Lead adsorption on copper sulphides and the relevance to its contamination in copper concentrates

Certain complex copper sulphide ores contain trace levels of radioactive elements, most of which can be separated from the copper sulphide minerals during flotation. However, the flotation process is less effective at removing some of these radionuclides, namely Pb-210. It is hypothesised that Pb-210 is interacting with copper sulphides and this interaction is contributing to flotation rejection inefficiency. Throughout this study, regular lead is used to simulate Pb-210. Cryogenic X-ray Photoelectron Spectrometry (Cryo-XPS) has been used to confirm an interaction between lead and copper sulphide minerals in which lead forms as a lead sulphide-like compound on the surface of copper sulphide minerals. Lead interacts with copper sulphide mineral surfaces via two mechanisms: chemically adsorbing to sulphur to form lead sulphide and lead sulphite species, and precipitating on the surface as various lead oxides species. The ratio of lead-sulphur species to lead-oxygen species on the copper sulphide surfaces is increased by regrinding due to the lead-sulphur species being more strongly associated with the mineral surfaces. Lead remains on the mineral surfaces during flotation and is carried to copper concentrates during cleaner flotation

The effect of gold coupling on the surface properties of pyrite in the presence of ferric ions

The surface properties of gold-associated pyrite play a determining role in pyrite dissolution in gold extraction. However, the surface properties of pyrite have been always studied without the consideration of gold coupling. In this study, the reactivity, surface speciation and topography of pyrite after its oxidation with and without gold coupling in the presence of Fe, a strong oxidant widely used in the industry, were studied and compared using EIS (Electrochemical Impedance Spectroscopy), Cryo-XPS (X-ray Photoelectron Spectroscopy at-145 °C) and AFM (Atomic Force Microscopy), respectively. It was interesting to find that gold could catalyse Fe reduction and gold coupling significantly enhanced pyrite oxidation with more oxidised iron species such as FeO/FeO and FeOOH and oxidised sulphur species such as S /S and SO formed on the pyrite surface. Gold coupling also resulted in a much rougher and larger surface area of pyrite, appreciably increasing the electrochemical reactivity of pyrite for its successive oxidation and dissolution. These findings provide insights into the physicochemical properties of gold-associated pyrite, which can be exploited to improve the gold extraction process

Re-evaluating the sulphidisation reaction on malachite surface through electrochemical and cryo XPS studies

Sulphidisation is an electrochemical reaction involving sulphide ions to form metal sulphides on the surface of metal oxides. It has been widely applied to promote the flotation of malachite where a conductive copper sulphide layer was believed to form on the malachite surface. The formation of a copper sulphide layer can promote the interaction of sulphidised malachite with sulfhydryl and other collectors. However, due to the limitation of traditional potentiometry and surface analysis, the reaction route of sulphidisation on the malachite surface and its related change in electrical property are always controversial. This leads to the uncertainty of its application in the industry. In this study, Electrochemical Probe Approach curves (PACs) were employed to re-evaluate the sulphidisation reaction on malachite through electron-transfer rate constant simulation, and the corresponding surface speciation was characterised using Cryo X-ray photoelectron spectroscopy (Cryo-XPS). It is interesting to find that the sulphidisation on malachite can be classified into two routes. The first route is the mild sulphidisation at a low concentration of the sulphidising agent. In this route, although the modified malachite surface presents a partially positive current feedback, it is not as conductive as a typical copper sulphide and covered by a large amount of elemental sulfur and polysulphide as well as Cu(OH) Cu(I)S complex. The second route is the strong sulphidisation at a high concentration of the sulphidising agent. In this route, the sulphidised surface is covered by a Cu(I)S layer and presents a similar electrical conductivity to a copper sulphide, but the pulp potential can be too low for a sulfhydryl collector to oxidise and adsorb on sulphidised malachite. The new finding explains the limitation of current sulphidisation in malachite flotation and provides guidelines to improve its application

