Ferric Precipitation Research Articles

Comparative study of Fe(II)/sulfite, Fe(II)/PDS and Fe(II)/PMS for p-arsanilic acid treatment: Efficient organic arsenic degradation and contrasting total arsenic removal

As a widely used feed additives, p-arsanilic acid (p-AsA) frequently detected in the environment poses serious threats to aquatic ecology and water security due to its potential in releasing more toxic inorganic arsenic. In this work, the efficiency of Fe(II)/sulfite, Fe(II)/PDS and Fe(II)/PMS systems in p-AsA degradation and simultaneous arsenic removal was comparatively investigated for the first time. Efficient p-AsA abatement was achieved in theses Fe-based systems, while notable discrepancy in total arsenic removal was observed under identical acidic condition. By using chemical probing method, quenching experiments, isotopically labeled water experiments, p-AsA degradation was ascribed to the combined contribution of high-valent Fe(IV) and SO4•−in these Fe(II)-based system. In particular, the relative contribution of Fe(IV) and SO4•− in the Fe(II)/sulfite system was highly dependent on the molar ratio of [Fe(II)] and [sulfite]. Negligible arsenic removal was observed in the Fe(II)/sulfite and Fe(II)/PDS systems, while ∼80% arsenic was removed in the Fe(II)/PMS system under identical acidic condition. This interesting phenomenon was due to that ferric precipitation only occurred in the Fe(II)/PMS system. As(V) was further removed via adsorption onto the iron precipitate or the formation of ferric arsenate-sulfate compounds, which was confirmed by particle diameter measurements, fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Through tuning solution pH, complete removal of total arsenic could achieve in all three systems. Among these three Fe-based technologies, the hybrid oxidation-coagulation Fe(II)/PMS system demonstrated potential superiority for arsenic immobilization by not requiring pH adjustment for coagulation and facilitating the in-situ generation of ferric arsenate-sulfate compounds with comparably low solubility levels like scorodite. These findings would deepen the understanding of these three Fe-based Fenton-like technologies for decontamination in water treatment.

Cell-shape assemblage and nanostructure of akaganéite bioformed in FeCl2 solutions

Akaganéite (β-FeOOH) with a tunnel structure typically occupied by chloride can undergo anion-exchange reactions in aqueous solutions for pollutant removal. In this work, we studied bioformation of akaganéite in FeCl2 solutions with Acidithiobacillus ferrooxidans cells at pH 2.9, during 36-h incubation. The obtained products were analyzed and characterized by XRD, FTIR, EDS, FETEM, and HRTEM. Results showed that in acidic media with pH 2.9, the cells facilitated ferrous biooxidation and ferric precipitation. The resulting ferric precipitates were identified as polycrystalline akaganéite powders and had a morphology of nanospindles with a length of less 100nm. The correlatively chemical formula for akaganéite collected at 1h was reckoned as Fe8O8(OH)6.71(Cl)1.29 with 6.6% Cl. It was observed that ferric precipitates along exterior structures of cells or their extruded organic polymers grew and assembled into cellular shape. The evolved cell-shape akaganéite assemblages were twice of cells (about 2µm) in size. These results could contribute to understanding of laboratorial bioformation of akaganéite and its biomineralization in acidic environments and promoting its practical applications.

Partitioning behavior and mechanisms of rare earth elements during precipitation in acid mine drainage

