Dissolution Products Research Articles

Reductive dissolution of pyrite by methanogenic archaea

The formation and fate of pyrite (FeS2) modulates global iron, sulfur, carbon, and oxygen biogeochemical cycles and has done so since early in Earth’s geological history. A longstanding paradigm is that FeS2 is stable at low temperature and is unavailable to microorganisms in the absence of oxygen and oxidative weathering. Here, we show that methanogens can catalyze the reductive dissolution of FeS2 at low temperature (≤38 °C) and utilize dissolution products to meet cellular iron and sulfur demands associated with the biosynthesis of simple and complex co-factors. Direct access to FeS2 is required to catalyze its reduction and/or to assimilate iron monosulfide that likely forms through coupled reductive dissolution and precipitation, consistent with close associations observed between cells and FeS2. These findings demonstrate that FeS2 is bioavailable to anaerobic methanogens and can be mobilized in low temperature anoxic environments. Given that methanogens evolved at least 3.46 Gya, these data indicate that the microbial contribution to the iron and sulfur cycles in ancient and contemporary anoxic environments may be more complex and robust than previously recognized, with impacts on the sources and sinks of iron and sulfur and other bio-essential and thiophilic elements such as nickel and cobalt.

Li leaching from Li carbonate-primer: Transport pathway development from the scribe edge of a primer/topcoat system

Depletion depths of inorganic components from a scribe edge in a polyurethane primer containing Li2CO3, MgO, BaSO4 and TiO2 beneath a topcoat, were determined using a range of techniques including SEM/EDS and proton induced X-ray and γ-ray emission spectroscopies. SEM of sections cut using an ion beam revealed scribe damage penetrating 20–25 μm away from the scribe edge prior to leaching. After neutral salt spray (NSS) exposure a leached zone developing from the scribe edge was observed. For longer NSS exposure times (>96 h) this leached zone of nearly complete Li and Mg depletion did not develop any deeper than the scribe damaged region indicating that the depletion zone was caused by mechanical damage due to scribing. At short times small voids were formed in Li2CO3 particles within the primer well away from the scribe (100–260 μm) whereas a mixture of void and detachment in and around Li2CO3 particles was observed at longer times. The detachment was assumed to be part of a channel network within clusters of particles. Internal stresses within the primer resulting from buildup of inhibitor dissolution product within the voids were modelled using finite element analysis. It was found that strains related to von Mises stresses were concentrated around the inorganic particles and developed preferentially within the plane of the primer beneath the topcoat with some indication of concentration towards the primer/metal interface. These stresses resulted from osmosis and swelling related to the voids. They were also attributed to the observed cracking of the binder at some locations. Leaching experiments showed that Li was released very rapidly from the primer. The leaching data was modelled using a power law where the mass released is proportional to tn where the n is an index that reflects the kinetic behavior dictated by the evolving primer porosity. In this study n values between 0 and 1 were observed for all species, with Li starting at around 0.7 but rapidly decreasing to close to zero.

Intensification of the wastewater treatment process with electrolytic gases

High regulatory requirements for the quality of treated water discharged into watercourses and wear and tear of local treatment facilities dictate the need to develop new technological solutions in the field of water treatment systems. In this regard, technologies that implement methods of electrophysical or electrochemical impact on polluting components in the processed liquid have found wide application in the treatment of waste and substandard waters. In this case, on the one hand, in order to increase the efficiency of collecting pollutants, it is necessary to strive to increase the number and decrease the size of electrolytic gas bubbles providing this collection, and on the other hand, it is necessary to optimize the operating modes of the electrode system and the material execution of the electrodes themselves, since the time of their operation depends on this. To solve this compromise problem, the design of an electroflotator has been developed, in which an electrode system is installed in the lower part of the tank, consisting of vertical anodes and cathodes. Each pair of them has the shape of cylinders and is fixed on the side surfaces of the dielectric ring separating them. The height of the ring from above and from below is made greater than the height of the anode and cathode by an amount equal to the annular gap between the adjacent anode and cathode. This design of the spacer ring prevents current leakage from the cathode to the anode and, accordingly, the dissolution of the anode ends. If the height of the ring above and below is executed by an amount less than the annular gap, there is a twofold increase in the density of the anode current at the ends of the anode and cathode, intensifying the dissolution of the anodes and the ingress of dissolution products into the solution and onto the walls of the electrodes, increasing their electrical resistance and reducing the performance of treatment facilities by liquid to be cleaned.

