Bacteria Acidithiobacillus Thiooxidans Research Articles

Geopolymers functionalised by antibacterial zeolite against biocorrosion

Aluminosilicate geopolymer with remarkable chemical and biological resistance is a promising material solution to the persistent challenge of microbial induced concrete corrosion (MICC) in sewers. In this work, novel Sor-zeolite, assembled by using microporous 13X zeolite as a host of antimicrobial ion sorbate, is incorporated into fly ash-slag geopolymer to form bio-resistant materials with long-lasting efficacy and densified microstructure. The inclusion of pure zeolite and Sor-zeolite increase the strength and refine the pore structure of geopolymer pastes owing to the seeding nuclei effects during the geopolymerisation process. The enhanced dissolution of FA and slag by the seeding effects of pure zeolite and Sor-zeolite, accelerates and enriches the precipitation of geopolymeric gels, mainly a mixture of K-A-S-H and C-A-S-H (abbreviated as K-(C)-A-S-H). The Sor-zeolite-functionalised geopolymer possesses outstanding antibacterial properties against sulphur oxidising bacteria Acidithiobacillus thiooxidans, inhibiting biofilm formation on the surface and reducing corrosion depth. The main biodegradation products of geopolymers are gypsum and silica-rich gels, resulted from decalcification and dealumination of Si–O–Al and Ca–O bonds in K-(C)-A-S-H.

Urban biomining: lithium recovery from spent batteries through multi-step bioprocesses

Multi-step design to evaluate the bio-recovery of lithium from spent batteries was studied. The first step consisted of lithium extraction from spent batteries, using bacterial and fungal acid extrolites. The second step explored lithium recovery in the form of carbonate salts by using MICP (Microbial Induced Carbonate Precipitation) bacteria from Sporosarcina species. For lithium extraction (Step 1) sulfuric acid produced by sulphur oxidizing bacteria Acidithiobacillus thiooxidans was evaluated for its capacity to leach lithium. Extraction with biogenic sulfuric acid and with fungal bio- produ-cts (from Aspergillus sp. and Simplicillum sp. isolated at our facilities) were compared with commercial sulfuric acid. For biorecovery processes (Step 2), two type strains of Sporosarcina sp. were tested due to their capacity to precipitate lithium carbonate. Results showed fungal bioextracts gave a lithium leaching yield close to 60% and a global recovery yield of 27%. These observations are reported for the first time and lay the foundations for continuing the study and scaling up of this combined process for lithium recovery.

Bioleaching of a lateritic ore (Piauí, Brazil) in percolators

Heap leaching of laterites for extraction of nickel and cobalt is an attractive alternative to capital and energy intensive high pressure acid leaching, the dominant hydrometallurgical processing technology for limonitic laterites. Conventional approach for heap leaching of laterites is leaching with sulfuric acid. Consumption of sulfuric acid during heap leaching is substantial and industrial-scale operations require construction of a sulfuric acid production plant on site. In this study, heap bioleaching of laterites was simulated in laboratory scale column percolators and bioleaching of nickel and cobalt from lateritic material was successfully demonstrated for the first time. The process is based on biooxidation of the bacterially modified “wet sulfur” inside column percolators by sulfur-oxidizing acidophilic bacteria Acidithiobacillus thiooxidans. The “wet sulfur“ was generated in a bioreactor with the bacterial culture, harvested, and mixed with lateritic ore before forming agglomerates to be filled in the percolator columns. Liquid was circulated with a flow rate of 8 mL/min. Maximum metal extraction was 66% nickel, 95% cobalt, 10% iron, 55% magnesium and 89% manganese from the Piauí lateritic ore after one month bioleaching. For comparison, chemical leaching with 1 M sulfuric acid with or without addition of 10 g/L of ferrous sulfate heptahydrate as reductant resulted in extraction of approximately 80% nickel, 86% cobalt, 33% iron, 50% magnesium and 81% manganese. With bioleaching a higher cobalt but lower nickel and iron extraction was achieved, i.e. a better selectivity of nickel over iron extraction, as well as a relatively higher pH of the pregnant leach solution requiring less limestone and, consequently, lower CO2 emission and generation of iron cake waste in case of laterite bioleaching. Overall, the results are promising and show potential of laterite heap bioleaching to be further developed to application on industrial scale.