Rare earth elements (REEs) are frequently found concentrated in acid mine drainage (AMD). The recovery of REEs from AMD has been successfully achieved using selective chemical precipitation. However, a portion of the REEs is often lost to the precipitates of the dominant metal contaminant ions. To better understand the REE partitioning behavior and mechanisms during the precipitation process, a systematic study was performed on both natural and synthetic AMD solutions. Precipitation test results show that REE removal was noticeably elevated at pH 4.0 after adding H2O2 to convert ferrous to ferric ions, causing nearly complete precipitation of iron. Solution equilibrium calculations suggested that the REE removal increase was realized through adsorption onto the surfaces of the ferric precipitates. The presence of aluminum species in the solutions reduced the adsorption of REEs on the ferric precipitates. Based on electro-kinetic test results, it was concluded that aluminum species neutralize the negative surface charge of the ferric precipitates and compete with REEs for the adsorption active sites. The presence of ferrous ions in the solutions reduced REE adsorption on the aluminum precipitates at lower pH values (e.g., 5.0) due to competitive adsorption. However, at higher pH values (e.g., 6.0), REE removal to the precipitate product increased due to the precipitation of ferrous ions. In addition to the electro-kinetic tests and solution equilibrium calculations, mineralogy characterization, specific surface area measurement, particle size analysis, and morphology analysis were also conducted to investigate and identify the partitioning mechanisms.

Biochar-templated surface precipitation and inner-sphere complexation effectively removes arsenic from acid mine drainage

Treatment of aqueous leachate from acid mine tailings with pristine biochar (BC) resulted in the removal of more than 90% of the dissolved arsenic with an attendant rapid and sustained pH buffering from 3 to 4. Pine forest waste BC was transformed to a highly effective adsorbent for arsenic remediation of acid mine drainage (AMD) because the dissolved iron induced “activation” of BC through accumulation of highly reactive ferric hydroxide surface sites. Physicochemical properties of the BC surface, and molecular mechanisms of Fe, S, and As phase transfer, were investigated using a multi-method, micro-scale approach (SEM, XRD, FTIR, XANES, EXAFS, and STXM). Co-located carbon and iron analysis with STXM indicated preferential iron neo-precipitates at carboxylic BC surface sites. Iron and arsenic X-ray spectroscopy showed an initial precipitation of ferrihydrite on BC, with concurrent adsorption/coprecipitation of arsenate. The molecular mechanism of arsenic removal involved bidentate, binuclear inner-sphere complexation of arsenate at the surfaces of pioneering ferric precipitates. Nucleation and crystal growth of ferrihydrite and goethite were observed after 1 h of reaction. The high sulfate activity in AMD promoted schwertmannite precipitation beginning at 6 h of reaction. At reaction times beyond 6 h, goethite and schwertmannite accumulated at the expense of ferrihydrite. Results indicate that the highly functionalized surface of BC acts as a scaffolding for the precipitation and activation of positively charged ferric hydroxy(sulf)oxide surface sites from iron-rich AMD, which then complex oxyanion arsenate, effectively removing it from porewaters.Graphical abstract

Comparison of four methods for phytate analysis in plant-based foods

Plant-based staple diets common in low-income countries (LICs) often contain high levels of phytic acid (myo-inositol hexaphosphate, IP6), an inhibitor of zinc absorption. Depending on food source, handling and preparation, varying amounts of IP6 may be broken down to less phosphorylated inositol phosphates such as inositol tetra- and pentaphosphates (IP4, IP5) which differ from IP6 in their impact on zinc absorption. IP4 has little impact, whereas IP5’s impact is moderately reduced as compared with IP6. Therefore to accurately estimate the risk of zinc deficiency, values both for phytic acid and IP5 may be required. High-Performance Liquid chromatography (HPLC) can separate and quantify IP6 and its breakdown products but requires specialized equipment and expertise and is relatively time-consuming and expensive. We compared HPLC and three low-tech and widely accessible alternative methods via an analysis of a sample of typical LIC staple foods. The “ferric precipitation” method and the much simpler “HL” colorimetric assay provide accurate data but they only assay total inositol phosphates. A Polyacrylamide Gel Electrophoresis (PAGE) method can separate IP5 and IP6 from IP4 and other breakdown products, and can provide valid quantitative data for these compounds. Therefore PAGE, alone or in combination with a simple colorimetric assay like the HL method, is an accessible, low-tech alternative to HPLC for estimating dietary total phytate, IP6 and IP5, and represents an appropriate technology for LIC laboratories.

