Mathematical modeling of thermophilic bioleaching of chalcopyrite

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

The effect of seawater based media on copper dissolution from low-grade copper ore

Due to the scarcity of water in the north of Chile, there is interest in small-scale mining using seawater to leach the minerals. This situation has led to this research aimed to determine the effect of different process variables on the extraction of copper based on the ore type of these small-scale mining activities. The extraction of copper from finely ground (<150 μm) low-grade mixed ore (0.36% Cu) was studied in different acidic media (H₂SO₄ and HCl). The effects of water quality (tap water, seawater and synthetic process water) and lixiviants on copper leaching were investigated at three temperatures (25 °C, 35 °C and 45 °C). Synthetic process water was prepared by adding Na⁺, Cl⁻, Cu²⁺ and SO₄²⁻ to seawater. Copper extractions between 70% and 80% were achieved in 48 h using seawater, similar to the extractions obtained using tap water. Rapid copper dissolution occurred when synthetic process water was used, from 90% to 97%. This marked increase was related to the addition of Cu²⁺, which promoted the formation of CuCl⁺. Seawater was comparable to freshwater in terms of leaching kinetics and yield potential by raising the chloride concentration and increasing the formation of copper chloride ions. The findings of this study also expanded our understanding of the consequences of substituting seawater for freshwater at industrial leaching operations.     

Synthesis of 2-ethyl-2-hexenal oxime and its flotation performance for copper ore

A novel collector 2-ethyl-2-hexenal oxime was synthesized from 2-ethyl-2-hexenal and hydroxylamine hydrochloride. The yield of oxime was 78.05% under the optimum experimental conditions. The oxime was characterized by elemental analysis, infrared spectrum, mass spectrum, ¹H NMR and ¹³C NMR spectroscopy. The results of ultraviolet spectrum showed that the oxime exhibited stronger reaction affinity with Cu²⁺ than with Ni²⁺ or Fe³⁺, etc. Infrared spectroscopic analysis implicated that the oxime bound to Cu²⁺ through both the CC and CN groups. Microflotation tests of pure malachite mineral and chalcopyrite mineral indicated that the recovery of chalcopyrite was 91.16% under the flotation condition of rougher pH 10 and collector concentration of 200 mg/L, and the recovery of malachite reached 90.56% under the flotation condition of rougher pH 11.5 and collector concentration of 250 mg/L. The results of flotation tests of sulfide–oxide copper from Dexing copper mine showed that 2-ethyl-2-hexenal oxime achieved an excellent mean concentration containing 4.52% Cu with 79.54% Cu recovery, and the Cu average recovery increased by 2.35% compared to that of butyl xanthate.     

Copper leaching from waste electric cables by biohydrometallurgy

This study examines the leaching of copper from waste electric cables by chemical leaching and leaching catalysed by Acidithiobacillus ferrooxidans in terms of leaching kinetics and reagents consumption. Operational parameters such as the nature of the oxidant (Fe³⁺, O₂), the initial ferric iron concentration (0–10 g/L) and the temperature (21–50 °C) were identified to have an important influence on the degree of copper solubilisation. At optimal process conditions, copper extraction above 90% was achieved in both leaching systems, with a leaching duration of 1 day. The bacterial leaching system slightly outperformed the chemical one but the positive effect of regeneration of Fe³⁺ was limited. It appears that the Fe²⁺ bio-oxidation is not sufficiently optimised. Best results in terms of copper solubilisation kinetics were obtained for the abiotic test at 50 °C and for the biotic test at 35 °C. Moreover, the study showed that in same operating conditions, a lower acid consumption was recorded for the biotic test than for the abiotic test.     

Passivation of chalcopyrite during its chemical leaching with ferric ion at 68 °C

The passivation of chalcopyrite in the presence of ferric sulphate solutions was investigated at 68 °C. The effect of different variables (pulp density, pH and the presence of oxygen) on both the copper dissolution rate and the formation of solid compounds was studied. The leaching tests were carried out in stirred flasks at 180 rpm with 100 mL of a Fe³⁺/Fe²⁺ sulphate solution, varying the pulp density between 0.1 and 5% and the pH between 0.5 and 2.0 and both in aerobic and anaerobic conditions. Ferric ion seems to be responsible for the oxidation of chalcopyrite but also promotes its passivation. Ferrous ion plays a key role in the process by controlling the nucleation and precipitation of jarosites, which finally cause the passivation of chalcopyrite.     