Cobalt‐containing spherical glass nanoparticles for therapeutic ion release

AbstractBioactive glass nanoparticles (BGNPs) can be internalized by cells, allowing the intracellular release of dissolution products with therapeutic benefit. Different therapeutic ions can be incorporated into the glass network that can promote angiogenesis via simulation of hypoxia conditions and consequent activation of pro‐angiogenic genes. Here, novel monodispersed spherical dense BGNPs were obtained by a modified Stöber method with the SiO2–CaO–CoO composition, with diameters of 92 ± 1 nm, with cobalt as the pro‐angiogenic ion. The presence of Co2+ species and the role of Co and Ca as network modifiers in the silica glass were confirmed by X‐ray photoelectron spectroscopy and 29Si solid‐state magic‐angle spinning nuclear magnetic resonance, respectively. Controlled Co2+ ion release was observed in culture media, and no cytotoxicity was observed by (4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide cell viability assay on human osteosarcoma cells in direct contact with the nanoparticles. This study demonstrated that Co2+ ions can be incorporated into dense and spherical BGNPs, and these materials exhibit great potential as intracellular ion delivery systems with therapeutic properties.

Photocorrosion of WO3 Photoanodes in Different Electrolytes.

Photocorrosion of an n-type semiconductor is anticipated to be unfavorable if its decomposition potential is situated below its valence band-edge position. Tungsten trioxide (WO3) is generally considered as a stable photoanode for different photoelectrochemical (PEC) applications. Such oversimplified considerations ignore reactions with electrolytes added to the solvent. Moreover, kinetic effects are neglected. The fallacy of such approaches has been demonstrated in our previous study dealing with WO3 instability in H2SO4. In this work, in order to understand parameters influencing WO3 photocorrosion and to identify more suitable reaction environments, H2SO4, HClO4, HNO3, CH3O3SH, as electrolytes are considered. Model WO3 thin films are fabricated with a spray-coating process. Photoactivity of the samples is determined with a photoelectrochemical scanning flow cell. Photostability is measured in real time by coupling an inductively coupled plasma mass spectrometer to the scanning flow cell to determine the photoanode dissolution products. It is found that the photoactivity of the WO3 films increases as HNO3 < HClO4 ≈ H2SO4 < CH3O3SH, whereas the photostability exhibits the opposite trend. The differences observed in photocorrosion are explained considering stability of the electrolytes toward decomposition. This work demonstrates that electrolytes and their reactive intermediates clearly influence the photostability of photoelectrodes. Thus, the careful selection of the photoelectrode/electrolyte combination is of crucial importance in the design of a stable photoelectrochemical water-splitting device.

In-situ detection of LiMn2O4 dissolution during electrochemical cycling by

Herein we describe a modified Swagelok electrochemical cell for characterizing individual electrode behavior as part of full cell operation, including individual electrode potentials and dissolution phenomena. The case study presented is that of the non-aqueous Li-LiMn2O4 system. Outcomes from the work include characterization of lithium negative electrode potential variation with applied current, lithium corrosion and passivation in the electrolyte, and LiMn2O4 dissolution with cycling. It is also demonstrated that Mn(III) is the dissolution product. Application of the technique to other systems, including electrode materials and electrolytes, is discussed.

Silver‐doped sol‐gel borate glasses: Dose‐dependent effect on Pseudomonas aeruginosa biofilms and keratinocyte function

AbstractBorate‐based glasses have generated great interest for wound healing applications due to their ability to incorporate biologically therapeutic ions which can then be released at the site of repair attributable to their high dissolution rates. In this study, the anti‐bacterial activity and cytocompatibility of sol‐gel–derived silver‐doped borate glasses (AgBGs) of the compositional range (60)B2O3–(36)CaO–(4–x)P2O5–(x)Ag2O, where x = 0.0, 0.3, 0.5, and 1 (mol.%) were investigated, in vitro. The dose‐dependent anti‐bacterial activity of AgBGs was demonstrated against Pseudomonas aeruginosa under both planktonic conditions and pre‐formed biofilms, with up to 99.7% reduction in bacterial cell counts. Lower concentrations of ionic dissolution products from AgBGs were non‐toxic to keratinocytes, stimulating their growth and metabolic activity. Furthermore, compositions containing 0.3 and 0.5 mol.% Ag significantly accelerated the migration of keratinocytes at two different concentrations in an in vitro 2D wound healing model. In summary, these therapeutic AgBGs have demonstrated potential for accelerated wound healing.

