(IV)-bearing titanite, V(V)-bearing Fe(-Al-Si-Mn) oxhydroxides, and V-bearing Al(OH)3 and/or clay minerals may have occurred. In the circumneutral pH environment of Hazeltine Creek, elevated V concentrations are likely naturally attenuated by formation of V(V)-bearing secondary Fe oxyhydroxide, Al(OH)3, or clay mineral colloids, suggesting that the V is not bioavailable. A conceptual model describing the origin and fate of V in Hazeltine Creek that is applicable to other river systems is presented.

Bacterial diversity in typical abandoned multi-contaminated nonferrous metal(loid) tailings during natural attenuation.

Abandoned nonferrous metal(loid) tailings sites are anthropogenic, and represent unique and extreme ecological niches for microbial communities. Tailings contain elevated and toxic content of metal(loid)s that had negative effects on local human health and regional ecosystems. Microbial communities in these typical tailings undergoing natural attenuation are often very poorly examined. The diversity and inferred functions of bacterial communities were examined at seven nonferrous metal(loid) tailings sites in Guangxi (China), which were abandoned between 3 and 31 years ago. The acidity of the tailings sites rose over 31 years of site inactivity. Desulfurivibrio, which were always coupled with sulfur/sulfide oxidation to dissimilate the reduction of nitrate/nitrite, were specific in tailings with 3 years abandonment. However, genus beneficial to plant growth (Rhizobium), and iron/sulfur-oxidizing bacteria and metal(loid)-related genera (Acidiferrobacter and Acidithiobacillus) were specific within tailings abandoned for 23 years or more. The increased abundance of acid-generating iron/sulfur-oxidizing and metal(loid)-related bacteria and specific bacterial communities during the natural attenuation could provide new insights for understanding microbial ecosystem functioning in mine tailings. OTUs related to Sulfuriferula, Bacillus, Sulfurifustis, Gaiella, and Thiobacillus genera were the main contributors differentiating the bacterial communities between the different tailing sites. Multiple correlation analyses between bacterial communities and geochemical parameters indicated that pH, TOC, TN, As, Pb, and Cu were the main drivers influencing the bacterial community structures. PICRUSt functional exploration revealed that the main functions were related to DNA repair and recombination, important functions for bacterial adaptation to cope with the multi-contamination of tailings. Such information provides new insights to guide future metagenomic studies for the identification of key functions beyond metal-transformation/resistance. As well, our results offers novel outlooks for the management of bacterial communities during natural attenuation of multi-contaminated nonferrous metal(loid) tailings sites.

China's most typical nonferrous organic-metal facilities own specific microbial communities.

The diversity and function of microorganisms have yet to be explored at non-ferrous metal mining facilities (NMMFs), which are the world's largest and potentially most toxic sources of co-existing metal(loid)s and flotation reagents (FRs). The diversity and inferred functions of different bacterial communities inhabiting two types of sites (active and abandoned) in Guangxi province (China) were investigated for the first time. Here we show that the structure and diversity of bacteria correlated with the types of mine sites, metal(loid)s, and FRs concentrations; and best correlated with the combination of pH, Cu, Pb, and Mn. Combined microbial coenobium may play a pivotal role in NMMFs microbial life. Arenimonas, specific in active mine sites and an acidophilic bacterium, carries functions able to cope with the extreme conditions, whereas Latescibacteria specific in abandoned sites can degrade organics. Such a bacterial consortium provides new insights to develop cost-effective remediation strategies of co-contaminated sites that currently remain intractable for bioremediation.

Dissolution of realgar by Acidithiobacillus ferrooxidans in the presence and absence of zerovalent iron: Implications for remediation of iron-deficient realgar tailings.

Realgar (As4S4)-rich tailings are iron-deficient arsenical mine wastes. The mechanisms and products of the dissolution of realgar by Acidithiobacillus ferrooxidans (A. ferrooxidans) in the presence (0.2 g and 2 g) and absence of zerovalent iron (ZVI) are investigated for three stages (each of 7 d with fresh A. ferrooxidans medium addition between the stages). SEM-EDX, FTIR, XPS and selective extraction analysis are used to characterize the solid-phase during the experiments. ZVI addition causes the systems to become more acid-generating, although pH increases are observed in the first day due to ZVI dissolution. Arsenic is released to solution due to realgar oxidation (∼30 mg L-1 in the 0 g ZVI system in Stage I), but low concentrations are observed in the ZVI-added systems (<5 mg L-1) and in Stages II and III of the 0 g ZVI system. As(III) dominates the released As(T) at day 1 (83-89% of As(T)), but is largely oxidized to As(V) at day 7 of each stage (53-98% of As(T)). Arsenic attenuation is attributed to the formation of mixed As-Fe oxyhydroxides and oxyhydroxy sulfates that take up released arsenic and are abundant in the 2.0 g ZVI system, and to passivation of the realgar surface. Consequently, a new strategy that combines A. ferrooxidans and exogenous ZVI addition for treating in-situ iron-deficient realgar-rich tailings is proposed, although its long-term effects need to be monitored.