Modification of ilmenite surface properties by superficial dissolution method

Acid surface dissolution as a pretreatment method converts Fe²⁺ ions on the ilmenite surface to Fe³⁺ ions. XPS analysis showed that the content of Fe³⁺ increases from 48.5% to 59.8% after surface dissolution for 15 min in a solution of sulfuric acid with a concentration of 10%. This conversion, without any phase transformation, decreases the zeta potential of ilmenite in a wide pH range, resulting in a shift in IEP (Iso-Electric Point) from a pH of 5.4 to 2.3. FTIR spectra and zeta potential measurements showed that the increase of oleate ions adsorption on the ilmenite surface, resulting from the surface dissolution process, is insignificant. After surface dissolution, the formation of more ferric iron oleate species (Ksp = 10^−29.7) being more stable than ferrous iron oleate (Ksp = 10^−15.5) compounds yields an increase of ilmenite hydrophobicity and floatability in a wide pH range. Using 3.65 × 10⁻⁴ M sodium oleate at a pH of 6.3, the maximum flotation recoveries are obtained as 73.5% and 92% for non-treated and acid pretreated ilmenite, respectively.     

Biological treatment of wastewater produced during recycling of spent lithium primary battery

Wastewater produced during recycling of spent lithium primary battery was biologically treated with Acidithiobacillus ferrooxidans to decrease the pH and metal concentration. Since the wastewater contains high concentrations of Cr, Ni, and Li, the effects of these metals on the bacterial activity in a 9 K medium were also investigated. Samples of the medium with different metal concentrations were treated, and the oxidation ratio of Fe²⁺ ions was measured to examine the activity of bacteria. In the treatment of simulated wastewater, the presence of Cr and Ni ions with concentrations of 8000 g m^?3 and 13,000 g m^?3, respectively, did not inhibit the bacterial activity, whereas the oxidation ratio of Fe²⁺ ions was observed to be low in the medium when Li ion was present with a concentration at 5000 g m^?3. This observation suggested that at this concentration, Li ion suppressed the bacterial activity. In the case of treatment of real wastewater containing Cr, Ni, and Li, the oxidation ratio of Fe²⁺ to Fe³⁺ was observed to be low while the Fe concentration and pH decreased to 21,633 g m^?3 and 1.8, respectively. Thus, the wastewater produced during the recycling of spent lithium primary batteries can be effectively treated biologically for re-circulating in the recycling process.     

Bioleaching of djurleite using Acidithiobacillus ferrooxidans

The bioleaching of djurleite using Acidithiobacillus ferrooxidans (LD-1) was investigated in this paper. Experiments were carried out in shake flasks at pH 2.0, 160 r/min and 30 °C. The leaching residues were analyzed using X-ray diffraction (XRD), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The total copper extraction of djurleite under optimal condition reached 95.12%. The XRD analysis indicated the residues mainly consisted of ammoniojarosites and S₈. It was observed by the SEM image that the djurleite was heavily etched. The XPS results confirmed the intermediate product formed during djurleite leaching was CuS. The result indicates the reaction pathway is: Cu₃₁S₁₆ → CuS → tCu²⁺ and S⁰.     

Electrocoagulation as a remediation tool for wastewaters containing arsenic

This work shows results of electrocoagulation of solutions containing arsenic. The continuous flow treatment consisted of an electrocoagulation reactor with two parallel iron plates and a sedimentation basin.The results showed that the electrocoagulation process of a 100 mg/L As(V) solution could decrease the arsenic concentration to less than 2 mg/L in the effluent with a current density of 1.2 A/dm² and a residence time of around 9 min. Liquid flow was 3 L/h, and the DC current was reversed each 2 min.Increasing the current density from 0.8 to 1.2 A/dm², the Fe³⁺ and OH⁻ dosages increase too, and thereby favouring the As removal. On the other hand, it seems that increasing the current density beyond a maximum value, the electrocoagulation process would not improve further. This could probably be explained by passivation of the anode.     

