Biological,chemical and electromagnetic treatment of three types of feldspar raw materials

Bioleaching processes in combination with electromagnetic separation can substantially improve the quality of feldspar raw materials. Bacterial destruction of silicates is necessary for releasing intergranular spaces of silicate grains. These are often impregnated with iron minerals which can be subsequently removed by electromagnetic separation. Bioleaching is also effective for the removal of surface layers of fine iron minerals. After the bioleaching, a new mineral, weddellite (calcium oxalate dihydrate), was identified in the fine grain fraction in samples. Weddellite is formed upon the destruction of Ca-plagioclase and its formation indicates that oxalic acid was one of the metabolites involved in the bioleaching process. Bioleaching resulted in a 35–41% decrease in Fe content of raw material from Strážov and the subsequent electromagnetic separation decreased the Fe content up to 69–74% of Fe. The second raw material was granite from Poproč and bioleaching removed 60% of Fe in spite of a high content of Fe₂O₃. The removal was increased up to 75% of Fe in combination with electromagnetic separation. Iron removal by biological leaching and electromagnetic separation ensures high quality and white color of raw material.     

Physical, Hydrologic, and Aqueous Chemical Characterization of the Ore Knob Tailings Pile (Ashe County, North Carolina, USA)

Oxidation of pyrrhotite and related sulfide minerals in the vadose zone of the Ore Knob Mine tailings pile generates dissolved Fe⁺², SO₄⁻², and acidity, which are rapidly transported through the pile by infiltrating surface water. Significant spatial variations in the physical and hydraulic characteristics of the tailings cause large variations in air-filled porosity and effective oxygen diffusion into the pile. Tailings in the upstream areas are more fine-grained, with less air-filled porosity and oxygen diffusivity. The original tailings in the downstream areas are more coarse-grained, with less water retention and greater oxygen diffusivity. However, weathering processes have increased the fine-grained fraction in the oxidized zone and hardpan layer, increasing water retention and lowering oxygen diffusivity. The thickness of the downstream oxidized zone combined with increased water retention due to weathering may have significantly reduced acid generation in these areas.     

Moderately thermophilic iron oxidising bacteria isolated from a pyritic coal deposit showing spontaneous combustion

Seven Fe²⁺-oxidising acidophilic bacterial strains were isolated at 50 °C from a pyritic coal from Collie, Australia and from a Fe²⁺-oxidising fluidised bed reactor running at 60 °C which was originally inoculated with the Collie coal. The 16S rRNA gene of five of the strains was partially sequenced. The strains isolated from the reactor were closely related (99% similarity in gene sequence) to Sulfobacillus thermosulfidooxidans and the strains isolated directly from the coal had a 97% gene sequence similarity to “Sulfobacillus yellowstonensis”. The sequenced strains each had an optimum temperature for growth using an organic carbon source of approximately 50 °C and a maximum temperature for growth of approximately 60 °C. All strains required a mixotrophic medium for growth on Fe²⁺ or on an organic carbon source. Of the five strains tested, all grew on pyrite whereas only three of the strains grew on chalcopyrite. The “S. yellowstonensis”-like strains grew better on S⁰ than the other strains. The S. thermosulfidooxidans -like strains were more tolerant then the other strains to Cu²⁺ and Cl⁻. The “S. yellowstonensis”-like strains contained ω-cycloheptyl-18:0 and ω-cycloheptyl-18:0 2OH phospholipid fatty acids, whereas the S. thermosulfidooxidans-like strains contained no ω-cyclofatty acids in the phospholipid fraction. These strains have potential to be used in the bioleaching of heaps, especially the S. thermosulfidooxidans-like strains. Work is continuing to further characterise their bioleaching abilities and their usefulness in a commercial heap leach environment.     

The effect of potential heap construction methods on column bioleaching of copper flotation tailings containing high levels of fines by mixed cultures

It is known that excess fines may reduce heap permeability and block channelings of leachate flow in heap bioleaching operation, and further cause low metal recovery. The purpose of this investigation was to compare the effects of three potential heap construction methods including layered heap construction method (Method A), agglomerate heap construction method (Method B) and pelletized sintering heap construction method (Method C) of copper flotation tailings on column bioleaching behaviors. In the three heap construction methods, the tailings copper extractions achieved 54.61%, 60.09% and 43.93%, respectively, in Method A, B and C on day 83. Copper extraction of Method B reached maximum. In addition, compositions and structures of microbial communities were examined using Illumina Miseq sequencing technology based on 16S rRNA amplification. Acidithiobacillus, Leptospirillum and Ferroplasma were main microorganisms in three heap construction methods. Detrended correspondence analysis showed that Method C had little effect on microbial communities. These studies revealed the influence of different heap construction methods on leaching behaviors and microbial dynamics, which will facilitate the bioleaching of fine-grained ores.     

