Mixed Mineral Systems Research Articles

Comparative Study on the Effect of Pyrophosphate and Tripolyphosphate on the Flotation Separation of Arsenopyrite and Muscovite

The aim of the study was to compare the effects and mechanism of tetrasodium pyrophosphate (TSPP) and sodium tripolyphosphate (STPP) as dispersants on the selective flotation of arsenopyrite from muscovite. The results of single-mineral flotation showed that the recovery of arsenopyrite was 81.4% when no dispersant was added. The recovery of arsenopyrite slightly decreased with increasing dosage of TSPP. When the dosage of STPP was 6 × 10−5 mol/L, the recovery of arsenopyrite was only 28.6%. Neither of the dispersants had significant influence on the muscovite flotation (<10%). However, in a mixed-mineral system, the recovery of arsenopyrite dropped significantly, and then under the action of dispersants, its recovery back up. The RPM results showed that the dispersion effect of TSPP was superior to that of STPP. The electrokinetic potential showed that the potential change value of muscovite with TSPP was −17.37 mV, while that of muscovite with STPP was −8.33 mV (pH = 8). The adsorption of TSPP onto muscovite was stronger than that of STPP. FTIR and XPS analysis confirmed that dispersants exhibited chemical adsorption with the Al atoms on muscovite and that dispersant STPP exhibited stonger adsorption than TSPP on arsenopyrite, which was consistent with flotation experiments.

Uncovering the hetero-hydrophobic attraction between the basal planes of molybdenite and talc under flotation conditions

The very close natural floatability of molybdenite and talc has been traditionally believed as the main reason for their separation problem. However, the interactions between the basal and edge planes of the two platy minerals remain unclear. Here the hydrophobic attraction between the basal planes was proposed as the dominating factor for that problem. Flotation tests in both single and mixed mineral systems were conducted using carboxymethyl cellulose (CMC) as talc depressant and sodium isobutyl xanthate (SIBX) as molybdenite collector. Zeta potential distribution, contact angle, in situ optical microscope observation, EDLVO calculation and surface energy analysis were applied to reveal the surfacial actions between the basal and edge planes of molybdenite and talc. Molybdenite and talc showed obvious floatability difference in single mineral system, however, their separation efficiency met with big decline in mixed mineral system. Zeta potential results demonstrated that, in the presence of CMC and SIBX, negatively charged particles of molybdenite and talc aggregated rather than electrostatically repulsed and dispersed. The contact angle and particle adhesion results showed a certain degree of selective attraction between the basal planes of molybdenite and talc. The EDLVO calculation suggested the attractive interactions were ranked as: Mb(basal)-Tlc(edge) > Mb(basal)-Tlc(basal) ≈ Mb(edge)-Tlc(edge) > Mb(edge)-Tlc(basal). The surface energy calculation pointed out that the fundamental reason for the separation problem was exactly the hetero-hydrophobic attraction between their basal planes.

Green separation of galena from molybdenite by flotation using DL-dithiothreitol as a depressant

Developing an environment-friendly depressant to separate galena from molybdenite by flotation remains greatly challenging. Herein, the nontoxic DL-dithiothreitol (DLD) was used as a galena depressant in a molybdenite–galena flotation system. Flotation experiments showed that a recovery difference of 88.45 % was achieved in a binary mixed-mineral system with a DLD dosage of 40.00 mg/L at pH 8.00, indicating that DLD significantly reduced the floatability of galena while barely altering that of molybdenite. The adsorption mechanism of DLD on the surfaces of galena and molybdenite were investigated by various characterization techniques. Results showed that DLD can coordinate with unsaturated lead ions on the galena surface through its sulfhydryl groups. DLD stably adsorbed onto the galena surface because of the presence of chemical bonding (Pb–S), which significantly changed the surface potential of galena. Molybdenite cannot chemisorb DLD because only saturated sulfur atoms were exposed on its cleavage surface. Hence, the selective adsorption of DLD enhanced the hydrophilicity of the galena surface without affecting the hydrophobicity of the molybdenite surface. Evidently, DLD was a high-performance and promising industrial application of galena depressant. This study provided new insights into the separation of molybdenite and galena, thereby facilitates the sustainable development of the mining industry.

