Precipitation Of Manganese Research Articles

Analysis of trace elements pollution within streambed sediments from the Shade River Watershed, southeastern Ohio

Streambed sediments collected from the Shade River Watershed within the Western Allegheny Plateau in Meigs and Athens counties (Ohio, USA) were analyzed for trace elements. Different pollution indices and statistical techniques were used to evaluate the relationship between the trace elements and determine their levels of contamination. The watershed was once mined for coal and has history of acid mine drainage (AMD). Treatment of this contamination is still being addressed by federal and local organizations. Sediment analyses indicated that iron, aluminum, and manganese, which are primary AMD species, are dominant within the sediments. Pollution indices indicated that the sediments were moderately to extremely polluted, with iron dominating. Relatively low trace element concentrations in the Middle Shade River can be attributed to the intense remediation or treatment of mine drainage. Although trace elements’ concentration in the Shade River Watershed was greater than their respective background values, the relationship between iron and other trace elements indicates that alkaline pH and redox conditions can influence the neutralization of AMD, and also result in the precipitation of iron and manganese oxide/hydroxides. This may have caused the contamination of the streambed sediment apart from factors including local geology, erosion of agricultural soil, mine discharge, and other anthropogenic input into the watershed.

RECOVERY OF VALUABLE METALS FROM ZINC PLANT RESIDUE THROUGH SEPARATION BETWEEN MANGANESE AND COBALT WITH N-N REAGENT

Recovery and separation of cobalt and manganese from one of zinc plant residues (ZPR), namely hot filter cake (HFC) using a hydrometallurgical process was studied. The process is carried out in four steps as follows: (1) washing zinc, (2) reductive leaching with hydrogen peroxide, (3) cadmium cementation with zinc powder and (4) separation of cobalt from manganese with beta naphthol. In this research, the separation between manganese and cobalt from the HFC using N-N reagent was investigated. The influence of several parameters on the course of the reaction such as N-N quantity, pH, temperature and reaction time was also examined. The optimum separation conditions were found to be N-N quantity: 8 times of stoichiometric value, time: 30 min, temperature: 25 °C and pH = 1.5. Using the optimized conditions, the cobalt and manganese precipitation was nearly 99% and 0%, respectively. A kinetic study of manganese precipitation through N-N reagent has been carried out to assess the effect of kinetics parameters. The data obtained for the leaching kinetics indicated that the precipitation of manganese is an ash diffusion controlled reaction and the reaction activation energy is equal to 1.4kJ/mol.

Blackening of the Surfaces of Mesopotamian Clay Tablets Due to Manganese Precipitation

Blackening was observed on the surfaces of Mesopotamian clay tablets from Umma, Dilbat, Larsa, Ur, Babylon, Uruk, Sippar, and Nippur produced between the Third Dynasty of Ur and the Early Achaemenid Dynasty. Portable X-ray fluorescence analysis revealed that manganese was concentrated on the blackened surfaces. Rod-shaped materials with a length of 100 - 200 nm and a width of 30 nm were observed using a field emission scanning electron microscope. Distinct peaks were not necessarily obtained by micro-X-ray diffractometer analysis, but several samples of the black material showed peaks identifiable as buserite. These results may suggest that blackening on the surfaces of the clay tablets can be ascribed to the activity of manganese-oxidizing microbe. However, the size of the rod-shaped materials is too small compared to common bacteria.

Zinc Sorption During Bio-oxidation and Precipitation of Manganese Modifies the Layer Stacking of Biogenic Birnessite

