Sustainable copper extraction from mixed chalcopyrite–chalcocite using biomass

This paper elaborated on the sustainability of the copper extraction process. In fact, an alternative copper extraction route from mixed sulphide ores, chalcopyrite and chalcocite using mesophilic biomass consortium at 33.3 °C and ferric leaching process were attempted. Bioleaching experiments were settled with a fraction size of −75+53 µm. Bacteria were used as the catalyst. A copper yield of 65.50% was obtained. On the other hand, in ferric leaching process, with a fraction size of −53+38 µm, when the temperature was increased to 70 °C, the copper leaching rate increased to 78.52%. Thus, comparatively, the mesophilic bioleaching process showed a more obvious advantage in copper extraction than leaching process with a high temperature. However, it has been resolved from the characterization performed using SEM−EDS, FTIR and XRD observations coupled with different thermodynamic approaches that, the indirect mechanism is the main leaching mechanism, with three transitory mechanisms (polysulphide, thiosulphate and elemental sulphur mechanisms) for the mixed chalcopyrite−chalcocite ore. Meanwhile, the speciation turns into Cu₂S−CuS−Cu₅FeS₄−Cu₂S before turning into CuSO₄. While ferrous oxidation and the formation of ferric sulphate occur, and there is a formation of strong acid as bacteria digest sulphide minerals into copper sulphate at low temperature, which is why this copper production scenario requires a redox potential more than 550 mV at room temperature for high copper leaching rate.     

Study of Reaction Mechanisms for Copper-Cobalt-Iron Sulfide Concentrates in the Presence of Lime and Carbon

The reaction mechanisms for the carbothermic reduction of complex mineral sulfide concentrates in the presence of lime were studied between 1073 K and 1323 K. The reaction mechanisms were studied by stopping the reduction experiments at different times and analyzing the reaction products by x-ray diffraction and scanning electron microscopy techniques. Magnetite (Fe₃O₄) and digenite (Cu_1.8S) were the initial phases formed during reduction of CuFeS₂ and Cu₅FeS₄ mineral particles, such that metallization of iron occurred before copper above 1173 K and at an equal stoichiometric ratio of CaO and C. The metallization of iron was found to take place via reduction of intermediate oxide phase (Fe₃O₄/FeO), whereas metallization of copper occurred via diffusion of S^2? ions away from the mineral particles or via formation of Cu-O-S liquid phase. Metallic iron and cobalt were embedded in the copper matrix due to a preferential reduction of iron and cobalt from the Cu-Fe-S and Cu-Co-S type of mineral particles. The effects of CaO/C ratio were analyzed and the rate of reactions was increasing with an increase in the CaO/C ratio. The formation of liquid phase has been discussed. The experimental results were found to be in good agreement with the thermodynamic predictions.     

Hydrometallurgical recovery of zinc from industrial hot dipping top ash

Top ash from hot-dip galvanizing plant was investigated as a source of secondary zinc to be returned to galvanizing bath. The waste material contained 63% Zn as metallic, oxide and hydroxychloride phases. It was leached in H₂SO₄ solutions (20% and 25%) at various bath loadings (100−300 g/L). Leaching behaviors of zinc, manganese, iron and chloride ions were investigated. A few strategies of iron elimination from leaching liquors were examined. Flocculant addition was harmful for subsequent filtration of iron precipitates due to increased viscosity of solution, while a combination of zinc oxide and calcium carbonate for rising pH resulted in the formation of dense suspension unenforceable to separate from zinc sulphate solution. Zinc electrowinning was carried out at different pH (from −0.5 to 2.8) using a range of current densities (3−10 A/dm²). Optimal conditions for pure metal recovery were: leaching in 20% H₂SO₄ solution at zinc ash content 100−150 g/L, Fe₂O₃·xH₂O precipitation using H₂O₂ and CaCO₃, zinc electrowinning at pH of 0.1−1.0 at 3−6 A/dm². Correlations between pH and free H₂SO₄ concentration in electrolyte solutions were also discussed. pH−acid concentration dependence for zinc electrolyte was between experimental and calculated curves for pure H₂SO₄ solutions, while the curve was shifted towards lower pH if ferric ions were in the solution.     

