Gangue Minerals Research Articles

Mineralogy and Conditions of Formation Genesis of Aggregates of Natural and Sulfide Minerals of the Poldnevskoe Demantoid Deposit (Middle Urals)

Polymineral aggregates of rounded shapes (“nodules”) composed of native and sulfide minerals of Cu, Ni, Fe, Ag, and other elements from vein magnetite–calcite–chrysotile rocks with jewelry demantoid in the Korkodinskoe hypermafic massif are described. A common feature of the six identified types of native sulfide nodules, composed of native copper, heazlewoodite, pentlandite, cuprite, and other native sulfide minerals, is their spheroidal shape, which makes them similar to individual grains of other gangue minerals (calcite, magnetite, etc.). In heazlewoodite–pentlandite nodules, specific symplectites of mercuric silver and nickel copper in heazlewoodite, as well as awaruite in Co–pentlandite, were found. The matching set of ore minerals in the host serpentinite vein mass (native copper, mercuric silver, heazlewoodite, pentlandite, awaruite) and nodules from the vein material indicates their genetic connection and the conjugation of demantoid mineralization with the evolving processes of serpentinization. It was established that the nodules formed at temperatures below 380°C under reducing conditions at very low sulfur fugacity values (10–17–10–27 bar) and oxygen (10–30 bar at 200°C to 10–21 bar at 350°C). For heazlewoodite–pentlandite nodules, such conditions persisted throughout the entire time of their formation, while, for other nodules, the reducing conditions of early parageneses were replaced by oxidative conditions in late parageneses, which is recorded by the replacement of native copper with cuprite. It is assumed that the features of the morphology and structure of native sulfide nodules and the presence of symplectite intergrowths of ore minerals in them are associated with specific conditions created during the decompression of the crust-mantle mixture rising to the surface in the fault zone. The source of the metals was a deep, high-temperature fluid interacting with mafic and ultramafic rocks under reducing conditions at a low water-to-rock ratio.

Geology, fluid inclusions and C−O−S−Pb isotopic compositions of the Chahmileh Pb-Zn deposit, Central Iran: Implications for ore genesis

AbstractThe Chahmileh Pb–Zn deposit, located northwest of the Central Iran Zone, is a sediment-hosted Pb–Zn deposit in the ‘Yazd-Anarak Metallogenic Belt’. It is hosted in Middle Triassic carbonate rocks and is mainly controlled by NW-trending faults. The main ore minerals are galena and sphalerite with minor chalcopyrite, pyrite, and quartz, dolomite, along with minor calcite and baryte as gangue minerals. Cerussite, hemimorphite, wulfenite, mimetite, smithsonite, malachite and iron oxy-hydroxides are the main non-sulphide ore minerals. The main styles of mineralization are vein-veinlet, breccia, disseminated and replacement in association with silicification and dolomitization. Microthermometry of fluid inclusions in dolomite and quartz indicates that the ore precipitated from a warm to hot basin-derived saline fluid. Dolomite samples have δ13CVPDB and δ18OVSMOW values of −0.99 to +1.99‰ and +20.74 to +25.48‰, respectively, and are plotted in the marine carbonate rocks field. These isotopic values suggest that CO2 in the hydrothermal fluids mainly originated from marine carbonate rock. The δ34S values range from +6.3 to +8.2‰ for galena, +5.9 to +6.2‰ for sphalerite, +1.4 to +3.4‰ for chalcopyrite and +15.0 to +17.4‰ for bayite are compatible with a predominant thermochemical sulphate reduction process, and with sulphur sourced from Triassic seawater. Galena samples have a homogeneous Pb isotopic composition that is indicative of a continental crustal reservoir as the main source of lead and probably for the other ore metals. Based on geology, mineralogy, texture and fluid characteristics, the Chahmileh deposit is classified as a carbonate-hosted Mississippi Valley-type deposit.

Arsenic Removal and Iron Recovery from Arsenic-Bearing Iron Ores by Calcification-Magnetic Roasting and Magnetic Separation Process.