Pharmaceutical blister waste recycling using biogenic sulfuric acid: Effect of sulfur source and blister material on bioleaching efficiency

Several thousand tons of plastic are produced globally for pharmaceutical blister packages every year, leading to an expected consumption of over 2.8 million tons by 2026. Comprising a complex multilayer structure, blisters cannot be recycled in conventional recycling processes, leading to a loss of aluminium and valuable polymers during incineration and landfilling. As a promising secondary source of aluminium, new recycling strategies need to be developed to selectively separate the different layers. In this study, three types of blister packaging materials consisting of 13–68% (w/w) aluminium were investigated regarding aluminium and polymer recovery by using biogenic sulfuric acid for bioleaching. Waste elemental sulfur from biogas desulfurisation was assessed for biogenic sulfuric acid production by the two sulfur-oxidizing bacteria Acidithiobacillus thiooxidans and Acidithiobacillus caldus and compared to commercial elemental sulfur. For biogenic sulfur, higher sulfate production yield (320 mM), lower pH-value (pH = 0.56) and complete sulfur oxidation within 14 days was observed when compared to commercial sulfur. Application of a more concentrated biogenic acid (pH = 0.22) led to more effective and complete (∼100%) aluminium bioleaching up to 7.5% (w/v) blister waste within 7–9 days of incubation compared to 83% and 63% chemical leaching efficiency of transparent and white blisters using commercial sulfuric acid at the same pH, respectively. In addition, the plastic fraction after bioleaching was characterized and tested regarding re-processability. Results showed that sulfur from a biological origin can be oxidized faster by bacteria and biogenic acid is more effective in aluminium bioleaching compared to commercial sulfuric acid. Furthermore, results indicated that the plastic material is suitable for re-processing making this process an economically and environmentally friendly treatment option.

Composition, nanostructure and stability of Cu-modified C-A-S-H in antibacterial alkali-activated slag

Antimicrobial alkali-activated slag (AAS) has been envisioned as a biologically resistant binder for potential application in sewer structures against biogenic sulfuric acid attacks. This work investigates the composition, phase assemblage, micro- and nano-structural alterations of AAS binders incorporating Cu-based antimicrobial agents (i.e., copper oxide and copper nitrate), as well as their antimicrobial properties and degradation mechanism under biological corrosion caused by sulphur-oxidising bacteria Acidithiobacillus thiooxidans. The results show that the incorporation of copper oxide or copper nitrate increases the degree of hydration of slag but reduces the mean chain length (MCL) of C-A-S-H as Cu preferably affects the bridging AlO4-tetrahedra over SiO4-tetrahedra. The substitution of Cu for the CaO polyhedral at the edges and corners of the C-A-S-H main chain makes the Al linkage blocked. Cu also possesses a charge-balancing role, resulting in a lower protonation of C-A-S-H in the Cu-doped AAS than that in the neat AAS, where C-A-S-H is a Tobermorite structure with MCL between 5 and 11. The Cu-doped AAS pastes show excellent antimicrobial efficiency, in particular, the CuO-doped AAS demonstrates 100 % effectiveness in inhibiting biofilm formation, with the corrosion depth significantly reduced by a factor of 10. The Cu ion is released initially from the outer surface of C-A-S-H due to its low bond dissociation energy, followed by the weak position, namely the AlO4-tetrahedra at the bridging position, rendering the rupturing of the C-A-S-H structure.

