Anaerobic Bioleaching Research Articles

Effect of mineralogy on Co and Ni extraction from Brazilian limonitic laterites via bioleaching and chemical leaching

Iron-rich, limonitic laterites may contain economic grades of nickel and cobalt, but efficient extraction of these metals from such ores is still a challenge. In this study, four samples of limonitic laterites originating from the Barro Alto mine in Brazil were subjected to detailed quantitative mineralogical examination followed by bioleaching and chemical leaching tests including mineralogical leaching residue analyses. Bioleaching experiments with pure cultures and addition of elemental sulfur were conducted in 2L bioreactors under aerobic conditions with the sulfur-oxidizing acidophilic bacteria Acidithiobacillus (At.) thiooxidans and At. caldus, and under anaerobic conditions with At. ferrooxidans. Aerobic bioleaching of laterites with At. thiooxidans and At. caldus allowed for a lower pH of 1.0 and 1.1 respectively, and thus a higher Ni and Co extraction than anaerobic bioleaching with At. ferrooxidans at pH 1.5. Extraction of cobalt via bioleaching was in the range of 68–88 %, while extraction of nickel was between 17 % and 56 %. Mineralogical and geochemical analysis (XRD, SEM- MLA, DSC, LA-ICP-TOFMS, XRF) was conducted to (i) identify mineral phases, which are attacked by bioleaching and (ii) estimate the portions of Co and Ni, which are released by bioleaching of different mineral phases. Cobalt was mostly hosted by Mn-rich mineral phases, which were dissolved after reduction with ferrous iron generated by bacterial metabolism during oxidation of sulfur. Nickel was mostly hosted by goethite, the most abundant mineral phase, but nickel was also present in Mn-rich minerals (e.g. asbolane) and magnesium silicates (e.g. serpentine). Mineralogical and geochemical data revealed that goethite was almost unleached in all samples and nickel was mostly released from Mn-rich mineral phases and magnesium silicates. Results of this research were able to confirm reductive bioleaching of Mn-rich phases. Chemical leaching tests performed with different concentrations of sulfuric acid and with hydrochloric acid, and with sulfuric acid plus ferrous iron as a reducing agent supported bioleaching results. The results are not supporting published data on substantial reductive dissolution of goethite via ferric iron reduction activity of acidophilic bacteria.

Cascade systems to recover resources from sludge by the integration of pretreatments to fermentation-based anaerobic bioleaching process

Future sustainable technological solutions need to balance the development of sludge as resource against the paramount necessity to protect human health and environment. Nutrients, metals, embedded energy, and the avoidance of sludge handling costs are important examples of recoverable assets. The virtuous shift to an efficient resource recovery platform should integrate pretreatments with biological conversion processes to extract values from complex waste streams as waste activated sludge. The aims of this study were: i. to assess the feasibility of sludge pretreatments as ultrasounds to promote the release of metals and organics; ii. to explore the potential of anaerobic microorganisms to leach out embedded resources from sludge through an enhanced hydrolysis/acidification step. The study proved that the acid addition to the sonicated feedstocks promoted a significant solubilization and acidification of the system during the feeding days. Crucial strategy was the inhibition of methanogens by thermal treatment of the start-up inoculum that assured pH stability, high VFAs production, and elements (As, Co and Se) solubilization. High throughput analysis of 16 S rRNA gene sequencing performed on this system revealed the presence of a high abundance of reads affiliated with hydrolytic and fermentative bacteria, in particular belonging to the phyla Bacteroidetes, Firmicutes, and Actinobacteria. The produced VFAs, fed into a semi-pilot digester with a short HRT of 15 days, were successfully converted into methane thanks to the dominant acetoclastic methanogenic population. Mass and energy balance for a full-scale scenario of this innovative biorefinery platform is reported and compared to a conventional sludge treatment scenario.

Extent of bioleaching and bioavailability reduction of potentially toxic heavy metals from sewage sludge through pH-controlled fermentation