Rust layer growth and modification by a tannin-based mixture for lowering steel corrosion rates in neutral saline solution

ABSTRACT Concomitant rust growth on a rust-free surface and conversion by a solution of tannin, propolis and benzoate has been investigated in the present study with the aim of producing a modified rust layer, more resilient and protective than a pure rust layer. Under such circumstances, balancing simultaneous but contradictory processes of corrosion acceleration by iron chelation and corrosion inhibition by ferric tannate precipitation is crucial for layer formation. Benzoate served as an iron corrosion inhibitor in the layer formation stage while the propolis added to the tannin solution improved the modified rust layer protective efficiency. Corrosion rates lower than 5 mpy that are acceptable from the practical viewpoint are attained with the inhibitor-modified rust layer, both, in quiescent solution and up to a linear velocity of the solution approximately equal to 1.5 m s−1.

Alkalic Leaching and Stabilization of Arsenic from Pyrite Cinders

Introduction: Pyrite cinder is one of the important secondary resources, but typically contains a certain amount of arsenic, which is harmful to metallurgical process. It usually hopes to remove the arsenic prior to recycle the valuable element in the pyrite cinders. Methods & Materials: In this study, the arsenic in the cinders was selectively removed using the alkalic leaching method so as to reduce the loss of ferric and other valuable elements. Results & Discussion: The content of arsenic in pyrite cinders was reduced to 0.08% through the investigation of the factors, including particle size, alkaline concentration, temperature, solid-liquid ratio (S/L) and leaching time. Then, the ferric precipitation method was used to remove the arsenic in the leaching solution. More than 99% of the arsenic can be removed by controlling the pH and the ratio of ferric and arsenic (Fe/As) in ambient temperature, and the arsenic concentration in the solution was reduced to less than 0.5mg/L. Conclusion: It was found that the precipitated arsenic was mainly amorphous based on the analysis of sediment.

Microbial Ferrous Ion Oxidation versus Ferric Ion Precipitation at Low Temperature Conditions

Ferric ion precipitation in a typical bioleach operation is known to be inevitable. However, its management has been emphasized as critical to efficiently maximize the potential that bioleach technique offers, especially in heap bioleach systems. Although there are some studies on ferric ion precipitation, limited studies exist in the context of a cold condition which often prevails in some operations. This study investigated ferrous ion biooxidation and ferric ion precipitation under cold temperature conditions. The results showed that maximum ferrous ion oxidation rates of 1.05, 1.25, 1.51 and 1.60 mmol/L/h at 6, 7, 8 and 10°C respectively were achieved in packed column reactor. The results further showed a simultaneous ferric ion precipitation during the oxidation process. The kinetics of ferric ion precipitation follows a first order kinetics with the rate constants of 0.0066, 0.0074, 0.0080 and 0.011 h-1. Activation energies of 68 and 77 kJ/mol were obtained for both ferrous ion biooxidation and ferric ion precipitation respectively. Although slow kinetics are expected for both processes, the kinetics information may be useful for design management consideration at least to predict when bioleach liquor would likely run out of dissolved ferric ion.

H+ -pyrophosphatase IbVP1 promotes efficient iron use in sweet potato [Ipomoea batatas (L.) Lam.

SummaryIron (Fe) deficiency is one of the most common micronutrient deficiencies limiting crop production globally, especially in arid regions because of decreased availability of iron in alkaline soils. Sweet potato [Ipomoea batatas (L.) Lam.] grows well in arid regions and is tolerant to Fe deficiency. Here, we report that the transcription of type I H+‐pyrophosphatase (H+‐PPase) gene IbVP1 in sweet potato plants was strongly induced by Fe deficiency and auxin in hydroponics, improving Fe acquisition via increased rhizosphere acidification and auxin regulation. When overexpressed, transgenic plants show higher pyrophosphate hydrolysis and plasma membrane H+‐ATPase activity compared with the wild type, leading to increased rhizosphere acidification. The IbVP1‐overexpressing plants showed better growth, including enlarged root systems, under Fe‐sufficient or Fe‐deficient conditions. Increased ferric precipitation and ferric chelate reductase activity in the roots of transgenic lines indicate improved iron uptake, which is also confirmed by increased Fe content and up‐regulation of Fe uptake genes, e.g. FRO2,IRT1 and FIT. Carbohydrate metabolism is significantly affected in the transgenic lines, showing increased sugar and starch content associated with the increased expression of AGPase and SUT1 genes and the decrease in β‐amylase gene expression. Improved antioxidant capacities were also detected in the transgenic plants, which showed reduced H2O2 accumulation associated with up‐regulated ROS‐scavenging activity. Therefore, H+‐PPase plays a key role in the response to Fe deficiency by sweet potato and effectively improves the Fe acquisition by overexpressing IbVP1 in crops cultivated in micronutrient‐deficient soils.