AES and XPS analyses of CuIn(s1-xsex)2thin films grown by spray pyrolysis technique

Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) analyses of CuIn(S_1−xSe_x)₂ thin films (x = 0.0, 0.5, 0.7 and 1.0) deposited by spray pyrolysis technique have been carried out. AES spectra of as-deposited films showed carbon, chlorine and oxygen as surface contaminants. Sputter etched spectra showed no trace of carbon and chlorine, but about 1.2% oxygen was found to be present. XPS analysis of CuIn(S_1−xSe_x)₂ thin films prepared under optimized conditions revealed the absence of binary secondary phases. However, Cu₂S or CuS was found to be secondary phase in CuIn(S_0.5Se_0.5)₂ thin films.     

Mechanism of electro-generating leaching of chalcopyrite-MnO2 in presence of Acidithiobacillus thiooxidans

A dual cell system with chalcopyrite anode and MnO2 cathode was used to study the relations between time and such data as the electric quantity and the dissolution rates of the two minerals in the electro-generating leaching（EGL） and the bio-electro-generating leaching（BEGL）, respectively. The results showed that the dissolution rates for Cu^2＋ and Fe^2＋ in BEGL were almost 2 times faster than those in EGL, and nearly 3 times for Mn^2＋; the electric output increased nearly by 3 times. The oxidation residue of chalcopyrite was represented by TEM and XRD, whose pattern was similar to that of the raw ore in EGL. The mechanism for leaching of CuFeS2-MnO2 in the presence of Acidithiobacillus thiooxidans was proposed as a successive reaction of two independent sub-processes for the anode. The first stage, common to both processes, is dissolution of chalcopyrite to produce Cu^2＋, Fe^2＋ and sulfur. The second stage is subsequent oxidization of sulfur only in BEGL, which is the controlling step of the process. However, the dissolution of MnO2 lasts until the reaction of chalcopyrite stops or the ores exhaust in two types of leaching.     

Corrosion behavior of Cu/Al casting-rolled clad plates in different alkaline solution

The effect of pH value and different kinds of anions on the corrosion behavior of Cu/Al casting-rolled clad plates in the alkaline solution was evaluated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), weight loss analysis, 3D confocal laser scanning microscopy (CLSM) and electrochemical test. Results show the corrosion mainly occurs on the aluminum side. The corrosion resistance of the Cu/Al decreases as the pH value increases. When pH≥12, the dissolution of the film layer is faster than the passivation process. The addition of Cl⁻ ions reduces the corrosion resistance of the Cu/Al clad plates, which leads to pitting corrosion. The higher the concentration of Cl⁻ ions, the more prone the pitting to occur. The addition of SO₄²⁻ ions causes the denudation of the samples. The corrosion resistance of the Cu/Al is better in the alkaline solution containing NO₃⁻ ions than that in the solution containing Cl⁻ ions or SO₄²⁻ ions. When adding SO₄²⁻, NO₃⁻ and Cl⁻ to the pure alkaline solution, the corrosion resistance of the Cu/Al clad plates decreases.

     

Effects of iron-containing phases on transformation of sulfur-bearing ions in sodium aluminate solution

Sulfides in the high-sulfur bauxite lead to serious steel equipment corrosion and alumina product degradation via the Bayer process, owing to the reactions of sulfur and iron-containing phases in the sodium aluminate solution. The effects of iron-containing phases on the transformation of sulfur-bearing ions (S^2–, S₂O₃^2?, SO₃^2? and SO₄^2?) in sodium aluminate solution were investigated. Fe, Fe₂O₃ and Fe₃O₄ barely react with SO₃^2? and SO₄^2?, but all of them, particularly Fe, can promote the conversion of S₂O₃^2? to SO₃^2? and S^2– in sodium aluminate solution. Fe can convert to Fe(OH)₃^? in solution at elevated temperatures, and further react with S^2– to form FeS₂, but Fe₂O₃ and Fe₃O₄ have little influence on the reaction behavior of S^2– in sodium aluminate solution. Increasing temperature, duration, dosage of Fe, mole ratio of Na₂O_k to Al₂O₃ and caustic soda concentration are beneficial to the transformation of S₂O₃^2? to SO₃^2? and S^2–. The results may contribute to the development of technologies for alleviating the equipment corrosion and reducing caustic consumption during the high-sulfur bauxite treatment by the Bayer process.     

