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The aqueous metal‐sulfide batteries (AMSBs) have attracted research interest due to their high capacity, environmentally friendly qualities, and the accessibility of raw materials. However, the design strategies for metal‐sulfide cathode have rarely been reported. Here, the copper‐activated sphalerite in which Zn2+ is substituted by Cu2+ through ion exchange has been introduced for the first time as cathode for aqueous Cu/ZnS batteries. After sphalerite transformed to CuS, a two‐step conversion of CuS→Cu7S4→Cu2S storage mechanism has been proposed. At 0.7 A g−1 current density, the capacity can reach 532.4 mAh g−1 after 100 cycles. When cycled once at a current density of 35 mA g−1, the initial reversible capacity can reach 461 mAh g−1 under 1 A g−1. Furthermore, the assembled Zn//ZnS hybrid ion cell delivers an energy of up to 460 Wh kg−1, which is better than for many AMSBs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The addition of ammonium sulfate enhanced the activation of copper sulfate for marmatite. • Introducing ammonium sulfate can dramatically reduce the consumption of copper sulfate. • After adding ammonium sulfate, more Cu-S component was formed on the marmatite surface. • Enhanced Cu activation promoted the adsorption of xanthate on the marmatite surface. The presence of iron atoms on the marmatite surface hinders effective interaction between the activator and the mineral, leading to unsatisfactory flotation performance through direct copper (Cu) activation. Hence, this study introduced ammonium sulfate to enhance the marmatite-activation capability by Cu ions. Additionally, the reinforcement mechanism was investigated through microflotation tests, atomic force microscopy (AFM), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and density-functional theory (DFT) calculations. Microflotation results demonstrated that the addition of ammonium sulfate as a complexing reagent increased the flotation recovery of marmatite by 17.36%. AFM analysis revealed that marmatite subjected to enhanced activation (i.e., in the presence of ammonium sulfate) exhibited a considerably higher surface roughness than that subjected to direct Cu activation. Moreover, the average height of hill-shaped materials on the marmatite surface notably increased to 9.6 nm after enhanced Cu activation. SEM-EDS analysis revealed that the concentration of Cu atoms (2.2%) on the marmatite surface after enhanced Cu activation was nearly three times that (0.8%) after direct Cu activation. Additionally, XPS results indicated a considerably higher presence of the Cu–S component on the marmatite surface after enhanced Cu activation than after direct Cu activation. ToF-SIMS analysis indicated an increase in the fragment peaks of Cu+, CuOCS 2 +, OCS 2 −, and OC 2 H 2 S 2 − on the surface of enhanced-activated marmatite. Additionally, DFT calculations indicated that the presence of NH 3 molecules enhanced electron transfer between Cu and S on the hydrated marmatite surface. The marmatite (1 1 0) surface exhibited more negative adsorption energy of Cu ions after the action of NH 3 molecules, and NH 3 –Cu showed a more stable adsorption configuration than Cu. Therefore, the addition of ammonium sulfate enhanced the Cu activation for marmatite, thereby improving flotation performance. [ABSTRACT FROM AUTHOR]

Thermus thermophilus laccase belongs to the sub-class of multicopper oxidases that is activated by the extra binding of copper to a methionine-rich domain allowing an electron pathway from the substrate to the conventional first electron acceptor, the T1 Cu. In this work, two key amino acid residues in the 1st and 2nd coordination spheres of T1 Cu are mutated in view of tuning their redox potential and investigating their influence on copper-related activity. Evolution of the kinetic parameters after copper addition highlights that both mutations play a key role influencing the enzymatic activity in distinct unexpected ways. These results clearly indicate that the methionine rich domain is not the only actor in the cuprous oxidase activity of CueO-like enzymes. • Mutations in T. thermophilus laccase CuT1 coordination spheres impact activity. • M456A is active only upon Cu2+ addition. • M455L presents a better ABTS affinity and 100 mV higher redox potential than WT. • Cu2+ inhibition of M455L suggests M455 involvement in cuprous oxidase activity. • Met-rich domains would not be the only actor in Cu+ oxidase activity. [ABSTRACT FROM AUTHOR]

A high auriferous arsenopyrite floatability is desirable to maximise gold recovery in sulphidic refractory gold ore flotation. This study examines the adsorption properties of sulphidic refractory gold ore (2.58 g/t Au) in the presence of sodium isobutyl xanthate (SIBX) collector, under different pH and CuSO 4 additions for maximum arsenopyrite and gold floatability. The SIBX adsorption studies showed that pH greatly influences SIBX adsorption on to the surface of sulphidic refractory gold ore. Very little effect of CuSO 4 on SIBX adsorption in acidic environment (pH 5–5.5) was observed due to low copper ions adsorption. Better flotation recoveries of arsenopyrite (86%) and gold (91%) were achieved at the ore's natural pH (8–8.5) than under acidic or basic environments. Pyrite floated poorly (<20% recovery) for all pH conditions. Based on the studies, conditions for maximum collector adsorption, arsenopyrite and gold flotation recovery for the ore were established. Unlabelled Image • Sodium isobutyl xanthate (SIBX) adsorption on to sulphidic refractory gold ore surface is greatly influenced by the pulp pH. • Copper activation of sulphidic refractory gold ore had very little impact on SIBX adsorption in acidic environment. • Arsenopyrite and gold floated very well at the ore's natural pH. • Pyrite floated poorly (<20%) for all pH conditions. [ABSTRACT FROM AUTHOR]