Utilization of anaerobically stabilized sewage sludge on arable lands serve as a renewable alternative to chemical fertilizers as it enables recycling of valuable nutrients to food chain. However, probable presence of heavy metals in sewage sludge restricts the use of stabilized sludge on lands. In this study, a novel approach based on pH-controlled fermentation and anaerobic metal bioleaching was developed to reduce ecotoxicity potential of fermented sludge prior to its land application. Sewage sludge was subjected to pH-controlled fermentation process at acidic, neutral, and alkaline pH levels with the aim of increasing metal solubilization and decreasing bioavailable metal fractions through anaerobic bioleaching. Alkaline reactor performed the best among all reactors and resulted in 3-fold higher hydrolysis (34%) and 6-fold higher acidification (19%) efficiencies along with 43-fold (in average) higher metal solubilization than that of neutral pH reactor. As a result of alkaline fermentation, 32–57% of the metals remained as bioavailable and 34–59% of the metals were encapsulated as non-bioavailable within solid fraction of fermented sludge (biosolid), whereas 8–12% of total metal was solubilized into fermentation liquor. Our results reveal that anaerobic bioleaching through alkaline fermentation enables biosolid production with less metal content and low bioavailability, facilitating its utilization for agricultural purposes.

Pre-treatments and anaerobic hydrolysis as strategical key steps for resource recovery from sludge: The role of disintegration degree in metals leaching

Future sustainable technological solutions need to balance the development of sewage sludge as resource against the paramount necessity to protect human health and environment. Nutrients, high value metals, embedded energy, and the avoidance of sludge handling costs are important examples of recoverable assets. Aim of this study was to assess the feasibility of sludge pre-treatments as ultrasound and thermal hydrolysis to promote the release of metals due to organics disintegration, and to investigate the efficiency of the anaerobic process to leach out metals from municipal sludge through an enhanced hydrolysis/acidification step. A preliminary deep analysis of elements concentration (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Ga, Mg, Mn, Na, Ni, Pb, Se, V and Zn) in solid residue and water phase of waste activated sludge and anaerobic digestate sampled at full scale wastewater treatment plant (WWTP) allowed to calculate partitioning coefficients and equilibrium concentrations, in order to predict metal mobility and bioavailability. The gradual sludge disintegration and organics hydrolysis significantly contribute to the leaching of toxic elements as As, Ga, Se and Zn, increasing their removal potential. A new anaerobic bioleaching approach will be presented, aiming to develop a sustainable platform to recover metals, together with methane and a clean recyclable digestate.

Removal of heavy metals from leaching effluents of sewage sludge via supported liquid membranes

Heavy metal content of sewage sludge is one of the factors preventing its agricultural use. Leaching processes have been used to solubilize heavy metals and thus reduce metal content of the sludge through chemical or biological routes. Subsequent to leaching processes, metal removal from the supernatant is attractive in terms of decreasing metal content of the effluent and recovering metals. This paper investigates application of supported liquid membrane (SLM) technology for metal removal from leaching effluents. SLM system was first optimized using synthetic metal mixtures. Optimized system was then used for the anaerobic bioleaching and chemical leaching effluents and metal removal efficiencies of 27.1 ± 1.3% and 46.0 ± 4.3% were obtained, respectively. Considering integrated leaching and membrane separation processes, metal removal efficiencies obtained in this study are valuable as it will decrease the metal content of sludge and increase the metal solubilization during leaching process. Future integration of metal leaching and removal technologies would make it possible to develop a sustainable system involving heavy metal removal from sewage sludge, land application of the sludge with a low metal content, and metal recovery.

Bioleaching of Copper Slag Material

Bioleaching is applied mainly for copper recovery from low-grade sulfide ores via heap leaching. The main copper processing route includes pyrometallurgy and the remaining copper slag from smelting may still contain copper in amounts found in the ore. Here bioleaching of copper slag material with a copper content of about 1 % (grain size < 63 µm) and fayalite (Fe2SiO4) und magnetite (Fe3O4) as main mineral phases was tested in aerobic shake flask experiments with a mixed culture of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Acidiphilium spp..To additionally test for reductive bioleaching, experiments under anaerobic conditions (80% N2, 20% CO2, v/v) with or without addition of elemental sulfur were run. The pH was adjusted to < 3 by addition of sulfuric acid. After the incubation period of more than 50 days at 30°C cell growth was observed in all biological assays. The redox potential was above 800 mV SHE in the aerobic biological assays and dropped to around 500 mV in the chemical control assays as well as in the anaerobic biological and chemical assays. A significant copper bioleaching was observed in the aerobic experiments with 91 % copper release (max. 35 % in the chemical controls). Anaerobic bioleaching experiments did not show a significant copper release, however the release of iron (as iron(II)) and sulfate was much higher than in the abiotic assays and several fold higher than in the classical aerobic bioleaching experiments. Overall the results show that copper bioleaching from slag material is possible, however the economic feasibility needs to be demonstrated.