Dissolved Mn(III) in water treatment works: Prevalence and significance.

Dissolved Mn(III) has been identified at all stages throughout a Water Treatment Works (WTW) receiving inflow from a peaty upland catchment in NE England. Ninety percent of the influent total manganese into the WTW is particulate Mn, in the form of Mn oxide (>0.2 µm). Approximately 9% (mean value, n = 22, range of 0-100%) of the dissolved (<0.2 µm) influent Mn is present as dissolved Mn(III). Mn(III) concentrations are highest (mean of 49% of total dissolved Mn; n = 26, range of 17-89%) within the WTW where water comes into contact with the organic-rich sludges which are produced as waste products in the WTW. These Mn(III)-containing wastewaters are recirculated to the head of the works and constitute a large input of Mn(III) into the WTW. This is the first report of Mn(III) being identified in a WTW. The ability of Mn(III) to act as both an oxidant and a reductant is of interest to the water industry. Understanding the formation and removal of Mn(III) within may help reduce Mn oxide deposits in pipe networks. Further understanding how the ratio of Mn(III) to Mn(II) can be used to optimise dissolved Mn removal would save the water industry significant money in reducing discoloration 'events' at the customers' tap.

In situ arsenic oxidation and sorption by a Fe-Mn binary oxide waste in soil.

The ability of a Fe-Mn binary oxide waste to adsorb arsenic (As) in a historically contaminated soil was investigated. Initial laboratory sorption experiments indicated that arsenite [As(III)] was oxidized to arsenate [As(V)] by the Mn oxide component, with concurrent As(V) sorption to the Fe oxide. The binary oxide waste had As(III) and As(V) adsorption capacities of 70mgg-1 and 32mgg-1 respectively. X-ray Absorption Near-Edge Structure and Extended X-ray Absorption Fine Structure at the As K-edge confirmed that all binary oxide waste surface complexes were As(V) sorbed by mononuclear bidentate corner-sharing, with 2 Fe at ∼3.27Ǻ. The ability of the waste to perform this coupled oxidation-sorption reaction in real soils was investigated with a 10% by weight addition of the waste to an industrially As contaminated soil. Electron probe microanalysis showed As accumulation onto the Fe oxide component of the binary oxide waste, which had no As innately. The bioaccessibility of As was also significantly reduced by 7.80% (p<0.01) with binary oxide waste addition. The results indicate that Fe-Mn binary oxide wastes could provide a potential in situ remediation strategy for As and Pb immobilization in contaminated soils.

Mining and Planetary Health: A GeoHealth-Led Special Collection.

Mining is a vital part of the global economy, but unmanaged releases of mine wastes can affect the health of humans, ecosystems, water, soil and Earth surface environments (e.g., rivers and estuaries). New technological developments and multidisciplinary collaborations are leading to new insights into the relationship between mining and the health of the Earth. In recognition of the importance of this topic, GeoHealth is leading in the creation of a special collection of papers on the theme of Mining and Planetary Health, to summarize the current state of knowledge, outline topics for urgent action and further research, and highlight positive efforts in environmental and health protection. Submissions are invited from researchers investigating the impacts of mining at the intersection of the Earth and environmental sciences and human, ecosystem, and planetary health.

Community exposure and vulnerability to water quality and availability: a case study in the mining-affected Pazña Municipality, Lake Poopó Basin, Bolivian Altiplano.