Highlights • XPS data demonstrated the importance of oxidation for pyrrhotite depression in primary nickel rougher. • CV demonstrated a higher oxidation rate of monoclinic pyrrhotite than that of hexagonal pyrrhotite. • ToF-SIMS results demonstrated that Ca2+ and Mg2+ depressed pyrrhotite flotation in a certain degree, meanwhile Cu2+ and Ni2+ activated pyrrhotite flotation. • ICP analysis suggested a higher Cu2+ activating effect onto hexagonal pyrrhotite as compared to the monoclinic pyrrhotite. Abstract In the Strathcona Mill, the rejection of pyrrhotite (Fe (1-x) S, 0 < x ≤ 0.125) is in high demand to meet the stringent environmental standards for SO 2 emission in downstream smelting operations. For this purpose, two plant surveys were conducted to study polymorphic pyrrhotite flotation and depression mechanisms in the Strathcona Mill via investigating polymorphic pyrrhotite distributions, pulp chemistry, and industrial settings (with combined Cu-Ni feed and split Cu-Ni feed). The plant survey data revealed that hexagonal pyrrhotite in the Ni concentrate demonstrated higher floatability than that of the monoclinic pyrrhotite. Surface analysis by ToF-SIMS of the primary nickel rougher circuit showed that lower copper activation effects were likely responsible for the decreased flotation recovery of pyrrhotite in the 2017 plant survey as compared with combined Cu-Ni feed in 2016 survey. The different oxidation rates of monoclinic and hexagonal pyrrhotite were also investigated. CV studies corroborated the higher floatability of hexagonal pyrrhotite with its lower oxidation rate than monoclinic pyrrhotite. XPS studies demonstrated the progressive oxidation of pyrrhotite from concentrate to tail, substantiating that pyrrhotite oxidation is essential for pyrrhotite depression. This study suggested that careful control of Cu ions in the Ni stream can depress polymorphic pyrrhotite in the flotation. The oxidation study of pyrrhotite demonstrated that proper ways to relatively increase pyrrhotite oxidation rate (particularly for hexagonal pyrrhotite) would help to depress pyrrhotite. [ABSTRACT FROM AUTHOR]

Highlights • In chalcopyrite flotation, pyrite recovery was much higher in seawater than in fresh water. • Seawater enhanced chalcopyrite oxidation and dissolution. • Seawater facilitated the copper activation process on pyrite surface. Abstract Saline water has been widely used in the flotation of copper sulfide minerals against pyrite where pyrite may be activated by copper ions emanating from copper sulfide minerals. The effect of saline water on copper activation on pyrite surface has not been studied before. In this study, the effect of seawater with a high ionic strength on the flotation of chalcopyrite against pyrite was investigated. Compared to fresh water, seawater significantly increased pyrite recovery in flotation and made the separation of chalcopyrite from pyrite more difficult. The significant increase in pyrite recovery in flotation using seawater mainly resulted from the increased copper activation on pyrite surface. Polarization analysis and EDTA extraction show that the use of seawater enhanced chalcopyrite oxidation and dissolution leading to the formation of a larger amount of copper ions available for copper activation. The flotation of pyrite in the presence of copper ions together with cyclic voltammetry (CV) measurements indicates that the copper activation process on pyrite surface was facilitated in seawater owning to the lower potential of seawater. [ABSTRACT FROM AUTHOR]

The copper activation and potassium butyl xanthate (PBX) adsorption on sphalerite and marmatite surfaces were comparatively investigated using in situ local electrochemical impedance spectroscopy (LEIS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and surface adsorption tests. Comparing the LEIS and surface adsorption results, it was found that the activation time is a key factor influencing the copper activation and PBX adsorption on marmatite surface, but it has a negligible influence on sphalerite. For a short activation time within 10 min, the Fe impurity in marmatite shows an adverse influence on the speed of Cu adsorption and ion exchange as well as on the subsequent PBX adsorption. For a long activation time of 30 min, the LEIS, ToF-SIMS and surface adsorption results suggested that the Fe impurity in marmatite enhances the copper adsorption, whereas such enhanced copper adsorption of marmatite cannot result in corresponding enhancing of PBX adsorption. DFT result showed that the Fe impurity in marmatite has harmful influence on the PBX interaction with the Cu-activated surface by increasing the interaction energy. ToF-SIMS result further indicated that the Cu distribution in the outermost surface of marmatite is less than that of the sphalerite, which also results in the less PBX adsorption for the marmatite. [ABSTRACT FROM AUTHOR]