Stability of Coatings on Sulfide Minerals in Acidic and Low-Temperature Environments

The effectiveness of silicate- and phosphate-based surface coating agents (Na₂SiO₃, CaSiO₃, and KH₂PO₄) in inhibiting the oxidation of sulfide minerals in acidic and low temperature conditions was studied. Rock samples were coated using two oxidation methods: H₂O₂ was mixed with the coating agents in one, whereas in the second, H₂O₂ was applied to the rock surface prior to the coating agent. The second approach was ineffective, but with Method 1, the pH (5) was above the pH (3.6) of the uncoated control sample. Oxidation, calculated after 14 weeks, had been suppressed by up to 96 and 65%, as indicated by the release of Fe²⁺ and SO₄ ^2?, respectively. All three coating agents (at concentrations of 0.1 and 0.3 M) suppressed the release of Fe²⁺ (<3 mg L^??1). Na₂SiO₃ inhibited Fe²⁺ and SO₄ ^2? release by 94 and 65%, respectively. Surface protection (or oxidation inhibition) efficiencies of KH₂PO₄ (in terms of Fe²⁺ release) were 67, 94, and 96% with 0.05, 0.1, and 0.3 M, respectively. The Na₂SiO₃ and CaSiO₃ coatings, irrespective of their concentrations, reduced iron oxidation by 94 and 84%, respectively. Fourier transform infrared spectroscopy analysis of the Na₂SiO₃ treated samples showed the presence of iron silicate coatings. Based on this work, coating of rock samples with silicate or phosphate can reduce the oxidation rate of sulfide minerals in acidic and low temperature conditions.     

The use of collectors mixture in the reverse cationic flotation of magnetite ore: The role of Fe-bearing silicates

The paper describes effective reagent combinations for removal of silicates by reverse cationic flotation from magnetic concentrate in magnetite ores processing. This work is based on a hypothesis that a further development in reverse cationic flotation of iron ores implies, a more detailed consideration of the nature of the Fe-bearing gangue minerals. Thus, the choice of reagent regime has been determined by the similar physicochemical properties of iron oxides and silicates such as amphiboles due to inclusion of iron into their crystal lattice. Zeta-potential studies of Fe-oxides, quartz and Fe-bearing amphibole samples have shown that amines of different molecular structure are equally well adsorbed both on the surface of Fe-oxides and on the surface of silicates within рН range of 4–10. Flotation studies of quartz and Fe-bearing amphibole samples have revealed that the use of starch as a depressant of Fe-oxides has a hydrophilic effect on the surface of Fe-bearing silicates and significantly decreases their flotation by ether amines. Flotation of these minerals is not possible by primary monoamines in the presence of starch due to the adsorption layer formation.The experimentally selected mixtures of ether amines with primary monoamines or with alcohols provide formation of a hydrophobic adsorption layer on the surface of amphiboles and magnetite–silicate aggregates, even in the presence of starch in the system. A total hydrophobic effect is sufficient for an effective flotation of the entire silicate complex and producing of magnetite concentrates with SiO₂ content <1.0% and Fe content up to 70.3% from magnetic concentrate with SiO₂ content ～3%.     

滇池地区磷块岩中倍半氧化物的赋存特征

磷矿中的倍半氧化物会导致后续湿法磷酸过滤困难,降低设备生产能力。为降低磷矿中的倍半氧化物含量,利用荧光光谱仪(XRF)、偏光显微镜、扫描电镜(SEM)、矿物参数自动定量分析系统(MLA)等分析手段,查明了磷矿矿物组成特征、倍半氧化物的赋存特征、磨矿分异特征、赋存矿物单体解离特征等。结果表明：Fe₂O₃主要赋存在褐铁矿中,主要呈集合体形式集中分布、星点状分散分布、侵染状分布、脉状分布;Al₂O₃主要赋存在白云母、水云母中,呈碎片状,为层状硅酸盐矿物;磨矿后,Fe₂O₃、Al₂O₃均有向细粒级富集的分异特征,且单体解离情况较好,为选矿脱除提供了基础条件。褐铁矿和层状硅酸盐矿物表面具亲水性,磷矿反浮选工艺难以脱除,建议采用正浮选工艺脱除。     