Anaerobic bioleaching of jarosites by Shewanella putrefaciens, influence of chelators and biofilm formation

Development of clean mining processes is a topic of increasing interest. Biotechnology could be a cost-effective and environmentally friendly alternative to conventional methods. Jarosites can have important economic and environmental impacts because of their content of valuable metals. The anaerobic reductive dissolution of jarosites and gossan mineral by Shewanella putrefaciens strain CN2 and its secondary products have been investigated. In addition, the ability of S. putrefaciens to reduce insoluble Fe(III) in presence of chelators (citrate and EDTA) was examined. The main components in the biofilm extracted from the cultures were determined. In addition, it was observed the formation of extracellular polymeric substances (EPS) during the biological process.

Anaerobic bioleaching of metals from waste activated sludge

Heavy metal contamination of anaerobically digested waste activated sludge hampers its reuse as fertilizer or soil conditioner. Conventional methods to leach metals require aeration or the addition of leaching agents. This paper investigates whether metals can be leached from waste activated sludge during the first, acidifying stage of two-stage anaerobic digestion without the supply of leaching agents. These leaching experiments were done with waste activated sludge from the Hoek van Holland municipal wastewater treatment plant (The Netherlands), which contained 342μgg−1 of copper, 487μgg−1 of lead, 793μgg−1 of zinc, 27μgg−1 of nickel and 2.3μgg−1 of cadmium. During the anaerobic acidification of 3gdry weightL−1 waste activated sludge, 80–85% of the copper, 66–69% of the lead, 87% of the zinc, 94–99% of the nickel and 73–83% of the cadmium were leached. The first stage of two-stage anaerobic digestion can thus be optimized as an anaerobic bioleaching process and produce a treated sludge (i.e., digestate) that meets the land-use standards in The Netherlands for copper, zinc, nickel and cadmium, but not for lead.

Reductive dissolution of manganese from manganese dioxide ore by autotrophic mixed culture under aerobic conditions

Reductive leaching of manganese from manganese dioxide ore has become increasingly important for production of electrolytic manganese. The anaerobic bioleaching has long received great concerns for reductive extraction of Mn by heterotrophic microorganisms in the presence of sacchariferous substances. Alternatively, the reductive dissolution of manganese from manganese dioxide ore by autotrophic mixed culture under aerobic conditions was investigated in this work. The results showed that the autotrophic mixed culture was capable of reductive liberation of Mn in the presence of cheap sulfur and pyrite. 99% of Mn extraction was achieved by the mixed culture at 10% of pulp density after 72–96 h under 24 g/L of mixed energy substrates, initial pH at 1.0 and pH control of process at 2.0. The diffusion controlled model fitted best for describing dissolution of Mn. The acid dissolution was the dominating mechanism for great improvement in leaching efficiency from 78% without pH control to 99% with pH control.

Anaerobic Growth of <i>Acidithiobacillus ferrooxidans</i> on Pyrite

In the bioleaching of mineral sulphides under the catalytic action ofAt. ferrooxidans,ferrous ion oxidation and sulfides/sulfur solubilization uses oxygen as the final electron acceptor. Also, under anaerobic conditions,At. ferrooxidanscan alternatively catalize the oxidation of sulfur or reduced inorganic sulfur compounds (RISC) using ferric iron as electron acceptor [1]. The formation of Fe (II) from pyrite and covellite in the ferric anaerobic bioleaching withA. ferrooxidans,has been studied and well documented [2,3]. The requirements of ferric iron as electron acceptor for the anaerobic growth ofAt. ferrooxidanson elemental sulfur has been demonstrated and a linear relationship was obtained between the concentration of ferrous iron accumulated in the cultures and the increase in cell density [4]. It has been suggested a possible role in the solubilization of metals from sulfide ores involving the participation of the enzyme sulfur (sulfide): Fe (III) oxidoreductase [5]. Bacterial growth ofAt. ferrooxidanshas also been reported in the oxidative anaerobic respiration using hydrogen as electron donor and ferric iron as electron acceptor [6]. Anaerobic reduction of ferric iron and ferrous iron production from pyrite byAt. ferrooxidanshas been demonstrated [2], however there are no reports about bacterial growth using this mineral. In this work, we studied the anaerobic bioleaching of pyrite with the aim to determine ifAt. ferrooxidansis capable to anaerobic growth on pyrite using ferric iron as electron acceptor.