Siderophore-Mediated Mobilization of Manganese Limits Iron Solubility in Mixed Mineral Systems.

Recent laboratory and field studies show the need to consider the formation of aqueous Mn(III)-siderophore complexes in manganese (Mn) and iron (Fe) geochemical cycling, a shift from the historical view that aqueous Mn(III) species are unstable and thus unimportant. In this study, we quantified Mn and Fe mobilization by desferrioxamine B (DFOB), a terrestrial bacterial siderophore, in single (Mn or Fe) and mixed (Mn and Fe) mineral systems. We selected manganite (γ-MnOOH), δ-MnO2, lepidocrocite (γ-FeOOH), and 2-line ferrihydrite (Fe2O3·0.5H2O) as relevant mineral phases. We found that DFOB mobilized Mn(III) as Mn(III)-DFOB complexes to varying extents from both Mn(III,IV) oxyhydroxides but reduction of Mn(IV) to Mn(III) was required for the mobilization of Mn(III) from δ-MnO2. The initial rates of Mn(III)-DFOB mobilization from manganite and δ-MnO2 were not affected by the presence of lepidocrocite but decreased by a factor of 5 and 10 for manganite and δ-MnO2, respectively, in the presence of 2-line ferrihydrite. Additionally, the decomposition of Mn(III)-DFOB complexes through Mn-for-Fe ligand exchange and/or ligand oxidation led to Mn(II) mobilization and Mn(III) precipitation in the mixed-mineral systems (∼10% (mol Mn/mol Fe)). As a result, the concentration of Fe(III) mobilized as Fe(III)-DFOB decreased by up to 50% and 80% in the presence of manganite and δ-MnO2, respectively, compared to the single mineral systems. Our results demonstrate that siderophores, through their complexation of Mn(III), reduction of Mn(III,IV), and mobilization of Mn(II), can redistribute Mn to other soil minerals and limit the bioavailability of Fe in natural systems.

Selective flotation separation of galena from sphalerite via chelation collectors with different nitrogen functional groups

Nitrogen functional groups often provide excellent collecting selectivity and efficiency for collector molecules because of the rational alkalinity as Lewis base and the delicate affinity for metal ions. In this work, 1,3-diphenylthiourea (DPTU), 2-acetylhydrazine-1-carbothioamide (ADCT), (E)-1,5-diphenylthiocarbazone (DPTZ) were used as novel selective collectors for the flotation of galena/sphalerite mixed system, and universal collector sodium ethyl-xanthate (SEX) was used as the reference collector. The flotation results showed that collector with more nitrogen atoms (DPTZ) offered better selectivity for the flotation separation of galena from a galena/sphalerite mixed mineral system. Separation selectivity, FTIR and XPS studies showed, in the case that collector solution environment pH value < pKa value, N atoms did not participate in the coordination reaction. But in the opposite case, almost all N atoms in the collector molecule participated in the coordination reaction. As a result, there is stronger interaction between the collector molecule and the lead ion on the surface of galena, which was conducive to the selective flotation separation. The contact angle results showed that suitable hydrophobic groups were also critical to efficient separation.

Electrochemical investigation of microbially and galvanically leached chalcopyrite

The effect of the galvanic interaction between anodic chalcopyrite and cathodic pyrite was investigated by long-term electrochemical measurements of the galvanic coupling current and verified by chemical leaching and bioleaching. For the first time galvanic corrosion measurements (in the absence and in the presence of microorganisms) over days are reported. Combined microbial and galvanic leaching of chalcopyrite showed increased Cu recovery in the presence of pyrite. Corrosion resulted in mineral dissolution depending on multiple parameters (like metal corrosion). However, maximal chalcopyrite dissolution via bioleaching occurred in the presence of a large cathodic pyrite surface. Highest copper recovery was observed in case of high rest potential differences between galvanically coupled minerals (pyrite coupled with copper concentrate). A comparison of electrochemical data of this study with scientific literature revealed a wide range of rest potential data for a single metal sulfide. Fundamental research on galvanic interaction of mixed mineral systems need to focus on unified experimental parameters to allow a comparison.