The formation and structural evolution of fungal mediate biogenic birnessite are dynamic processes. Although the associations of Zn with the pre-formed biogenic Mn oxides are relatively well understood, the reactivity of the intermediate precipitate at the initial stage of Mn bio-oxidation appears to differ from the final precipitate. In the present work, Zn sorption during precipitation of biogenic Mn oxides was investigated contrasting Zn sorption to pre-formed biogenic Mn oxides, using the Mn-oxidizing fungus Paraconiothyrium sp. WL-2. A substantially higher Zn uptake was found during precipitation of biogenic Mn oxides compared to Zn sorption to pre-formed biogenic Mn oxides. The presence of Zn during Mn oxidation resulted in a biogenic Mn oxide with reduced ordering in the c-axis. The precipitate was identified by X-ray diffraction (XRD) as a layer-type Mn oxide with structural properties similar to hexagonal birnessite. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that Zn forms triple-corner-sharing tetrahedral coordination (IVTCS-Zn) complexes on the surface of birnessite, which may inhibited layer stacking of birnessite in the final products. This study emphasizes the importance of the intermediate precipitates on Zn sorption, and provides insight regarding the dynamic interaction between Zn and Mn oxide in the process of microbiological oxidation. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.

Apolipoprotein-defined lipoproteins and apolipoproteins: Associations with abnormal albuminuria in type 1 diabetes in the diabetes control and complications trial/epidemiology of diabetes interventions and complications cohort

AimsDyslipoproteinemia has been associated with nephropathy in diabetes, with stronger correlations in men than in women. We aimed to characterize and compare plasma lipoprotein profiles associated with normal and increased albuminuria in men and women using apolipoprotein-defined lipoprotein subclasses and simple apolipoprotein measures. MethodsThis is a cross-sectional study in a subset (154 women and 282 men) of the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) cohort, using samples obtained in 1997–9. Immunochemical methods were used to quantify plasma apolipoprotein-based lipoprotein subclasses and individual apolipoprotein levels. ResultsIn adjusted analyses, elevated Lipoprotein-B (Lp-B) was significantly associated with macroalbuminuria in men [odds ratios (OR) and 95% confidence interval (CI): 2.13 (1.15–3.97)] and women [3.01 (1.11–8.12)], while association with Lp-B:C was observed only in men [1.84 (1.19–2.86)]. For individual apolipoproteins the following significant associations with macroalbuminuria were observed in men only: Apolipoprotein B (ApoB) [1.97 (1.20–3.25)], Apo-AII [0.52 (0.29–0.93)], ApoC-III [1.95 (1.16–3.30)], “ApoC-III in VLDL” (heparin–manganese precipitate) [1.88 (1.16–3.04)], and “ApoCIII in HDL” (heparin–manganese supernatant) [2.03 (1.27–3.26)], all P<0.05). ConclusionsAtherogenic apolipoprotein-based profiles are associated with nephropathy in Type 1 diabetic men and to a lesser extent in women. The difference could result from the greater prevalence and severity of dyslipoproteinemia, and from the greater prevalence of renal dysfunction, in men vs women.

Classification and quality of groundwater supplies in the Lower Shire Valley, Malawi – Part 1: Physico-chemical quality of borehole water supplies in Chikhwawa, Malawi

This paper presents data on the physico-chemical quality of groundwater supplies in Chikhwawa, Malawi. Eighty-four water samples were collected and analysed for a range of chemical constituents (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Ni, Pb, Se, V, Zn, K, Na,Cl , F , NO 3 , SO 4 2), pH, temperature, electrical conductivity and turbidity, from 28 boreholes located in 25 remote, rural villages (n=3 per village) distributed along the east (n=15) and west (n=10) banks of the Shire River. Samples were collected every 2 months during the wet season, over a period of 5 months (December to April). Results were compared with national (Malawi Bureau of Standards Maximum Permissible Levels (MBS MPL)) and international (World Health Organization Guideline Values (WHO GV)) drinking-water standards. In general, most parameters complied with the Malawi Bureau of Standards Maximum Permissible Levels (MBS MPL) for borehole water supplies. The MBS MPL stand ards for iron, sodium and nitrate were slightly exceed at a few boreholes, technically rendering the water supply unwholesome but not necessarily unfit for human consumption. In contrast, significantly high nitrate ( < 200 mg/l) and fluoride (< 5 mg/l) concentrations at levels which constitute a significant risk to the health of the consumer were detected in bore hole samples in a number of villages and warrant further investigation. Water committee members complained of problems associated with taste (saltiness or bitterness) and appearance (discoloured water) primarily on the west bank, presumably as a result of the high sodium and chloride levels, and precipitation of soluble iron and manganese, respectively. This resulted in some water collectors reverting to the use of surface water sources to obtain drinking-water, a practice which should be dissuaded through the education of water and village health committees.