Effectiveness of anaerobic iron bio-reduction of jarosite and the influence of humic substances

Nowadays there is a growing interest in developing clean mining processes free of toxic chemicals. Biotechnology could be a cost-effective and environmentally friendly alternative to traditional leaching methods. Jarosite is an important sulfate mineral that occurs naturally and also can be produced as a waste in industrial processes. In this work, bioreduction of jarosite using Shewanella putrefaciens and a natural consortium under anaerobic conditions is presented as an acceptable bioleaching method. Moreover, the influence of humic substances that appear in natural environments acting as electron shuttles between microorganisms and insoluble oxides has been investigated. One key factor for the industrial implementation of anaerobic bioleaching is the metal recovery from minerals. The precipitates formed as products of dissimilatory iron reduction, the bacterial ability to obtain ferrous ions in solution and the stimulation of insoluble Fe(III) ores reduction by electron shuttles have been examined in this research.

Bio-reduction of Fe(III) ores using three pure strains of Aeromonas hydrophila, Serratia fonticola and Clostridium celerecrescens and a natural consortium

The present work describes a research approach to the anaerobic bioleaching of Fe(III) ores. Three strains ( Serratia fonticola, Aeromonas hydrophila and Clostridium celerecrescens) isolated from an acidic abandoned mine were selected to test their ability to reduce dissimilatory Fe(III). Total iron bio-reduction was achieved after 48 h using either the consortium or the Aeromonas cultures. In the latter case, there was no evidence of precipitates and Fe(II) remained in solution at neutral pH through complex formation with citrate. None of the other cultures tested (mixed culture and the two isolates) exhibited this behaviour. Biotechnologically, this is a very promising result since it obviates the problem associated with undesirable precipitation of iron compounds in Fe(III)-reducing bacterial cultures. The performance of the Aeromonas culture was improved progressively by adaptation to moderately acidic pH values (up to 4.5) and to three different Fe(III)-oxyhydroxides as the sole source of iron: ferrihydrite, hematite and jarosite, commonly found as weathering compounds at mine sites. Dissimilatory Fe(III)-reducers for iron extraction from ores is therefore especially attractive in that acidification of the surrounding area can be minimized.

A Novel Combination of Anaerobic Bioleaching and Electrokinetics for Arsenic Removal from Mine Tailing Soil

This study provides evidence that a hybrid method integrating anaerobic bioleaching and electrokinetics is superior to individual methods for arsenic (As) removal from mine tailing soil. Bioleaching was performed using static reactors in batch tests and flow conditions in column test, and each test was sequentially combined with electrokinetics. In the bioleaching, indigenous bacteria were stimulated by the injection of carbon sources into soil, leading to the mobilization of As with the concurrent release of Fe and Mn. Compared with the batch-type bioleaching process, the combined process showed enhanced removal efficiency in the equivalent time. Although the transport fluid bioleaching conditions were inadequate for As removal, despite long treatment duration, when followed by electrokinetics the combined process achieved 66.5% removal of As from the soil. The improvement of As removal after the combined process was not remarkable, compared with single electrokinetics, whereas a cost reduction of 26.4% was achieved by the reduced duration of electrokinetics. The As removal performance of electrokinetics was significantly dependent on the chemical species of As converted via microbial metal reduction in the anaerobic bioleaching. The synergistic effect of the combined process holds the promise of significant time and cost savings in As remediation.

Evaluation on the Feasibility of Microbially Enhanced Electrokinetic Removal of Multiple Heavy Metals from Tailing Soil

Lab-scale experiments were conducted to evaluate the efficacy of the enhanced electrokinetics combined with anaerobic and aerobic bioleaching processes for remediation of tailing soil. The tailing soil contained multiple heavy metals, such as As, Cd, Co, Cu, Cr, Fe, Mn, Ni, Pb, and Zn. To begin with, the applicability of both anaerobic and aerobic bioleaching was investigated as a pretreatment step to transform them into more mobile forms. In the anaerobic bioleaching, the supply of carbon source into the soil stimulated anaerobic metal reducing bacteria with dissolution of heavy metals, As, Fe, Mn, and Zn. In the aerobic bioleaching, on the other hand, indigenous sulfur oxidizing bacteria oxidized elemental sulfur with acidifying soil and mobilizing heavy metals, such as As, Fe, Mn, Pb, and Zn. To compare the removal efficiencies between individual and combined processes, individual electrokinetics was conducted as a control with only electrolyte conditioning and the tailing soils pretreated by bioleaching were sequentially applied to the electrokinetics to simulate the combined process. Generally speaking, the microbially enhanced electrokinetics showed higher removal efficiencies of almost all the heavy metals tested than the individual electrokinetics, because bioleaching process converted the heavy metals to be labile. One more synergistic effect of the combined processes was that bioleaching enhanced the rate of acidification of tailing soil, which offers a more suitable condition for electrokinetics. The highest removal efficiency of Co, Mn, Ni, and Zn was accomplished in the electrokinetic process combined with anaerobic bioleaching (72.5%, 66.4%, 57.9%, and 76.7%, respectively), whereas that of As, Cd, and Pb was rendered in the process combined with aerobic bioleaching (27.2%, 46.6%, and 25.0%, respectively). The results indicate that the performance of the combination between bioleaching and electrokinetics is significantly dependent on the species of heavy metals to be removed. In addition, this study verifies that the electroosmotical injection of carbon sources is feasible to activate the indigenous microorganisms in the anaerobic bioleaching coupled with the electrokinetics.