ELECTROCHEMICAL SYNTHESIS OF DISPERSED BARIUM FERRITE USING ANODIC DISSOLUTION OF METAL

The process of anodic dissolution of iron (purity not less than 99%) in aqueous solutions of barium chloride, barium nitrate and binary electrolytes under galvanostatic conditions and by registration of potentiodynamic polarization curves was investigated. The influence of solution composition and concentration and the value of applied direct current on the intensity of anodic oxidation of iron was shown. It was revealed that the oxidation rate of metal in binary electrolytes containing barium chloride and barium nitrate is comparable with the intensity of anodic dissolution in a solution based on barium chloride. It was found that anodic polarization curve in solutions containing BaCl2 and Ba(NO3)2 has a complex form typical of passivated metals. There is a clear maximum of anodic oxidation current on this curve, as well as in barium nitrate solution, however the peak height is much higher (50-150 times). A method for the synthesis of dispersed barium ferrite, based on the anodic oxidation of iron in aqueous barium chloride and barium nitrate solutions with subsequent thermal treatment of the product of electrochemical dissolution was suggested. The phase and elemental composition and structural characteristics of obtained precursor and ferrite samples were examined using X-ray phase analysis. The influence of the heat treatment mode on the phase composition of the synthesized samples is shown. It is found that electrolysis with a soluble iron electrode using direct anode current in 0.05M BaCl2 + 0.5M Ba(NO3)2 solution and subsequent thermal treatment of the dissolution product at 1200 ° C provide the formation of dispersed system, whose phase composition is predominantly Ba0.87Fe11.08O17.15 (74%) and BaFe2O4 (17%).

Impact of Zinc- or Copper-Doped Mesoporous Bioactive Glass Nanoparticles on the Osteogenic Differentiation and Matrix Formation of Mesenchymal Stromal Cells.

Mesoporous bioactive glass nanoparticles (MBGNs) have gained relevance in bone tissue engineering, especially since they can be used as vectors for therapeutically active ions like zinc (Zn) or copper (Cu). In this study, the osteogenic properties of the ionic dissolution products (IDPs) of undoped MBGNs (composition in mol%: 70 SiO2, 30 CaO) and MBGNs doped with 5 mol% of either Zn (5Zn-MBGNs) or Cu (5Cu-MBGNs; compositions in mol%: 70 SiO2, 25 CaO, 5 ZnO/CuO) on human bone marrow-derived mesenchymal stromal cells were evaluated. Extracellular matrix (ECM) formation and calcification were assessed, as well as the IDPs’ influence on viability, cellular osteogenic differentiation and the expression of genes encoding for relevant members of the ECM. The IDPs of undoped MBGNs and 5Zn-MBGNs had a comparable influence on cell viability, while it was enhanced by IDPs of 5Cu-MBGNs compared to the other MBGNs. IDPs of 5Cu-MBGNs had slightly positive effects on ECM formation and calcification. 5Zn-MBGNs provided the most favorable pro-osteogenic properties since they increased not only cellular osteogenic differentiation and ECM-related gene expression but also ECM formation and calcification significantly. Future studies should analyze other relevant properties of MBGNs, such as their impact on angiogenesis.

Ionic dissolution products of Cerium-doped bioactive glass nanoparticles promote cellular osteogenic differentiation and extracellular matrix formation of human bone marrow derived mesenchymal stromal cells

Cerium (Ce) is a promising candidate ion for application in bone tissue engineering (BTE) since it reduces the presence of reactive oxygen species. Ce-doped mesoporous bioactive glass nanoparticles (MBGNs) serving as vectors for the local application of Ce already demonstrated stimulating effects on the expression of pro-osteogenic genes in Saos-2 cells. So far, there is no evidence available about the effects of Ce-doped MBGNs on the viability, osteogenic differentiation and the formation of the osseous extracellular matrix (ECM) of primary human bone marrow-derived mesenchymal stromal cells (BMSCs). Therefore, in this study, the biocompatibility of the ionic dissolution products (IDPs) of MBGNs containing increasing concentrations of CeO2 (0.05 MCe-MBGNs, composition in mol%: 86.6SiO2-12.1CaO-1.3CeO2; and 0.2 MCe-MBGNs, composition in mol%: 86.0SiO2-11.8CaO-2.2CeO2) and unmodified MBGNs (composition in mol%: 86SiO2-14CaO) was evaluated using human BMSCs. Eventually, the impact of the MBGNs’ IDPs on the cellular osteogenic differentiation and their ability to build and mature a primitive osseous ECM was assessed. The Ce-doped MBGNs had a positive influence on the viability and stimulated the cellular osteogenic differentiation of human BMSCs evaluated by analyzing the activity of alkaline phosphate as a marker enzyme for osteoblasts in the present setting. Furthermore, the formation and calcification of a primitive osseous ECM was significantly stimulated in the presence of Ce-doped MBGNs in a positive concentration-dependent manner as demonstrated by an elevated presence of collagen and increased ECM calcification. The results of this in-vitro study show that Ce-doped MBGNs are attractive candidates for further application in BTE.

