Hydrometallurgical process for the recycling of copper using anodic oxidation of cuprous ammine complexes and flow-through electrolysis

Flow-through electrolysis for copper electrowinning from cuprous ammine complex was studied in order to develop a hydrometallurgical copper recycling process using an ammoniacal chloride solution, focusing on the anodic oxidation of cuprous to cupric ammine complexes. The current efficiency of this anodic oxidation was 96% at a current density of 200 A m⁻² under a batch condition. In a flow-through electrolysis using a sub-liter cell and a carbon felt anode, the anodic current efficiency increased with the flow rate and was typically higher than 97%. This tendency was explained by the backward flow of the cupric ammine complex, which was formed on the anode, through the diaphragm. The anodic overpotential was lower than 0.3 V even at an apparent current density of 1500 A m⁻². A similar current efficiency and overpotential were also achieved in a liter scale cell, which indicates the scale flexibility of this electrolysis. The power consumption requirements for copper electrowinning in this cell were 460 and 770 kWh t⁻¹ at the current densities of 250 and 500 A m⁻², respectively, which were much lower than that of the conventional copper electrowinning despite the longer interpolar distance.     

Copper recovery and simultaneous COD removal from copper phthalocyanine dye effluent using bipolar disc reactor

Electrochemical treatment of real acidic effluent of copper phthalocyanine dye manufacturing plant with a view to explore the feasibility of the simultaneous removal of copper and phthalocyanine using a bipolar disc electrochemical reactor has been investigated. Experiments were conducted in a bipolar capillary gap disc stack electrochemical reactor under batch recirculation mode. Electrodes were RuO₂ and IrO₂ coated on titanium as anode and titanium as cathode. Effects of current density, electrolysis time and effluent flow rate on copper recovery and simultaneous COD removal and energy consumption were critically examined. The current density of 2.5 A dm⁻² and flow rate of 20 L h⁻¹ achieved 91.1% COD removal and 90.1% copper recovery with the energy consumption of 50.86 kWh kg⁻¹ for COD removal and simultaneous recovery of copper in a bipolar disc stack reactor.     

Nanotribology at single crystal electrodes: Influence of ionic adsorbates on friction forces studied with AFM

We present friction force measurements on Au(1 1 1) single crystal electrode surfaces performed under electrochemical conditions using an atomic force microscope (AFM). At monoatomic steps friction is increased in both scan directions. In 0.05 M sulfuric acid an increase of friction is observed with the increase of adsorbed sulfate. Friction force increases non-linearly with load. Cu UPD also increases friction in presence of sulfate. However, in presence of 4 × 10⁻⁴ M chloride friction is much smaller for all deposited Cu coverages - ranging from a submonolayer up to bulk copper compared to the solution without chloride. After dissolution of bulk copper clusters deposited on Au(1 1 1) we observed an area with higher friction forces due to the formation of an alloy between gold and copper.     

Influence of 8-aminoquinoline on the corrosion behaviour of copper in 0.1 M NaCl

The corrosion behaviour of copper in aerated 0.1 M NaCl solution in presence of 8-aminoquinoline (8-AQ), using open circuit potential (OCP) measurements, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) measurements and atomic force microscopy (AFM), was studied. The measurements revealed that the effect of 8-AQ is dependent on its concentration. For concentrations up to 10⁻³ M, the organic compound displaces the corrosion potential following no trend and also reduces the anodic current. In contrast, for concentrations higher than 10⁻³, 8-AQ reduces markedly both, the anodic and cathodic currents and consequently, the corrosion current density of copper. After 9 days of exposure in chloride solution, containing the organic compound, potentiodynamic polarization analyses showed a significant reduction in the anodic response and a less significant reduction in the cathodic response, which is associated with a film formed at the copper surface of about 10 μm in thickness and visually observed by a colour change of the copper surface.In order to elucidate the most likely interaction between the 8-AQ molecule and the different molecular structures probably present on copper surfaces in chloride solutions, some results obtained from theoretical calculations are presented. The following molecular structures were considered: CuCl molecule, CuCl₂⁻ complex, and little copper clusters defect representation built as five atoms on C_4v symmetry. Thus, based on the geometric, energetic, frontier orbital, and Total Electronic Density analysis done for the optimized states found for the systems investigated, we suggest that the most probable interaction of 8-AQ proceeds above CuCl units and free copper sites.     