Arsenic removal from waste water by ozone oxidation combined with ferric precipitation

The oxidation of As(III) to As(V) followed by precipitation and adsorption is thought to be the most effective process for removal of arsenic in industrial wastewater. In this work, the oxidation of As(III) to As(V) with ozone was carried out in an acidic solution. After oxidation, arsenic was removed by precipitation in an iron (III) sulfate system under ambient pressure at 90°C in acid. Batch experimental results show that ozone is quite effective in oxidizing As(III) at low pH. And more than 90% of 5g/l As(III) was removed from the acidic solution by precipitation with Fe2(SO4)3 in 7-8 hours.

Remarkable efficiency of phosphate removal: Ferrate(VI)-induced in situ sorption on core-shell nanoparticles

Despite the importance of phosphorus as a nutrient for humans and its role in ecological sustainability, its high abundance, resulting in large part from human activities, causes eutrophication that negatively affects the environment and public health. Here, we present the use of ferrate(VI) as an alternative agent for removing phosphorus from aqueous media. We address the mechanism of phosphate removal as a function of the Fe/P mass ratio and the pH value of the solution. The isoelectric point of γ-Fe2O3 nanoparticles, formed as dominant Fe(VI) decomposition products, was identified to play a crucial role in predicting their efficiency in removing of phosphates. Importantly, it was found that the removal efficiency dramatically changes if Fe(VI) is added before (ex-situ conditions) or after (in-situ conditions) the introduction of phosphates into water. Removal under in-situ conditions showed remarkable sorption capacity of 143.4 mg P per gram of ferric precipitates due to better accessibility of active surface sites on in-situ formed ferric oxides/oxyhydroxides. At pH = 6.0–7.0, complete removal of phosphates was observed at a relatively low Fe/P mass ratio (5:1). The results show that phosphates are removed from water solely by sorption on the surface of γ-Fe2O3/γ-FeOOH core/shell nanoparticles. The advantages of Fe(VI) utilization include its environmentally friendly nature, the possibility of easy separation of the final product from water by a magnetic field or by natural settling, and the capacity for successful phosphate elimination at pH values near the neutral range and at low Fe/P mass ratios.

Iron Cycling Potentials of Arsenic Contaminated Groundwater in Bangladesh as Revealed by Enrichment Cultivation

ABSTRACTThe activities of iron-oxidizing and reducing microorganisms impact the fate of arsenic in groundwater. Phylogenetic information cannot exclusively be used to infer the potential for iron oxidation or reduction in aquifers. Therefore, we complemented a previous cultivation-independent microbial community survey covering 22 arsenic contaminated drinking water wells in Bangladesh, with the characterization of enrichments of microaerophilic iron oxidizers and anaerobic iron reducers, conducted on the same water samples. All investigated samples revealed a potential for microbial iron oxidation and reduction. Microbial communities were phylogenetically diverse within and between enrichments as was also observed in the previous cultivation-independent analysis of the water samples from which these enrichments were derived. Enrichment uncovered a larger diversity in iron-cycling microorganisms than previously indicated. The iron-reducing enrichments revealed the presence of several 16S ribosomal RNA (16S rRNA) gene sequences most closely related to Acetobacterium, Clostridium, Bacillus, Rhizobiales, Desulfovibrio, Bacteroides, and Spirochaetes, in addition to well-known dissimilatory iron-reducing Geobacter and Geothrix species. Although a large diversity of Geobacteraceae was observed, they comprised only a small part of the iron-reducing consortia. Iron-oxidizing gradient tube enrichments were dominated by Comamonadaceae and Rhodocyclaceae instead of Gallionellaceae. Forty-five percent of these enrichments also revealed the presence of the gene encoding arsenite oxidase, which converts arsenite to less toxic and less mobile arsenate. Their potential for ferric (oxyhydr)oxides precipitation and arsenic immobilization makes these iron-oxidizing enrichments of interest for rational bioaugmentation of arsenite contaminated groundwater.