A theoretical analysis method of the solution chemistry characteristic of Cu(II) at various pH values was developed. Using such method, the existence form of Cu species and their proportions in aqueous solution can be clearly determined. After that, the copper adsorption and ion exchange ratio (E) during the copper activation of sphalerite were investigated. The results indicated that the copper activation of sphalerite can be divided into two stages, i.e., the fast activation stage (t =4 min) and slow activation stage (t >4 min). The general form of the copper adsorption rate was determined as GCu=K1ln(t) +G1, which is confirmed by the data fitting of the fast activation stage. The lower activation pH results in higher ion exchange efficiency for Cu substituting Zn. For a strong acid pH of 4.1, the E maintains about 1:1 in the entire activation time range and is not dependent on the activation time. However, the value of E is greater than 1 under weak acidic (pH=6.2) and alkaline (pH=9.1) pH conditions and it significantly depends on the activation time. For such conditions, E decreases with increase in the activation time, which supports the ion exchange mechanism, but within short activation time, it is not a 1:1 ion exchange process. [ABSTRACT FROM AUTHOR]

Pyrite is a gangue mineral in the flotation of sphalerite activated by copper sulphate (CS). In this study, the attachment of air bubbles onto sphalerite and pyrite surfaces activated by CS was comparatively studied using a novel approach with High-Speed Video Microscopy (HSVM) and X-ray photoelectron spectroscopic (XPS). HSVM allowed for the in-situ determination of the liquid film Drainage Rate (DR) and Contact Angle (CA) of the bubble attachment. The results showed that after the activation sphalerite became hydrophobic by the formation of polysulphide as confirmed by XPS while pyrite remained hydrophilic. With increasing activation time and CS concentration, both DR and CA on the sphalerite surface rapidly increased at the beginning and reached constant values, while those on pyrite remained unchanged. The changes in the CA values of the sphalerite was successfully modelled by considering a second-order rate process for the CS activation which was proportional to initial copper concentration and available Zn active sites on the sphalerite surface. If both sphalerite and pyrite were simultaneously exposed to CS solutions (but not in the physical contact), the rate of CS activation of sphalerite remained unchanged when the ratio of sphalerite to pyrite surface areas exposed to CS solutions was equal to 1:1. However, the activation rate of sphalerite significantly dropped with increasing the sphalerite:pyrite surface area ratio from 1:3 to 1:6. The effect of the surface area ratio on the CS activation rate was prominent at activation times higher than 3 min. The XPS results for the mixed minerals showed the reduction in sphalerite Cu/Zn exchange and polysulphide/Cu ratios with increasing available pyrite surface area in CS solutions, indicating the significant drop in the CS activation of sphalerite in the presence of pyrite. The outcomes of this study provided further insights into the selective flotation of sphalerite from pyrite. [ABSTRACT FROM AUTHOR]

Adsorption of copper sulphate onto the sphalerite and pyrite surfaces during the selective flotation is not fully understood. In this paper, this phenomenon is investigated by Cryogenic X-ray Photoelectron Spectroscopy (Cryo-XPS) and zeta potential measurements. The Cryo-XPS results have showed that the copper activation occurs in two steps. For sphalerite, surface Zn 2+ is substituted by Cu 2+ by ion exchange reaction, and then CuS-type layer is formed by reduction of the exchanged Cu 2+ to Cu + and oxidation of surface S 2− to S − . Cu 2+ can also activate pyrite, first, through reduction of Cu 2+ to Cu + and oxidation of surface S 2− species to S − , then surface Fe 2+ is oxidised to Fe 3+ by reduction of S − to S 2− , leading to the formation of CuFeS 2 -type layer. In the reducing potential of the activation, enhancement of copper adsorption on the pyrite surface is confirmed by XPS. Depth profiling after 10 min activation revealed copper diffusion into the sphalerite lattice up to 10 nm, while the thickness of the activation product on pyrite surface was less than 3 nm. The zeta potential studies confirmed CuS-type layer formation on copper activated sphalerite, whereas the surface product of the activated pyrite was CuFeS 2 -type. This study leads to a better understanding of sphalerite-pyrite Cu 2+ activation during flotation for an effective separation. [ABSTRACT FROM AUTHOR]

The depression of pyrite flotation is normally difficult especially when pyrite is activated by copper ions. In this study, different biopolymers, modified from lignosulfonate, were examined to depress the flotation of copper-activated pyrite. It was found that the biopolymers (DP-1775, DP-1777 and DP-1778), differing in composition, were able to depress the flotation of copper-activated pyrite. The depression was associated with the copper(I)-biopolymer complex formed on pyrite surface which enhanced the oxidation of copper(I) and inhibited xanthate adsorption. While the molecular weight corresponded to the adsorption capacity of biopolymers on pyrite, the content of functional groups of biopolymers interfered with xanthate adsorption. [ABSTRACT FROM AUTHOR]