Electrochemical treatment of drainage water from toxic dump of pesticides and degradation products

Polluted drainage water from a dump of toxic chemical waste containing organophosphoric pesticides and their natural degradation products was treated with electrochemical oxidation in order to investigate the applicability of the technique in remediation of natural complex polluted water. The dump is located adjacent to the sea in sand dunes, the natural salinity of the investigated water was 0.7 w/w% and sodium chloride served as main electrolyte. A commercial available flow cell with a tubular design, Ti/Pt₉₀-Ir₁₀ anode, and 316 SS cathode was applied, and the electrolysis experiments were conducted in a batch recirculation experimental set-up.COD measurements showed that the overall oxidation of organic and inorganic substances followed first-order kinetics by the current densities investigated, 310-1131 mA cm⁻², and the COD removal rate increased by increased current density and to a minor extent by increased salinity up to 2.0 w/w%. Evaluation of ICE and energy consumption showed that further optimization is possible and needed. The target organic pollutants parathion, methyl-parathion, malathion, ethylaminoparathion, paraoxon, and several phosphoric triesters were all degraded during the treatment except O,O,O-triethylphosphoric acid, a compound formed during the electrochemical process with a highly stable low energy structure, rendering it recalcitrant to participate in the oxidation reaction. The degradation of the subjected organics was found to be caused by indirect oxidation by the hypochlorous/hypochlorite pair as the main oxidizing agent, produced by the anodic oxidation of chloride. The study has showed that electrochemical chloride mediated indirect oxidation is a relevant, neat and possible solution for the remediation of organophosphoric pesticide polluted natural water.     

Current efficiency studies of the zinc electrowinning process on aluminum rotating cylinder electrode (RCE) in sulfuric acid medium: Influence of different additives

This work studies the effect of three additives, sodium lauryl sulfate (SLS), cetyltrimethylammonium bromide (CTABr) and arabic gum (AG) on zinc electrowinning on aluminum in a solution of 85 g L⁻¹ Zn(II) (1.3 M) in 108 g L⁻¹ H₂SO₄ (1.1 M). The influence of these three additives is analyzed during the different stages of the reduction process using chronopotentiometric techniques on an aluminum rotating disk electrode (RDE). Potential ranges (−1.05 < E < −0.85 V versus SHE) and current density (−51 < i < −0.2 mA cm⁻²) within which zinc electrodeposition takes place in the presence of the three different additives were established. These parameters were used to determine current efficiencies (Φ), evaluated by electrolysis on an aluminum rotating cylinder electrode (RCE); the zinc deposition efficiency in the presence of SLS, CTABr and AG, was 95%, 96% and 99%, respectively, were all greater than the efficiency obtained without any additive (WA), Φ = 84%. The homogeneity of the deposits at the end of electrolyses implied that the (RCE) promotes uniform current density on the electrode surface and, hence, can be considered a model cell to evaluate current efficiencies.     

Electroreduction of nitrate ions on Pt(1 1 1) electrodes modified by copper adatoms