Investigation of the Interaction Between Cu2-x S +So Coatings and Pd(II) Ions by Cyclic Voltammetry and X-ray Photoelectron Spectroscopy

The interaction between Pd²⁺ ions and Cu_2-xS coating formed by three cycles and containing ~30 at.% of elementary S has been investigated by the methods of cyclic voltammetry and photoelectron spectroscopy (one cycle of coating formation includes treatment of the surface with Cu(I)+Cu(II) ammoniate solution, hydrolysis of the adsorbed copper compounds and sulphidation of copper oxygen compounds in Na₂S_n solution). After exposure of such a coating to Pd²⁺ ions (1.7 mM PdCl_2’ pH-2), an exchange as well as a redox interaction between the coating components and Pd²⁺ ions has been shown to occur. Due to this the amount of copper in the coating decreases from 2 to 4 times and that of sulphur from 1.5 to 5 times. The coating modified in such a way has been found to contain up to 75 at.% of palladium, ~90% of it being in a metallic state.

It has been determined that at the beginning S^o is bound into a soluble compound:

2Pd²⁺ + S^o + 3H₂O → 2Pd^o + H₂SO₃ + 4H⁺.

The Cu₂S present in the coating is considered to interact with Pd²⁺, with the formation of Pd⁰ and CuPdS_2’, while CuS reacts most likely according to the reaction:

CuS + 3Pd²⁺ + 3H₂O → 3Pd^o; + H₂SO₃ + Cu²⁺ + 4H⁺.

The Cu_2-xS +S^o coating formed on a dielectric and modified with Pd²⁺, contrary to the initial Cu_2-xS +S^o coating, can be plated with copper from any electrolyte for copper deposition.     

A Study of the Interaction of Cu2-xS Coatings with S42- Ions by the Method of Cyclic Voltammetry

The interaction between Cu_2-xS (1<(2-x)<2) coatings without elemental sulphur and 0.01 M Na₂S₄ has been studied by cyclic voltammetry in 0.05 M H₂SO₄.

It has been shown that elemental sulphur forms in the Cu_2-xS coating exposed to Na₂S₄ solution. The highest S^o amount (2·10^?8 mol cm² during the first 30 s) has been found to be formed when the coating held in Na₂S₄ solution was Cut_1.25S. This is explained by the fact that during interaction of a Cu_2-xS coating with Na₂S₄ solution the unstable mixed polysulphides of Cu(I) and Cu(II) can be formed, e.g. in the case of Cu_1.25S (Cu₂S₄) the compound Cu₅S₇ can arise:

Cu^I₂Cu^II₃S₄ + Na₂S₄ → Cu^I₂Cu^II₃S₇ + Na₂S

which is again decomposed, initially into Cu₅S₄ and S^o:

Cu^I₂Cu^II₃S ₇ → Cu^I₂Cu^II₃S₄ + 3S^o

It is supposed that this process can recur and due to this four modifications of S^o arise as the time of treatment is increased. Stoichiometric sulphide Cu_l.99S does not interact and CuS interacts insignificantly with Na₂S₄ (after 30 s 0.4·10⁸ mol cm² of S is formed).

In a real process the contribution from the coating is supposed not to exceed several per cent.     