Assessing water sources for drinking and irrigation along with community vulnerability, especially in developing and rural regions, is important for reducing risk posed by poor water quality and limited water availability and accessibility. We present a case study of rural mining-agricultural communities in the Lake Poopó Basin, one of the poorest regions on the Bolivian Altiplano. Here, relatively low rainfall, high evaporation, salinization and unregulated mining activity have contributed to environmental degradation and water issues, which is a situation facing many Altiplano communities. Social data from 72 households and chemical water quality data from 27 surface water and groundwater sites obtained between August 2013 and July 2014 were used to develop locally relevant vulnerability assessment methodologies and ratings with respect to water availability and quality, and Chemical Water Quality Hazard Ratings to assess water quality status. Levels of natural and mining-related contamination in many waters (CWQHR ≥ 6; 78% of assessed sites) mean that effective remediation would be challenging and require substantial investment. Although waters of fair to good chemical quality (CWQHR ≤ 5; 22% of assessed sites) do exist, treatment may still be required depending on use, and access issues remain problematic. There is a need to comply with water quality legislation, improve and maintain basic water supply and storage infrastructure, build and operate water and wastewater treatment plants, and adequately and safely contain and treat mine waste. This study serves as a framework that could be used elsewhere for assessing and mitigating water contamination and availability affecting vulnerable populations.

Enhancing As(V) adsorption and passivation using biologically formed nano-sized FeS coatings on limestone: Implications for acid mine drainage treatment and neutralization.

The iron-reducing bacterium Acidiphilium cryputum JF-5 and a sulfate reducing bacterium (SRB) collected and purified from the mine drainage of a copper mine in the northwest of Sichuan Province, China, were used to biologically synthesize nano-sized FeS-coated limestone to remove As(V) from solution. The adsorption efficiency of As(V) is improved from 6.64 µg/g with limestone alone to 187 µg/g with the FeS coated limestone in both batch and column experiments. The hydraulic conductivity of the columns are also improved by the presence of the nano-sized FeS coatings, but the solution neutralization performance of the limestone can be reduced by passivation by gypsum and Fe(III) precipitates. Calculations for FeS-coated limestone dissolution experiments show that the process can be described as nCa.sol = At1/2 - nCa,gyp. The results suggest that FeS-coated limestone may be an effective medium for remediating As(V)-bearing solutions such as acid mine drainage in systems such as Permeable Reactive Barriers.

The role of nano-sized manganese coatings on bone char in removing arsenic(V) from solution: Implications for permeable reactive barrier technologies.

Although the removal of arsenic(V) (As(V)) from solution can be improved by forming metal-bearing coatings on solid media, there has been no research to date examining the relationship between the coating and As(V) sorption performance. Manganese-coated bone char samples with varying concentrations of Mn were created to investigate the adsorption and desorption of As(V) using batch and column experiments. Breakthrough curves were obtained by fitting the Convection-Diffusion Equation (CDE), and retardation factors were used to quantify the effects of the Mn coatings on the retention of As(V). Uncoated bone char has a higher retention factor (44.7) than bone char with 0.465 mg/g of Mn (22.0), but bone char samples with between 5.02 mg/g and 14.5 mg/g Mn have significantly higher retention factors (56.8-246). The relationship between retardation factor (Y) and Mn concentration (X) is Y = 15.1 X + 19.8. Between 0.2% and 0.6% of the sorbed As is desorbed from the Mn-coated bone char at an initial pH value of 4, compared to 30% from the uncoated bone char. The ability of the Mn-coated bone char to neutralize solutions increases with increased amounts of Mn on the char. The results suggest that using Mn-coated bone char in Permeable Reactive Barriers would be an effective method for remediating As(V)-bearing solutions such as acid mine drainage.

Remediation of a historically Pb contaminated soil using a model natural Mn oxide waste.

A natural Mn oxide (NMO) waste was assessed as an in situ remediation amendment for Pb contaminated sites. The viability of this was investigated using a 10 month lysimeter trial, wherein a historically Pb contaminated soil was amended with a 10% by weight model NMO. The model NMO was found to have a large Pb adsorption capacity (qmax 346±14 mg g(-1)). However, due to the heterogeneous nature of the Pb contamination in the soils (3650.54-9299.79 mg kg(-1)), no treatment related difference in Pb via geochemistry could be detected. To overcome difficulties in traditional geochemical techniques due to pollutant heterogeneity we present a new method for unequivocally proving metal sorption to in situ remediation amendments. The method combines two spectroscopic techniques; namely electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). Using this we showed Pb immobilisation on NMO, which were Pb free prior to their addition to the soils. Amendment of the soil with exogenous Mn oxide had no effect on microbial functioning, nor did it perturb the composition of the dominant phyla. We conclude that NMOs show excellent potential as remediation amendments.