Solid State Phenomena Vol. 262

Abstract: Using a commercially available solvent impregnated resin, Lewatit TP272, in an ion exchange process, it was possible to extract up to 90 % indium from a feed containing as little as 1 mg/L indium in the presence of high amounts of impurities, i.e. 1000 mg/L iron and zinc each. It was demonstrated that through gradient regeneration of obtained loaded ion-exchange resin, it is possible to yield a solution containing as much as 400 mg/L indium along with 400 mg/L iron, thereby upgrading its purity more than 600 times. Moreover, it was shown that this solution can be fed into an existing solvent extraction procedure which would yield an indium oxide with more than 99 % purity.

Abstract: Bioreduction of ferric iron-rich wastes is a rapidly emerging technology for the extraction/ recovery of metals from low-grade ores and metallurgical wastes. However, despite studies being successful, they have only been demonstrated at laboratory scale and issues relating to economic, industrial scale application have yet to be studied. Using bioreduction as a pre-treatment to increase recovery yield is a relatively new concept. This study examines the biostimulation of microbial communities to induce bioreduction of metalliferous sludge and the effect that this has on the leachability of metals from the waste using dilute sulphuric acid. Data shows an increase in both zinc and copper leachability after bioreduction, with maximum six fold and eleven fold increase (compared to pre-treatment) in the amount of zinc and copper leached respectively.

Abstract: Silver-catalyzed bioleaching of enargite concentrate with three bacteria (Acidimicrobium ferrooxidans ICP, Sulfobacillus sibiricus N1, Acidithiobacillus caldus KU) and one archaeon (Ferroplasma acidiphilum Y) was conducted in order to elucidate the catalytic mechanism of silver sulfide in enargite bioleaching. Whereas Cu recovery remained relatively low (43%) and Fe dissolved completely without silver sulfide, Cu recovery was greatly enhanced (96%) and Fe dissolution was suppressed (29%) in the presence of 0.04% silver sulfide. In the latter case, 52% of the solubilized As was re-immobilized, in contrast to only 14% As re-immobilization in the former. The silver-catalyzed bioleaching (at 0.04% silver sulfide) proceeded at low redox potentials within the optimal range, which likely promoted enargite dissolution via formation of intermediate Cu₂S. XAFS analysis revealed that As was mainly immobilized as As (V), which was in agreement with the EPMA results detecting ferric arsenate passivation on some enargite grains. Furthermore, formation of trisilver arsenic sulfide (Ag₃AsS₄) was detected by XRD and EPMA, covering the surface of enargite particles. An intermediate layer, consisting of (Cu,Ag)₃AsS₄, was also observed between the enargite grain and trisilver arsenic sulfide layer, implying that Cu in enargite may be gradually substituted by solubilized Ag. The overall mechanism of silver-catalyzed bioleaching of enargite concentrate will be proposed.

Abstract: The bioleaching behaviors of chalcopyrite with two different metallogenic types by iron- and sulfur-oxidizing Sulfobacillus thermosulfidooxidans were investigated. It was found that the skarn-type chalcopyrite (STC) exhibited much faster leaching rate and the copper extraction was 33.34% after 21 days of biooxidation, while that of the porphyry-type chalcopyrite (PTC) was only 23.53%. The reasons were explained from the perspective of mineralogy. The analysis of XRD indicated that STC had slightly larger cell parameters than PTC. More stepped and bulgy structures were observed on the STC surface, as displayed in SEM images. The XPS spectra showed that copper on the surfaces of the two types of chalcopyrite mainly existed in the form of Cu(I), and STC had much higher copper content and lower Cu 2p3/2 binding energy than PTC. These differences in mineralogy resulted in the more excellent bioleaching kinetics of STC. This study is pretty useful in understanding the relation between the bioleaching behaviors of chalcopyrite and the mineralogical properties.