Rapid Separation of Photofissioned Uranium Products via a Single-Pass Multiplexed Chromatographic Fission Product Separation System.

Current state-of-the-art fission product separations frequently involve multiple independent separation columns and sample manipulation processes; to couple these processes together, multiple evaporation and transposition steps are often required. The addition of these steps results in lengthy separation times, increased analysis costs, the potential for sample loss, and release of radioactive contamination. We report a new semiautomated method for the rapid separation of U, Zr, Mo, Ba, Sr, Te, and lanthanide fission products from irradiated uranium samples. Chemical yields for U, Zr, Ba, Sr, Te and the lanthanides from less than 3-day old uranium fission product samples are consistently greater than 90%, while those of Mo are greater than 70%. This method minimizes the use and addition of oxidation and reduction reagents that often cause issues with retention and separation. Uranium dissolution and fission product separations using this single-pass method are achievable in under 2 h, representing a significant improvement over traditional gravimetric uranium fission product separation procedures.

The dissolution kinetics of raw and mechanochemically treated kaolinites in industrial spent liquor – The effect of the physico-chemical properties of the solids

Using industrial spent Bayer-liquor solution and 95 °C temperature, the dissolution and desilication products formation kinetics of five raw kaolinite samples obtained from different sources were found to display profound differences. It was hypothesized that these differences were connected to the physico-chemical properties of the solids. The solids were characterized by powder X-ray diffractometry, N2 adsorption-desorption isotherms, temperature-programmed NH3 desorption, infrared and ultraviolet–visible diffuse reflectance spectroscopies, scanning electron microscopy connected with energy dispersive X-ray analysis, dynamic light scattering and thermal analysis. The detailed structural study of the as-received samples was supplemented by exploring the effect of mechanochemical treatment. It was found that beside specific surface area and pore volume, the amount of the Lewis acid sites proved to be the most important factors, and the picture was found to be modulated by the degree of aggregation of the primary particles. On mechanochemical treatment (60 min milling in a mixer mill), the number of the acid sites increased significantly (from 0.004–0.013 to 0.055–0.066 mmol/g), and largely as a result of this, the dissolution of all raw kaolinites became practically instantaneous and source-independent.

Bioactive glasses and electrospun composites that release cobalt to stimulate the HIF pathway for wound healing applications

BackgroundBioactive glasses are traditionally associated with bonding to bone through a hydroxycarbonate apatite (HCA) surface layer but the release of active ions is more important for bone regeneration. They are now being used to deliver ions for soft tissue applications, particularly wound healing. Cobalt is known to simulate hypoxia and provoke angiogenesis. The aim here was to develop new bioactive glass compositions designed to be scaffold materials to locally deliver pro-angiogenic cobalt ions, at a controlled rate, without forming an HCA layer, for wound healing applications.MethodsNew melt-derived bioactive glass compositions were designed that had the same network connectivity (mean number of bridging covalent bonds between silica tetrahedra), and therefore similar biodegradation rate, as the original 45S5 Bioglass. The amount of magnesium and cobalt in the glass was varied, with the aim of reducing or removing calcium and phosphate from the compositions. Electrospun poly(ε-caprolactone)/bioactive glass composites were also produced. Glasses were tested for ion release in dissolution studies and their influence on Hypoxia-Inducible Factor 1-alpha (HIF-1α) and expression of Vascular Endothelial Growth Factor (VEGF) from fibroblast cells was investigated.ResultsDissolution tests showed the silica rich layer differed depending on the amount of MgO in the glass, which influenced the delivery of cobalt. The electrospun composites delivered a more sustained ion release relative to glass particles alone. Exposing fibroblasts to conditioned media from these composites did not cause a detrimental effect on metabolic activity but glasses containing cobalt did stabilise HIF-1α and provoked a significantly higher expression of VEGF (not seen in Co-free controls).ConclusionsThe composite fibres containing new bioactive glass compositions delivered cobalt ions at a sustained rate, which could be mediated by the magnesium content of the glass. The dissolution products stabilised HIF-1α and provoked a significantly higher expression of VEGF, suggesting the composites activated the HIF pathway to stimulate angiogenesis.