Preparation and application of cellulose acetate/Fe films in the degradation of Reactive Black 5 dye through photo-Fenton reaction

ABSTRACTIn this study, the Reactive Black 5 dye degradation and textile effluent were investigated using the photo-Fenton process employing immobilized Fe3+ in acetate cellulose films. The films prepared were characterized through Fourier transform infrared spectroscopy, atomic absorption spectroscopy, scanning electron microscopy – energy-dispersive spectroscopy and ultraviolet visible spectroscopy. The factorial design revealed that the best conditions for the Reactive Black 5 dye degradation were obtained using the film containing 5% Fe (w/w), 100 mg L−1 H2O2 and pH 4.0. In studies using artificial light, the dye degradation was 99.29% and the chemical oxygen demand (COD) reduction was 90% after 45 min of treatment. In the process assisted by sunlight, the degradation was 86% and the COD reduction was 70% considering the same time of treatment. At pH 6.0 and artificial light, the dye degradation was 98.90% and the COD reduction was 78%, indicating that the material prepared can be used at pH values greater than 3 without the occurrence of hydrated ferric oxides precipitation. It was also observed that the material can be reused seven consecutive times without substantial loss of efficacy in dye degradation. Furthermore, the proposed material reduces the COD of a textile effluent by 72% after 300 min of treatment.

Arsenic removal from acidic solutions with biogenic ferric precipitates

Treatment of acidic solution containing 5g/L of Fe(II) and 10mg/L of As(III) was studied in a system consisting of a biological fluidized-bed reactor (FBR) for iron oxidation, and a gravity settler for iron precipitation and separation of the ferric precipitates. At pH 3.0 and FBR retention time of 5.7h, 96–98% of the added Fe(II) precipitated (99.1% of which was jarosite). The highest iron oxidation and precipitation rates were 1070 and 28mg/L/h, respectively, and were achieved at pH 3.0. Subsequently, the effect of pH on arsenic removal through sorption and/or co-precipitation was examined by gradually decreasing solution pH from 3.0 to 1.6 (feed pH). At pH 3.0, 2.4 and 1.6, the highest arsenic removal efficiencies obtained were 99.5%, 80.1% and 7.1%, respectively. As the system had ferric precipitates in excess, decreased arsenic removal was likely due to reduced co-precipitation at pH<2.4. As(III) was partially oxidized to As(V) in the system. In shake flask experiments, As(V) sorbed onto jarosite better than As(III). Moreover, the sorption capacity of biogenic jarosite was significantly higher than that of synthetic jarosite. The developed bioprocess simultaneously and efficiently removes iron and arsenic from acidic solutions, indicating potential for mining wastewater treatment.

Significance of oxygen supply in jarosite biosynthesis promoted by Acidithiobacillus ferrooxidans.