Element dissolution from Zn-bearing rocks treated with chemical and biotic agents: A prospective circular economy strategy for metal recovery from secondary resources

Calamine susceptibility to dissolution requires a detailed experimental evaluation to uncover an alternative management option for these materials. This study aimed to investigate the (bio)leaching behaviours of Zn/Pb-bearing calamines to quantify their potential as a Zn resource. Chemical treatments, including the application of mineral (H2SO4, HCl and HNO3) and organic acids (citric and oxalic acids), along with biotic treatments involving the bacteria Acidithiobacillus thiooxidans and Pseudomonas fluorescens, were used to analyse the mobilisation mechanisms, namely acidification and complexation. The results showed that HCl and HNO3 were the most efficient chemical agents, with an extraction efficiency as high as 39 % (Zn). A. thiooxidans extracted the largest amount of Zn (40 %), which proves that the efficiency of the biotic process can be nearly the same as that of the chemical process. However, the main mechanism governing element mobility was the pH factor. This study shows the potential of calamines as prospective materials for the recovery of Zn and other elements (Ge, Tl), even in those treatment conditions that require further optimisation.

Bioleaching of Iron and Zinc from a galvanized steel waste from automotive industry using Acidithiobacillus thiooxidans: a case of study of the bajío area in México

Biohydrometallurgy has been defined as a collection of techniques that involve the use of microbial metabolisms, such as the bacterium Acidithiobacillus thiooxidans, for the extraction of metals. Therefore, in the current study, we tested the potential of a pure culture of A. Thiooxidans in the removal of zinc and iron from galvanized waste of the automotive industry. Starkey medium was employed and was added 0.5% w/v of solid sample, and incubation took place at 30°C, and 180 rpm for 7 days. The experiment showed a biological removal of 100% of Fe and Zn after 72 hours, as shown with the measurements taken using inductively coupled plasma spectrophotometer (ICP-OES). Additionally, an increase of the concentration of sulphates is reported alongside the process. The present study thus suggests that a fast, efficient, and low energy biological process for the recovery of these metals coming from galvanized steel waste is possible.

Structural composition of antibacterial zinc-doped geopolymers.

Elucidating the structural composition of a three-dimensional amorphous sodium-aluminosilicate-hydrate (Na2O-Al2O3-SiO2-H2O, N-A-S-H) gel in geopolymers is a prerequisite for its prevailing application in biomaterials, construction, waste management, and climate change mitigation. An unsolved challenge in geopolymer science is the clear structural understanding of amorphous N-A-S-H doped with desired metals. Here, we uncover the molecular structure of (Zn)-N-A-S-H, confirming the tetrahedral coordination of Zn with O and the presence of Si-O-Zn bonds. The Zn-Si distance of ∼3.0-3.1 Å proves the connection of the corners of ZnO42- tetrahedra and SiO4 tetrahedra by slight twisting. The stoichiometric formula of the ZnO-doped geopolymer is quantified as (Na0.19Zn0.02AlSi1.74O5.095)·0.19H2O. The remarkable antimicrobial efficacy of the Zn modified-geopolymer in inhibiting the formation of biofilms by the sulphur-oxidising bacteria Acidithiobacillus thiooxidans and inhibiting biogenic acidification is evidenced. The biodegradation process of the geopolymer featuring the rupture of the Si-O-Al and Si-O-Zn bonds of the networks leads to the expelling of tetrahedral AlO4- and ZnO42- from the aluminosilicate framework and the eventual formation of the siliceous structure. This work demonstrates that the (Zn)-N-A-S-H structure of our new geopolymer provides a solution to optimising geopolymer materials and provides further possibilities for designing novel geopolymer composites for use in construction materials, antibacterial biomaterials in dental or bone surgery, and management of hazardous and radioactive waste.