Biogenic signature and ultra microfossils in ferromanganese nodules of the Central Indian Ocean Basin

Theories related to the precipitation mechanism of the metallic elements in marine manganese nodules have remained controversial between two schools of thoughts (1) chemical oxidation (abiotic origin) and (2) deposition of the metals through microbial enzymatic processes (biogenic origin). One of the most important evidence in support of the biogenic origin is the occurrence of fossilized microbes. However, well-documented literature in this regard is either lacking or very scanty in case of Indian Ocean nodules. Using high resolution FEG-SEM we have recorded various biogenic signatures and ultra microfossils in the ferromanganese nodule samples from Central Indian Ocean Basin (CIOB) that are presented in this paper. The microfossils are mostly protozoans belonging to varieties of bacteria, diatoms and foraminifera. Some of the features recorded in this study have perhaps never been reported before from any manganese nodules. The chemical compositions of these ultra microfossils indicate a high-level of manganese precipitation in and around them in comparison to the distant surrounding areas. While clumpy microbes are enriched with nickel, the rod shaped bacteria are rich in copper. Up to 4.70wt.% nickel and 5.31wt.% Cu have been recorded in the fossilized microbe bodies. The high abundance of biogenic features as well as microfossils in the ferromanganese nodules and their chemical compositions support arguments in favor of a dominant role of the microorganisms in the construction of the nodules of the CIOB.

The Effect of Homogenization on the Annealing of Al-1,5%Mn Aluminium Alloy

The softening of Al-Mn base alloys not only depend on the degree of deformation and the parameters of annealing, but the pre-treatment of as-cast alloy. Large extent of the Mn remains in the solid solution during the crystallization process. During a high temperature heat treatment the manganese precipitate from the solid solution phase. The size and amount of the precipitations mainly of the processes takes place during annealing. In this article this effect is studied through the heat treatment and deformation of a specific alloy.

Manganese precipitation kinetics and cobalt adsorption on MnO2 from the ammoniacal ammonium sulfate leach liquor of Indian Ocean manganese nodule

Precipitation of manganese from the SO2-roast leach ammoniacal ammonium sulfate solution bearing both high and low concentrations of manganese in the presence of copper, cobalt and nickel ions was carried out in a stainless steel reactor fitted with a turbo grid. Air/O2 was used to precipitate Mn as MnO2 from the solution. There was adsorption loss of cobalt from the solution. Precipitation of manganese from the solution was 57.2–99.9%. The maximum adsorption loss of Co was 22.1%. The precipitation of Mn and adsorption loss of cobalt from the solution followed the first order kinetics. The rate constants for the precipitation of manganese and loss of cobalt were evaluated and the experimental data were fitted to Freundlich and Langmuir adsorption isotherms.

Production of Chemical Manganese Dioxide from Lithium Ion Battery Ternary Cathodic Material by Selective Oxidative Precipitation of Manganese

We have conducted studies to produce chemical manganese dioxides (CMDs) from ternary cathodic materials by oxidative precipitation. In this study, a cathodic material was concentrated by pretreatment and leached with sulfuric acid to recover 1L of a leachate containing 22.0g/dm 3 of Co, 21.6g/dm 3 of Mn, 24.2g/dm 3 of Ni, 9.5g/dm 3 of Li and 8mg/dm 3 of Al as valuable metals. For selective oxidative precipitation of Mn (II), the leachate was reacted with 1 equivalent of Na2S2O8 based on the Mn concentration with stirring at 500rpm at a temperature of 363K for 18000s. As a result of the reaction, it was confirmed that the majority of Mn was precipitated from the solution. XRD, PSA, TG­DTA, LECO and ICP analyses were performed to characterize the precipitate. The analytical results revealed the production of a chemical manganese dioxide (CMD) having a chemical composition of 84.60% MnO, 1.40% Co3O4, 0.11% Li2O, 0.25% NiO, 0.02% Al2O3, 0.06% S and 0.52% Na2O, an average particle diameter of 10.7µm, a crystal form of £-MnO2, and a purity of at least 98%. [doi:10.2320/matertrans.M2012379]