Kinetics and mechanism of nitrate ion reduction on Pt(1 1 1) and Cu-modified Pt(1 1 1) electrodes have been studied by means of cyclic voltammetry, potentiostatic current transient technique and in situ FTIRS in solutions of perchloric and sulphuric acids to elucidate the role of the background anion. Modification of platinum surface with copper adatoms or small amount of 3D-Cu crystallites was performed using potential cycling between 0.05 and 0.3 V in solutions with low concentration of copper ions, this allowed us to vary coverage θ_Cu smoothly. Following desorption of copper during the potential sweep from 0.3 to 1.0 V allowed us to estimate actual coverage of Pt surface with Cu adatoms. Another manner of the modification was also applied: copper was electrochemically deposited at several constant potentials in solutions containing 10⁻⁵ or 10⁻⁴ M Cu²⁺ and 5 mM NaNO₃ with registration of current transients of copper deposition and nitrate reduction.It has been found that nitrate reduction at the Pt(1 1 1) surface modified by copper adatoms in sulphuric acid solutions is hindered as compared to pure platinum due to induced sulphate adsorption at E < 0.3 V. Sulphate blocks the adsorption sites on the platinum surface and/or islands of epitaxial Cu(1 × 1) monolayer thus hindering the adsorption of nitrate anions and their reduction. The extent of inhibition weakly depends on the copper adatom coverage. Deposition of a small amount of bulk copper does not affect noticeably the rate of nitrate reduction.Nitrate reduction on copper-modified Pt(1 1 1) electrodes in perchloric acid solutions occurs much faster as compared to pure platinum. The steady-state currents are higher by 4 and 2 orders of magnitude at the potentials of 0.12 and 0.3 V, respectively. The catalytic effect of copper adatoms is largely caused by the facilitation of nitrate adsorption on the platinum surface near Cu_ad and/or on the islands of the Cu(1 × 1) monolayer (induced nitrate adsorption).Hydrogen adatoms block the adsorption sites on platinum for NO₃⁻ anion adsorption and inhibit reactions of nitrate reduction even at moderate surface coverage.The products of nitrate reduction in sulphuric and perchloric acids are essentially the same (NO and ammonia) irrespective of the presence or absence of Cu on the platinum surface.     

Marine microbial fuel cell: Use of stainless steel electrodes as anode and cathode materials

Numerous biocorrosion studies have stated that biofilms formed in aerobic seawater induce an efficient catalysis of the oxygen reduction on stainless steels. This property was implemented here for the first time in a marine microbial fuel cell (MFC). A prototype was designed with a stainless steel anode embedded in marine sediments coupled to a stainless steel cathode in the overlying seawater. Recording current/potential curves during the progress of the experiment confirmed that the cathode progressively acquired effective catalytic properties. The maximal power density produced of 4 mW m⁻² was lower than those reported previously with marine MFC using graphite electrodes. Decoupling anode and cathode showed that the cathode suffered practical problems related to implementation in the sea, which may found easy technical solutions. A laboratory fuel cell based on the same principle demonstrated that the biofilm-covered stainless steel cathode was able to supply current density up to 140 mA m⁻² at +0.05 V versus Ag/AgCl. The power density of 23 mW m⁻² was in this case limited by the anode. These first tests presented the biofilm-covered stainless steel cathodes as very promising candidates to be implemented in marine MFC. The suitability of stainless steel as anode has to be further investigated.     

Optimization of process parameters for electrochemical nitrate removal using Box-Behnken design

Electrochemical reduction of nitrate in an undivided cell was studied in the present experiments. The optimization of the influencing factors on electrochemical reduction of nitrate by response surface methodology (RSM) was also studied. An ideal condition of performing both cathodic reduction of nitrate and anodic oxidation of the formed by-product in the presence of NaCl was achieved in the present experiment. The Box-Behnken design can be employed to develop mathematical models for predicting electrochemical nitrate removal geometry. The removal is sensitive to the current density and time in the present study. The value of R² > 0.99 for the present mathematical model indicates the high correlation between observed and predicted values. The optimal NaCl dosage, current density and electrolysis time for nitrate removal in the present experiment are 0.47 g L⁻¹, 26.06 mA cm⁻², and 111.88 min, respectively, at which the nitrate nitrogen (nitrate-N) and ammonia nitrogen (ammonia-N) concentration in the treated solution are 9.80 and 0 mg L⁻¹, respectively, which will meet the standards for drinking water.     

Electrowinning of copper in two- and three-compartment reactive electrodialysis cells

Two- and three-compartment copper electrowinning (EW) cells based on reactive electrodialysis (RED) have been studied. The catholyte was cupric sulphate and the anolyte was ferrous sulphate, both dissolved in sulphuric acid. Copper mesh cathodes and graphite bar anodes have been used. The effects of cell current density, temperature, electrolyte recirculation flowrate and nitrogen sparging flowrate on cell performance (cathodic current efficiency, cell voltage and specific energy consumption (SEC)) have been determined. The cell voltage increased with cell current and it decreased with temperature and nitrogen sparging flowrate. The effect of nitrogen sparging flowrate on the cell voltage is stronger than the effect of electrolyte recirculation flowrate, whereas its enhancing effect on mass transfer is stronger than its deleterious effect on electrolyte conductivity. The SEC ranged from 0.94 to 1.39 kW h/kg at cell current densities between 200 and 600 A/m². These values are considerably better than those for conventional copper EW (about 2 kW h/kg at 350 A/m²). The morphology of the electrodeposits has been observed and a comparison between a three-compartment cell and a previously studied squirrel-cage cell (both based on RED) has been drawn.     