Extracting iron while minimizing the health and environmental risks associated with arsenic contamination necessitates the removal of arsenic from arsenic-bearing iron ores to ensure a safe and sustainable supply of this metal for industries. The beneficiation of iron minerals and arsenic-bearing minerals from arsenic-bearing iron ores with a calcification-magnetizing roasting and low-intensity magnetic separation (CMR-LMS) process is investigated in this work. The results show that the process is successful in extracting iron minerals and eliminating arsenic-containing minerals. The roasting involves two key steps: calcification and magnetizing, which change hematite and goethite into magnetite and arsenic-bearing minerals into calcium arsenates. The process's separation efficiency of the CMR-LMS is closely linked to the parameters such as roasting temperature, roasting time, coke, alkalinity, and the liberation of gangue minerals from iron minerals. Through grinding and secondary magnetic separation, the iron minerals and gangue components, as well as arsenic, in roasted sand can be further separated. The optimum procedure results in a high-grade iron concentrate with an iron assay of 65.65%, an Fe recovery rate of 80.07%, and an arsenic content of 0.085%, while achieving a 93.29% As removal rate from the original ore that has 45.32% Fe and 0.70% As.

Axial or turn-by-turn particle recovery in a spiral concentrator

ABSTRACT Spiral concentrators (“spirals”) are commonly used to separate valuable heavy minerals from light gangue minerals by gravity. This paper examines the classification of particles as they flow down a spiral concentrator and relates the results to the number of turns. The tests show the possibility of reproducing the performance of industrial spirals with a spiral operating in a closed circuit in a laboratory. Results show that knowing the mineral size distributions in the spiral feed is necessary to forecast spiral performance. Further, in the case of iron ore processing, the separation process is practically complete after four turns, with wash water affecting the process rate of recovery. This observation is readily explained by considering the mineral size distribution.

Study on the Reverse Flotation Separation of Smithsonite from Dolomite Using the Saponified 2-(4,4-Dimethylpentan-2-yl)-5,7,7-trimethyloctanoic Acid as a Collector

Dolomite, a prominent calcium-bearing gangue mineral found in carbonate-type zinc oxide ores, poses a significant challenge for effective flotation separation alongside smithsonite due to their highly similar surface properties. The present study explores the potential of 2-(4,4-dimethylpentan-2-yl)-5,7,7-trimethyloctanoic acid (2-DMPT) as a collector for the reverse flotation of smithsonite from dolomite. Micro-flotation experiments indicated that saponified 2-DMPT exhibited superior collecting ability and selectivity for dolomite over smithsonite under highly alkaline conditions. Specifically, the flotation recovery of dolomite reached 62%, whereas only 6% of smithsonite was recovered in the flotation foam products. Zeta potential and attenuated total reflectance–Fourier transform infrared (ATR-FTIR) analysis revealed that changes in pH values had minimal influence on the collector’s adsorption onto dolomite, while significantly hindering its adsorption on the smithsonite surface. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis showed that 2-DMPT could form hydrophobic complexes with the active Ca2+ sites on the dolomite surface at pH 11.5. However, the interaction between smithsonite and carboxylic groups of 2-DMPT under the same conditions was relatively weaker, facilitating their reverse flotation separation. As a result, 2-DMPT shows promise as a potential collector for the reverse flotation process, effectively removing dolomite from smithsonite and reducing acid consumption in subsequent acid-leaching processes.

Multi-stage magmatic fluid recharge and fluid mixing developed the Gongdongchong intermediate-sulfidation type epithermal Pb-Zn deposit, North Huaiyang, China: Constraints from petrography, fluid inclusion and in situ geochemistry studies of sphalerite

The Gongdongchong (GDC) lead and zinc deposit is located in the North Huaiyang (NHY) metallogenic belt, northern part of the Dabie orogen. Its Pb-Zn orebodies are predominately in the breccia pipe hosted by the Early Paleozic Foziling Group. Three stages of mineralization could be divided according to replacement relationships and petrography, and the ore and gangue mineral assemblages at the main base metal stage were recognized as combination of Fe-poor sphalerite + galena + pyrite + chalcopyrite + tetrahedrite with quartz and calcite. Three successive generations of sphalerite were distinguished through detailed petrographic observation on crystal-scale, namely Spc (core), Spm (mantle), and Spr (rim). Fluid inclusion petrography result shows that two-phase liquid-rich fluid inclusions are the dominant type in sphalerite. Microthermometric results show the homogenization temperatures and salinities of Spc ranged from 233 °C to 268 °C and 6.6 to 10.4 wt% NaCl equiv. While fluid inclusions in the Spm display homogenization temperatures of 241 °C to 284 °C, with salinities of 8.7 to 11.3 wt% NaCl equiv. This increasing trend may imply a magmatic fluid recharging from core to mantle. However, fluid inclusions in the Spr have homogenization temperatures of 231–254 °C, with salinities of 6.3–9.1 wt% NaCl equiv. A trend of mixing with meteoric water is manifested by the decrease of temperatures with decreasing salinities from mantle to rim. It suggests the combination of the magmatic fluid recharging and mixing of meteoric water should be the key mechanism responsible for the sphalerite precipitation at the GDC deposit. Meanwhile, the GDC deposit shows a similar range of homogenization temperatures and salinities with typical intermediate-sulfidation epithermal deposits, and these homogenization temperatures also correspond well with the geological thermometer results acquired by trace element concentrations of sphalerite. In addition, the sphalerite geochemical results obtained from trace elements as Mn, Co, In and Ge illustrate that the GDC Pb-Zn deposit shares a good consistence with epithermal Pb-Zn deposit.Based on the evidences presented above, combined with the geological and geochemical features, the GDC deposit can be classified as an intermediate-sulfidation epithermal deposit. Intermediate-sulfidation epithermal deposits usually share spatial and genetic relationships with porphyry deposits. This may provide new implication for the mineral exploration of porphyry deposits at depth in the NHY metallogenic belt.