Oxidative Precipitation of Manganese from Acid Mine Drainage by Potassium Permanganate

Although oxidative precipitation by potassium permanganate is a widely recognised process for manganese removal, research dealing with highly contaminated acid mine drainage (AMD) has yet to be performed. The present study investigated the efficiency of KMnO4 in removing manganese from AMD effluents. Samples of AMD that originated from inactive uranium mine in Brazil were chemically characterised and treated by KMnO4 at pH 3.0, 5.0, and 7.0. Analyses by Raman spectroscopy and geochemical modelling using PHREEQC code were employed to assess solid phases. Results indicated that the manganese was rapidly oxidised by KMnO4 in a process enhanced at higher pH. The greatest removal, that is, 99%, occurred at pH 7.0, when treated waters presented manganese levels as low as 1.0 mg/L, the limit established by the Brazilian legislation. Birnessite (MnO2), hausmannite (Mn3O4), and manganite (MnOOH) were detected by Raman spectroscopy. These phases were consistently identified by the geochemical model, which also predicted phases containing iron, uranium, manganese, and aluminium during the correction of the pH as well as bixbyite (Mn2O3), nsutite (MnO2), pyrolusite (MnO2), and fluorite (CaF2) following the KMnO4 addition.

Effect of the sintering temperature of ceramic manganites La0.7Mn1.3O3 ± Δ on their grain sizes, magnetic and electrical properties

The effect of the sintering temperature from 1070 to 1670 K of ceramic samples of lanthanum manganite La0.7Mn1.3O3 on their grain size, structure, magnetic and resistive properties has been studied. An increase in the sintering temperature to 1270 K is shown to lead to an insignificant increase in the grain size and an increase in the density, fraction of the ferromagnetic phase in a grain, and colossal magnetoresistance. The ceramics sintering at temperatures higher than 1470 K is found to sharply increase the grain size; simultaneously, the grain takes a layered structure. The grain growth at these temperatures is established to be accompanied by manganese precipitation at the grain boundaries and likely in the grain interior. The increase in the sintering temperature is accompanied by appearance of a magnetically phase heterogeneity and a decrease in the Curie temperature and magnitude of the colossal magnetoresistance effect.