Bio-leaching of valuable metals from marine nodules under anaerobic condition

The present paper studies anaerobic bio-leaching of manganese nodules by Thiobacillus ferrooxidans separated from mining water. With the addition of suitable nutrient and reductant, the metals existing in the nodules, such as Cu, Co, Ni and Mn can be leached effectively in an acidic and anaerobic system under ambient temperature in 3 days. Manganese oxide and nickel sulfide participate in the respiration of the microbe as electron acceptor and donor respectively. Meanwhile, the ferric/ferro ions act as electron shuttles to accelerate the process.

Leaching of Mn, Co, and Ni from manganese nodules using an anaerobic bioleaching method

An anaerobic bioleaching of a manganese nodule by anaerobic Mn-reducing bacteria was evaluated for the leaching of metals, Mn, Co, and Ni. Insoluble Mn 4+ in the nodule could be reduced to soluble Mn 2+ by dissimilatory Mn-reducing bacteria that use a carbon source and Mn 4+ as an electron donor and acceptor, respectively. As a result of the Mn reduction, Co and Ni could be leached from the loosed Mn matrix. Leaching experiments were carried out to optimize various process parameters, such as inoculation, pH, temperature, mineral salts, and particle size of the nodule used. The leaching efficiencies of Mn, Co, and Ni increased from 18, 7, and 10% to 77, 70, and 75%, respectively by the inoculation of the Mn-reducing enrichment culture broth. Metals could be efficiently recovered from the nodule in the ranges of pH from 5.0 to 6.5 and temperature from 30 to 45°C by anaerobic bioleaching. External addition of mineral salts was not necessary for Mn, Co, and Ni leaching from the nodule. The optimum ratio of nodule to glucose was 0.1 (w/w). To obtain a leaching efficiency above 70%, the particle size of the nodules must be less than 0.6 mm.

Leaching of Mn, Co, and Ni from Manganese Nodules Using an Anaerobic Bioleaching Method.

An anaerobic bioleaching of a manganese nodule by anaerobic Mn-reducing bacteria was evaluated for the leaching of metals, Mn, Co, and Ni. Insoluble Mn4+ in the nodule could be reduced to soluble Mn2+ by dissimilatory Mn-reducing bacteria that use a carbon source and Mn4+ as an electron donor and acceptor, respectively. As a result of the Mn reduction, Co and Ni could be leached from the loosed Mn matrix. Leaching experiments were carried out to optimize various process parameters, such as inoculation, pH, temperature, mineral salts, and particle size of the nodule used. The leaching efficiencies of Mn, Co, and Ni increased from 18, 7, and 10% to 77, 70, and 75%, respectively by the inoculation of the Mn-reducing enrichment culture broth. Metals could be efficiently recovered from the nodule in the ranges of pH from 5.0 to 6.5 and temperature from 30 to 45 degrees C by anaerobic bioleaching. External addition of mineral salts was not necessary for Mn, Co, and Ni leaching from the nodule. The optimum ratio of nodule to glucose was 0.1 (w/w). To obtain a leaching efficiency above 70%, the particle size of the nodules must be less than 0.6 mm.

Anaerobic leaching of covellite by Thiobacillus ferrooxidans

Thiobacillus ferrooxidans was able to grow under anaerobic conditions on copper sulphide with ferric ion as the electron acceptor. The dissolution of covellite under these conditions (68% after 35 days) was higher than values observed aerobically in cultures with similar media composition and almost as high as under aerobic conditions without iron. From these results we propose a mechanism for anaerobic bioleaching of covellite in the presence of ferric iron and speculate that it may occur in leach dumps where the oxygen concentration is, as reported elsewhere, very low.