Mathematical modeling of thermophilic bioleaching of chalcopyrite

Previous studies have shown that the different preferences of thermophiles to oxidize S⁰ or Fe²⁺ is reflected by different [Fe³⁺]/[Fe²⁺] levels in solution. In those studies it was concluded that [Fe³⁺]/[Fe²⁺] governs the thermophilic bioleaching of chalcopyrite rather than temperature or pH. Therefore, the proposed model is mainly based on the finding that thermophilic bioleaching of chalcopyrite is governed by [Fe³⁺]/[Fe²⁺] that result from the activity of thermophiles. A direct interaction between chalcopyrite and thermophiles is neglected because it has been reported that this is not a general behavior for all thermophiles. The case of constant temperature, initial pH 1.5–2.5, and chalcopyrite concentrates is considered. The main assumption is that chalcopyrite can be anodically oxidized or cathodically reduced depending on [Fe³⁺]/[Fe²⁺] in solution. When chalcopyrite is oxidized at high [Fe³⁺]/[Fe²⁺] levels, Cu²⁺ is formed directly at low rates: CuFeS₂ + 4Fe³⁺ → Cu²⁺ + 5Fe²⁺ + S⁰. Whereas, when chalcopyrite is reduced at low [Fe³⁺]/[Fe²⁺] levels, an intermediate (Cu₂S) is formed at higher rates: CuFeS₂ + Fe²⁺ + Cu²⁺ + 2H⁺ → Cu₂S + 2Fe³⁺ + H₂S. Because the oxidation of Cu₂S is relatively fast: Cu₂S + 4Fe³⁺ → 2Cu²⁺ + S⁰ + 4Fe²⁺, its accumulation is assumed to be negligible. To take into account the possibility of chalcopyrite being oxidized or reduced depending on [Fe³⁺]/[Fe²⁺] in solution, the principle of mixed potentials is used. The model is validated by comparing the calculated and measured values of copper extraction, total iron in solution, and pH.     

Enrichment and characterisation of thermophilic acidophiles for the bioleaching of mineral sulphides

Thermophilic acidophilic Archaea were enriched from samples collected from geothermally active sites in Papua New Guinea. Pure cultures (JP2 and JP3) were obtained from mixed culture enrichments and were characterised and tested for their bioleaching ability. All cultures possessed Sulfolobus-like morphology, and the presence of distinctive cyclized tetraether lipids. The two pure cultures were identified by their 16S rRNA gene sequences as being most closely related to Sulfolobus solfataricus. Each isolate was able to oxidise both Fe²⁺ and sulphur, and grow on both pyrite and chalcopyrite under autotrophic conditions. Leaching experiments showed that the isolates were capable of rapidly leaching a chalcopyrite concentrate (up to 91% Cu release in 108 h). Optimal temperatures for growth and chalcopyrite leaching were determined for each strain. Chalcopyrite dissolution rates for JP2 at different temperatures were determined using a previously described kinetic model. An Arrhenius plot to investigate the relationship between dissolution rate and temperature, showed that for JP2, an increase in temperature from 70 to 83 °C resulted in a 6.6-fold rate increase. Studies with both mixed and pure cultures showed that these cultures were capable of rapidly leaching a chalcopyrite concentrate at very high temperatures (up to 90 °C), but also were capable of bioleaching at 50 °C. These thermophilic acidophiles possess the ability to bioleach over a wide range of temperatures. They are potentially well suited to industrial leaching applications where considerable temperature fluctuations limit the growth of other non-thermophilic bioleaching microorganisms.     

Electrochemical dissolution process of chalcopyrite in the presence of mesophilic microorganisms

The dissolution process of chalcopyrite in the presence of mesophilic microorganisms was investigated by electrochemical measurements. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis, accompanied by leaching experiments. Results proved that the presence of Acidithiobacillus ferrooxidans enhanced the initial reduction of chalcopyrite to intermediate species (Cu₂S), thus promoting the dissolution of chalcopyrite in the initial stage of bioleaching. However, chalcopyrite tended to be directly oxidized to polysulfide (S_n²⁻) and CuS in the later stage of bioleaching when redox potential was higher than 0.5 V (vs. Ag/AgCl), the formed polysulfide and jarosite can be responsible for the passivation of chalcopyrite in the later stage of bioleaching by A. ferrooxidans. On the contrary, Chalcopyrite was mainly directly oxidized to polysulfide and CuS in the presence of sterile 9K medium or Acidithiobacillus thiooxidans, and the initial reduction reaction was still the rate-limiting step, thus resulting in low copper extraction rate.     