Influence of anions on the formation of artificial steel rust particles prepared from acidic aqueous Fe(III) solution

For simulation of atmospheric corrosion of steels, artificial steel rust particles were prepared in acidic aqueous solutions containing FeCl₃, Fe(NO₃)₃ and Fe₂(SO₄)₃. A single phase α-FeOOH was formed in only Fe(NO₃)₃ system. The β-FeOOH was formed by added Cl⁻ in FeCl₃–Fe(NO₃)₃ system. Adding SO₄²⁻ in Fe(NO₃)₃, FeCl₃ and a mixture of FeCl₃–Fe(NO₃)₃ solutions turned the products following as α- or β-FeOOH → Schwertmannite (Fe₈O₈(OH)₆(SO₄)·nH₂O). Further, increasing the added SO₄²⁻ suppressed the formation of steel rust particles. Accordingly, the influence of anions on the formation of steel rust particles was to be suggested in order of SO₄²⁻ ≫ Cl⁻ > NO₃⁻.     

Corrosion and deposition during the exposure of carbon steel to hydrogen sulphide-water solutions

Complex multi-phase corrosion films develop on rotating carbon steel discs exposed to aqueous hydrogen sulphide solutions; their structure and morphology can have a profound effect on the corrosion process. Iron sulphide corrosion products formed on corroding carbon steel discs in titanium autoclaves have been characterized after exposure periods ranging from 1 to 840 h at temperatures of 308, 373 and 433 K and a total initial pressure of 1.5 MPa. These reaction conditions pertain to the Girdler-Sulphide process for separating heavy water. In oxygen-free solutions, the evolution of corrosion products on the discs progresses from iron-rich to sulphur-rich phases according to the sequence, mackinawite (tetragonal FeS_1?x) → ferrous sulphide (cubic FeS) → troilite (hexagonal FeS) → pyrrhotite (hexagonal Fe_1?xS) → pyrite (cubic FeS₂), the latter phase being thermodynamically favoured. All phases except mackinawite appear as characteristic microcrystals of regular geometry, indicating relatively slow solution growth at low supersaturation. Higher temperatures accelerate the sequential transformations while higher speeds of rotation of the disc retard it. Edge turbulence induced at high rotation frequencies prevents the formation of solution-grown phases. Added oxidants promote the formation of the disulphide ion required for FeS₂ formation. Fe²⁺ ions released to the bulk solution by dissolution of the base metal and metastable sulphides are deposited as pyrrhotite or pyrite on the titanium vessel. The S₂^2? ion required for pyrite deposition is thought to arise by electro-oxidation of a sulphide species at the titanium surface.     

Influence of high concentration Zn2+ on floatability of sphalerite in acidic system

The influence of high concentration Zn²⁺ on the floatability of sphalerite in an acidic system was investigated via flotation experiments, zeta potential measurements, contact angle measurements, and X-ray photoelectron spectroscopy. The results indicated that Zn²⁺ was adsorbed on the sphalerite surface and a Zn-hydroxyl complex was formed at a pH of 4 and a Zn²⁺ concentration of 4×10⁻² mol/L. The zeta potential increased and the contact angle decreased from 84.80° to 36.48°, strongly inhibiting the floatability of sphalerite. When S²⁻ or Cu²⁺ activator was used alone, sphalerite was not activated after Zn²⁺ was adsorbed, and its contact angle did not change significantly. However, by using a combination of S²⁻ and Cu²⁺ activators, its floatability was realized after Zn²⁺ adsorption. This result was attributed to the removal of the Zn-hydroxyl complex on the surface of sphalerite by S²⁻. After this removal, Cu²⁺ was adsorbed on the sphalerite surface to form a Cu₂S·S⁰ hydrophobic film.     

