Scorodite precipitation in the presence of antimony

publisher: Elsevier articletitle: Scorodite precipitation in the presence of antimony journaltitle: Chemical Geology articlelink: http://dx.doi.org/10.1016/j.chemgeo.2015.04.013 content_type: article copyright: Copyright © 2015 The Authors. Published by Elsevier B.V.© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license. The attached file is the published version of the article

Converting rain into drinking water: Quality issues and technological advances

With growing pressures on water supplies worldwide, rainwater harvesting is increasingly seen as a viable option to provide drinking water to an ever expanding population, particularly in developing countries. However, rooftop runoff is not without quality issues. Microbiological and chemical contamination have been detected in several studies, well above local and international guidelines, posing a health risk for consumers. Our research explores the use of silver ions, combined with conventional filtration and settling mechanisms, as a safe and affordable model for purification that can be applied on a small scale. The complete systems were installed and tested in rural communities in a Mexican semi-arid region. Efficiencies up to 99.9% were achieved in the removal of indicator microorganisms, with a marked exception where cross-contamination from external seepage occurs. Sites without overhanging branches or with relatively clean surfaces show an absence of total coliforms in the untreated runoff, compared with others where values as high as 1,650 CFU/100 ml were recorded. Thus, given adequate maintenance, the system can successfully deliver high quality drinking water, even when storage is required for long periods of time. © IWA Publishing 2011

Evaluation of a silver-ion based purification system for rainwater harvesting at a small-scale community level

Silver has been known for centuries to be a powerful disinfectant, with no known harmful effects to humans if applied in adequate doses. Although its use was partially discontinued with the advent of chlorination and modern antibiotics, the discovery of bacterial resistance and disinfection by-products has enabled its re-emergence as a viable water purification option. On the other hand, implementation in small-scale rainwater harvesting (RWH) systems has received little attention, possibly due to a general perception that it is a complex and/or expensive technology. This can be overcome by efficient designs that dose silver ions into the water at a minimal cost. The authors evaluated a dozen RWH systems equipped with silver releasing devices, which have been providing drinking water to schools and clinics in a rural area of Mexico. This paper represents a follow-up to a previously published study on an evaluation performed in the same region. A number of water quality parameters have been analysed, examining the long-term efficiency of the projects. Our observations show that the silver ion devices act as an effective disinfection mechanism, as long as adequate maintenance is provided. The combination with conventional settling tanks and filtration units seems to greatly enhance the overall performance of the system

Weathering of Zinc-(Zn)-bearing Mine Wastes in a Neutral Mine Drainage Setting, Gunnerside Gill, Yorkshire

This is the final version of the article. Available from Elsevier via the DOI in this record.Numerous areas throughout the world are affected by circum-neutral pH, low iron (Fe) drainage with high concentrations of zinc (Zn) arising from discharges from, and weathering of, mine wastes. Gunnerside Gill, a small upland tributary in the headwaters of the River Swale in Yorkshire, is such a site affected by historic lead and zinc mining. The aim of the study is to assess the controls on Zn mobilisation from the mine tailings and floodplain sediments to the river water through a column leaching experiment. Sphalerite has been identified as the primary Zn mineral in the bedrock within Gunnerside Gill. However, there is more evidence of secondary phases of Zn were including Fe oxides and phosphates present within the samples and the BCR data suggests it is these phases that appear to be undergoing the majority of the Zn dissolution

Influence of pH and temperature on alunite dissolution: Rates, products and insights on mechanisms from atomistic simulation

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordThe processes, rates, controlling factors and products of alunite (KAl3(SO4)2(OH)6) dissolution were assessed using batch dissolution experiments at pHs of c. 3, 4, 4.6, 7 and 8, and temperatures of c. 280, 293 and 313K. Alunite dissolution is roughly congruent at pH3, while at pH≥3.9 the process is incongruent, giving a lower Al/K ratio in solution than in the pristine alunite sample. The decrease in the Al/K ratio appears to be caused by precipitation of secondary aluminium sulfate/hydroxysulfate minerals coating the surface of the dissolving alunite, as inferred from SEM images and XPS determinations, but these minerals do not passivate the alunite surface for the time frame of the experiments (up to 400h). The lowest dissolution rates are obtained for pH4.6 and 280K. Both the temperature increase and any pH variation from that point lead to faster dissolution rates. Based on the potassium release to solution, the influence of pH and temperature on the alunite dissolution rate for pH of 4.8 and below can be expressed as;. rateK= 104.4 ± 0.5aH+0.10 ± 0.02e32±3/RTwhere rateKis the alunite dissolution rate (in mol·m-2·s-1); aH+is the activity of hydrogen ions in solution; R is the Universal gas constant (in kJ·mol-1·K-1) and T is temperature (in K).For pH of 4.6 and above, the alunite dissolution rate can instead be expressed as;. rateK= 102.5±0.8aOH0.14±0.02e-39±4/RTwhere aOH-is the activity of hydroxyl ions in solution. In light of the calculated values for the activation energy under the two sets of pH conditions (32 ± 3 and 39 ± 4 kJ·mol-1), alunite dissolution appears to be surface-controlled. Examination of the most stable solvated alunite surfaces obtained by atomistic computer simulations suggests that the least energetically favourable steps during alunite dissolution are the detachment of either Al atoms or SO4tetrahedra from exposed surfaces. Thus, these processes are most probably the rate-determining steps in alunite dissolution.This work has been funded by the EC Marie Curie Intra-European Fellowship program (Project entitled ‘Reactivity of Aluminium Sulfate Minerals in Mine Wastes’; RASMIM) through a fellowship to P.A. The authors acknowledge also the NERC (National Environmental Research Council, United Kingdom) for partially funding the characterisation of mineral samples through the project ‘Characterisation of nanometre-sized aluminium sulphates: implications for mobility of aluminium from mine wastes’ (FENAC/2013/11/001)