1-Hydroxyethylidene-1,1-diphosphonic acid used as pH-dependent switch to depress and activate fluorite flotation I: Depressing behavior and mechanism

Fluorite is usually separated from calcite by froth flotation method using large amounts of sodium silicate depressant, which can cause trouble in the loss of fluorite and wastewater treatment. In this study, green and low-cost 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP or H4L) was used as pH-dependent switch to initially depress fluorite for calcite pre-removal at pH 6.0, and then activate fluorite for further upgrading fluorite concentrate at pH 8.0. The depressing behavior and mechanism were reported in this work. H2L2− was the dominant form of HEDP, and a stronger chemical adsorption of H2L2− on fluorite hindered the subsequent adsorption of sodium oleate (NaOL), while that of the calcite showed the opposite result. Two active O atoms in H2L2− could well match in interatom distance with two Ca sites on fluorite to form Ca-H2L complexes. The pH-dependent switch reagent reported here may open a new avenue for more selective separation among mixed mineral systems.

Enhanced Immobilization of Arsenic from Acid Mine Drainage by Detrital Clay Minerals

Arsenic (As) is a potent carcinogen and the most common metal(loid) contaminant in drinking water sources globally. In acidic, Fe-rich systems, nanocrystalline Fe(III) precipitates (Fe(III)NP) are the main scavengers of As. However, the redox cycling of Fe(III)NP highly enhances As mobility and bioavailability. Notably, the irreversible release of As in runoff resulting from reductive dissolution of Fe(III)NP makes the effective remediation of As an ongoing environmental challenge. Here, we show for the first time that detrital clay minerals originating from the partial weathering of coal mining waste substantially increased total As uptake by acid mine drainage (AMD) sediments. The As immobilization mechanisms by the AMD sediments were investigated by the combined use of microbial community structure characterization (16S rRNA), chemical extractions, and synchrotron-based X-ray fluorescence (XRF), diffraction (XRD), and absorption (XANES). The use of an X-ray spot size as small as one micrometer allowed a detailed examination of the heterogeneous AMD sediments. Our results suggest that during sustained redox cycling of iron in Fe(III)NP-clay mixed-mineral systems, the clays controlled As mobility by (1) enhancing heterogeneous precipitation of Fe(III)NP under oxic conditions, which then adsorbed or incorporated As; and (2) facilitating the transfer of As from Fe(III)NP to clay during microbially mediated reduction of Fe(III)NP coatings under anoxic conditions. Designing remediation strategies that incorporate clay could become a promising low-cost strategy for As remediation in mining-impacted areas.

Predicting Kinetics of As(V) Adsorption and Desorption on Mixed Minerals of Ferrihydrite and δ‐MnO2

Core Ideas Adsorption and desorption kinetics of As(V) on Fe and Mn oxide mixture was studied. A predictive kinetics model based on component additivity approach was developed. The kinetics model predicted the kinetic data of As(V) well for the mixed oxides. Ferrihydrite and δ‐MnO2 controlled As(V) reaction kinetics differently. Arsenate [As(V)] soil contamination is a great concern worldwide because of its high toxicity, carcinogenicity, and mobility. The adsorption of As(V) on soil minerals such as ferrihydrite and δ‐MnO2 controls the transport and bioavailability of As(V) in the soil environment. A large number of studies have investigated the equilibrium and mechanisms of As(V) adsorption onto ferrihydrite and δ‐MnO2 individually. However, both ferrihydrite and δ‐MnO2, commonly coexisting within soils has been overlooked and little information is available for the kinetics of As(V) adsorption and desorption in this mixed mineral system. Therefore, in this work, kinetics of As(V) adsorption and desorption onto ferrihydrite and δ‐MnO2 mixed minerals is studied using the stirred‐flow method. A kinetics model for the mixed mineral system was developed using the component additivity approach, which incorporated the nonlinear binding of As(V) to both ferrihydrite and δ‐MnO2 simultaneously. The kinetics model successfully predicted the kinetics of As(V) adsorption and desorption in the mixed mineral system under varying solution chemistry conditions and properly accounted for the heterogeneity of the binding sites of both ferrihydrite and δ‐MnO2. For As(V) adsorption kinetics, the ferrihydrite bidentate non‐protonated sites (Fh‐bi‐np) played a dominant role, followed by the δ‐MnO2 binding sites and the ferrihydrite bidentate protonated sites (Fh‐bi‐p). After the 4‐h desorption, As(V) was mainly retained on ferrihydrite binding sites. This study helps to quantitatively elucidate the kinetic behavior and mechanisms of As(V) in the Fe oxide and Mn oxide systems, thus enhancing our understanding of the fate and transport of As in soil environments.