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

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

The effect of redox control on the continuous bioleaching of chalcopyrite concentrate

A continuous bioleaching process was developed for the dissolution of chalcopyrite concentrate with electrochemically redox control. Therefore, using a flotation concentrate containing 46% chalcopyrite and 23% pyrite, bioleaching tests were carried out at 47 °C with 15% pulp density under controlled and uncontrolled redox conditions. To increase the copper recovery in contrast to the conventional bioleaching (∼39.62%), the effect of redox potential on the chalcopyrite bioleaching was investigated by electrochemically controlled bioleaching. The results showed that by controlling the redox potential, faster copper leach kinetics could be achieved. At last, reducing the redox potential from high levels to optimum window (420–440 mV SCE) caused an increase in copper recovery from around 39% to higher than 69% (over 25 g/L Cu²⁺).     

Selective and direct sorption of zirconium from acidic leach liquor of zircon concentrate by rice bran

A new method for extraction of zirconium from leach liquor of zircon concentrate is proposed. The procedure is based on the adsorption of Zr(IV) ions on rice bran. The sorption capacity of the biomass for zirconium is 50 mg g^?1. Adsorption equilibrium was achieved in less than 1 min and slightly affected by solution acidity. In the optimum conditions, the adsorption efficiencies of other associated metal ions such as Ti⁴⁺, Fe³⁺, Al³⁺, La³⁺, Ce³⁺ were significantly lower than Zr(IV) ion and this biomass is excellent sorbent for the selective uptake of zirconium from acidic aqueous solutions.     

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

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

Possibilities for Co(III) dissolution from an oxidized ore through simultaneous bioleaching of pyrite

Solubilisation of Co(III) from a heterogenite met in copper cobaltiferous oxide ore has been realized through reductive leaching using ferrous iron generated via bio-oxidation of pyrite. Biotic and abiotic experiments at various pulp densities and redox potentials have been performed and results compared. Cobalt leaching at elevated redox potential is possible, offering cost reduction benefits due to reduced consumption of ferrous iron. At elevated potential of 625 mV, however, the initial rate of cobalt leaching has been found as 115 mg/(g ore)⋅(24 h), lower than the rate of 865 mg/(g ore)⋅(24 h) registered at 505 mV. Less stochiometric amount of ferrous iron was required when cobalt leaching was coupled to pyrite bioleaching, with 75% of cobalt recovered for 12 h at the optimally found conditions. It could be inferred that the Fe³⁺–Fe²⁺ cycle exists and is efficiently maintained through bacterial presence in the studied system.     

The effect of flotation and parameters for bioleaching of printed circuit boards

Waste electrical and electronic equipment (WEEE) is currently one of the fastest growing waste streams in the world. Typical for WEEE is the high content of valuable and precious metals, as well as harmful contaminants like halogens, flame retardant chemicals and plastics. Currently, WEEE treatment and metal recovery methods are imperfect, polluting and energy intensive. In this paper, novel treatment possibilities are outlined for printed circuit boards (PCB) utilizing both the flotation separation technique and acid bioleaching. Flotation, conducted after crushing and sieving of PCB, produced two fractions: metal-rich concentrate, which is more suitable for pyrometallurgical treatment than untreated PCB, and metal-poor froth suitable for acid bioleaching. It was seen that especially low pH (1.6), high initial Fe²⁺ concentration (7.8 g/l) and low PCB froth concentration in the bioleaching solution (50 g/l) were beneficial for the rapid and selective dissolution of copper. With these parameters, 99% of copper was solubilized from PCB froth in bioreactor treatment, with Cu (6.8 g/l) and Fe (7.0 g/l) being the only major metallic elements in bioleaching solution.     

Kimberlite weathering: Effects of organic reagents

Kimberlite material is one of the primary sources of diamonds. Accelerated weathering that leads to a physical breakdown of the material over a short period of time has possible benefits in diamond processing such as reduction in the energy consumption when used as a pre-comminution stage. This study investigated accelerated weathering by utilising organic reagents; acetic acid, ethanol, formamide, n-hexane, oxalic acid, and urea, in comparison to the use of Cu²⁺ solution that was previously shown to be very effective in weathering kimberlite. Oxalic acid was the organic agent that showed promising weathering capabilities. However, the use of organic solutions was not as efficient as with Cu²⁺ solutions. Results showed that 67% of the particles passed 12 mm screen size in Cu²⁺ weathering compared to 48% in oxalic acid. It was also found that time of exposure had a small effect on weathering. Increasing the organic chemical concentration twofold, from 0.025 M to 0.5 M, improved weathering by ∼20% points. Different weathering mechanisms were observed at different solution concentration between oxalic acid (1st to 2nd order) and Cu²⁺ (2nd to 3rd order).     