Bioleaching of phosphorus from rock phosphate containing pyrites by Acidithiobacillus ferrooxidans

Pyrites can be oxidized by the bacterium Acidithiobacillus ferrooxidans (At. f.), producing H₂SO₄ and FeSO₄. Rock phosphate is dissolved by H₂SO₄, forming soluble phosphorus. Fe²⁺ in FeSO₄ is oxidized to Fe³⁺, producing energy to sustain the growth of At. f. The effects of four factors (rock phosphate dosage, pyrite dosage, culture temperature and time) on the fraction of phosphorous leached were investigated. It is suggested that the optimal conditions are as follows: rock phosphate dosage 1 g/L, pyrite dosage 30 g/L, culture temperature 30 °C, culture time 84 h. The fraction of phosphorous leached is up to 11.8%.     

Bioleaching of chalcopyrite by Acidianus manzaensis under different constant pH

The bioleaching of pure chalcopyrite by thermophilic Archaea strain Acidianus manzaensis YN-25 under different constant pH was first comparatively investigated. Then the relevant sulfur speciation was analyzed by synchrotron radiation based X-ray diffraction (SR-XRD) and S K-edge X-ray absorption near edge structure (XANES) spectroscopy. The acidity of the leaching solution was monitored at 3-h intervals to make it steady at pH 1.25, 1.50, 1.75, 2.00, 2.25 and 2.50, respectively. Leaching results showed that the copper ion extraction increased during chemical leaching but decreased during bioleaching when pH value decreased from 2.50 to 1.25. SR-XRD analysis showed that, during bioleaching, new elemental sulfur (S⁰) phase was detected at all tested pH cases; new jarosite phase was detected at cases of pH 1.50 to 2.50; and jarosite gradually became a major phase when pH value increased. XANES analysis further showed that covellite was detected during bioleaching at cases of pH 1.25 to 2.00 at higher redox potential (ORP) value, while chalcocite and bornite were detected at cases of pH 2.25 and 2.50 at lower ORP value. These results suggested that the formation of S⁰ was mainly accounting for hindering the dissolution of chalcopyrite while the formation of bornite could accelerate the dissolution of chalcopyrite by A. manzaensis.     

Solid state reduction of a natural ilmenite

An ilmenite concentrate was reduced with graphite under argon gas between 1250 °C and 1350 °C by using a thermogravimetric analysis (TGA) system. Specimens were reacted for various periods of time during which the mass loss values were recorded. Samples representing different reduction stages were examined by optical microscopy, image analyzer, X-ray diffraction and SEM (EDAX) techniques. Reduction of Fe³⁺ to Fe²⁺, Fe²⁺ to Fe and Ti⁴⁺ to Ti³⁺ took place within 50% reduction during which a secondary oxide phase was formed and replaced the natural ilmenite. Reduction of Ti³⁺ to Ti²⁺ took place after 50% reduction which altered the composition of the secondary oxide phase by decreasing its oxygen content. Reduction of Ti²⁺ took place while the oxygen deficient TiO_1−x phase formed. Formation of any titanium carbide or oxycarbide phases depended on the completion of the reduction which was not possible at the specified temperatures.     

Bioleaching of anilite using pure and mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus caldus

Anilite oxidation was evaluated with two acidophilic thiobacilli that are important in bioleaching processes. The experiments were carried out in shake flasks in the absence and presence of energy sources such as 2 g/L powdered sulphur and 10 g/L Fe²⁺ (as ferrous sulphate) at pH 2.0, 150 rpm, 35 °C. Tests showed that copper extraction in a mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus caldus was higher than in pure cultures with added sulphur in the presence of anilite. The effect of supplemental iron clearly improved Cu leaching by the A. ferrooxidans culture and the mixed culture. The oxidation of anilite by A. caldus was negligible and this bacterium seemed to have no ability to initiate anilite solubilization. On the other hand, an important potential of A. caldus to leaching anilite was indicated. It can decrease pH of the medium and supply a suitable bioleaching environment.     