Study of the electroreduction of nitrate on copper in alkaline solution

The electrocatalytic activity of a Cu electrode for the electroreduction of nitrate in alkaline medium was investigated by linear sweep voltammetry at stationary and rotating disc electrodes. Nitrate-reduction products generated upon prolonged electrolyses at different potentials were quantified. In addition, adsorption phenomena associated with the nitrate electroreduction process were characterized by electrochemical quartz crystal microbalance (EQCM) experiments. This data revealed that nitrate electroreduction process strongly depends on the applied potential. Firstly, at ca. −0.9 V vs. Hg/HgO, the electroreduction of adsorbed nitrate anions to nitrite anions was identified as the rate-determining step of the nitrate electroreduction process. Between −0.9 and −1.1 V, nitrite is reduced to hydroxylamine. However, during long-term electrolyses, hydroxylamine is not detected and presumably because it is rapidly reduced to ammonia. At potential more negative than −1.1 V, nitrite is reduced to ammonia. At ca. −1.45 V, i.e. just before the hydrogen evolution reaction, the abrupt decrease of the cathodic current is due to the electrode poisoning by adsorbed hydrogen. In addition, during the first minutes of nitrate electrolysis, a decrease of the copper electrode activity was observed at the three investigated potentials (−0.9, −1.1 and −1.4 V). From polarization and EQCM measurements, this deactivation was attributed to the adsorption of nitrate-reduction products, blocking the electrode surface and slowing down the nitrate electroreduction rate. However, it was demonstrated that the Cu electrode can be reactivated by the periodic application of a square wave potential pulse at −0.5 V, which causes the desorption of poisoning species.     

Modelling effects of current distributions on performance of micro-tubular hollow fibre solid oxide fuel cells

A three-dimensional model, considering mass, momentum, energy and charge conservation, was developed and the equations solved to describe the physico-chemical phenomena occurring within a single, micro-tubular hollow fibre solid oxide fuel cell (HF-SOFC). The model was used to investigate the spatial distributions of potential, current and reactants in a 10 mm long HF-SOFC. The predicted effects of location of current collectors, electrode conductivities, cathode thickness and porosity were analysed to minimise the ranges of current density distributions and maximise performance by judicious design. To decrease the computational load, azimuthal symmetry was assumed to model 50 and 100 mm long reactors in 2-D. With connectors at the same end of the HF-SOFC operating at a cell voltage of 0.5 V and a mean 5 kA m⁻², axial potential drops of ca. 0.14 V in the cathode were predicted, comparable to the cathode activation overpotential. Those potential drops caused average current densities to decrease from ca. 6.5 to ca.1 kA m⁻² as HF-SOFC length increased from 10 to 100 mm, at which much of the length was inactive. Peak power densities were predicted to vary from 3.8 to <2.5 kW m⁻², depending on the location of the current collectors; performance increased with increasing cathode thickness and decreasing porosity.     

Plasma electrochemistry: Absorption of flame borne species in platinum electrodes

Electrochemical potentiometric measurements have been shown to be possible in flame plasma using solid electrodes. The properties of the solid metal electrodes can effect the magnitude of the potential measured, due to the material's capacity to absorb flame borne species. Through this process, a surface alloy is formed and so alters the work function of the electrode. The study presented in this paper is concerned with understanding the mechanism by which copper, present in the flame, can absorb into platinum (Pt) electrodes at 1880 K. Electrodes were sectioned and the weight percent of copper was measured using an electron probe, to a distance of 100 μm from the surface. The distribution profiles of copper (Cu) measured for electrodes held in a flame doped with a solution containing copper chloride (5 × 10⁻² M) for 1, 5, 10 and 30 min modelled using finite element modelling. The predominant mechanism of absorption was unambiguously found to be instantaneous pulse, where a thin layer of copper was first deposited on the electrode surface by condensation followed by absorption. The layer was found to be 240 ± 30 nm and the copper diffusion coefficient was 8.0 ± 0.6 × 10⁻¹³ m² s⁻¹ in Pt at 1880 K.     