Jarosite [(Na+, K+, NH4 +, H3O+)Fe3(SO4)2(OH)6] is an efficient scavenger for trace metals in Fe- and SO4 2--rich acidic water. During the biosynthesis of jarosite promoted by Acidithiobacillus ferrooxidans, the continuous supply of high oxygen levels is a common practice that results in high costs. To evaluate the function of oxygen in jarosite production by A. ferrooxidans, three groups of batch experiments with different oxygen supply levels (i.e., loading volume percentages of FeSO4 solution of 20%, 40%, and 70% v/v in the flasks), as well as three groups of sealed flask experiments with different limiting oxygen supply conditions (i.e., the solutions were not sealed at the initial stage of the ferrous oxidation reaction by paraffin but were rather sealed at the end of the ferrous oxidation reaction at 48 h), were tested. The formed Fe-precipitates were characterized via X-ray powder diffraction and scanning electron microscope-energy dispersive spectral analysis. The results showed that the biosynthesis of jarosite by A. ferrooxidans LX5 could be achieved at a wide range of solution loading volume percentages. The rate and efficiency of the jarosite biosynthesis were poorly correlated with the concentration of dissolved oxygen in the reaction solution. Similar jarosite precipitates, expressed as KFe3 (SO4) 2(OH)6 with Fe/S molar ratios between 1.61 and 1.68, were uniformly formed in unsealed and 48 h sealed flasks. These experimental results suggested that the supply of O2 was only essential in the period of the oxidation of ferrous iron to ferric but was not required in the period of ferric precipitation.

The advantages of a superconducting magnetic intensity greater than 1 T for phosphate–ferric flocs separation in HGMS

High-gradient magnetic separation (HGMS) is widely used for water treatment. However, the effects of high magnetic intensities on removing magnetized flocs are unclear. In this study, separating phosphate–ferric flocs via HGMS at different magnetic intensities and gradients were evaluated. The TP removal efficiencies in the 5% #1 steel wool matrix were 65.1%, 82.1%, 89.1%, and 97.5% when the magnetic intensity was 0, 1.0, 3.5 and 5.5T, respectively. The TP removal rate increased by 21.9% when the magnetic gradient increased from 6×103 to 15×103 at 5.5T. The magnetic susceptibility of flocs in 1.0-T HGMS effluents was 1.5emu/g, and saturation magnetization was not observed at 5.0T. The volume mean particle size D(4,3) of the phosphate–ferric flocs decreased as the magnetic intensity increased. Magnetite was the primary mineral phase in the 0-T HGMS effluents, whereas no mature crystals were detected in the 1.0-T HGMS effluents. Microanalysis showed that magnetite particles in phosphate–ferric flocs were captured by the steel wool matrix by the magnetic force. It is expected that some of the phosphate–ferric flocs will break into magnetite and ferric precipitates. Increasing the magnetic intensity from 1.0T to 5.5T captured more ferric precipitates, which subsequently improved the TP removal efficiency.

Lamella dissolved air flotation treatment of fish farming effluents as a part of an integrated farming and effluent treatment concept

Nutrient emissions from fish farming can be reduced by a bag pen, i.e., a floating circular basin which serves simultaneously both as a fish cultivation tank and a swirl separation tank. Solid matter (excreta and uneaten feed) is collected at the bottom of the bag pen and pumped as an underflow to a dissolved air flotation (DAF) unit for nutrient removal. DAF equipped with lamella elements was studied in real conditions. Altogether 3000 rainbow trout females (2.0 kg each) were cultivated. Solid–water mixture was pumped from the bottom of the bag pen to an equalizing basin using a sequence of 2-min pumping followed by a 4-min pause. In some tests the influent was pumped directly and continuously from the bag pen to DAF. The influent quality changed substantially: average suspended solids (SS) and phosphorus (P) concentrations were 290 mg l−1±110 mg l−1 and 3.2 mg l−1±1.2 mg l−1, respectively. When the influent was fresh and P strongly associated with SS, DAF without precipitation chemicals produced up to 86% SS and 83% P removals. The influence of chemical doses was studied using 6.4–29.2 mg Fe l−1 with hydraulic loadings (HLs) of 11.0–11.7 m h−1. SS and P removal did not change substantially and the effluent concentration levelled at 30 mg SS l−1 and 0.20–0.30 mg P l−1, respectively. The lamella DAF, coupled with ferric precipitation, produced up to 90% P and 80% nitrogen reductions. HLs, excluding recycle water flow and lamella projection, up to 21 m h−1 could be used.

Addition of citrate to Acidithiobacillus ferrooxidans cultures enables precipitate-free growth at elevated pH and reduces ferric inhibition.