Evaluation of lactic and succinic acids as green depressants for selective flotation separation of bastnaesite from calcite

Bastnaesite is a primary natural source of light rare earth elements. Adequate flotation of bastnaesite, as a fluoro carbonate mineral, in the presence of various Ca-containing gangue minerals, such as calcite, is complex due to similar surface characteristics. This study aimed to develop an environmentally benign flotation reagent scheme using organic acids to enhance bastnaesite flotation while selectively depressing calcite. Systematic flotation, zeta potential, adsorption density, and X-ray photoelectron spectroscopy analyses were carried out using lactic acid (LA) and succinic acid (SA) as depressants and sodium oleate as a collector. The results of flotation and surface chemistry analyses demonstrated that organic acids preferentially adsorbed on the calcite surface, significantly reducing calcite recovery to below 20% and 10% when using lactic acid and succinic acid, respectively. The collective findings of this study demonstrate the tremendous potential of organic acids to be used as effective calcite depressants in bastnaesite flotation system.

Effect of Nanobubbles on the Flotation Behavior of Microfine-Grained Serpentine

At present, scholars mainly study the relationship between nanobubbles and useful minerals, often ignoring the influence of bubbles on fine gangue minerals. When selecting nickel sulfide ore, scholars often faced with mudded and irrepressible serpentine, which seriously affects the quality of the concentrate. This mudded serpentine mineral often enters foam products with bubbles. In this study, the role of nanobubbles in the flotation behavior of hydrophilic serpentine was examined. Nanobubbles were successfully prepared via ultrasonic cavitation, with sizes ranging from 50 to 250 nm. The size and number of bubbles produced at 1 min and 2 min of sonication were significantly better than those of the prolonged test group, and it was found that longer sonication time did not produce better results. The stability of the nanobubbles produced via ultrasound was studied, and it was found that the nanobubbles were stable, with no change in size and only a slight decrease in number as the resting time increased. Nanobubbles were introduced into serpentine flotation, we found that the presence of nanobubbles significantly reduced the flotation recovery of serpentine. The presence of nanobubbles reduced the froth entrainment rate of microfine-grained serpentine, which in turn reduced its flotation rate. In the depressant group trials, it was found that the nanobubbles also reduced the amount of depressant. In short, the presence of nanobubbles can prevent the floating of fine hydrophilic gangues during flotation.