Antimicrobial alkali-activated slag through self-intercalation of benzoate in layered double hydroxides

Antimicrobial alkali-activated slag (AAS) with biocidal effectiveness is a promising cementitious binder for concrete infrastructure threatened by microbially induced concrete corrosion (MICC). In this work, the influence of sodium benzoate on the chemical reaction, phase assemblage, microstructure, and nanostructure of AAS was studied, with a particular focus on the potential in-situ formation of benzoate-intercalated layered double hydroxides (BZ-LDHs). In addition, the lattice structure, molecular bonds, and intercalation chemistry of pure BZ-LDHs synthesised using rehydration method were investigated. The results evidence the in-situ formation of BZ-LDHs in AAS incorporating sodium benzoate during alkaline activation. The benzoate anions are spontaneously intercalated in a bilayer manner in the interlayers of LDHs, with an average basal spacing of 1.568 nm. The incorporation of BZ slightly lowers the reaction degree of slag in AAS, but barely affects the composition and structure of calcium-aluminosilicate-hydrate (C-A-S-H) formed. The developed antimicrobial AAS with BZ-LDHs demonstrates remarkable bactericidal efficacy with a 95.0% effectiveness (when admixed with 3% BZ) in suppressing the growth of sulphur-oxidising bacteria Acidithiobacillus thiooxidans in this study.

Innovative bio-acid leaching method for high recovery of critical metals from end-of-life light emitting diodes

The main objective of this work is to introduce a new green recycling process for recovering valuable metals from electronic waste. One of the fastest-growing electronic waste streams is end-of-life light emitting diodes (LEDs). Due to environmental risk and a worldwide shortage of metals, recycling and recovering their valuable metal is an urgent task. In this study, an innovative bio-hydrometallurgical method for the extraction of valuable metals from end-of-life LED lamps is proposed. The present study evaluated a direct multi-step regulation strategy of waste content to enhance the bio-acid leaching of LED at a high pulp density (40 g/L) using a culture of sulfur-oxidizing bacteria Acidithiobacillus thiooxidans (A. thiooxidans). Through a step-wise feeding strategy (10 g/d), the extraction of the metal was further improved due to balancing of A. thiooxidans population and stabilization of pH, ORP, and sulfuric acid concentration in the bioleaching solution. By comparing the results of multi-step and one-stage contact bioleaching, with multi-step contact bioleaching, Cu, Ni, and Ga extraction yields increased from 67%, 92%, and 39% to 100%, 100%, and 75%. Furthermore, this study demonstrates that the presence/addition of EPS did not only adsorb metal ions but also increased diffusion barriers, thus diminishing metal ion transfer from LED into bioleaching solution for an extended period of time. The multi-step non-contact bio-acid leaching method enhanced strategic critical element leaching yields to 100% from end-of-life LEDs. The final product, enriched in Au and Ag, could be used as a secondary source of precious metals.

Performance of Urea-Based Fertilizers Associated With Elemental Sulfur or Polymers on Ammonia Volatilization

High N-NH3 losses are expected when conventional urea is applied to the soil surface. In order to reduce it, urea granules could be coated with different materials to decrease fertilizer dissolution rate or to stabilize N-NH4+ by acidification. In this study, we investigated the effect of a polymer-coated urea and powdered S0 added to urea, in the presence or absence of a S-oxidizing bacterium (Acidithiobacillus thiooxidans), on soil pH, SO42- availability, NH4+, and NH3 volatilization. Applying S0 before urea and the inoculation with bacteria have promoted the highest S0 oxidation rates. The greater decrease in soil pH occurred when S0 was applied before urea at a higher dose, which also decreased NH3 volatilization by 83% up to 4 days after urea application. However, the decrease in soil pH did not increase the concentration of NH4+, nor did it decrease the accumulated amount of volatilized NH3 over time. The inoculation of A. thiooxidans accelerates S0 oxidation process, but it was insufficient to counteract the H+ consumption by urea hydrolysis. Therefore, the S0 application with urea did not offer chemical protection against NH3 loss, but a physical barrier in the controlled-release urea had less dissolved urea in soil and reduced NH3 losses.