A facile synthesis of mono-dispersed, spherical and mesoporous bioactive glass nanoparticles for biomedical applications

Bioactive glasses (BG) have become a popular class of biomaterials for a range of medical applications due to their enhanced dissolution rate, cell internalization capability and ionic dissolution products with therapeutic benefits. Here, we introduce, for the first time, a simplified synthesis procedure in order to create nanoparticles with uniform, spherical and mesoporous BG structure with a ternary composition of SiO2-CaO-P2O5. The hydroxyapatite forming ability is also evaluated to confirm the bioactivity. Doxorubicin, a model drug, is loaded within BG nanoparticles with an encapsulation efficiency was 35%. Cytotoxicity evaluations confirmed the non-toxic nature of the nanoparticles when exposed to MG63 cell line. Overall, results suggest the diverse orthopedic and dental application of mesoporous bioactive glass (MBG) nanoparticles.

PRECIPITATE EXTRACTION FROM 3003 ALUMINUM ALLOY PRODUCED BY TWIN ROLL CASTING/ EXTRAÇÃO PRECIPITADA DE 3003 LIGAS DE ALUMÍNIO PRODUZIDAS POR FUNDIÇÃO EM ROLO DUPLO

In the present study four different precipitate extraction techniques were investigated on a 3003 aluminium alloy samples (twin-roll cast and homogenized conditions). The dissolution product was analyzed with the help of X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. The performance of four chemical solutions (iodine solution, perchloric acid, oxine solution, and phenol solution) was compared, and the phenol solution presented the best precipitate extraction results. The phases in the cast and homogenized microstructures were identified, explaining some aspects of the phase transformation during the homogenization.

Preparation and physical‐biological characterization on titanium doped fluorophosphate nanobioglass: Bone implants

AbstractIn bone tissue repair, metallic implants like screws, pins, plates, stents are considered as boon for patients but it has the disadvantage of being a foreign body and can never get absorbed or get converted to bone. These metallic implants serve the purpose often temporarily, but it fails to attain the mechanical, elastic properties near to that of the normal human bones. To circumvent these drawbacks, the preparation of nanobioglasses having titanium and different proportions of fluoride using melt quenching method is reported. The physical, thermal, and elastic properties of the materials were characterized by their densities, thermal transitions, and elastic moduli by ultrasonic study. The in vitro degradation and bioactivity of these nanobioglasses were assessed by immersion in simulated body fluid (SBF). The hydroxyapatite(HAp) formation was assessed by the variation in pH over 21 days and its presence was confirmed by FTIR, XRD, SEM, and EDS. Human osteo sarcoma MG‐63(ATCC‐1427), SAOS‐2(ATCC‐85), and gastric adenocarcinoma (AGS)(ATCC‐1739) cell lines were used to evaluate cytotoxicity of the bioglasses by MTT assay. The biological efficiency of titanium doped fluorophosphate enhancing bone formation was assessed by the capacity of the ionic dissolution products of the bioglasses to enhance the osteocalcin and ALP activity. The phosphate‐based titanium nanobioglasses doped with fluoride possesses elastic strength nearer to the normal human bone, higher bone bonding ability and the rate of biodegradation equaling the rate of bone formation than the commercially available bioglass.

Distinguishing the effects of Ce nanoparticles from their dissolution products: identification of transcriptomic biomarkers that are specific for ionic Ce inChlamydomonas reinhardtii