Kinetic studies of amyl xanthate adsorption and bubble attachment to Cu-activated sphalerite and pyrite surfaces

Kinetic studies of bubble attachment and amyl xanthate (AX) adsorption to CuSO4 (Cu) activated sphalerite and pyrite surfaces were investigated by a novel in-situ approach with high-speed video microscopy (HSVM) and cryogenic X-ray photoelectron spectroscopic (Cryo-XPS). The drainage rate (DR) of thin films between the bubble and the surfaces was linked with the rate of AX adsorption onto the mineral surfaces. The single minerals studies revealed that the drainage (and adsorption) rate on polished pyrite was higher than on polished sphalerite after treatment with AX. However, the AX adsorption rate exhibited a higher value on the Cu-activated sphalerite than on the Cu-activated pyrite, indicating different surface components formed on the minerals surfaces and their different abilities to uptake Cu ions. Modeling AX adsorption rate on the unactivated and activated minerals by a pseudo-first order rate equation revealed the dependence of the drainage (and adsorption) rate on the initial AX concentration and the available active sites on the minerals surfaces. For the two minerals system, AX treatment results showed a significant drop in the adsorption rate of AX on the activated sphalerite with increasing the sphalerite to pyrite surface area ratio from 1:1 to 1:6. It confirmed the dependence of the AX adsorption rate on the available active sites on the minerals. Cryo-XPS confirmed that Cu-xanthate complex on the Cu-activated sphalerite and dixanthogen on the Cu-activated pyrite were the dominant surface components after treating with AX. It showed a selectivity of AX on the activated sphalerite with chemisorbed Cu-xanthate formation. However, consumption of AX with Cu-activated pyrite in the form of dixanthogen as well as Cu- or Fe-xanthate complexes were inevitable, especially when the available pyrite surface area was high in the mixed mineral system.

Characterization and Geochemical Modeling of Cu and Zn Sorption Using Mineral Systems Injected with Iron Sulfide: Case Study of Mine Waste Water, Wales, United Kingdom

Sorption of Cu and Zn was investigated using single and mixed mineral systems under sulfidic-anoxic condition to treat wastewater obtained from disused mine pits at Parys Mountain in, United Kingdom. Water courses are the recipients of these contaminants. In these water courses fishing activities exist. Attempt was made to reduce the Cu and Zn levels intake in the watercourses using mineral systems of clays and goethite. These were tested with the mine waste water for characterization of copper and zinc removal at variable pH, solid concentration and contact time. In addition, levels of saturation of hydroxyl complexes were modeled. Batch reactions conducted at ambient temperature (23±2°C) reveal all systems of assorted minerals sorbed more Cu than Zn. In addition, Cu sorbed on iron sulfide exhibited increase in sorption with increasing pH. There was cross cutting effect of Cu and Zn sorbed on iron sulfide at pH 6 and Cu sorbed on goethite at about pH 7, These indicate similar metal removal characteristics. Differences in removal of copper and zinc ions may be assigned to outer sphere complexation and specific adsorption of copper and zinc ions. Non-promotive Cp effect (i.e. decrease in metal removal with increase in concentration of particle) was observed in all minerals. This effect may be assigned to increase in aggregation of the mineral particle size. Ageing characterization progresses as residence time was increased. This may be assigned thiol (=S-H) and hydroxyl (=Me-OH) groups and sites of reactions. There is no link to stable hydroxylation of copper and zinc species that could significantly contribute to the removal of these metals.

