The use of graphite cloth electrodes for the recovery and separation of gold

The electrodeposition and recovery of gold from spent electroplating bath solutions using a graphite cloth electrode in a flow-through cell is described. Optimized conditions of flow rate, current densities, screen potentials and additives were established to achieve high-percentage recoveries and good separation of the Au from admixtures of base metals (Cu, Cd). The results are sufficiently encouraging to serve as the basis for a scaled-up process.     

Electrochemical oxidation of sulphite ions at graphite electrodes

The electrochemical oxidation of sodium sulphite has been studied in aqueous sodium sulphate solution at two different graphite electrodes, one being of natural graphite (EC) and the other impregnated with phenol (ECK). The objective of the present work was to obtain some insight into the direct oxidation as well as the indirect oxidation, via produced oxygen radical species, of sulphite on non-metal electrodes. For this reason a study of the oxidation of sulphite in the concentration range between 0–0.10m in aqueous sodium sulphate using a batch electrochemical reactor, operating potentiostatically, was undertaken. The potential range was chosen between 1.0 to 2.5 V/SCE, and the concentration of the supporting electrolyte, sodium sulphate, was kept constant at 0.5m. A kinetic Tafel type law, considering irreversible behaviour for the direct sulphite oxidation and the mass transfer performance in regards to the experimental conditions were applied to predict the time variations of the sulphite conversion.     

Selective recovery of metals from spent desulfurization catalyst

Valuable metals including V, Mo, Ni, Co, and Al were selectively recovered from spent desulfurization catalyst by means of extractive separation. Prior to selective metal recovery the spent catalyst was roasted at temperatures of 400–800 °C, and BET, SEM, and XRD data showed that roasting the spent catalyst at 550 °C gave birth to the surface and pore structures accounting for good extractibility of the roasted spent catalyst. A sequential scheme consisting of leaching and chelate extraction was developed to recover the metals from the spent catalyst roasted at 550 °C and oxygen space velocity of ca. 1800 hr⁻¹.     

Selective electrodeposition of metals from simulated waste solutions

Most industrial waste streams contain a number of different heavy metals. The feasibility of selective electrodeposition of cadmium, cobalt and nickel as their pure metals (99%) from binary mixtures has been investigated. Single cation linear sweep voltamograms and nucleation potential measurements have been made and used to predict the optimum potentials and conditions for selective electro-deposition from the mixed-cation solutions. The anions used in this work are SO₄ ^2–, Cl^– and BF₄ . The optimum potential for removal by electrodeposition of Cd from a solution containing Cd(ii) and Co(ii) or Ni(ii) without codepositing Co or Ni has been evaluated from a simple diagram constructed from nucleation potential measurements. It is shown that the [Cd(ii)] remaining in the solution after exhaustive electrolysis at a fixed potential is determined by the Nernst equation, and not by the electrolysis time provided that a critical minimum time has been exceeded.     

Copper electrodeposition on pyrolytic graphite electrodes: Effect of the copper salt on the electrodeposition process

The electrodeposition of copper on pyrolytic graphite from CuSO₄ or Cu(NO₃)₂ in a 1.8 M H₂SO₄ aqueous solution was investigated. The Cu deposits were formed potentiostatically and characterized by electrochemical methods, scanning electron microscopy, energy dispersive X-ray and X-ray photoelectron spectroscopy. It was found that the deposition of copper in the presence of CuSO₄ induced the codeposition of sulfate anions. In addition, electrochemical quartz crystal microbalance revealed that the increase of the Cu mass was higher than expected from Faraday's law with the CuSO₄/H₂SO₄ solution. These results confirmed the specific adsorption of anions during the Cu deposition. On the other hand, the use of Cu(NO₃)₂ resulted in a non-contaminated surface with different surface morphologies. The Cu nuclei size, the population density and the surface coverage were monitored as a function of the deposition potential. From the analysis of the chronoamperometric curves, the nucleation kinetics was studied by using various theoretical models. Independently of the Cu source, the nucleation mechanism follows a three-dimensional (3D) process. Copper nucleates according to an instantaneous mode when the deposition potential is more negative than −300 mV versus Ag/AgCl, while the nucleation was interpreted in terms of a progressive mode at −150 mV. The nuclei population densities were also determined by using two common fitting models for 3D nucleation and growth (Scharifker-Mostany and Mirkin-Nilov-Heerman-Tarallo). Their values are reported here as a function of the deposition potential.     

Selective nickel recovery from iron-rich solutions

This study aims to demonstrate the selective removal of iron from acidic leach solutions using an effective purification method and to convert nickel into a usable form. The method of removing iron by using CaCO₃, which is a better precipitation reagent, was optimized using Response Surface Methodology. A further evaluation was carried out on the complexation of Ni(II) ions with dimethylglyoxime to obtain a high-yield nickel-dimethylglyoxime complex from nickel remaining in the solution after iron precipitation. Taking into account nickel losses to remove iron, pH should be within the range of 3–4, and low temperatures around 25°C should be used.     

Silver recovery from spent photographic solutions by a magnetically assisted particle bed

The work presents experimental results on silver cementation from spent photographic fixer thiosulphate solutions by iron in magnetically controlled particle beds. Axial magnetic field created by Helmholtz pair was used. The increase in the fluid flow rate yields an increased silver recovery due to reduction in the external mass transfer resistance irrespective of the particle bed structures used for cementation. The field intensity slightly boosts the silver recovery and results in granular structures appearing at the surface of the deposits. The bed structures when the iron is used as a particle beds in column operation has major role in the efficient performance of the cementation process. With flow rate slightly exceeding the minimum fluidization point in the absence of a field the preferable operating regimes are: a fixed bed (FB) and moderately expanded magnetically stabilized beds (MSB) regimes, both of them with the Magnetization FIRST mode. However, when high flow throughputs are required, the frozen beds with the Magnetization LAST exhibit higher separation efficiencies and higher mass transfer coefficients than those with FB and MSB.     