Optimization of spodumene flotation with a fatty acid collector

An increasing demand for lithium-ion batteries is driving the development of new lithium mineral projects. Spodumene, a major lithium-bearing mineral found in pegmatite deposits, is often recovered by froth flotation. The primary collectors in spodumene flotation are fatty acids which are known for their poor selectivity. Fatty acid collectors tend to recover common gangue minerals in spodumene deposits due to their similar surface properties, making it difficult to produce high-grade concentrates with high lithium recovery. The ionic collector behavior is sensitive to pulp conditions like pH and concentration, but there is a weak understanding of this behavior during conditioning. There is a consensus that the conditioning stage is vital to flotation performance and should be conducted at high pulp-density (∼60% solids) to ensure proper collector adsorption. If not executed properly, rougher flotation suffers, making it challenging to achieve high final concentrate grades and recovery. This study uses a central composite experimental design and linear regression analysis to investigate and model the effects of four parameters of high-density conditioning with fatty acids on the responses of rougher concentrate grade and recovery: initial pulp pH, collector dosage, conditioning time, and power density. The models developed for both responses were determined to be statistically significant in the tested region. Initial pulp pH, collector dosage, and power density were significant terms in both models, while conditioning time was insignificant. Increased power density, ∼31 W/L, was necessary to achieve high rougher concentrate grades but increasing beyond 37 W/L was harmful to recovery. In general, higher collector dosages (>500 g/t) resulted in high recoveries, but initial pH must be adjusted accordingly to maintain concentrate grade. The most robust conditions to achieve > 90% recovery at a concentrate grade > 5.5% Li2O with this material were determined to be 31 W/L energy input and 625 g/t collector at an initial pH of 8.25. The flotation performance in this study is strongly connected to the behavior of fatty acid collectors reported in the literature and the findings provide good insight for operators and researchers aiming to improve spodumene flotation performance with fatty acids.

Rheological properties of rare earth minerals flotation pulp in the presence of anions

Water quality has been found to significantly influence the flotation operations due to the alteration of surface properties of minerals. The effect of cations on the flotation of RE minerals has been studied, however, there are still very limited information regarding the effect of anions. The present study examined the impact of specific anions such as Cl−, SO42−, and HCO3− on the flotation performance of rare earth (RE) ore. This study integrates flotation experiments, rheology measurements, entrainment experiments, zeta potential measurements and settling experiments. It is observed that an increase in the concentration of these anions lead to a decrease in the recovery of RE minerals and an increase in the recovery of FeO minerals and thus negatively affecting flotation efficiency. This adverse effect is most pronounced with Cl− and least noticeable with HCO3−. An increase in the non-selective entrainment of gangue minerals is observed when the flotation pulp has higher viscosity. The reduction in the zeta potential of fine particles in the presence of these results in a higher pulp viscosity due to increased attractive forces between particles. These findings were verified by settling experiments and calculations based on the DLVO theory.

Effect of concentration sulfuric acid on alumina extraction from napa soil

West Sumatra is one of Indonesia's provinces with abundant and diverse natural potential. Based on data from the Department of Energy and Mineral Resources, West Sumatra province has a rich potential for metal and non-metallic minerals. Some types of minerals include gold lead (Au), zinc (Zn), manganese (Mn), coal, ironstone, and others. In iron ore, metal minerals contained iron minerals and gangue minerals such as silica and alumina. Napa soil is one of the materials found in West Sumatra containing aluminosilicate with a SiO2/ Al2O3 ratio of 63.20 %/ 16.55 %. It also contains TiO2, CaO, and K2O. Extraction of alumina generally using HCl or H2SO4 solvent. In previous research, HCl has been used as a solvent in extracting alumina from napa soil. Based on the literature search, no one has used H2SO4 as a solvent in the extraction of alumina from napa soil; therefore, it is necessary to conduct research as a material for further study. Therefore, this study will be conducted on variations in the concentration of acid solvents to determine the optimum amount of alumina products in the extraction of alumina in napa soil. In this study, the optimum results obtained alumina extraction with variations in the sulfuric acid concentration at a concentration of 6.0 M, with a % yield of 26.73%. The XRF analysis of alumina extraction showed that the Al2O3 content increased by 72.89%. Characterization of Alumina by FTIR indicated the presence of Al-O, Al-OH.

Geology, Pb and S Isotope Geochemistry, and Genesis of the Na Bop-Pu Sap Lead-Zinc Deposit in the Cho Don area, Northeastern Vietnam