Declining Cholesterol Levels in US Youths

ATHEROSCLEROTIC DISEASE APPEARS TO BE LESS DEADLY than it was in the past; from 1998 to 2008, fatalities fromcardiovasculardisease (CVD)declinedby31%. However, that CVD is still listed as the cause for 1 of every 3 US deaths indicates a persistent burden of disease related to the obesity epidemic, inactive lifestyles, and poor eating habits, which contribute both to obesity and to CVD risk directly. Some epidemiologists project that by the year 2030, the rate of myocardial infarction may increase again by as much as 16.6% more than current levels. Despite this bleak picture, the improvement in lipid values in US children and adolescents reported by Kit and colleagues in this issue of JAMA, is a reason for optimism. In this study based on cross-sectional National Health and Nutrition Examination Survey (NHANES) data involving more than 16 000 participants from 1988-1994 to 2007-2010, the authors report that total cholesterol (TC) declined a mean 5 mg/dL in children aged 6 to 19 years over the past 2 decades. Atherogenic lipoproteins, represented by non–highdensity lipoprotein (non-HDL), decreased a mean of 8 mg/dL across all ages. Among adolescents aged 12-19 years with available fasting serum specimens, low-density lipoprotein (LDL) and triglyceride levels both declined (5 mg/dL and 9 mg/dL, respectively). Furthermore, high-density lipoprotein (HDL) increased by 2 mg/dL. There were important decreases in rates of high TC (11.3%-8.1%) and high nonHDL (17.3%-14.8%), as rates of low HDL also declined, although the change did not reach statistical significance (P=.05). In adolescents, the prevalence of high LDL and high triglycerides also declined. When considered on a population basis, the changes Kit et al report are clinically meaningful, and since they likely reflect population trends, are cause for optimism. The strong relationship between TC, LDL and non-HDL, and CVD events, and the effect in adults of lowering lipid levels on CVD mortality whether by pharmacotherapy or diet, suggest these types of changes could modify future mortality. For example, a 10% decline in TC is associated with a 15% lower rate of coronary heart disease (CHD) mortality; similar relationships are seen with LDL and non-HDL. But why would childhood cholesterol improve? The concurrent increase in pediatric obesity, decrease in physical activity, increase in screen time, and the overall poor diet of the US population would suggest lipid levels should worsen, not improve. Several possible explanations are worth considering. Although unlikely, it is conceivable that the data are inaccurate. NHANES has set standards for state-of-the art health surveillance. However, temporal changes in laboratory techniques may have caused or contributed to the findings. The authors chose not to include data sets from 2003-2004 and 2005-2006, in part, because the HDL-C values were “positive[ly] biased”. They noted that a change in laboratory methods did occur over the course of the survey; early on, HDL was measured by heparin manganese precipitation and later a direct immunoassay was used. An increase in HDL levels related to changes in laboratory methods could explain an improvement in LDL if TC and triglyceride levels remained constant; based on the Friedewald calculation, LDL would by necessity be calculated at a lower value. However, Kit et al found not only an increase in HDL levels, but also a decline in both TC and triglyceride levels, indicating that the change in HDL methods is unlikely to be the sole explanation for the improvement in US childhood cholesterol profiles. Another possible explanation is that the changes in pediatric lipid values reported by Kit et al merely represent a temporary decline that will worsen in the coming years and be reflected in the next survey. However, cholesterol levels also declined in US adults between 1960 to 2006, according to NHANES data, suggesting a population-wide trend may also be at play during childhood. A plausible explanation for improved childhood lipid values could be individual interventions to improve CVD risk— either lifestyle modification or pharmacotherapy. For a number of years lipid-lowering interventions have been recommended by the American Academy of Pediatrics and the American Heart Association, including statins for select high-risk children. Controversy in the popular and scientific press around lipid screening and treatment is long

Biotransformation of manganese oxides by fungi: solubilization and production of manganese oxalate biominerals

The ability of the soil fungi Aspergillus niger and Serpula himantioides to tolerate and solubilize manganese oxides, including a fungal-produced manganese oxide and birnessite, was investigated. Aspergillus niger and S. himantioides were capable of solubilizing all the insoluble oxides when incorporated into solid medium: MnO(2) and Mn(2) O(3) , mycogenic manganese oxide (MnO(x) ) and birnessite [(Na(0.3) Ca(0.1) K(0.1) )(Mn(4+) ,Mn(3+) )(2) O(4) ·1.5H(2) O]. Manganese oxides were of low toxicity and A. niger and S. himantioides were able to grow on 0.5% (w/v) of all the test compounds, with accompanying acidification of the media. Precipitation of insoluble manganese and calcium oxalate occurred under colonies growing on agar amended with all the test manganese oxides after growth of A. niger and S. himantioides at 25°C. The formation of manganese oxalate trihydrate was detected after growth of S. himantioides with birnessite which subsequently was transformed to manganese oxalate dihydrate. Our results represent a novel addition to our knowledge of the biogeochemical cycle of manganese, and the roles of fungi in effecting transformations of insoluble metal-containing compounds in the environment.