Acidithiobacillus ferrooxidans is an acidophilic chemolithoautotroph that is important in biomining and other biotechnological operations. The cells are able to oxidize inorganic iron, but the insolubility and product inhibition by Fe(3+) complicates characterization of these cultures. Here we explore the growth kinetics of A. ferrooxidans in iron-based medium in a pH range from 1.6 to 2.2. It was found that as the pH was increased from 1.6 to 2.0, the maintenance coefficient decreased while both the growth kinetics and maximum cell yield increased in the precipitate-free, low Fe(2+) concentration medium. In higher iron media a similar trend was observed at low pH, but the formation of precipitates at higher pH (2.0) hampered cell growth and lowered the specific growth rate and maximum cell yield. In order to eliminate ferric precipitates, chelating agents were introduced into the medium. Citric acid was found to be relatively non-toxic and did not appear to interfere with iron oxidation at a maximum concentration of 70 mM. Inclusion of citric acid prevented precipitation and A. ferrooxidans growth parameters resumed their trends as a function of pH. The addition of citrate also decreased the apparent substrate saturation constant (KS ) indicating a reduction in the competitive inhibition of growth by ferric ions. These results indicate that continuous cultures of A. ferrooxidans in the presence of citrate at elevated pH will enable enhanced cell yields and productivities. This will be critical as these cells are used in the development of new biotechnological applications such as electrofuel production.

Benthic Communities of Low-Order Streams Affected by Acid Mine Drainages: A Case Study from Central Europe

Only little attention has been paid to the impact of acid mine drainages (AMD) on aquatic ecosystems in Central Europe. In this study, we investigate the physico-chemical properties of low-order streams and the response of benthic invertebrates to AMD pollution in the Banská Štiavnica mining region (Slovakia). The studied streams showed typical signs of mine drainage pollution: higher conductivity, elevated iron, aluminum, zinc and copper loads and accumulations of ferric precipitates. Electric conductivity correlated strongly with most of the investigated elements (weighted mean absolute correlation = 0.95) and, therefore, can be recommended as a good proxy indicator for rapid AMD pollution assessments. The diversity and composition of invertebrate assemblages was related to water chemistry. Taxa richness decreased significantly along an AMD-intensity gradient. While moderately affected sites supported relatively rich assemblages, the harshest environmental conditions (pH &lt; 2.5) were typical for the presence of a limited number of very tolerant taxa, such as Oligochaeta and some Diptera (Limnophyes, Forcipomyiinae). The trophic guild structure correlated significantly with AMD chemistry, whereby predators completely disappeared under the most severe AMD conditions. We also provide a brief review of the AMD literature and outline the needs for future detailed studies involving functional descriptors of the impact of AMD on aquatic ecosystems.

Formation of jarosite and its effect on important ions for Acidithiobacillus ferrooxidans bacteria

The precipitation of jarosite adversely affects the bio-leaching of copper sulfides in the Sarcheshmeh heap bio-leaching process. The variables of the initial concentration of ferrous iron in the growth medium, pH, and temperature were examined in the laboratory to determine how they affect the precipitation of jarosite in the presence of Acidithiobacillus ferrooxidans bacteria. It was found that the maximum ferric precipitate occurred at a ferrous sulfate concentration of 50 g/L, a temperature of 32 °C, and an initial pH value of 2.2. The effects of the precipitation of ferric iron on the quantities of ions that are important for A. ferrooxidans bacteria in aqueous phase, i.e., ferric, sulfate, potassium, phosphate, and magnesium ions, also were assessed. The results showed relatively similar patterns for the ferric and potassium ions, and then reason might have been the co-precipitation of these ions as constituent elements of jarosite mineral. At pH values greater than 1.6, the solubility of phosphate ions decreased dramatically due to the co-precipitation of phosphate ions with the jarosite precipitate and due to the significant growth rate of A. ferrooxidans bacteria in this pH range. Due to the dissolution of a gangue constituent in the ore, the magnesium levels increased in the first few days of the bio-leaching process; thereafter, it decreased slightly.