Arsenite Removal from Aqueous Solution using Mixed Mineral Systems Injected with Iron Sulfide under Sulfidic- Anoxic conditions 1: Reactivity and Removal Kinetics

The reactivity and removal kinetics of arsenite treated with single and mixed mineral systems of kaolinite, montmorillonite and goethite injected with iron sulfide under sulfidic- anoxic conditions has been investigated. Using empirical models derived from Freundlich isotherm model, injection of sulfidic-anoxic solution of iron sulfide onto the mixed mineral systems enhanced proton coefficient of all single minerals. Differences in sorption kinetics between the single and mixed mineral phases may be attributed to different types of reactive sites on the single and mixed mineral systems Except for iron sulfide, kinetic studies demonstrated three phase reactions attributed to outer sphere complexation, inner sphere complexation and intra-particle diffusion. Injection of sulfidic-anoxic solution of iron sulfide could not change the three phase reaction trend.

Arsenite Removal from Aqueous Solution using Mixed Mineral Systems Injected with Iron Sulfide under Sulfidic-Anoxic condition II. The role of solution composition and ageing

The role of solution composition and ageing of arsenite treated with single and mixed mineral systems of kaolinite, montmorillonite and goethite injected with iron sulfide under sulfidic- anoxic conditions have been investigate. Variability in arsenite sorption exists over the range of pH investigated. This variability in sorption may be attributed to the presence of thiol (≡S-H) functional group contained in solution under sulfidic-anoxic condition. Arsenite sorption exhibits a non-promotive Cp effect (i.e. sorption decreases as Cp increases for all mineral systems. the nature of ionic species formed in solution is affected by changes in the mineral/ solution ratio. All mineral systems but kaolinite-goethite exhibits a step up arsenite sorption up to 288 hours residence time and flattens g out over the remaining residence time of the reactions.

Mercury Removal from Aqueous Solution by Mixed Mineral Systems I. Reactivity and Removal Kinetics

This study investigates the reactivity and removal kinetics of arsenite on mixed mineral systems from aqueous solution related to contaminated waters. The sorbents used were kaolinite, montmorillonite, goethite, and their mixtures. The effects of, proton coefficient, and sorption kinetics were studied at room temperature (23 ± 2 ◦C). Reactivity studies demonstrate enhancement of proton coefficient and the acidity of reactive sites by mixed mineral systems except for kaolinite-montmorillonite, thus increasing mercury removal by proton exchange. Kinetic studies demonstrate two- phase reactions attributed to outer sphere complexation and inner sphere complexation. In the first-phase reaction, mineral mixing based on our empirical model decrease the mass transfer rates for kaolinite-montmorillonite and montmorillonite-goethite, not affecting kaolinite-goethite. For the second-phase reaction, mineral mixing did not change the mass transfer rates for the mixed mineral systems except for montmorillonite-goethite. The behaviors of the mixed mineral systems in mercury sorption suggest that different reactive sites were involved at the onset of sorption, with reactions and sorption ending with inner-sphere complexation. Differences between actual and theoretical % sorption progressed from negative to positive for all mixed minerals as contact time was increased. This means that increase in contact time during Hg-sorbent interaction could help increase mercury removal based on mineral mixing.

Mercury Removal from Aqueous Solution by Mixed Mineral Systems II. The Role of Solution Composition and Ageing

This study investigates Hg(II) removal onto binary mixed mineral sorbents from simulated mercury contaminated water, relevant to surface and groundwater impacted environment. However, sorption pattern appeared to be controlled by outer sphere complexation, inner sphere complexation and intra-particle diffusion for Hg (II) sorbed on goethite and mixed mineral system of goethite-montmorillonite with respect to pH. Decrease in Hg (II) sorption as Cp was increased may be attributed to increase in particle size and aggregation of the mineral suspensions. The Cp effect is also related to effective surface area, pressure, and force at the mineral/water interface The complex behavior of mineral systems over the range of residence time investigated may be attributed to increased hydroxylation of the mineral surface resulting in the formation of new reactive sites.