The effect of the precipitation conditions on the morphology and the sorption properties of CuS particles

The effect of the nature of the copper salt precursor anion and the pH of a solution on the morphology and the phase composition of CuS particles has been studied upon precipitation from thiourea solutions. It has been established that, irrespective of the precipitation conditions, generation of the CuS phase and the chalcanthite impurity phase CuSO₄ ? 5H₂O is recorded according to the X-ray diffraction analysis data. At pH 8 and a c((NH₂)₂CS): c(Cu²⁺) ratio of 1: 1, from nitrate solutions a fine powder is formed that consists of spherical particles smaller than 100 nm in size. An increase in the c((NH₂)₂CS): c(Cu²⁺) ratio and in the precipitation pH results in coarser particles of up to 1.5 μm in size. The replacement of the salt precursor anion by SO₄^2- facilitates the decrease in the spherical particle size to 1 μm and that by Cl^– to 0.7 μm. The synthesis conditions of the CuS sorbent that control the latter’s morphological properties have an effect on the sorption of cadmium from aqueous solutions.     

Laboratory scale investigation into the corrosion of copper in a sulphur-containing environment

The effect of temperature and gas composition on the corrosion rate and corrosion by-product of copper foil was studied by exposing it to sulphur (S₂), S₂ + hydrochloric acid (HCl) and hydrogen sulphide. The temperature was varied from 80 to 140 °C. Copper foil reacted with S₂ to form CuS, Cu₉S₈ and Cu_1.8S. Corrosion rates ranged from 9.6 μm/h at 110 °C to 0.5 μm/h at 140 °C. The presence of HCl caused pitting and enhanced the corrosion rate above 112 °C. Cu₂S formed when copper was exposed to hydrogen sulphide gas. Sulphide scale that formed was friable and non-adherent.     

Selective leaching of arsenic from copper converter flue dust by Na2S and its stabilization with Fe2(SO4)3

The alkaline leaching of arsenic (As₂O₃) by Na₂S, together with its precipitation by Fe₂(SO₄)₃ was studied. Response surface methodology based on central composite design was employed to quantify and qualify the effect of pertinent factors and to develop statistical models for optimization purposes. Based on the obtained results, 89% of arsenic is removed from the dust under following optimum predicted conditions: Na₂S concentration of 100 g/L and solid to liquid ratio of 0.163 g/mL at 80 °C. It is found that solid to liquid ratio and Na₂S concentration are the significant factors influencing the leaching process. In the precipitation process, more than 99.93% of arsenic from the leaching solution is removed in the form of amorphous ferric arsenate, at pH 4.8 when Fe³⁺ to arsenic and H₂O₂ to arsenic molar ratios are set at 5:1 and 4:1, respectively. Also, Fe³⁺ to arsenic ratio and pH are the most significant factors, and the interaction between these terms is significant.     

Extraction of valuable metals from low nickel matte by calcified roasting−acid leaching process

A calcified roasting−acid leaching process was developed as a highly effective method for the extraction of valuable metals from low nickel matte in the presence of CaO additive. The influences of process parameters on the metal extraction were studied, including the roasting temperature, roasting time, addition of CaO, H₂SO₄ concentration and liquid−solid ratio. Under the optimum condition, 94.2% of Ni, 98.1% of Cu, 92.2% of Co and 89.3% of Fe were recovered. Additionally, 99.6% of Fe was removed from the leachate as goethite by a subsequent goethite iron precipitation process. The behavior and mechanism of CaO additive in the roasting process was clarified. The role of CaO is to prevent the formation of nonferrous metal ferrite phases by a preferential reaction with Fe₂O₃ during the roasting process. The metal oxides (CuO and Ni_xCu_1−xO) remained stable during high-temperature roasting and were subsequently efficiently leached using a sulfuric acid solution.     