The surface properties of pyrite coupled with gold in the presence of oxygen

Gold often exists with pyrite and there is an urgent need to separate the low-gold-content pyrite from the high-gold-content pyrite when gold is recovered from refractory pyritic ores. This separation may be achieved by exploring the change of surface properties on pyrite upon contact with gold. For the first time, the current study investigated the galvanic interaction between gold and pyrite in the presence of oxygen as well as the oxidation products formed on pyrite surfaces with and without the galvanic coupling. It was interesting to find that gold was slightly more active than pyrite under ambient conditions, and the coupling of gold with pyrite generated a low negative galvanic current. However, under oxygen-enriched conditions, gold became much nobler than pyrite, and the coupling of gold with pyrite generated a high positive galvanic current resulting in an oxidation layer on pyrite. It is evident that oxygen can change the surface reactivity of gold and enhance the galvanic interaction between gold and pyrite. A combination of cyclic voltammetry measurements and Cryo-XPS (X-ray Photoelectron Spectroscopy) analyses was used to characterize pyrite surfaces after self-oxidation and galvanically induced oxidation. Additional oxidation products consisting of elemental sulphur, iron hydroxyl-oxide and iron sulphate, in particular the latter two, formed on pyrite surfaces when coupled with gold especially under oxygen-enriched conditions. This indicates that gold can alter pyrite surface properties once in contact with pyrite under oxygen-enriched conditions. This study provides new insights into the electrochemistry of base metal and precious minerals as well as the separation of different types of pyrite during the process of gold recovery

The galvanic interaction between gold and pyrite in the presence of ferric ions

The current study investigated the galvanic interaction between gold and pyrite in the presence of Fe to identify a means of facilitating the exposure of gold from its carrier mineral pyrite. It was found that gold was nobler than pyrite in the presence of ferric ions and a static current was generated once gold and pyrite were coupled. Dynamic polarization studies indicated that gold could catalyse the reduction of Fe, and Fe provided a more oxidizing effect on pyrite coupled with gold than that on pyrite without the coupling. This resulted in a significant increase in the oxidation rate of pyrite coupled with gold. Electrochemical characterization of pyrite surface and aqueous solution was also conducted after pyrite was oxidised with and without coupling with gold. A more extensive sulphur-rich layer was formed on pyrite after coupled with gold. The solution from galvanic oxidation also contained a much higher amount of oxidation products dissolved from pyrite surface. This study suggests that Fe can enhance the oxidation and dissolution of pyrite coupled with gold

The critical degree of bornite surface oxidation in flotation

The net effects of the alterations of surface chemistry of copper sulphide minerals on their flotation upon oxidation are documented to be either beneficial or detrimental, depending on the extent of mineral surface oxidation. However, there were limited reports in literature that established a quantitative relationship between surface oxidation and flotation, which renders the exercise of flotation optimisation for oxidised ores difficult, until our recent work on chalcopyrite and chalcocite. The degree of surface oxidation was quantified as the ratio of hydrophilic to hydrophobic oxidation species, which were characterised by X-ray Photoelectron Spectroscopy (XPS), and correlated with flotation recovery. Herein we tailored the method, which was previously developed on chalcopyrite and chalcocite, to establish a quantitative relationship between the degree of surface oxidation and flotation of bornite, one of the most valuable sources of commercial copper. The critical oxidation degree, beyond which bornite flotation becomes impossible, was determined to be 5.66. This is half that of chalcopyrite flotation and slightly higher than the upper limit of the range within which the critical degree of surface oxidation in chalcocite flotation was estimated to lie. Such knowledge betters the holistic understanding of the quantitative relationship between surface oxidation and copper sulphide flotation and will aid in providing insights on how to better handle ores of various oxidation degrees and susceptibilities. A comprehensive comparative case between bornite, chalcopyrite and chalcocite is presented in the paper

The interactions of radioactive lead with sulphide minerals

Radionuclides, specifically\ua0210Pb, can be recovered to copper concentrates potentially by associating with copper sulphide surfaces. This presents regulatory and health issues around radionuclide activity in concentrates. It is hypothesised that\ua0210Pb forms a stable PbS species on the copper sulphide surfaces allowing\ua0210Pb to be “carried” through the flotation process. It is the presence of such a species that this paper seeks to confirm. The minerals examined in this study are chalcocite (Cu2S), chalcopyrite (CuFeS2) and pyrite (FeS2) with lead nitrate providing Pb2+\ua0to simulate\ua0210Pb. Thermodynamic modelling and Cyclic Voltammetry studies indicate that PbS does form on the mineral surfaces with Cryogenic X-ray Photoelectron Spectroscopy confirming its presence. The mechanism of PbS formation is via the adsorption of Pb2+\ua0to sulphur-rich regions on the mineral surfaces and subsequent reaction to form PbS. Various oxygen-associated lead species were also detected, forming via the interaction of Pb2+\ua0with mineral oxidation products. Total lead on the mineral surfaces was 9.69 at%, 19.62 at% and 12.62 at% for pyrite, chalcocite and chalcopyrite, respectively. The ratio of lead-sulphur species to lead-oxygen species was 0.27, 0.84 and 1.00 for pyrite, chalcocite and chalcopyrite, respectively. Under flotation conditions, PbS is a stable species, meaning that it likely remains on mineral surfaces throughout the flotation process, facilitating\ua0210Pb recovery to concentrates