Leveraging strategies to increase gold cyanidation in the presence of sulfide minerals — Packed-bed electrochemical reactor approach

Several leveraging strategies were explored to improve gold leaching during cyanidation in the presence of pyrite, chalcopyrite, sphalerite and chalcocite. Galena, used a source of lead, was found to largely neutralize the negative effect of sulfide minerals dissolution on gold leaching, especially in the cases of pyrite, chalcopyrite and sphalerite. Pyrite–galena galvanic interactions improved gold leaching while for chalcopyrite, sphalerite and chalcocite active galvanic interactions with galena were found to be detrimental to gold leaching. Pre-oxidation of metal sulfides prior to cyanidation significantly increased gold leaching rate when gold–pyrite galvanic interactions were disabled, while their enablement identified pyrite pre-oxidation as counter-productive. Pre-oxidation of mixed mineral systems of pyrite–chalcopyrite and pyrite–sphalerite showed that enabling galvanic interactions between the associated minerals during pre-oxidation controlled gold leaching in the subsequent cyanidation process. For pyrite, lead nitrate addition during pre-oxidation resulted in a significant increase of gold leaching, whereas its addition to subsequent cyanidation canceled the positive effects of pre-oxidation on gold dissolution.

Aqueous interfacial chemistry of kaolinite for the removal of Cu(II) in the presence of birnessite: Kinetic and spectroscopic studies

In this study, the aqueous interfacial chemistry of kaolinite was investigated during the removal of Cu(II) in birnessite suspensions. Adsorption kinetic experiments and X-ray absorption spectroscopy (XAS) were coupled to better understand the complexity of Cu(II) reactivity and uptake mechanisms in the mixed mineral system. Throughout all experiments (ionic strength = 0.01 M NaNO 3, [Cu] total = 100 μM), the two minerals' surface areas (6 and 8.6 m 2/500 mL) were maintained by altering the mass ratio of kaolinite (0–0.34 g) and birnessite (0–0.48 g). Copper sorption generally increased with increasing pH from 4 to 6 in all samples. The “birnessite only” system showed the fastest kinetics while the Cu uptake in the “kaolinite only” system was slowest under the respective reaction conditions. The first order kinetic model indicated that the apparent rate constants ( ka′) of kaolinite are 7.92E−6 s − 1 at pH 4 and 6.14E−6 s − 1 at pH 6. However, the addition of birnessite to kaolinite enhanced the Cu uptake when the respective systems (i.e., same surface area) were compared. For both surface areas, ka′ nearly doubled at pH 4 and was seventeen times greater at pH 6. XAS analyses show that the sorption of Jahn–Teller distorted Cu(II) octahedral molecules retain not only on birnessite surface but also on kaolinite surfaces. In the “kaolinite only” system, Cu(II) readily forms outer-sphere Cu dimer surface species (R Cu–Cu: 2.89–2.96 ± 0.02 Å, CN Cu–Cu 0.7 ± 0.2) at pH ~ 6 while the “birnessite only” system contains corner-sharing inner-sphere surface species (R Cu–Mn: ~ 3.45 Å, CN Cu–Cu 2.9 ± 0.2) in layered MnO 6 structures at pH ~ 4. Interestingly, these two surface species co-existed when the two minerals were mixed. Regardless of changes in total surface area and pH, the fraction of tridentate species in birnessite was always greater than the fraction of dimers in kaolinite. However, the fraction of tridentate corner-sharing surface species decreased with increasing pH from 4 to 6, while the dimers in kaolinite became important surface species at higher pH. The results reported in this study provide new information about the ability of kaolinite to retain metals in a mixed mineral environment. Metal surface speciation on phyllosilicate surfaces in heterogeneous media might be as important as in metal (oxyhydr)oxides in predicting metal transport processes in soils and sediments.