Copper sulphate is used as an activator in the flotation of base metal sulphides as it promotes the interaction of collector molecules with mineral surfaces. It has been used as an activator in certain platinum group mineral (PGM) flotation operations in South Africa although the mechanisms by which improvements in flotation performance are achieved are not well understood. Some investigations have suggested these changes in flotation performance are due to changes in the froth phase rather than activation of minerals by true flotation in the pulp zone. In the present study, the effect of copper sulphate on froth stability was investigated on two PGM containing ores, namely Merensky and UG2 (Upper Group 2) ores from the Bushveld Complex of South Africa. Froth stability tests were conducted using a non-overflowing froth stability column. Zeta potential tests and ethylenediaminetetraacetic acid (EDTA) tests were used to confirm the adsorption of reagents onto pure minerals commonly found in the two ores. The results of full-scale UG2 concentrator on/off copper sulphate tests are also presented. The UG2 ore showed a substantial decrease in froth stability in the order of reagent addition: no reagents > copper > xanthate > copper + xanthate, while Merensky ore showed a slight decrease. It was shown through zeta potential measurements that copper species were to be found on plagioclase, chromite, talc and pyrrhotite surfaces and through EDTA extraction that this copper was in the form of almost equal amounts of Cu(OH) 2 and chemically reacted copper ions on the Merensky and UG2 ore surfaces. In certain cases, the presence of copper sulphate and xanthate substantially increased the recovery, and therefore the implied hydrophobicity, of pure minerals in a frothless microflotation device. It was, therefore, proposed that increases in hydrophobicity beyond an optimum contact angle for froth stability, were the cause of instabilities in the froth phase and these were found to impact grade and recovery in a full-scale concentrator. Differences in the extent of froth phase effects between the different ores can be attributed to differences in mineralogy. [ABSTRACT FROM AUTHOR]

Abstracts The interaction of collector with the mineral surface plays a very important role in the froth flotation of sphalerite. The adsorptions occurred at the interface between the mineral surface and waters; however most of DFT simulations are performed in vacuum, without consideration of water effect. Semiconductor surface has an obvious proximity effect, which will greatly influence the surface reactivity. To understand the mechanism of xanthate interacting with sphalerite surface in the presence of water molecules, the ethyl xanthate molecule adsorption on un-activated and Cu-activated ZnS(110) surface in the absence and presence of water molecules were performed using the density functional theory (DFT) method. The calculated results show that the adsorption of water molecules dramatically changes the properties of ZnS surface, resulting in decreasing the reactivity of surface Zn atoms with xanthate. Copper activation of ZnS surface changes the surface properties, leading to the totally different adsorption behaviors of xanthate. The presence of waters has little influence on the properties of Cu-activated ZnS surface. The xanthate S atom can interact with the surface S atom of Cu-substituted ZnS surface, which would result in the formation of dixanthogen. [ABSTRACT FROM AUTHOR]

Hydrophobicity and many other surface properties of copper (Cu) activated sphalerite can be changed by calcium, magnesium and sulphate ions in solutions, but have not been quantitatively investigated previously. Here, the effect of Ca(NO 3 ) 2 , Mg(NO 3 ) 2 , MgSO 4 and CaSO 4 on the surface properties of Cu-activated sphalerite was studied using contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), and zeta potential measurements. The CA measurements show that the hydrophobicity of sphalerite developed after copper activation, but the presence of 30 mM Ca(NO 3 ) 2 or Mg(NO 3 ) 2 or MgSO 4 decreased its hydrophobicity: CA reduced from 67° to 48°. The presence of 30 mM of Ca 2+ and SO 4 2− ions in solutions reduced CA further to 42°. This CA change could be due to the simultaneous presence of ionic calcium species and calcium sulphates that precipitated as gypsum. The XPS data show Cu presence on the sphalerite surface after copper activation in the salt solutions was in the Cu(I) state. The effect of Ca(NO 3 ) 2 , Mg(NO 3 ) 2 , MgSO 4 and CaSO 4 on the copper activated sphalerite surface appeared to be the same, namely a decrease in Cu(I) adsorption and polysulphide formation. Neither Ca 2+ nor CaSO 4 were detected by surface analysis, but some Mg ions were found on the surface. Zeta potential measurements confirmed the presence of calcium and magnesium ions on the sphalerite surface. The role of calcium and magnesium ions in copper activation of sphalerite appears to be that of moderators which act to reduce the amount of Zn replaced by Cu on the sphalerite surface, whether SO 4 is present or not. [ABSTRACT FROM AUTHOR]

Copper activation has been a standard diagnostic for measuring 14.1-MeV neutron yields in deuterium-tritium fusion experiments, which is essential to evaluate their performance for potential ignition in the future. Copper-activation equipment, especially data-acquisition systems, is updated constantly thanks to the rapid developments in electronics. Here, a multi-function digital coincidence spectrometer for neutron copper-activation diagnostics was developed. The digital pulse processing includes pulse shaping, multichannel pulse analysis, coincidence event picks, and coincidence multichannel time analysis were implemented on a single field-programmable gate array (FPGA) chip. The results demonstrate that the coincidence background is 0.013 counts per second. By using the multi-function digital coincidence spectrometer, the copper-activation diagnostics could be performed at the SG-III Laser facility when the neutron yield is ≥ 1.0 × 1010/hit. • Multi-function real-time digital signal processing are implemented on FPGA. • Details of the FPGA structure are described. • Dynamic energy spectrum and coincidence data with time stamp can store and display on the computer synchronously. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the effect of regrinding conditions on copper activation on the pyrite surface and subsequent pyrite flotation in the cleaner stage was investigated. Pyrite was activated by copper ions during primary grinding, and the rougher flotation concentrate was reground in a tumbling mill prior to the cleaner flotation. The regrinding condition was manipulated by two types of grinding media, stainless steel and mild steel. It was found that pyrite flotation in the cleaner stage was depressed especially when mild steel media was used during regrinding. An additional amount of collector improved pyrite flotation especially when stainless steel media was used during regrinding. An additional amount of copper ions further increased pyrite flotation after regrinding with mild steel media but decreased pyrite flotation after regrinding with stainless steel media. XPS (X-ray photoelectron spectroscopy) analyses and EDTA (ethylene diamine tetraacetic acid) extraction revealed that the different response of pyrite flotation in the cleaner stage to stainless steel and mild steel media used during regrinding was associated with the modified property of the Cu-activated pyrite surface carried from the rougher flotation concentrate and the new pyrite surface created during regrinding. [Copyright &y& Elsevier]