AbstractCerium (Ce) is a rare earth element that is incorporated in numerous consumer products, either in its cationic form or as engineered nanoparticles (ENPs). Given the propensity of small oxide particles to dissolve, it is unclear whether biological responses induced by ENPs will be due to the nanoparticles themselves or rather due to their dissolution. This study provides the foundation for the development of transcriptomic biomarkers that are specific for ionic Ce in the freshwater alga, Chlamydomonas reinhardtii, exposed either to ionic Ce or to two different types of small Ce ENPs (uncoated, ∼10 nm, or citrate-coated, ∼4 nm). Quantitative reverse transcription PCR was used to analyse mRNA levels of four ionic Ce-specific genes (Cre17g.737300, MMP6, GTR12, and HSP22E) that were previously identified by whole transcriptome analysis in addition to two oxidative stress biomarkers (APX1 and GPX5). Expression was characterized for exposures to 0.03–3 µM Ce, for 60–360 min and for pH 5.0–8.0. Near-linear concentration–response curves were obtained for the ionic Ce and as a function of exposure time. Some variability in the transcriptomic response was observed as a function of pH, which was attributed to the formation of metastable Ce species in solution. Oxidative stress biomarkers analysed at transcriptomic and cellular levels confirmed that different effects were induced for dissolved Ce in comparison to Ce ENPs. The measured expression levels confirmed that changes in Ce speciation and the dissolution of Ce ENPs greatly influence Ce bioavailability.

Characterization of Cathode/Electrolyte Interfacial Processes By Scanning Electrochemical Microscopy

Lithium transition metal oxides (LiMn2O4 and LiMO2 where M=Ni, Mn, Co, etc.) are widely applied in lithium ion batteries due to their considerable capacity and energy density. Multiple processes occurring at the cathode/electrolyte interface lead to performance degradation, one of which is the dissolution of transition metals. While transition metal dissolution has been known to occur for some time, open questions remain about mechanistic details of these processes. This work uses the scanning electrochemical microscope (SECM) to observe active cathode degradation processes in situ and immediately at the cathode/electrolyte interface. These results are also paired with complementary analysis employing inductively coupled plasma (ICP) and electron paramagnetic resonance (EPR) spectroscopies to yield insight into the properties of cathode degradation products and their reactivity.This work focuses on studies of LiMn2O4 thin films as model cathodes and characterizes products of the Mn dissolution process. The degradation process of binder-free LiMn2O4 thin films prepared by polymer assisted deposition was investigated in varied electrolytes. The properties of Mn dissolution products from cathode degradation is compared to Mn salt solutions introduced into complementary electrolytes. Our results appear to indicate substantial variations between the properties of dissolved Mn salts and actual cathode degradation products. Moreover, electrolyte composition appears to affect the electrochemical behavior of metal dissolution products significantly. This likely indicates that the LiMn2O4 degradation mechanism in differing electrolytes undergo different degradation reaction pathways.

A comparison of spent resin degradation by Fenton and O3-Fenton process

The treatment of spent resin generated by nuclear power plants using Fenton and O3-Fenton process as an alternative to the present cementation method is an attractive solution. A comparison among O3-Fenton and Fenton process for spent resin degradation were performed in this investigation. The different effects of reaction temperature and ozone concentration was compared between Fenton and O3-Fenton process. In addition the resulted COD removal ratio, residue weight, iron ions concentration change, resin dissolution, degradation intermediates and final products were also compared in these two processes. The results showed that the addition of O3 to Fenton process can improve the degradation ratio of spent resin. With an O3 concentration of 161.3 mg/L, the resin degradation ratio reached 97.1%. The residue COD of O3-Fenton process was 60.0% lower than Fenton process. With O3 addition, the dissolution rate of spent resin was reduced and the mineralization rate of dissolved organics increased by 19.3%. The residual organic matters in the final solution included mainly oxalic acid. The degradation of spent resin after dissolution conformed to the first-order kinetic equation in both Fenton and O3-Fenton process. O3-Fenton process could get better results and save processing costs.

The impact of light on the rate and mechanism of dissolution and leaching of natural iron-containing sphalerite, (Zn,Fe)S

The effect of UV light on the rate of dissolution of sphalerite, (Zn,Fe)S, has been investigated for samples from different sources. These different samples had different amounts of substitutional iron, ranging between 0.55 and 8.62%. It was found that the rate of dissolution of sphalerite is proportional to the content of substitutional iron, and that the rate of dissolution increased in the presence of UV light. Analysis of the data indicated that the effect of light was more pronounced for samples with lower iron content. A mechanism is described for the dissolution reaction that envisages that the oxidant preferentially accepts electrons from (or injects holes into) the d-band orbitals arising from the iron in substitutional positions in the lattice. The resulting hole in the d-band reacts with the surface causing the removal of the dissolution products from the surface. The effect of light was proposed to be due to the excitation of a valence band electron to the conduction band to create electron-hole pairs. The holes react with the surface, resulting in dissolution products, while the excited electrons are captured by the oxidant. Rate equations are derived that describe these mechanisms. These rate equations are shown to agree with the experimental data.