Abstract: Various methods of controlling redox potential (ORP) with electrochemical bioreactor and others have been investigated to increase copper extraction of chalcopyrite in bioleaching,but less attention has been paid to reducing ferric to ferrous ions. Therefore, in this work, the redox potential of chalcopyrite bioleaching system in the presence of mixed moderately thermophiles containing Leptospirillum. ferriphilum, Acidithiobacillus. caldus and Sulfobacillus. thermosulfidooxidans has been controlled by pyrite. It was found that at a constant pH of 2.0, the addition of pyrite can reduce ferric to ferrous ion to a large extent, and the lower ORP values can be obtained. Bioleaching experiments indicated that the time for adding pyrite caused different bioleaching behaviors of chalcopyrite. The high copper extraction can be obtained by added pyrite at a low ORP values (<420 mV vs. Ag/AgCl). The XRD tests and SEM images showed that the amounts of formed jarosite increased as the pyrite addition, and the loose and porous jarosite can be found at low ORP values.

Abstract: The huge industrial data recorded by several years in copper bioleaching operations represents an opportunity for the technology improvement. A systematic approach is being developed to get insights from the field data from an industrial process and to deliver the obtained knowledge with the aim to serve as the foundation for optimal industrial decision making even in presence of inherent process variations. The development of this Decision Support System (DSS) considers a Q-PCR array, a database for data logging and storage, the application of suitable statistical and computational tools for data analyses and knowledge acquiring and finally the creation of a system of knowledge translation to transform it into action (operational suggestions). The user can accurately retrieve data and design similar matches to the historic operation to get e.g. the expected metallurgical performance of a strip based on its mineralogical parameters. In addition, the user can get computed information and recommendations that should be analyzed. We will discuss the process followed to construct the base of knowledge of the DSS.

Abstract: Mine wastes and control soils from twelve sites around Cornwall and West Devon (UK) were analysed for microbial community structure, pH and readily extractible metals (an indication of mobility). About 70% of total diversity observed was constituted by six phyla (Acidobacteria, Chloroflexi, Planctomycetes, Proteobacteria, Verrucomicrobia, and candidate division AD3). Microbial community structure revealed patterns of distribution that mostly differed between waste samples and controls. Cluster analysis of the geochemical data (pH and readily extractible metals) indicated the presence of four groups; two groups of controls and two of samples defined by similar features. pH appeared to correlate with the portion of shared community.

Abstract: A large number of microbial species commonly called phosphate solubilizing microorganisms (PSMs) are efficient at converting insoluble phosphate to soluble forms to prevent phosphorus limitation. This study examined the impact that PSMs had on a sterile and non-sterile monazite source and determined that they could be applied for bioleaching purposes to recover rare earth elements (REEs). On sterile monazite, Penicillum sp. released a total REE concentration of 12.32 mg L^-1 after incubation for 8 days, however, this doubled when inoculated on to non-sterile ore (23.7 mg L^-1). Similar results were recorded with Enterobacter aerogenes, Pantoea agglomerans and Pseudomonas putida. Abiotic controls leached a total REE level of 0.65 mg L^-1. Examination of the leachate by HPLC identified several low molecular weight organic acids that corresponded with decreases in the media pH. The presence of a native consortia from the monazite ore combined with a known PSMs was more effective at leaching REEs from the monazite matrix than a single isolates or by the native population alone.

Abstract: Lateritic deposits containing rare earth elements (REE) are important resources in Brazil, where monazite is the main REE-bearing mineral and is frequently associated with iron hydroxy-oxides and quartz. In order to recover valuable metals such as REE and uranium, experiments were carried out under reductive mineral dissolution using Acidithiobacillus species. In terms of phosphate, aerobic reductive dissolution at pH 0.9 using A. thiooxidans extracted about 35% of that present in the ore which is and indicator of the dissolution of monazite. Although only ~9% of the cerium and 5% of the lanthanum were extracted, ~72% of the uranium was solubilized, indicating that it was more susceptible to extraction by reductive dissolution than the other two REE.

Abstract: In and Ge can be found in Sphalerite crystal which can influence bio-leaching properties of Sphalerite significantly. Occurrence states of In and Ge in Sphalerite crystal and their influence on Sphalerite was calculated by Castep package. The most stable occurrence states are In and Ge substitute for Zn atom in Sphalerite crystal. When In and Ge existed in Sphalerite crystal, the Density of states (DOS) of Sphalerite crystal moved to left, meaning a more reducibility structure. It can explain why In and Ge bearing Sphalerite is easier to bio-leach than the pure sphalerite.