The effect of acrylamide-co-vinylpyrrolidinone copolymer on the depression of talc in mixed nickel mineral flotation

Copolymers of acrylamide and vinylpyrrolidinone with varying compositions have been synthesised and employed to depress talc in a model flotation system with process plant operation conditions. Adsorption isotherms indicated that the hydrophilic acrylamide homopolymer has a very low affinity for the hydrophobic talc surface, whereas vinylpyrrolidinone homopolymer strongly adsorbs onto the talc surface. Micro-flotation experiments revealed that the copolymer system can induce stronger talc depression than the homopolymer variants, with the most effective copolymer depressant having 25–30% vinylpyrrolidinone incorporation. The copolymer system is observed to have inherited the strong talc affinity of vinylpyrrolidinone polymer and the strong hydrophilic property from polyacrylamide. This combined effect facilitates the desired strong talc depression in single mineral flotation. However, this copolymer system has similar adsorption affinity on both the talc and pentlandite, hence depressing both talc and pentlandite in the mixed mineral flotation system. This research shows that a sufficient hydrophobic balance on the polymer is necessary for the adsorption and subsequent depression for talc. However, polymer with high adsorption selectivity is required to be a successful synthetic talc depressant for mixed mineral system.

Inferring the distribution of iron oxidation species on mineral surfaces during grinding of base metal sulphides

Electrochemistry plays an important role in the flotation of base metal sulphide minerals. During grinding a galvanic interaction occurs between minerals and grinding media and controls the iron contamination on mineral surfaces, which depresses mineral flotation significantly. In this study, the galvanic interaction was quantified by measuring the iron oxidation species originated from grinding media by ethylene diamine-tetra acid (EDTA) extraction in single mineral and mixed mineral systems. It was found that the extent of galvanic interaction between minerals and grinding media was intimately associated with the electrochemical reactivity of minerals. The nobler the mineral, the stronger the galvanic interaction with grinding media, and the higher the amount of iron oxidation species from grinding media. For both galena and chalcopyrite a linear relationship was observed between the amount of iron oxidation species and flotation recovery in single mineral systems. This relationship was able to predict the iron oxidation species on galena and chalcopyrite surfaces when they were mixed with pyrite separately. The distribution of iron oxidation species onto the two minerals in the mixture changed with the ratio of the mineral surface areas and was correlated with mineral flotation recovery. The major cathodic mineral in the mixture was dictated by the combination of mineral surface area and reactivity and drew iron oxidation species from the grinding media.

Iron phase transformations resulting from the respiration of Shewanella putrefaciens on a mixed mineral phase

The initial Fe(III) minerals and the secondary mineralization products of Shewanella putrefaciens CN32 grown in the presence of dissolved phosphate and a commercial Fe(III) oxide, nominally nanoparticulate lepidocrocite, were determined using XRD and XAFS. The starting material was transformed by the bacteria from a reddish brown, rust colour mineral to a dark green phase over 90 days. Acid extraction of the bioreduced solids with 0.75 M HCl recovered 83% of the total iron as Fe(II), leaving a solid, acid-resistant phase. The latter was identified as nanoparticulate hematite by EXAFS. Subsequently, the starting Fe(III) phase was determined to be a mixture of 60% lepidocrocite, 26% ferrihydrite, and 14% hematite, using linear combination EXAFS analysis. For the acid-extractable phase, XANES and EXAFS indicated a predominantly Fe(II) valence state and a spectrum consistent with a mixture of brucite-type minerals(e.g., green rust or ferrous hydroxide) and siderite. The observed transformations suggest that in this mixed-mineral system, lepidocrocite and ferrihydrite are readily reducible to green rust and siderite, whereas hematite is less amenable to bacterial reduction. This study also demonstrates the utility of XAFS spectroscopy in the quantitative characterization of dissimilatory metal transformations, particularly in complex systems such as nanoparticulate minerals in hydrated mineral-bacteria assemblages.