Preparation and application of a magnetic composite (Mn3O4/Fe3O4) for removal of As(III) from aqueous solutions

The introduction of magnetic properties in adsorbent materials has the aim of improving solid-liquid separation processes. In this work, a magnetic composite was synthesized through the precipitation of manganese oxide in the presence of magnetite particles using O2 as an oxidant. The composite proved to be chemically and physically stable within a wide range of pH values. The composite characterization indicated that hausmannite (Mn3O4) represents the precipitated manganese phase and that magnetite undergoes no phase transformation during the synthesis. The composite and Mn3O4 particles were used to remove As(III) from aqueous solutions. The magnetic composite and Mn3O4 sample presented high and similar affinity for As(III), with maximum sorptive capacities of 14 mgAs gsolid-1 (0.0048 mmolAs m-2solid) and 20 mgAs gsolid-1 (0.0049 mmolAs m-2solid), respectively, at pH 5.0. The combination of an active high surface area sorbent (Mn3O4) with a magnetic phase (Fe3O4) allows for efficient As(III) removal and solid/liquid separation.

Treatment of high-manganese mine water with limestone and sodium carbonate

Manganese is one of the most difficult elements to remove from mine waters, due to its high solubility in both acid and neutral conditions; thus it can be found in quite high concentrations, depending on the rock’s mineralogy. Metal carbonate precipitation can be an effective way for its removal, as manganese carbonate has been detected in net alkaline mine waters. However, limestone is effective in removing manganese only if the metal content is low. This research sought to study manganese precipitation from high-manganese (140 mL) content mine waters applying sodium carbonate and limestone mixtures. It was observed that besides the total carbonate concentration, pH plays a key role on manganese carbonate formation. Provided the pH solution is above 8.5, 99.9% manganese removal can be achieved with carbonate ions. Although not required for manganese precipitation, limestone acts as a solid substrate for the nucleation of fine manganese carbonate grains. Infrared spectroscopy showed manganese carbonate precipitation on the limestone surface. Magnesium was also removed from the mine water but magnesium carbonate formation was not observed.

Precipitation in long term thermally aged high copper, high nickel model RPV steel welds

Copper precipitation in irradiated RPV steels is well known to have a deleterious effect on mechanical properties. In order to understand the contribution of thermal ageing to RPV embrittlement a high copper (0.44 at.%), high nickel (1.6 at.%) model RPV weld was thermally aged at 365 °C for times up to 90,000 h. Atom Probe Tomography (APT) was employed to study the precipitation of solutes, primarily copper, nickel, manganese and silicon within the matrix and at grain boundaries. As expected, a high number density of 1–4 nm radius copper rich precipitates was observed. Nickel, manganese and silicon were found at the precipitate matrix interface, and the evolution of the composition of this interface was investigated with ageing time. Segregation of solutes to grain boundaries particularly P, Mo and C was observed, along with enrichments of Ni, Mn and Si, which have not previously been reported in long term thermally aged RPV steels. Preliminary results on several large (>10 nm) Ni–Mn–Si rich features observed at a grain boundary are also presented. These features are rich in Ni (∼30%), Mn (∼15%) and Si (∼12%) and are virtually copper-free.

A Holocene record of endogenic iron and manganese precipitation and vegetation history in a lake-fen complex in northwestern Minnesota