Abstract: Nitrate determination plays a very important role in the analysis of environmental samples. In this paper, an activation procedure for nitrate sensing using a modified copper electrode made from flat flexible cables in presence of a low amount of chloride is reported. The proposed method exhibits enhanced electrocatalytic behaviour in the reduction of nitrate compared to a bare copper electrode. The proposed method showed linear response for nitrate in the concentration range 10–1070μmolL−1, with a regression coefficient R 2 =0.999 (n =12) and a limit of detection of 1.8μmolL−1. According to the procedure based on the standard addition technique, the recovery values obtained were 93–103%, showing the accuracy of the proposed method. In addition, the proposed sensor was applied to the determination of nitrate in mineral water samples and the results are in good agreement (for a 95% confidence level according to the Student's t-test) with those obtained using the capillary electrophoresis procedure. [Copyright &y& Elsevier]

Abstract: The findings of synchrotron based spectromicroscopic investigations of Cu and xanthate adsorption onto pyrite surfaces are reported. Synchrotron based photoemission electron microscopy measurements have revealed that Cu adsorbs only onto specific surface sites on pyrite. The Cu 2p X-ray absorption near edge structure and position (2p 3/2 peak at 934.3eV) confirms the presence of Cu+ with transitions from 2p to 4s states being apparent. Moreover, the peak position is typical of Cu+ bonded to S, Cu(I)s confirmed by S 2p X-ray photoelectron spectroscopy with oxidised S2− species (S−), most likely resulting from electrochemical interaction of solution Cu2+ and surface S2− species, being observed. Fe 2p X-ray absorption spectroscopy shows that surface Fe does not take part in the Cu adsorption or subsequent restructuring processes. Synchrotron FTIR microscopy analysis of xanthate (potassium ethyl xanthate, KEX) adsorbed onto Cu activated surfaces also shows a heterogeneous distribution on pyrite. The use of a dilute (10−5 M) KEX concentration shows Cu(I)–xanthate as the only surface xanthate containing species. This species may have formed through a chemical process involving previously adsorbed Cu+ and the xanthate from solution. When a greater (10−3 M) concentration of KEX is used significant concentrations of Cu(I)–xanthate precipitate from solution onto the pyrite surfaces and cannot be easily removed. Under this condition, the predominant surface species remains Cu(I)–xanthate with smaller concentrations of diethyl dixanthogen also being present. The latter species may form in solution although some previous studies also suggest direct surface formation. [Copyright &y& Elsevier]

In this work, the effect of copper sulphate on the flotation of Mt Keith pentlandite ores was studied. As Mt Keith operates separate size flotation circuits, e.g. slime (-8 μm), fine (-25 μm) and coarse (-160 μm) circuits, tests were conducted on streams of different particle size distributions prepared with the use of cyclones. The flotation response with and without the addition of copper sulphate was examined, first, on feed streams prepared by a laboratory grinding mill and cyclone and, second, on streams collected directly from the plant. It was found that copper sulphate had an adverse effect on flotation performance when the flotation feeds were prepared in the laboratory. In the flotation of slime-fine fractions that combined slime and fine particles, the addition of copper sulphate depressed nickel flotation while increasing gangue entrainment. In the flotation of coarse fractions, the addition of copper sulphate depressed nickel flotation without affecting gangue entrainment. However, when samples were collected directly from the plant streams and floated in a laboratory flotation cell, the addition of copper sulphate increased nickel recovery without affecting gangue entrainment in the flotation of slime, fine and coarse fractions. To explain this discrepancy, pulp chemistries in the two different types of tests were compared. It was found that the plant mills at Mt Keith produced a much more reducing grinding environment than the laboratory mill. This might contribute to the completely different behaviour which copper sulphate exhibited on flotation performance. This study also demonstrates the importance in considering plant pulp chemistry during research development in a laboratory. [ABSTRACT FROM AUTHOR]

• Cu(II) ions can activate the floatability of xanthate-treated millerite at alkaline pH. • The main Cu species formed on millerite is Cu (I) sulphide. • Millerite surface oxidation is affected, surface monosulphide is oxidized to disulphide. • Less sulphoxy species are formed in the presence of Cu. The presence of copper(II) ions in the process water used in the mineral processing industry has an impact on iron and nickel sulphide mineral flotation in both acidic and alkaline environments. Millerite (β-NiS) – a nickel sulphide mineral, has been found misreported to Cu concentrate, which negatively impact the performance of Cu/Ni separation. In this paper, we present a fundamental study on the effect of Cu(II) ions on millerite flotation and surface properties in alkaline solutions. Micro-flotation tests indicated that millerite flotation can be activated by conditioning with copper ions prior to KEX addition at both pH 9 and 12. The surface chemistry of millerite in the presence of Cu(II) was studied by mineral dissolution and EDTA extraction tests as well as XPS analysis to probe the underlying activation mechanism. At alkaline pH, the main copper species on millerite surface was Cu(I) sulphide with minor Cu(II) sulphide and Cu(II) oxide/hydroxide. The Cu(I) sulphide arose from the adsorption and reduction of Cu(II) species. Meanwhile, sulphur oxidation was affected upon the reduction of Cu(II) to Cu(I). Monosulphide species (S2-) at the surface was oxidized into disulphide species (S 2 2-), resulting in less sulphoxy species (S x O y 2-). There was no remarkable increase in nickel dissolution and growth in nickel hydroxide passivation layer upon the adsorption of Cu. In essence, copper ion activated millerite flotation under alkaline pH through affecting millerite surface oxidation. [ABSTRACT FROM AUTHOR]