The Na Bop-Pu Sap Pb-Zn ore bodies represent a typical vein-type lead-zinc deposit situated in the Cho Don area and are currently being extracted for their lead and zinc resources. This deposit is characterized by its significant scale and quality and is considered one of the prominent lead-zinc deposits in the Cho Don area. Despite its significance, this deposit has not received adequate attention, resulting in limited knowledge of its geology, mineralization, and deposit genesis model. To address this knowledge gap, our study utilized several methodologies, including field surveying, ore mineral analysis under a microscope, and S and Pb isotopic geochemistry. By employing these approaches, we were able to obtain specific insights into the origin of mineralization and the deposit model. Our field survey suggests that the ore deposits are formed as Pb-Zn-bearing veins along Devonian shale, claystone, and limestone faults. Microscopic analyses of the veins reveal the presence of galena, sphalerite, chalcopyrite, pyrite, arsenopyrite, and pyrrhotite as ore minerals, and quartz, calcite, dolomite, and chalcedony as gangue minerals. Sulfur-isotope values (δ34SCDT) of galena 5.3 to 0.1‰ (average 2.8‰), sphalerite 6.8 to 2.5‰ (average 5.3‰), and pyrite 5.8 to 4.1‰ (average 4.9‰) indicate that the sulfide mineralization may be related to a deep source, possibly originating from magmatic activity in the region and contaminated by carbonate-bearing marine sedimentary rocks. Lead-isotope studies indicate a model age of 598-424 Ma for the lead reservoir, consistent with the possible presence of local source rocks containing sulfur. The lead and sulfur in the ore veins were probably contaminated by Devonian carbonate-bearing marine sedimentary rocks and leached from Neoproterozoic to Cambrian magmatic activity. The lead-zinc deposits in Na Bop-Pu Sap do not display any Mississippi valley-type (MVT) or Sedimentary exhalative (SEDEX) lead-zinc deposit characteristics, as they appear to be related to shear zone-hosted lead-zinc deposits.

Flotation Behavior and Interface Characteristics of Apatite with Co-Depression by Sulfuric Acid and Phosphoric Acid

Phosphate ore is an important strategic mineral resource. The efficient utilization of phosphate resources faces challenges such as low grade of raw ore and difficulty in discharging gangue minerals. One of the key problems to be solved urgently in the reverse flotation of phosphate ore is the effective depression of apatite. However, research on the influence mechanism of acid depressants on the surface properties and adsorption characteristics of apatite is still insufficient. In this study, the influence of different depressants (such as sulfuric acid, phosphoric acid or mixed acid of sulfur acid and phosphorus acid) on the flotation separation performance of an artificial mixture of apatite and dolomite (gangue mineral) was investigated through laboratory flotation tests. On this basis, with the addition of different depressants, the contact angle, zeta potential, XPS and TOC were used to investigate the surface wettability, surface charge, surface species and the adsorption characteristics of the collector (sodium oleate) on the apatite surface, and, accordingly, the inhibiting mechanism was discussed. The results show that, when mixed acid of sulfur acid and phosphorus acid is used as a depressant, a concentrate with a P2O5 grade of 33.53% and a recovery of 88.92% can be obtained, and the parameters are better than when using phosphoric acid with a P2O5 grade of 30.15% and a recovery of 80.12% or sulfuric acid with a P2O5 grade of 30.12% and a recovery of 80.58%. Our analysis shows that the mixed acid has the best inhibiting effect on apatite, which is mainly due to the following: (a) after adding the mixed acid, chemicals such as CaSO4, CaHPO4/Ca(H2PO4)2 are generated on the surface of apatite, resulting in a significant reduction in the contact angle and stronger surface hydrophilicity; (b) the mixed acid reduces the zeta potential of apatite, produces new species and weakens the non-selective adsorption of negatively charged oleate on the surface of apatite, thus preventing the apatite from floating.

Research Progress with Scheelite Flotation Reagents: A Review

With the depletion of easily mined and separated wolframite, scheelite has become the primary source of tungsten. Flotation is the primary technique used to enrich scheelite. However, flotation separation of scheelite from calcium-bearing gangue minerals, such as calcite and fluorite, has always been challenging due to their similar surface properties. To date, various flotation reagents and related mechanisms have been proposed for scheelite, which have attracted considerable attention. This paper reviews the scheelite flotation reagents, including collectors and regulators, and introduces recent research progress on the mechanisms for the interactions between the flotation reagents and mineral surfaces. The advantages and limitations of different flotation reagents are discussed. Inorganic or organic inhibitors in combination with fatty acids, chelate collectors, and cationic collectors are commonly used to separate scheelite from calcium-bearing gangue. Flotation differences between the scheelite and calcium-bearing minerals can be explained by variations in the electrical charges and steric hindrance at the mineral surfaces. In the future, fatty acid collectors will be still the main collectors used in scheelite flotation due to their low cost and strong collecting ability, and new collectors with high selectivity (such as metal complex collectors, new chelate collectors, new environmental collectors) will become a new research hotspot in the future due to their good selectivity.