Deterioration of sandstones: Insights from experimental weathering in acidic, neutral and biotic solutions with Acidithiobacillus thiooxidans

The susceptibility of sandstones to deteriorative factors when used for construction requires detailed experimental evaluation. This study investigated the (bio)weathering behaviour of Lower-Silesian Cretaceous sandstones (quartz arenites) to quantify the deteriorative effect of bacterium Acidithiobacillus thiooxidans. For controls, ultrapure water (in undersaturated conditions) and sterile acidic medium (in abiotic acidic conditions pH 2.5) were used. Sandstone exposure to A. thiooxidans mimicked the extremely acidic conditions (pH up to 0.9) that may develop under long-term weathering, which promote microbial activity and acidic metabolite production. Element release was assessed using triple quadrupole inductively coupled plasma mass spectrometry (QQQ-ICP-MS) and identifying potential element donor minerals through scanning electron microscopy, coupled with energy dispersive spectrometer (SEM-EDS). The results demonstrated that sandstones were relatively susceptible to weathering, especially when exposed to aggressive acidic conditions, where the presence of bacteria apparently acts as an accelerating factor in deterioration. Based on Si release, sandstone degradation under biotic conditions was 0.27% within 86 days, whereas the dissolution achieved in ultrapure water did not exceed 0.02%. A highly pronounced weathering feature observed on sandstones was the dissolution of goethite and/or kaolinite cement, whereas quartz was less susceptible to weathering under the conditions studied. Bioweathering investigations may help solve deterioration issues in sandstone building materials.

Nutrient availability in phosphate and potassic rocks induced by Acidithiobacillus oxidizing bacteria to produce biofertilizers

Production of conventional fertilizers requires significant energy consumption which increases the price of the product. In recent years, a growing interest on the application of natural products has been shown by public. The aim of this work is to evaluate the effectiveness of the sulfur bacteria Acidithiobacillus thiooxidans to promote mineralogy changes and increase nutrient availability, using phosphate and potassic rocks to produce PK biofertilizers. The study was set up in Petri dishes using 30 g of phosphate rock + 30 g of potassium rock, each rock mixed with elemental sulfur applied at two levels 10% and 20% (3 g and 6 g) in dish. The experiment was conducted in a completely randomized design with eight replications (each rock). The bacterium was inoculated applying 1 ml per g of elemental sulfur. The rocks were incubated during 180 days and mineralogical analysis by XRD and chemical analysis were processed at 30, 60, 120, 150 and 180 days after inoculation. The Acidithiobacillus produced sulfuric acid, which promoted mineralogical changes especially at 180 days after inoculation, compared with the initial time. The inoculation of Acidithiobacillus reduced pH and promoted mineralogical changes in P and K rocks with a significant increase in P and K availability, becoming a viable alternative to plant nutrition instead of soluble PK fertilizers. In addition, it showed great potential for a sustainable agriculture system.

Acidithiobacillus thiooxidans IW16 and Sulfur Synergistically with Struvite Aggrandize the Phosphorus Bioavailability to Wheat in Alkaline Soil

Environmentally hazardous wastewaters from various origins could prove an impending source for phosphorus (P) recovery as struvite. This study aimed to employ an eco-friendly approach for P utilization from struvite, and to neutralize its alkaline effect in the soil through supplementation of sulfur-oxidizing bacteria (SOB) Acidithiobacillus thiooxidans IW16. Struvite precipitated and recovered from wastewater was tested for P release and bioavailability to grow wheat in alkaline soil under greenhouse conditions. Treatments were control (no P application), P from single superphosphate (SSP) fertilizer, P from struvite, P from struvite + sulfur (100 mg kg−1 of soil), and P from rock phosphate; and all these treatments were compared with and without SOB inoculation through irrigation water. Struvite application, especially with sulfur and/or SOB, maintained an adequate P level (as with SSP fertilizer) in both wheat plants and soil throughout the growing period. Wheat plant agronomic attributes were also improved with struvite as for SSP fertilization. Moreover, supplementation of SOB inoculum with struvite and other P sources significantly improved the P bioavailability and crop yield through increased phosphate solubility in alkaline soil. In conclusion, inoculation of SOB especially with sulfur (S) supplementation in struvite treatment caused the pH reduction of alkaline soil through S oxidation (H2SO4 formation), which solubilized the fixed-P in struvite as well as soil and thus improved P bioavailability to wheat plants. These findings strengthen the concept of struvite scavenging from wastewater for environmental safety, and to introduce it as an alternative resource for P fertilization.