Abstract: A review of the considerable, but often contradictory, literature examining the specific surface reactions associated with copper adsorption onto the common metal sulfide minerals sphalerite, (Zn,Fe)S, and pyrite (FeS2), and the effect of the co-location of the two minerals is presented. Copper “activation”, involving the surface adsorption of copper species from solution onto mineral surfaces to activate the surface for hydrophobic collector attachment, is an important step in the flotation and separation of minerals in an ore. Due to the complexity of metal sulfide mineral containing systems this activation process and the emergence of activation products on the mineral surfaces are not fully understood for most sulfide minerals even after decades of research. Factors such as copper concentration, activation time, pH, surface charge, extent of pre-oxidation, water and surface contaminants, pulp potential and galvanic interactions are important factors affecting copper activation of sphalerite and pyrite. A high pH, the correct reagent concentration and activation time and a short time delay between reagent additions is favourable for separation of sphalerite from pyrite. Sufficient oxidation potential is also needed (through O2 conditioning) to maintain effective galvanic interactions between sphalerite and pyrite. This ensures pyrite is sufficiently depressed while sphalerite floats. Good water quality with low concentrations of contaminant ions, such as Pb2+and Fe2+, is also needed to limit inadvertent activation and flotation of pyrite into zinc concentrates. Selectivity can further be increased and reagent use minimised by opting for inert grinding and by carefully choosing selective pyrite depressants such as sulfoxy or cyanide reagents. Studies that approximate plant conditions are essential for the development of better separation techniques and methodologies. Improved experimental approaches and surface sensitive techniques with high spatial resolution are needed to precisely verify surface structures formed after copper activation. Sphalerite and pyrite surfaces are characterised by varying amounts of steps and defects, and this heterogeneity suggests co-existence of more than one copper–sulfide structure after activation. [Copyright &y& Elsevier]

Abstract: Initial stages of copper activation in chloride-ion containing neutral aqueous solution were studied. The results point that activation of copper passivity is initiated once the potential exceeds the breakdown value, occurring with well-defined incubation period, similar to that of other passive metals in chloride environments. The effect of applied potential and Cl− ion concentration on the incubation period is presented. The results indicate that an incubation period for copper activation in chloride containing solutions can be associated with the formation of a two-dimensional CuCl layer on the metal surface. The incubation period is relatively long at negative potentials and it is decreases with a positive shift in the potential. At a certain potential, the incubation period is sharply decreased. The time-frame of incubation period is attributed to the formation rate of two-dimensional CuCl layer and its reduction rate. The formation of a stable salt film on the metal surface facilitates localized rapid dissolution of the copper. [Copyright &y& Elsevier]

Abstract: The change in collectorless flotation of sphalerite with pH and Cu(II) concentration was correlated with the type and proportion of species present on the sphalerite surface. The solution and surface species were determined using a combination of analytical techniques including zeta potential measurement and X-ray photoelectron spectroscopy. An optimum copper concentration for maximum sphalerite flotation was identified, beyond which flotation decreased. This decrease in flotation coincided with the precipitation of copper hydroxide in neutral to mildly alkaline pH conditions. The hydrophobic polysulfide and hydrophilic copper hydroxide species were the main surface species influencing sphalerite flotation. [Copyright &y& Elsevier]

Abstract: The effect of sodium bisulphite on the collectorless flotation of copper-activated sphalerite has been studied at pH 9 with nitrogen purging. X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (ToF-SIMS) and ion chromatography (IC) have been used to identify a mechanism of interaction of sulphite ions with sphalerite particles. The results indicate that sodium bisulphite acts as an effective depressant for the collectorless flotation of copper-activated sphalerite and has a specific effect on the surface chemistry of sphalerite particles under the experimental conditions studied. It is suggested that sulphite ions react with the surface of copper-activated sphalerite and subsequently decompose the hydrophobic sulphur-like species responsible for flotation. Most likely, sulphite ions specifically interact with the reduced coordination sulphur atoms associated with copper activation and report into solution as a thiosulphate, which is then oxidised to sulphate. At the same time, zinc hydroxide is formed at the sphalerite surface. The consequent reduction in surface hydrophobicity explains the depression of copper-activated sphalerite in the presence of sulphite. [Copyright &y& Elsevier]