Investigation on flotation separation of bastnaesite from calcite with a novel collector: Octylamino-bis-(isobutanohydroxamic acid)

Bastnaesite is an important mineral resource, usually associated with calcite and other minerals, flotation is one of the most widely used methods in the selection process. Collector is the key to achieve flotation separation of bastnaesite from gangue mineral. The effect of a new hydroxamic acid collector with two functional groups: Octylamino-bis-(isobutanohydroxamic acid) (OIBHA), on the flotation separation of bastnaesite from calcite was investigated. The Single mineral and artificial mixed ore flotation results revealed that OIBHA exhibited better collecting ability and selectivity compared with the conventional hydroxamic acid collector octanohydroxamic acid (OHA). Effective separation between bastnaesite and calcite can be realized. The concentrate with 68.82 % REO grade and 90.23 % REO recovery was obtained with 3 × 10−4 mol/L OIBHA. Fourier transform infrared (FTIR) analysis, zeta potential measurements and quantum chemical calculations were used to investigate the selective adsorption mechanism of OIBHA. The results of FTIR analysis and zeta potential measurements showed that OIBHA was strongly adsorbed on the surface of bastnaesite, but did not interact with calcite. Quantum chemical calculations results indicated OIBHA matched well with bastnaesite surface, thereby improved the selectivity. The results in this paper are instructive for the study of the spatial matching properties of collectors and mineral surfaces.

Molecular design of multiple ligand metal–organic framework (ML-MOF) collectors for efficient flotation separation of minerals

Metal–organic framework (MOF) collectors formed by the coordination of lead ions and benzohydroxamic acid (Pb–BHA) are favorably selective for the flotation separation of calcium-containing minerals. However, the large dosage requirement and foam instability have hindered the industrial applications of MOF collectors. To enhance the collecting ability and hydrophobicity of the Pb–BHA structure, this paper introduces new ligands to form multiple ligand–MOF (ML–MOF) collectors. Through a molecular-design approach, the study analyzes the crystal and electronic structures of the target and gangue minerals, calculates the quantum chemical properties of the organic ligands, constructs the ML–MOF collectors, and determines the interaction strengths between the ML–MOF collectors and mineral surfaces to predict the flotation performances. Finally, the flotation performance of the newly developed collector is confirmed through a series of micro-flotation tests. Among the ML–MOF collectors constructed with four candidate ligands—octylhydroxamic acid (OHA), sodium dodecyl sulfate (SDS), oleic acid, and styrene phosphonic acid—Pb–BHA–SDS and Pb–BHA–OHA excellently and selectively absorbed scheelite, wolframite, and cassiterite in flotation. In addition, they form stable froths and can be applied at low dosage. The correctness of the design results was quantified in terms of their collecting-ability index and selectivity index obtained in a flotation test. The proposed design methodology realizes ML–MOF collectors for the flotation separation of complex multi-mineral systems.

Insight on the mechanism of hexagonal pyrrhotite depression by starch during flotation

Polysaccharides such as gelatinized starch have been largely employed to depress specific minerals during froth flotation. In this study, two samples of caustic gelatinized starch (paste starches) with different molecular weights (MW) were used as depressants for hexagonal pyrrhotite. There is an increasing interest in finding more environmentally friendly strategies to depress hexagonal pyrrhotite since this mineral is one major gangue minerals in nickeferrous ore deposits, for instance. The mechanism of adsorption of paste starches on hexagonal pyrrhotite was evaluated by different techniques. Equilibrium adsorption tests suggested that the adsorption is dependent on the depressant molecular weight if it is used in high concentrations. The sequence of conditioning also showed to be relevant. Pre-adsorbed collector highly influenced the adsorption of higher MW paste starch. Langmuir and Brunauer–Emmett–Teller (BET) model fittings of adsorption data in combination with Quartz Crystal Microbalance with Dissipation (QCM-D) results demonstrated a looser packing density of the higher MW paste starch. This conformation provides more room for water molecules within this depressant’s chains. Since trapped water molecules may generate a repulsive hydration force to air bubbles near the mineral surface, pyrrhotite conditioned with the high MW paste starch showed a lower flotation recovery. Higher hydration levels of the higher MW paste starch were also proven by Atomic Force Microscopy (AFM) tests, and indirectly quantified in the contact angle measurements (Washburn method). Although the higher MW paste starch adsorbs less, this depressant still provides a higher surface wettability. This study has reinforced the importance in considering the molecular size of a polysaccharide for sulfide mineral depression.

The Influence of Kaolinite and Quartz on Stability of Coal Froths - A Rheology and Structure Study.