油酸钠浮选体系中蓝晶石族矿物与石英的交互影响

对蓝晶石族矿物和石英进行浮选交互影响的规律研究,运用扩展DLVO理论分析、显微镜观察和TOC法测定药剂吸附量等手段对浮选交互影响的机理进行分析。结果表明：在pH值为8、FeCl₃·6H₂O用量20 mg/L、油酸钠用量150 mg/L时,随着各粒级蓝晶石族矿物与石英颗粒间的界面力相互作用距离越小,总E-DLVO势能的负值越大,说明各粒级石英与不同粒级蓝晶石族矿物的作用力为吸引力,相互之间存在着粘附罩盖作用,又通过显微镜观察进一步验证了不同粒级蓝晶石族矿物与石英之间确实发生了粘附现象。蓝晶石族矿物与石英之间E-DLVO作用能顺序为：硅线石与石英>红柱石与石英>蓝晶石与石英。颗粒之间的粘附罩盖是造成蓝晶石族矿物与石英浮选过程中交互影响的主要原因之一,包括细粒级石英可以向粗粒级蓝晶石族矿物粘附,表现为矿泥罩盖;细粒级蓝晶石族矿物可以向粗粒级石英粘附;细粒级蓝晶石族矿物可以与细粒级石英粘附聚集。在油酸钠体系中,可以利用柠檬酸来有效削弱石英与蓝晶石族矿物之间的粘附罩盖作用。     

A novel approach for recovery of rare earths and niobium from Bayan Obo tailings

It is difficult to economically recover rare earths (RE) and niobium (Nb) from Bayan Obo tailings by the existing metallurgical processes. In this study, a novel hydrometallurgy process was employed for separating and recovering RE and Nb from Bayan Obo tailings. Firstly, by sulfating roasting at 250 °C and subsequent leaching at 60 °C, the RE and Nb present in the polymetallic minerals can be efficiently extracted into the leach solution. Secondly, after the reduction of Ti⁴⁺ and Fe³⁺ ions (to Ti³⁺ and Fe²⁺ ions) with iron powders followed by hydrolysis at pH 2.01, the Nb can be efficiently precipitated from the leach solution. The impurities present in the precipitated product can then be removed by treating with NH₃⋅H₂O–H₂C₂O₄ system at pH 4.50. Thirdly, the RE can be efficiently precipitated at pH 7.15 from the filtrate of above hydrolysis reaction mixture. Finally, the impurities present in the crude RE can be removed by oxalate co-precipitation method. The yield of RE and Nb in this novel process reaches up to 90% and 78%, respectively. Both the Nb (60.67 wt% Nb₂O₅) and RE products (>88.65 wt% RE_xO_y) have high application value.     

Comparison of the electrochemical mechanism of chalcopyrite dissolution in the absence or presence of Sulfolobus metallicus at 70 °C

The electrochemical mechanisms of chalcopyrite dissolution in the absence and presence of Sulfolobus metallicus at 70 °C were studied using cyclic voltammetry and Tafel methods. The cyclic voltammetry experiments show that S. metallicus does not change the oxidative and reductive mechanisms of chalcopyrite dissolution. The initial oxidation potentials of chalcopyrite dissolution are equal in the absence and presence of S. metallicus. However, the current density of oxidation in the presence of S. metallicus increases significantly. At about 0 V, the products on the surface of chalcopyrite are CuS, elemental S⁰, and Fe²⁺. At about 0.384 V, CuS may be oxidized, and chalcopyrite may be transferred to CuO, Fe₂O₃, and elemental S⁰. The Tafel experiments show that S. metallicus may increase the corrosion potential and corrosion current density of chalcopyrite. S. metallicus may also reduce the polarization resistance of chalcopyrite in bioleaching. These results indicate that S. metallicus may accelerate the oxidation of chalcopyrite.     