Geochemistry and mineralogy of wastes from lithium-bearing granite-pegmatite mining: resource potential and environmental risks

This is the final version. Available on open access from Frontiers Media via the DOI in this recordThe global need for lithium (Li) is increasing due to its use in batteries which are used to make electric vehicles, wind turbines and fuel cells to facilitate the world’s ‘green transition’ to low carbon economies. The mining of Li, like that of other Earth materials, produces large volumes of waste such as tailings and processing chemicals. A growing body of research is addressing the resource potential and environmental impacts of wastes from mining of Li-bearing granites and pegmatites that produce around 40% of the world’s Li. The wastes are dominated by SiO2 and Al2O3, with lesser Na2O, K2O and Fe2O3, that are hosted in quartz, feldspar and micas. They can contain around 1 wt% Li2O that is found in residual spodumene, lepidolite and zinnwaldite, and trace (<1 wt%) amounts of Rb, Cs, U and Be. Some exploitation of the Li from granite-pegmatite tailings is occurring on a commercial scale. There is also good potential for the waste quartz, feldspar and mica to be used in ceramics and building materials, and for the Rb, Cs and Be to be used for photovoltaic cells, alloys and other applications. Spodumene-bearing wastes can contain potentially toxic and/or radioactive U, Th and Tl, but the concentrations are generally low. Overall, Li-bearing granite-pegmatite mine wastes have good potential to be reused, remined and recycled. More research is required to characterize their geochemistry and mineralogy in detail to improve recovery and to understand how processing and weathering may affect environmental risk.Natural Environment Research Council (NERC

Partitioning of Co2+ and Mn2+ into meridianiite (MgSO4·11H2O): Ternary solubility diagrams at 270 K; cation site distribution determined by single-crystal time-of-flight neutron diffraction and density functional theory

This is the final version of the article. Available from Elsevier via the DOI in this record.We have grown single crystals of M 2+ SO 4 hydrates at 270 K from aqueous solutions in the ternary systems CoSO 4 –MgSO 4 –H 2 O and MnSO 4 –MgSO 4 –H 2 O. These systems exhibit broad stability fields for a triclinic undecahydrate on the Mg-rich side (i.e., Co- or Mn-bearing meridianiite solid solutions) and stability fields for monoclinic heptahydrates on the Mg-poor side (i.e., Mg-bearing solid solutions of bieberite or mallardite). The solubility curves and distribution coefficients, describing the partitioning of M 2+ ions between liquid and solid phases, have been determined by thermo-gravimetric and spectroscopic techniques. A subset of M 2+ SO 4 ·11H 2 O specimens were selected for single-crystal time-of-flight neutron diffraction analysis in order to evaluate preferential occupancy of symmetry-inequivalent coordination polyhedra in the structure. Considering the nearly identical dimensions of the first coordination shells, there is a surprising difference in the distribution of Co and Mn over the two available sites.This work was supported in part by the Science and Technology Facilities Council, Fellowship number PP/E006515/1 and by STFC grant number ST/K000934/1

Coupling effect of Fe3+(aq) and biological, nano-sized FeS-coated limestone on the removal of redox-sensitive contaminants (As, Sb and Cr): Implications for in situ passive treatment of acid mine drainage

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordNano-sized FeS particles have been shown to improve the adsorption performance in permeable reactive barrier (PRB) technologies that are used to treat acid mine drainage. To investigate the coupling effect of Fe3+and biological nano-sized FeS on removal of redox-sensitive contaminants and the permeability of a limestone system, Fe-reducing bacteria (FRB) and sulfate-reducing bacteria (SRB) were used to form nano-sized FeS coatings on limestone grains. For initial acidic solutions containing 0.5 mg/L As(V), Cr(VI) and Sb(V), retardation factors increase from 26, 5 and 7, respectively, in a limestone-only (pristine) system to »367, 89 and 9, respectively, in an FeS-coated limestone system, and to 345, 367 and 308, respectively, in an FeS-Fe3+(aq)system. The permeability coefficient of the FeS-coated limestone system is better than that of the pristine limestone system, but declines to two-thirds of the pristine limestone system in the presence of Fe3+(aq), possibly due to the formation of secondary ferric hydroxides. XPS analysis suggests that the FeS particles are effective at reducing As(V), Sb(V) and Cr(VI) and removing them from solution. These results demonstrate that FeS particles improve retention of redox-sensitive contaminants with and without Fe3+(aq). These new findings give new insights on the coupling effect of redox systems used in PRBs.This study was supported by the National Basic Research Program of China (973 Program: 2014CB846003)

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

This is the author's accepted manuscript.The final version is available from Elsevier via the DOI in this record.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.This study was supported by the National Natural Science Foundation of China (Grant No. 4177236) and National Key R&D Program of China (2016YFC0502204)