铜镉渣酸浸液旋流电积提铜对比分析

针对湿法炼锌副产物铜镉渣氧化酸浸液成分特点,采用旋流电积工艺回收其中的金属铜。研究了不同旋流电积工艺对电积过程中相关技术参数及杂质离子迁移规律的影响,并对不同电积工艺的优缺点进行了对比分析。结果表明：一段旋流电积可使溶液中铜离子浓度从44.14g/L降低到1.42g/L,而分段旋流电积可使溶液中终点铜离子浓度从1.42g/L继续降低至0.5g/L以下,溶液中铜离子在阴极上的电沉积率可从96.78%提高到99.20%,阴极电流效率可从90.52%提高到98.49%。当溶液中铜离子浓度降低到10g/L左右及以下时,杂质离子在阴极与铜发生共沉积现象逐渐明显,分段旋流电积得到的阴极铜产品光泽度及形貌质量较一段电积更好。与一段旋流电积工艺相比,分段旋流电积工艺具有电流效率高、能耗低、产品质量好等优点。     

Electrochemical study of calcium carbonate deposition on iron. Effect of the anion

Deposition of calcium carbonate on iron from supersaturated solutions containing 1 M sodium chloride, bromide, iodide, or nitrate as supporting electrolyte was studied at 60 °C under open-circuit conditions using impedance spectroscopy, chronopotentiometry, voltammetry, and scanning electron microscopy. The anions were found to fall into two groups with respect to their effect on scaling. On the one hand, chloride and, especially, nitrate favor faster scaling kinetics and lead to compact carbonate films composed of entangled aragonite crystals. On the other hand, in the presence of bromide and iodide the scaling rate is lower and the resulting films feature aragonite crystals more or less freely scattered on what appears to be a uniform sublayer of unknown structure. The experimental data are adequately described using quasi-uniform film model accounting for the cathodic and anodic electrode reactions. As deduced from the electrochemical measurements, the barrier properties of the carbonate films formed in different supporting electrolytes increase in the order of Cl⁻ < NO₃⁻ ≈ Br⁻ < I⁻.     

Evaluation of the photoelectrocatalytic method for oxidizing chloride and simultaneous removal of microcystin toxins in surface waters

The production of chlorine was investigated in the photoelectrocatalytic oxidation of a chloride-containing solution using a TiO₂ thin-film electrode biased at current density from 5 to 50 mA cm⁻² and illuminated by UV light. Such parameters as chloride concentrations from 0.001 to 0.10 mol L⁻¹, pH 2-12, and interfering salts were varied in this study in order to determine their effect on this oxidation process. At an optimum condition this photoelectrocatalytic method can produce active chlorine at levels compatible to water disinfections processes using a chloride concentration higher than 0.010 mol L⁻¹ at a pH of 4 and a current density of 30 mA cm⁻². The method was successfully applied to treat surface water collected from a Brazilian river. After 150 min of photoelectrocatalytic oxidation, we obtained a 90% reduction in total organic carbon removal, a 100% removal of turbidity, a 93% decrease in colour and a chemical oxygen demand (COD) removal of around 96% (N = 3). The proposed technology based on photoelectrocatalytic oxidation was also tested in treating 250 mL of a solution containing 0.05 mol L⁻¹ NaCl and 50 μg L⁻¹ of Microcystin aeruginosa. The bacteria is completely removed after 5 min of photoelectrocatalysis following an initial rate constant removal of −0.260 min⁻¹, suggesting that the present method could be considered as a promising alternative to chlorine-based disinfections.     