The research on improving the salt resistance of bentonite used in Geosynthetic Clay Liner

Geosynthetic Clay Liner, a water-proofing material which takes polymer as its carrier and bentonite as its basis, has been widely applied in the seepage-proofing projects including irrigation works, gardening and roadbed. In order to improve salt-resistance of bentonite used in Geosynthetic Clay Liner in saline environment, this paper innovatively uses chemical methods to modify the bentonite material. The experimental result shows that the optimum conditions are 100% of acrylic neutralization degree, 0.04%MBA, 1.2%KPS and holding at 70 degrees C for 1 h. According to results of soil moisture supply capacity (MSC), swelling capacity of modified samples raises 30% similar to 170%

Effect of Calcium Ion on the Flotation of Fluorite and Calcite Using Sodium Oleate as Collector and Tannic Acid as Depressant

In the flotation of semi-soluble minerals such as calcite and fluorite, Ca2+ is one of the common dissolved components influencing the collector adsorption behaviors on the mineral surfaces. However, there is very limited research focusing on how the dissolved Ca2+ affects the separation of fluorite and calcite. In the study, with sodium oleate (NaOL) as a collector and tannic acid (TA) as a depressant, a flotation test, zeta potential measurement, and adsorption experiment in the presence of Ca2+ were conducted. Flotation tests indicated that in the presence of Ca2+, fluorite and calcite were both significantly depressed by TA, leading to difficulty in the separation of the two minerals. It was also found that the depression effect on fluorite flotation was minimized with a high concentration of NaOL. Zeta potential measurement and the adsorption experiment results are consistent with the flotation results, revealing that it is only in the low concentration of NaOL that the flotation of fluorite was depressed by TA in the presence of Ca2+. Specifically, in the low concentration of NaOL, TA adsorbed on the fluorite surface and depressed the flotation of fluorite due to the preferential interaction between NaOL and Ca2+ in the solution leading to a shortage in the effective NaOL in the solution. In the high concentration of NaOL, the adsorbed TA on the fluorite surface was displaced by the excessive NaOL in the solution; hence, the flotation of fluorite was recovered. In contrast, TA always hinders the interaction of NaOL with calcite regardless of the presence and absence of Ca2+ and NaOL, hence, depressing the flotation of calcite. The study presented that a high concentration of NaOL may mitigate the negative effect of Ca2+ on the fluorite surface and improve the separation of fluorite from calcite

Mineral phase and structure changes during roasting of fine-grained carbonaceous gold ores and their effects on gold leaching efficiency

While roasting has been widely applied to reduce the negative effect of carbonaceous matters on gold extraction from fine-grained carbonaceous gold ores, the phase and structure changes of minerals during roasting and their influences on the leaching rate of gold have not been fully understood. This limits the extraction of carbonaceous gold deposits. The current work examines the oxidation process of a fine-grained carbonaceous gold ore during roasting using a range of techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy Dispersive Spectrometer (EDS) analysis and pore structure analysis together with gold leaching tests. The results show that during the process of oxidative roasting, the carbonaceous matters (organic carbon and graphitic carbon) and pyrite were completely decomposed at 600 °C with the carbonaceous components burned and pyrite oxidized into hematite. At 650 °C, while dolomite was decomposed into calcia, magnesia, calcium sulfate etc., the calcine structure became loose and porous, leading to a high gold leaching rate from the roasted product. Above 750 °C, the porous calcite structure started to collapse along with the agglomeration, leading to the secondary encapsulation of gold particles, which contributed to the sharp drop in the gold leaching rate of the roasted product. This study suggests optimum phase and structure changes of minerals during roasting to achieve maximum gold extraction from fine-grained carbonaceous gold deposits