Solubilization of a K-silicate rock by Acidithiobacillus thiooxidans

Sulfur-oxidizing bacteria are used in bioleaching processes to recover metals such as gold and copper. The mechanisms for solubilizing metals used by the bacterium Acidithiobacillus thiooxidans involve sulfur oxidation reactions, with the consequent formation of acid. In this study, solubilization of a K-silicate rock (verdete rock, VR) was investigated in a biological trial using A. thiooxidans and elemental sulfur (S0). Erlenmeyer flasks containing modified 9 K medium, bacterial cultures and VR were incubated at 30 °C for periods ranging from 0 to 49 days. pH, redox potential were determined, and chemical and mineralogical analyses were performed after each incubation period. In the presence of A. thiooxidans, the estimated initial pH of 4.2 was reduced to 0.57 after 49 days of incubation. Under acidic conditions, partial solubilization of VR was detected by increases in the concentrations of structural elements of rock minerals, such as K, Al, Fe and Si in the medium containing bacteria, which corresponded to 6.6, 5.8, 14.1 and 1.7% of the total content of these elements in VR, respectively. Mineralogical analysis showed similar changes in X-ray Diffraction spectra (XRD) for VR samples in the absence and presence of A. thiooxidans at 49 days. Our study shows that solubilization of VR occurs when A. thiooxidans and S0 are included in the culture medium, suggesting potential use of a biological route to leach value metals from silicate minerals using low energy input, compared to conventional processes in which pure acids/bases or high temperatures are used.

An Investigation of the Bacterial Influence of Acidithiobacillus Thiooxidans on Concrete Composites

Vegetation and microorganisms present the biological factors that deteriorate concrete. These problems are very visible in places like sewage, underground and hydraulic structures, chemical plants, industrial structures, liquid-containing structures, agricultural structures or marine environments. The most significant biodeteriogens are the sulphur-oxidising bacteria Acidithiobacillus thiooxidans (A. thiooxidans) and the sulphatereducing bacteria (Desulfovibrio spp.) that are responsible for the so-called sulphuretum consortium. Microorganisms that produce sulphuric acid accelerate the deterioration of concrete sewer pipes in a process termed Microbially Induced Concrete Corrosion (MIC). The paper considers the assessment of the release of calcium and silicon from concrete composites with and without coal fly ash by sulphur-oxidizing bacteria. The concrete mixture contained coal fly ash as 5 wt. % and wt. 10 % cement replacement. Prepared composites were exposed to an aggressive microbial environment under laboratory conditions for 3 months. The pH values were measured and studied during this time period. A different resistance against MIC was observed for the concrete composites of different compositions. The highest amount of calcium leached-out from the concrete was in the case of the composites where 10 % cement was replaced by fly ash.

ПЕРЕРАБОТКА УПОРНЫХ СУЛЬФИДНЫХ КОНЦЕНТРАТОВ, СОДЕРЖАЩИХ БЛАГОРОДНЫЕ МЕТАЛЛЫ, НА ОСНОВЕ БАКТЕРИАЛЬНОГО ОКИСЛЕНИЯ

The aim of the research was to evaluate the potential possibility of bacterial oxidation of sulphide minerals of gold-containing flotation pyrite concentrate. The results of studying the concentrate material composition are presented. Laboratory studies of the bacterial oxidation of sulphides are carried out with a mixture of autotrophic bacterial populations consisting of thionic mesophilic bacteria Acidithiobacillus Ferrooxidans, Acidithiobacillus Thiooxidans and Leptospirillum Ferrooxidans. Bacterial adaptation was carried out at a pulp density of 10% solids, followed by an increase to 18%, with a constant measurement of process parameters (pH, Eh, Fe 2+ , Fe 3+ ). Three test experiments were conducted in periodic mode. The optimal parameters of bacterial oxidation were established during the studies: pH, Redox potential, concentration of Fe 2+ , Fe 3+ - ions in the liquid phase of the pulp. The results of chemical analysis of bio-oxidation products are presented. Indicators of gold recovery during cyanide leaching from bacterial oxidation cakes of BIOX-1,2 experiments were respectively 77.99% and 76.86%; in the test without microorganisms, the value was 60.47%. The results of the studies demonstrate the possibility of processing sulphide concentrates by bacterial oxidation.