Gemini trisiloxane surfactant: Synthesis and flotation of aluminosilicate minerals

In this paper, an amino-trisiloxane Gemini cationic surfactant, butane-1,4-bis(dimethyl-(3-(3-aminopropyl trisiloxane-3-yl)-propyl)-ammonium bromide) (BBAB) was prepared, and its flotation potential was assessed on kaolinite, pyrophyllite and illite minerals. The flotation results showed that changes to the pulp pH did not significantly influence BBAB’s collecting power in floating three aluminosilicate minerals. In addition, BBAB was a stronger collector than the conventional monomeric surfactant dedecyl trimethylammonium bromide (DTAB) or dodecylamine (DDA). The results of FTIR spectra, zeta potential measurements and density functional theory (DFT) calculations indicated that the interaction of BBAB with the three aluminosilicates was mainly through electrostatic attraction. BBAB’s unique properties, such as high positive grouping Mulliken charge of –CH₂N⁺(CH₃)₂(CH₂)₄(CH₃)₂N⁺CH₂–, and “parachute” shape structure of [(CH₃)₃SiO]₂SiCH₃, resulted in superior collecting powers for the aluminosilicate minerals.     

Mineralogical characterisation of Secunda gasifier feedstock and coarse ash

The formation of clinkers in a Sasol–Lurgi fixed bed dry bottom (FBDB) gasifier is a complex process controlled by coal mineralogy and operating conditions. This paper explores the link between the coal mineralogy and the mineralogy of the corresponding clinkers/coarse ash. CCSEM and XRD results indicate that kaolinite (Al₂Si₂O₅(OH)₄) and to a lesser extent quartz (SiO₂) are the major coal minerals. Minor minerals are calcite (CaCO₃), dolomite (CaMg(CO₃)₂) and pyrite (FeS₂). Kaolinite and quartz are associated with rock fragments (“stone”) or as fine inclusions in organic rich coal particles. Calcite/dolomite and pyrite occur in coarse and fine cleats or fine inclusions in carbon-rich particles. The coarse ash and clinker samples contain the following phases: (1) Ca- and Fe-bearing aluminosilicate glass, (2) Crystallised phases in glass (anorthite and mullite), (3) Remnant rock fragments, (4) Large extraneous Fe-oxide/pyrrhotite/Fe–S–O particles (originally coarse pyrite cleat fragments), (5) Large extraneous Ca-oxide/Ca–Mg-oxide/carbonate particles (originally coarse carbonate cleat fragments) and (6) Uncombusted carbon-rich particles (char) with their associated minerals (kaolinite, quartz and carbonates). The equilibrium phases (as calculated with Factsage) for temperatures above 1220 °C correspond approximately to the phases which were identified in ash and clinker by CCSEM.     

The generation of toxic reactive oxygen species (ROS) from mechanically activated sulphide concentrates and its effect on thermophilic bioleaching

Two types of laboratory mills, planetary and vibratory, were used to activate sulphide mineral concentrates mechanically before thermophilic (bio)leaching. These samples were analysed in terms of particle size, surface area, density, SEM, XRD line profile analysis and reactivity. The product particle size distributions indicated different particle breakage mechanisms of the two mills. The surface area for pyrite milled with the planetary mill was three fold that milled in the vibratory mill for the same length of time. Planetary milled samples showed lower densities, up to 4% less for pyrite samples, compared to vibratory milled samples. Particle surface oxidation, observed by SEM, occurred post milling. Surface oxidation products were more prevalent with planetary milled sulphide samples. XRD line profile analysis showed more line broadening effects with the planetary mill. This indicated that more bulk particle-related structural defects were present in the planetary milled samples. The reactivity in acidic solution was measured in terms of the generation of toxic reactive oxygen species (ROS): hydrogen peroxide and hydroxyl radicals. The ROS generation from milled sulphides, normalised to constant surface area loading, increased with increased mechanical activation. The planetary milled samples generated greater ROS per sample surface area than vibratory milled samples, more than 4-fold for pyrite after 60 min of milling. Increased ROS generation was postulated to result from increased surface area defects, solubilisation of iron oxidation products and bulk particle-related defects.The effect of mechanical activation on performance on thermophilic leaching and bioleaching tests was investigated using milled samples at 2% (w/v) pulp density. Short mill times improved leach rates from both mills, up to 7-fold cf. unactivated feed leach rates. Poor bioleaching performance resulted following long periods of mechanical activation (20-60 min). Pyrite and chalcopyrite bioleaching performance decreased dramatically above surface area loadings of 25 and 125 m²/L respectively. Planetary milled samples were less amenable to bioleaching. For pyrite milled for 20 and 60 min and chalcopyrite milled for 40 min, no viable cells were observed following inoculation via fluorescence microscopy, suggesting culture death supported by compromised ferrous iron oxidation. The generation of ROS was postulated to cause poor bioleaching performance under these conditions.