Performance and cycling of the iron-ion/hydrogen redox flow cell with various catholyte salts

A redox flow cell utilizing the Fe²⁺/Fe³⁺ and H₂/H⁺ couples is investigated as an energy storage device. A conventional polymer electrolyte fuel cell anode and membrane design is employed, with a cathode chamber containing a carbon felt flooded with aqueous acidic solution of iron salt. The maximum power densities achieved for iron sulfate, iron chloride, and iron nitrate are 148, 207, and 234 mW cm^?2, respectively. It is found that the capacity of the iron nitrate solution decreases rapidly during cycling. Stable cycling is observed for more than 100 h with iron chloride and iron sulfate solutions. Both iron sulfate and iron chloride solutions display moderate discharge polarization and poor charge polarization; therefore, voltage efficiency decreases dramatically with increasing current density. A small self-discharge current occurs when catholyte is circulating through the cathode chamber. As a result, a current density above 100 mA cm^?2 is required to achieve high Coulombic efficiency (>0.9).     

Phosphorus recovery from centralised municipal water recycling plants

Depletion of world phosphorus reserves is driving research into options to recover and recycle this essential, non-renewable resource. Phosphate (PO₄³⁻) recovery at centralised wastewater treatment plants can be achieved through biosolids reuse or sidestream precipitation though the PO₄³⁻ levels are low compared with decentralised systems based on source separation. However, the recent growth in membrane based water recycling projects, where reverse osmosis is used to produce high quality water has resulted in the production of liquid waste streams with elevated concentrations of PO₄³⁻. Four recycling scenarios using different membrane processes and anaerobic treatment were compared and the potential PO₄³⁻ recovery via struvite (magnesium ammonium phosphate) from membrane concentrate examined. By incorporating an anaerobic reactor in the process we have been able to investigate the possibility of cogeneration of electricity from methane. Modelling of struvite recovery from membrane concentrate with co-generation indicates a net power requirement of 260 kWh/kg P recovered compared with 510 kWh/kg P for a system without cogeneration at a water consumption level of 250 L/p/d. When water consumption is limited to 80 L/p/d, this scenario compares favourably with literature values for recovery from source separated urine which range from 18 to 43 kWh/kg P.     

Effect of plating mode, thiourea and chloride on the morphology of copper deposits produced in acidic sulphate solutions

The influence of plating mode, chloride and thiourea (TU) on morphology of copper deposits has been studied. All experiments were conducted on disc electrodes rotating at 500 rpm and an average current density of 4 A dm⁻² to produce 10 μm thick deposits. In additive-free solutions, the use of pulsed current (PC) improved deposit morphology and brightness over DC plating. In the presence of thiourea (no Cl⁻), the deposits obtained by DC and PC plating were similar under most plating conditions. The presence of thiourea generally improved deposit quality over that obtained in additive-free solutions, but caused the formation of microscopic nodules and the deposits to appear slightly cloudy, resulting in lower reflectances than that of a polished uncoated copper surface. The addition of Cl⁻ to thiourea-containing solutions strongly influenced deposit morphology at both microscopic and macroscopic scales depending on chloride concentration and pulse conditions. It prevented nodule formation and created microscopically bright and reflective deposits, but caused extreme macroscopic roughness. Nevertheless, PC plating at 50 Hz in solutions containing appropriate amounts of thiourea and Cl⁻ was found to yield macroscopically and microscopically smooth deposits with reflectance similar to that of a polished uncoated copper substrate.     

Non-catalyzed cathodic oxygen reduction at graphite granules in microbial fuel cells

Oxygen is the most sustainable electron acceptor currently available for microbial fuel cell (MFC) cathodes. However, its high overpotential for reduction to water limits the current that can be produced. Several materials and catalysts have previously been investigated in order to facilitate oxygen reduction at the cathode surface. This study shows that significant stable currents can be delivered by using a non-catalyzed cathode made of granular graphite. Power outputs up to 21 W m⁻³ (cathode total volume) or 50 W m⁻³ (cathode liquid volume) were attained in a continuous MFC fed with acetate. These values are higher than those obtained in several other studies using catalyzed graphite in various forms. The presence of nanoscale pores on granular graphite provides a high surface area for oxygen reduction. The current generated with this cathode can sustain an anodic volume specific COD removal rate of 1.46 kg_COD m⁻³ d⁻¹, which is higher than that of a conventional aerobic process. This study demonstrates that microbial fuel cells can be operated efficiently using high surface graphite as cathode material. This implies that research on microbial fuel cell cathodes should not only focus on catalysts, but also on high surface area materials.