Kaolinite and quartz are the common gangue minerals found in raw coal; however, their effects on stability of coal froths and subsequent settling of coal flotation products have not been investigated. In this study, in the coal froths batch settling tests, the amount of froth floating on top of water was 275, 325, 355, and 405 mL for coal concentrates generated with 0, 20, 40, and 60 wt % kaolin Q38, respectively, while that was almost the same (300-306 mL) for coal froth concentrates generated with 0, 20, 40, and 60 wt % quartz added in flotation, respectively, which turned out that the kaolinite could increase the stability of coal froth, while quartz could not. To investigate the mechanism, oscillatory rheology and scanning electron microscopy (SEM) were applied. The results of the oscillatory rheology suggested that the structural strength in coal froth was strengthened with the addition of kaolinite. In addition, images of Plateau borders by SEM illustrated that the addition of kaolinite in flotation increased the size of Plateau borders and generated network structures in the Plateau borders. However, as a comparison, the addition of quartz did not cause an obvious change for the oscillatory rheology and SEM results of coal froth. Based on the results, it can be concluded that network structures were generated in the Plateau border of coal froth with the addition of kaolinite, which increased its structural strength and retarded the drainage in froth. As a result, the stability of the coal froth increased.

The importance of reaction mechanisms and coupled dissolution with reprecipitation (CDR) reactions when modelling copper leaching in heap systems

Chalcopyrite is an abundant source of copper, which can be extracted from low-grade ores in heaps. The dissolution of chalcopyrite is relatively slow partly because of the formation of secondary minerals at the chalcopyrite surface also referred to as surface ‘passivation’. Although the passivation mechanism has been extensively studied, present models do not adequately account for it. Hence, a surface-passivate model (SPM) was used in a reaction path model (RPM) to examine and illustrate how passivation limits copper recovery from chalcopyrite. In addition, the role of different gangue minerals and different chalcopyrite dissolution mechanisms were assessed by incorporating rate equations from Kimball et al. (2010) and Rimstidt et al. (1994) into the RPM, and the state of saturation was determined for various minerals to constrain limiting conditions for copper recovery. RPM with different rate laws describing proton-promoted, ferric-iron promoted, and combined ferric-iron-proton promoted chalcopyrite dissolution in the presence of gangue minerals in chloride system were used. Ferric-iron promoted chalcopyrite dissolution was the fastest reaction mechanism leading to the highest copper mobilization. However, copper mobilization was limited by the formation of iron-hydroxy sulphates (e.g., jarosite), and iron oxide (e.g., hematite) and different gangue minerals, pointing to the importance of accurate representation of primary and secondary reactions, their co-location, and their reaction kinetics. The SPM was capable to simulate surface coverage of the chalcopyrite surface by jarosite, thereby lowering the reactive surface area and consequently suppressing chalcopyrite dissolution. Conversely, the SPM failed to model the incongruent dissolution of chalcopyrite leading to a copper sulfide layer deficient in iron in the form of covellite because covellite was continuously undersaturated in trial models. Further, the presence of gangue minerals like hematite and gypsum may have a positive effect on chalcopyrite dissolution, whereas the presence of silicates (e.g., feldspar and muscovite) have a negative influence. The findings of this study are important as it provides new insights into concurrent reactions controlling the recovery of copper in heaps and how these reactions can be best modelled.

The Effects of Chloride on the High Temperature Pressure Oxidation of Chalcopyrite: Some Insights from Batch Tests—Part 2: Leach Residue Mineralogy

The complete reaction of chalcopyrite at ≥220 °C under pressure oxidation conditions (10 or 20% w/w pulp density, PO2 700 kPa) is a clean process producing a residue consisting of hematite and un-reacted gangue minerals. However, when the process water contains chloride ions, covellite intermediate formation is significant and subsequently generates elemental sulphur that can persist for up to 60 min. Increasing the temperature to 230 °C reduces this time, although the dissolution of copper and the oxidation of sulphur still follows non-parallel reaction pathways. At 245 °C, the production of elemental sulphur in the presence of moderate chloride levels, 15 g/L, is no longer significant. The effects of other chemical additions (including enhancement of aluminium content) are also examined. Particular emphasis is given to the mineralogy of the leach residues and the deportment of iron in these residues to various phases that include hematite, basic ferric sulphate and natrojarosite. The residues are found to also contain a number of other intermediate phases in addition to covellite and sulphur, such as antlerite and clinoatacamite, depending upon the leach conditions employed.