Phosphorus recovery from high concentrations of low-grade phosphate rocks using the biogenic acid produced by the acidophilic bacteria Acidithiobacillus thiooxidans

In this paper, we are presenting a two-step biological process to recover phosphorus solubilizing low-grade phosphate rocks. We start with a “growing” stage, where the biogenic acid produced by the acidophilic bacteria Acidithiobacillus thiooxidans endows the proper conditions for solubilization. It is followed by a “recovery” stage, where the phosphate rock is added to the culture once desired levels of acidity are reached. We varied the concentration of the phosphate rock and the bacterial growing time to elucidate optimal conditions and to get insight into the biological process. We found that 10% (w/v) of phosphate rock with 23days of bacterial growth results in a recovery of 94%. FTIR spectrums and XRD-Rietveld quantification reveal that the high phosphorus solubilization is correlated with gypsum as the predominant phase, whereas, for less efficient conditions, a significant proportion of fluorapatite, predominant in the un-treated rock, is still observed. As a general trend, increasing the bacterial growing time results in higher amounts of phosphorus recovery. However, the biogenic acid is unable to efficiently solubilize rock concentrations higher than 20% due to an inhibition in the diffusion-controlled reaction. We present a one-to-one comparison with a chemical acidulation using sulfuric acid. The biogenic acid shows better performance and achieves higher percentages of recovery at all conditions, thereby suggesting that additional metabolites in the A. thiooxidans culture enhance the bioleaching. Finally, we delineated an economical viability that indicates that the chemical recovery is four times more expensive than the biogenic method. From a technological perspective, our process offers fertile grounds for non-conventional and efficient phosphorus recovery in tropical soils or for low-grade phosphate rock reservoirs.

Bioelectrochemical system for the biooxidation of a chalcopyrite concentrate by acidophilic bacteria coupled to energy current generation and cathodic copper recovery.

To develop a bioelectrochemical system (BES) to couple the biooxidation of chalcopyrite (CuFeS2), bioelectrogenesis, and the cathodic Cu2+ reduction, bioanodes of acidophilic (pH<2) and aerobic chemolithoautotrophic bacteria Acidithiobacillus thiooxidans (sulfur oxidizing) and Leptospirillum sp. (Fe2+ oxidizing) were used. CuFeS2 biooxidation increases the charge transfer from the media due to the bioleaching of Cu and Fe. The biofilm on a graphite bar endows a more electropositive (anodic) character to the bioelectrode. By adding the bioleachate generated by both bacteria into the anodic chamber, the acidic bioleachate provides the faradaic intensity. The maximum current density was 0.86±19mAcm-2 due to the low potential of the BES of 0.18±0.02V. Such low potential was sufficient for the cathodic deposit of Cu2+. This work demonstrates a proof of concept for energy savings for mining industries: bioanodes of A. thiooxidans and Leptospirillum sp. are electroactive during the biooxidation of CuFeS2.

Investigation of slag-based concrete by mathematical analysis considering air pollution prevention

Carbon dioxide is non-toxic greenhouse gas emitted from sources as cement production. Concrete samples with different percentage of cement replacement by slag and also samples prepared according to standard recipe were prepared for the experiment. Sets of samples were exposed to aggressive environment (acid solution and medium with bacteria Acidithiobacillus thiooxidans) during 6 months. Quantities of calcium and silicon leached out into the liquid solution have been measured. Dissolved quantities were used for statistical analysis of trend of leaching and its influence on properties of concrete samples.Results point to the positive contribution of slag incorporation into concretes (exposed to chemical attack) and its important role in air pollution prevention by reduction of CO2 cement emissions.