The Sulfidation of Two-Phase Fe-Cu Alloys in H2-H2S Mixtures at 500-700°C

The sulfidation behavior of three two-phaseFe-Cu alloys containing 25, 50, and 75 wt.% copper hasbeen investigated in H₂-H₂Smixtures at 500-700^°C under gas-phase sulfur pressures, which is significantly abovethose for the dissociation of both FeS andCu₂S. In all cases, the three alloyssulfidized more slowly than both pure metals under thesame conditions. At all temperatures, Fe-25Cu showed the slowestgrowth rates, whereas Fe-50Cu sulfidized more rapidlythan the other two alloys. However, the kinetics curvesfor the three alloys tended to overlap, particularly at the higher temperatures. The scales werecomplex and contained an outer layer composed of amixture of two different Cu-Fe double sulfides,Cu₅FeS₄ and CuFeS₂,plus an inner zone containing a mixture of metalliciron with the double sulfideCu₅FeS₄formed by completesulfidation of the copper-rich phase and partialsulfidation of the iron-rich phase. This region also contained large voids,possibly because of outward diffusion of metal cations,whereas the iron-rich islands were mainly unattacked.The depth of internal attack increased with increasing temperature and/or iron content. Finally,particles of almost pure copper metal, probably formedduring cooling from the reaction temperature, werepresent at the scale-subscale interface, as inclusions in the scale and as whiskers protruding out ofthe external scale surface.     

The Role of Cu(I) in the Process of Forming Cu2–xS Coatings by a Chemical Route

The interaction of the Cu₂O adsorbed with Na₂S_n (n = 1–4), during formation of the Cu_2–xS coatings has been investigated by cyclic voltammetry.

The summarized reaction of this process has been shown to correspond to the equation:

Na₂S_n + Cu₂O_ad + H₂0 → Cu₂S_ad + (n–1)S^o + 2NaOH,

where S^o/Cu=(n–1)/2. Such a stoichiometry of reaction can be explained by the formation of an intermediate—the adsorbed polysulphide of Cu(I)—and by its subsequent decomposition into Cu₂S and S^o.

When a thicker coating is being formed, i.e., when the surface being coated is repeatedly immersed into an ammoniate solution of Cu(I) and S^o fully bounded:

S^o_ad + 2 Cu⁺ → CuS + Cu²⁺.

At the same time due to different solubility products (L=2.5·10^?48 and 6.3·10^?36 for Cu₂S and CuS respectively), an exchange

CuS_ad + 2(1–x)Cu⁺ → Cu_2–xS_ad+ (1–x)Cu²+ occurs.

After formation of Cu²⁺, parallel processes characteristic for the interaction of Cu(II) with Na₂S_n start to take place, during which S^o is also formed.     

Thermodynamic analysis of Na-S-Fe-H2O system for Bayer process

Thermodynamic diagrams of Na-S-Fe-H₂O system were constructed to analyze the behavior of sulfur and iron in the Bayer process. After digestion, iron mainly exists as Fe₃O₄ and Fe₂O₃ in red mud, and partial iron transfers into solution as Fe(OH)₃^-, HFeO₂^-, Fe(OH)₄^- and Fe(OH)₄^2-. The dominant species of sulfur is S^2-, followed by SO₄^2-, and then SO₃^2- and S₂O₃^2-. The thermodynamic analysis is consistent with the iron and sulfur species distribution in the solution obtained by experiments. When the temperature decreases, sulfur and iron can combine and precipitate. Controlling low potential and reducing temperature are beneficial to removing them from the solution. XRD patterns show that NaFeS₂·2H₂O, FeS and FeS₂ widely appear in red mud and precipitates of pyrite and high-sulfur bauxite digestion solution. Thermodynamic analysis can be utilized to guide the simultaneous removal of sulfur and iron in the Bayer process.     

Studies on copper-semiconducting layer-electrolyte systems—I. Electrode potentials of copper and electrodeposited copper sulphide in S2− and Cu2+ media

Copper sulphide layers electrodeposited from a Na₂S bath consist chiefly of cuprous sulphide. Calculated values of the specific conductance of the deposited sulphide average around 3·8 × 10^?5 ohm^?1.cm^?1.Electrode potentials, E_H, of the Cu/Cu_2?δS in unbuffered Na₂S solutions and in solutions buffered at pH 9, correspond to the behaviour of a Cu/Cu_2?δS, overlayered with CuS/electrolyte. Steady reproducible potentials are obtained with the above electrodes in 0·5–10^?3M CuSO₄ solutions, closely comparable with those of the reversible Cu/Cu²⁺ couple.