A specially designed mill which allowed the control of pH throughout grinding was used to study the effect of grinding conditions on chalcopyrite flotation and chalcopyrite separation from pyrite. The mechanism of galvanic interaction between minerals and grinding media was investigated by ethylene diamine-tetra acetic acid disodium salt (EDTA) extraction and X-ray photoelectron spectroscopy (XPS) measurements.Chalcopyrite flotation was strongly dependent on both iron oxidation species and metal deficiency on the chalcopyrite surface. Iron oxidation species from grinding media played a dominant role in depressing chalcopyrite flotation, while metal deficiency from chalcopyrite oxidation improved chalcopyrite flotation. Therefore, chromium grinding medium produced a higher chalcopyrite recovery than mild steel grinding medium while gas purging during grinding had little effect on chalcopyrite flotation.Chalcopyrite separation from pyrite was affected by the activation of pyrite flotation by copper species dissolved from chalcopyrite. Grinding media had a large effect on the reduction of copper(II) to copper(I) on the pyrite surface. The reducing grinding condition generated by mild steel medium favoured formation of copper(I) sulphide phase, which resulted in high pyrite activation. Thus, chromium medium produced better chalcopyrite selectivity against pyrite than the mild steel medium. [Copyright &y& Elsevier]

The iron sulfide mineral, pyrrhotite (Fe(1− x)S), has long been known to be more difficult to recover by flotation from alkaline slurries than many other base metal sulfide minerals. This paper summarizes the results of an electrochemical study of the surface reactions that occur during the flotation of nickeliferous pyrrhotite in the recovery of nickel and the platinum group metals. Mixed potential measurements conducted with natural pyrrhotite electrodes in various stages of an operating flotation plant showed that the mineral potential is positive to the equilibrium potential of the xanthate/dixanthogen couple. Similar results were obtained during batch flotation experiments and in synthetic solutions in the laboratory. Cyclic voltammetric and potentiostatic current/time transient experiments were used to investigate the oxidation of pyrrhotite under various conditions. In addition, the reduction of oxygen, the reaction of copper ions and the oxidation of xanthate ions at the mineral surface were investigated. The formation of dixanthogen on pyrrhotite surfaces is thermodynamically favourable in plant flotation slurries. However the interaction with xanthate at pH values above 7 is inhibited by a surface species formed during the conditioning prior to xanthate addition. In acidic solutions copper ions react readily with pyrrhotite to form a species, possibly CuS that can be oxidized at potentials above 0.4 V. At pH 9 this species does not form and there is no electrochemical reaction between pyrrhotite and copper ions. The beneficial effects of copper ions to flotation performance appear to be related to an enhancement of the oxidation of xanthate. [ABSTRACT FROM AUTHOR]

Acidithiobacillus ferrooxidans has been shown to be a good depressant of pyrite in freshwater and seawater flotation. However, the effect of these bacteria over copper-activated pyrite has not been studied. At the industrial scale, the activation of pyrite with copper is a common process that occurs because Cu 2 + ions, released from other minerals, react with pyrite. This is a problem because Cu 2 + ions facilitate the reaction of pyrite with the xanthate collectors, becoming hydrophobic and reaching the froth. In this study, microflotation experiments in a Hallimond tube were conducted to evaluate the depressant effect of A. ferrooxidans over non-activated and Cu-activated pyrite in freshwater and seawater flotation. The experiments were carried out at pH 4, 6, 8, 10 and 12 and pyrite was mixed with CuSO4 at 2.5 × 10 − 5 and 5 × 10 − 5 M in order to activate its surface. Considering the results obtained in the microflotation tests, it is possible to conclude that Acidithiobacillus ferrooxidans is able to depress non-activated and Cu-activated pyrite at the entire pH range studied (4–12) in freshwater. On the other hand, the use of bacteria in flotation with seawater proved to be effective to depress non-activated and Cu-activated pyrite at pH 8 and 10 with better results achieved at pH 10. At this pH, the non-activated pyrite recovery dropped from 96% to 15%, and the recovery of Cu-activated pyrite dropped from 95% to 32% when the activation was carried out at 2.5 × 10 − 5 M, and from 87% to 50% when the activation was conducted at 5 × 10 − 5 M of CuSO4. The XPS analysis showed that chalcopyrite and copper (II) hydroxide were formed on the pyrite surface when it is contacted with CuSO4. [ABSTRACT FROM AUTHOR]

• Oxidation adversely influences xanthate-induced pyrite flotation. • Lead and copper ions are equally efficient in activating slightly oxidised pyrite. • Copper ions are superior to lead ions in activating moderately oxidised pyrite. • Lead ions are better than copper ions in activating severely oxidised pyrite. • Oxidation species inhibit the adsorption of lead and copper ions on pyrite surface. • More lead ions can adsorb on pyrite surface but more are required for the activation. Copper ions are often added in the flotation of gold-bearing pyrite to activate pyrite so that high gold and pyrite recoveries can be achieved. However, the residual copper ions are problematic in subsequent cyanidation by consuming cyanide. There is a great need to replace copper ions by lead ions which are beneficial to cyanidation. This study compared lead and copper activation on pyrite with different degrees of surface oxidation at pH 5.0. Flotation tests indicated that lead and copper ions were equally efficient in activating slightly oxidised pyrite and both produced a high pyrite recovery. For moderately oxidised pyrite, copper ions were superior to lead ions in activating pyrite. However, for severely oxidised pyrite, lead ions prevailed over copper ions in activating pyrite. By Cryogenic X-ray photoelectron spectroscopy analysis, it was found that the different behaviour of lead and copper ions in activating pyrite was governed by the lead and copper species adsorbed on pyrite surface. In general, pyrite oxidation generated iron and sulphur oxidation species which inhibited the adsorption of lead and copper ions on pyrite surface. Lead ions had stronger affinity to oxidised pyrite than copper ions but pyrite flotation required a higher amount of lead-activating products than copper-activating products. [ABSTRACT FROM AUTHOR]