Little Shingobee Lake and Fen are part of the extensive network of lakes and wetlands in the Shingobee River headwaters of northwestern Minnesota, designed to study the interactions between surface and ground waters. Prior to about 11.2 cal. ka, most of these lakes and wetlands were interconnected to form glacial Lake Willobee, which apparently formed when a debris flow dammed the Shingobee River. Between 11.2 and 8.5 cal. ka, the level of Lake Willobee fell as a result of breaching of the dam, transforming the deep lake into the existing lakes and wetlands. Analyses of a 9-m core from Little Shingobee Lake (LSL-B), and lacustrine sediments under 3.3 m of peat in a 17-m core from Little Shingobee Fen (LSF-10), show that the dominant components are allogenic clastic material, and endogenic CaCO3 and organic matter. In both cores almost all of the iron (Fe) and manganese (Mn) are incorporated in endogenic minerals, presumed to be X-ray amorphous oxyhydroxide minerals, that occur in significant quantities throughout the cores; almost no Fe and Mn are contributed from detrital aluminosilicate minerals. This suggests that, for most of the Holocene, the allogenic watershed contributions to lake chemistry were minor compared to the dissolved mineral load. In addition, prior to 3.5 cal. ka, pollen zone boundaries coincide with large changes in lake-sediment mineralogy, indicating that both landscape and climate processes were linked to early- and mid-Holocene lake chemistry. The pollen time series, with sequential domination by spruce, pine, sagebrush-oak, birch-oak and, finally, white pine is typical of the region and reflects the changing location of the prairie-forest transition zone over time. These changes in vegetation had some profound effects on the geochemistry of the lake waters.

Investigation of As, Mn and Fe fixation inside the aquifer during groundwater exploitation in the experimental system imitated natural conditions

Water-dissolved oxygen was supplied into anaerobic aquifer , which oxidized Fe(II), Mn(II) and trivalent arsenic and changed them into undissolved solid matter through hydrolysis, precipitation, co-precipitation and adsorption processes. The experiment was carried out on the column imitated a bore core of anaerobic aquifer with water phase containing Fe(II), Mn(II), As(III) concentration of 45.12 mg/L, 14.52 mg/L, 219.4 μg/L, respectively and other ions similarly composition in groundwater. After 6 days of air supply, concentration of iron reduced to 0.38 mg/L, manganese to 0.4 mg/L, arsenic to 9.8 μg/L (equivalent 99.16% of iron, 97.25% of manganese and 95.53% of arsenic fixed), and for other ions, the concentration changed almost according to general principles. Ion phosphate and silicate strongly influenced on arsenic removal but supported iron and manganese precipitation from water phase. Based on the experimental results, new model of groundwater exploitation was proposed.

Anaerobic precipitation of manganese and co-existing metals in mine impacted water treated with crab shell-associated minerals

Abstract The chemical and physical treatment mechanisms by which crab shell removes metals from mine impacted water (MIW) were evaluated under anaerobic and biologically limited conditions in closed systems and kinetic tests. Raw (R-SC20) and deproteinized (DP-SC20) crab shell were tested and compared to limestone to quantify the contribution of chitin-associated minerals and proteins to alkalinity generation and metal precipitation. Single-metal closed systems (initial Mn and Fe = 0.18 mM and Al = 0.34 mM) containing 5 g/L of either R- or DP-SC20, yielded an increase in pH from 3 to 9.2–10.2, generation of 0.83–1.87 mM of alkalinity, and resulted in ⩾95% removal of metals within 72 h. In contrast, 5–125 g limestone/L only raised the pH to 7.8–8.3, produced lower alkalinity (0.56–0.63 mM), and resulted in less metal removal (⩽85%). In kinetic tests with 5 g-DP-SC20/L, removal of ⩾95% of the initial metal load was achieved after 0.5, 6, and 48 h for Al, Fe, and Mn, respectively. Geochemical calculations (PHREEQC) indicate that limestone-treated systems were close to equilibrium with calcite (CaCO3), whereas octacalcium phosphate (Ca4H(PO4)3) appears to be a controlling phase in systems treated with R- and DP-SC20. The probable mechanisms for Mn removal are the precipitation of rhodochrosite (MnCO3) and/or sorption. In the case of Al and Fe, geochemical calculations point to the precipitation of hydroxides; however, visual observations in Fe systems suggest the formation of green rust, a precursor of other, more stable phases like goethite or lepidocrocite. Several factors may account for the faster changes observed with R- and DP-SC20 compared to limestone: increased dissolution and degree of supersaturation, the presence of phosphates, the release of organic compounds, and a significantly larger surface area. These results are the first to verify and quantify the capacity of crab shell-associated minerals to treat MIW under biologically limited conditions.