Release of arsenic from cyanidation tailings

At a gold mine in northern Sweden, gold occurring as inclusions in pyrrhotite and arsenopyrite is leached by cyanidation of the ore. The main sulphide minerals in the ore are pyrrhotite and arsenopyrite. Effluents from the cyanidation process are treated with Fe₂(SO₄)₃ to form Fe-precipitates suitable for the co-precipitation of As. The aim of this study was to perform static and kinetic leaching tests on the ore and tailings to define geochemical processes governing As mobility. Sequential leaching tests suggested that the majority of dissolved As deriving from the sulphide fraction in the ore was incorporated in newly formed Fe-precipitates in the tailings. The mobility of As in the tailings was therefore mainly dependent on the stability of these As-bearing Fe-precipitates. Weathering cell tests (WCT) involving 31 weekly cycles of wetting and air exposure were conducted to assess the stability of the As in the tailings under accelerated weathering conditions. The first stage of the WCT was characterized by a pH ≈ 5 and low As leaching, probably driven by the dissolution of amorphous Fe-As species. In the second stage of the WCT, leaching of Fe, S and As increased and the pH decreased to <3.5. An increase of the leachate’s molar Fe/S-ratio suggested that pyrrhotite oxidation was occurring. The falling pH destabilized As-bearing Fe-precipitates, causing further As release. The total As release during the WCT corresponded to only a small proportion of the tailings’ total As content. The accelerated As-leaching observed towards the end of the WCT could thus indicate that its release could increase progressively over time.     

Investigating heap bioleaching: Effect of feed iron concentration on bioleaching performance

This paper describes an investigation into the effect of iron concentration in the leach solution on the bioleaching of a low grade copper ore, where chalcopyrite was the dominant copper sulphide. The concentration of dissolved iron is primarily controlled by pH and the relative proportion of ferric to ferrous iron, with significant jarosite precipitation occurring above pH ≈ 1.8 in a highly oxidised system. The solution pH may be increased by the dissolution of acid soluble gangue and when iron oxidation is significantly higher than sulphur oxidation. The study was approached using two experimental systems. In the former, the leach solution was recycled through an ore bed of low aspect (reactor height divided by diameter) ratio for a portion of the experiment. During the recycle phase, no acid was added to the system and acid consumption by gangue material led to a pH increase (1.6–2.2). The resulting jarosite precipitation reduced soluble iron from 2.5 g/l to less than 250 mg/l. Copper recovery decreased, but not in proportion to the decrease in iron. This was partly attributed to adsorption on, or entrainment within, the jarosites. To study the effect of reduced iron concentration on leach performance under more controlled conditions, bioleaching was performed in packed bed column reactors with feed iron concentrations ranging from 5 g/l to 200 mg/l. Observations indicated an initial decreased rate of copper liberation with reduced iron concentration in the feed. The relationship between available Fe³⁺ concentration and copper liberation was not proportional. However, with time, the liberation of copper became independent of iron concentration in the percolation liquor. Further, the specific rate of copper liberation was consistently below the theoretical value on a basis of ferric iron concentration. The highest values of copper liberation were reported at the lowest iron concentrations. In summary, while increased iron concentration in solution may enhance the initial rate of leaching, mineral availability appears to dominate CuFeS₂ leach kinetics through the majority of the leach. Furthermore, high iron concentrations in solution aggravate jarosite formation with concomitant retention of copper in the ore bed.     

Simultaneous determination of iron and copper in pregnant liquid solutions

A new method for the determination of Fe_Total and Cu is proposed. The method is based on the formation of the iron and copper complexes with 5-sulfosalicylic acid (SSA), the optimal conditions were found, using SSA 5.1 g L⁻¹ in the presence of ammonia 7.5 g L⁻¹ (pH = 10). Under these conditions the selected analytical wavelengths were 488.5 and 423.5 nm for the determination of iron and copper, respectively, by using the zero crossing approach. The detection and quantification limits were 0.02 mg L⁻¹ and 0.07 mg L⁻¹ for iron and 1.14 mg L⁻¹ and 3.80 mg L⁻¹ for copper. The proposed method was applied to the determination of both analytes in pregnant liquid solutions and the recovery was between 98% and 100% and in all cases the relative standard deviation was minor to 2%.