• CuSO 4 could activate sphalerite that was depressed with ZnSO 4. • ZnSO 4 + CuSO 4 treatment changed the chemical environment of sphalerite surfaces. • Copper species adsorbed on the depressed sphalerite surface after CuSO 4 treatment. • TOF-SIMS showed an adsorption layer of copper species on the sphalerite surface depressed with ZnSO 4. The activation mechanism of copper sulfate (CuSO 4) for sphalerite surfaces depressed with zinc sulfate (ZnSO 4) and their interactions were investigated through microflotation experiments, zeta-potential determination, X-ray photoelectron spectroscopy (XPS), xanthate adsorption experiments, time-of-flight secondary-ion mass spectrometry (TOF-SIMS) and local electrochemical impedance spectroscopy (LEIS). The microflotation experimental results indicated that addition of ZnSO 4 decreased sphalerite recovery and that CuSO 4 can activate sphalerite depressed with ZnSO 4 during flotation. The highest negativity of the zeta potential was achieved after adding xanthate + ZnSO 4 + CuSO 4 , indicating that the addition of copper ions can improve adsorption of the collector on depressed sphalerite surfaces. XPS was used to identify the mechanisms of the interactions of ZnSO 4 and CuSO 4 with the sphalerite surface. Xanthate adsorption experiments showed that the xanthate adsorption capacity increased greatly after treatment of depressed sphalerite with copper ions. TOF-SIMS indicated that copper ions were adsorbed on the surface of the depressed sphalerite. LEIS analysis showed that, copper ion can replaces zinc ion on mineral surface. These results show a sphalerite surface depressed with ZnSO 4 can be activated by copper ions, thereby increasing its hydrophobicity and floatability. [ABSTRACT FROM AUTHOR]

• MBS promotes copper activation on pyrite surface in the absence of oxygen. • Sulphite ions and oxygen form a radical S O 5 · - to oxidise Cu(I)S products. • MBS is more effective in depressing pyrite when added in flotation than during grinding. In response to the high pyrite recovery in copper flotation using seawater, this study investigated the role of sodium metabisulphite (MBS), a widely used pyrite depressant, in depressing the flotation of copper-activated pyrite to identify a solution to maximising pyrite rejection. It started with chalcopyrite flotation against pyrite with MBS added in the mill before grinding and in the conditioning cell before flotation. The surface properties of pyrite exposed to different reagent schemes were investigated by X-ray photoelectron spectroscopy (XPS) analysis. The reactions on pyrite surface responsible for different flotation results were then investigated by cyclic voltammogram (CV) measurements and discussed in terms of a radical chain mechanism involving the redox cycling of Cu(I/II) induced by sulphite species. It was found that the addition of MBS during the conditioning stage was more efficient in depressing the flotation of copper-activated pyrite. This is because the combination of sulphite ions and oxygen may form a strongly oxidising radical S O 5 · - which can oxidise Cu(I)S, the copper activation product on pyrite surface, to form hydrophilic Cu(OH) 2 /CuSO 4. The addition of MBS at low dosages in the mill depressed pyrite flotation to a less extent due to the less oxygen available, while its depression effect was even weakened at high dosages due to the consumption of dissolved oxygen and a strongly reducing environment which favoured copper activation on pyrite surface. [ABSTRACT FROM AUTHOR]

To investigate whether the copper activation of sphalerite can result in the adsorption of xanthate on the S-site of sphalerite surface at the atomic level, the adsorption of ethyl xanthate (EX) molecule on the un-activated and Cu-activated sphalerite (1 1 0) surface in the presence of water molecule were fully investigated. • EX absorption on the S-site of sphalerite surface was simulated using DFT. • For the un-activated sphalerite surface, it only exists weak physical adsorption. • However, for the Cu-activated surface, there is a strong chemical adsorption. • Cu atom on the Cu-activated surface changes the properties of its adjacent S atom. • EX can not only adsorb on the metal atom-site, but also adsorb on the S-site. The research investigates whether the copper activation of sphalerite can result in the adsorption of xanthate on the S-site of sphalerite surface at the atomic level. The adsorption of ethyl xanthate (EX) molecule on the un-activated and Cu-activated sphalerite (1 1 0) surface in the presence of water molecule was conducted by using the density functional theory (DFT). The DFT results showed that there was little chemical interaction between EX and S atom of the un-activated sphalerite (1 1 0) surface. However, the copper activation of sphalerite changed the properties of S atom by inducing a strong covalent interaction between EX and the S atom. The EX molecule did not only adsorbed on the metal atom, but also adsorbed on the S-site. [ABSTRACT FROM AUTHOR]