电沉积法从含金浸出液中回收金研究进展

介绍了电沉积法从采用不同浸金方法产生的浸出液中回收金的基本原理,并结合国内外电沉积法提金的研究进展,叙述了电解槽的设计优化和影响金沉积率的主要因素。最后总结了电沉积法提金的优点和发展前景以及目前存在的不足之处。     

电沉积法从含金浸出液中回收金研究进展

介绍了电沉积法从采用不同浸金方法产生的浸出液中回收金的基本原理,并结合国内外电沉积法提金的研究进展,叙述了电解槽的设计优化和影响金沉积率的主要因素。最后总结了电沉积法提金的优点和发展前景以及目前存在的不足之处。     

Aluminium electrodeposition from AlCl3-NaCl melts on glassy carbon,platinum and gold electrodes

The electrochemical deposition and dissolution of aluminium on glassy carbon, platinum and gold electrodes in chloraluminate melts have been investigated using linear sweep voltammetry and potentiostatic pulse techniques. It was shown that deposition of aluminium on the glassy carbon electrode at low overpotentials takes place by 3-D progressive nucleation and growth, with the incorporation of atoms in the crystal lattice as the rate-determining step. At overpotentials higher than –100 mV vs Al, in the melts containing more than 52 mol % of AlCl₃, diffusion of Al₂Cl ₇ ^– , takes over the control of deposition of aluminium. Alloying of platinum and gold electrodes with aluminium from the melt occurs in the underpotential region.     

Electrolytic generation of hydrogen on Pt-loaded porous graphite electrodes from flowing alkaline solutions

The aim of this work was to test the feasibility of using porous graphite electrodes as cathodes for the electrolytic production of hydrogen fro_m flowing alkaline solutions. The platinum loading on the graphite substrate was found to decrease the potential required to sustain a certain rate of hydrogen production, and hence the energy consumed during electrolysis. The experimental i/E relations agreed with those theoretically predicted on the basis of a mathematical model up to a current density of about 200 mA cm^–2. The excessive polarization at higher current is attributed to trapping of hydrogen gas bubbles within the porous electrode.     

Recovery of metals from complexed solutions by electrodeposition

Electrolytic recovery of metals from aqueous solutions containing complexing chelating agents such as EDTA, NTA, and citrate was studied in a two-chamber cell separating with a commercial cation-exchange membrane (CEM). Equimolar solutions of metal and a chelating agent as a catholyte and NaNO₃ as an anolyte were used; the effect of current densities, initial catholyte and anolyte pH, metal concentration and the type of the CEM, chelating agent and metal on the recovery of metals was determined. The recovery of metal increased with higher initial anolyte pH, concentration and current density, whereas it decreased with lower initial catholyte pH. The results show that electrodeposition seems to be an applicable method for the recovery of metals under appropriate conditions.     

Absorption of oxygen by aqueous sodium sulphite solutions

New data have been reported on the absorption of oxygen by aqueous sodium sulphite solutions with cobalt sulphate as catalyst at 30°C. It is observed that the absorption rate increases up to a critical sulphite concentration beyond which the absorption rate becomes constant and this critical concentration varies with the catalyst concentration. The order of reaction with respect to sulphite and oxygen in the constant absorption rate regime was found to be zero and two respectively. The absorption rate is affected by the total ionic strength (sulphite and sulphate) in addition to the effect of pH and catalyst concentraion. The reported data were also analysed to ascertain the effect of temperature and a relationship has been proposed for prediction of the second order reaction rate constant.     

Carbon nitride films deposited from organic solutions by electrodeposition

An electrodeposition process was applied to synthesize and deposit CN_x thin films from organic solution. The depositions from acetonitrile (CH₃CN) and dicyandiamide–acetone (C₂H₄N₄–C₃H₆O) solution were reported. The processes were performed near to room temperature. The films deposited from acetonitrile liquid contained 25% nitrogen, the nitrogen content in the films obtained from dicyandiamide solution reached to 48%. X-ray photoelectron spectrometry (XPS) and Fourier transform infrared (FTIR) were used to characterize the structure of the films. It indicated that high nitrogen content films contained CN bonds besides the CN, and CN bonds which composed both films.     

Selective iron removal from spent passivation baths by ion exchange

BACKGROUND: Post‐treatment of zinc plated surfaces is required to provide corrosion protection; for this purpose chromium passivation is usually used. In the EU, the older hexavalent chromium passivation baths have been replaced by trivalent chromium conversion coatings. However, the life of Cr(III) passivation baths is reduced due to iron and zinc impurities generated in the process. Thus, the objective of this work was to investigate the regeneration of spent passivation baths from the plating industry by ion exchange using a new chelating resin (Purolite S‐957). RESULTS: Three genuine passivation baths with different iron and zinc concentrations were investigated; the effect of loading flow rate, temperature and resin regeneration conditions on the uptake of iron ions was also studied. The removal performance of iron was increased at higher temperature (55 °C) and lower flow rates. The best regeneration conditions were found to be 6 bed volumes (BV) of 30 wt% HCl. CONCLUSION: This work has shown that iron can be selectively removed from trivalent chromium passivation baths using a new chelating resin (Purolite S‐957) and no addition of chromium (III) is required. Low feed flow rate and high bath temperature (up to 55 °C) are recommended for high iron uptake. Copyright © 2008 Society of Chemical Industry     

Cementation-induced recovery of self-assembled ultrafine copper powders from spent etching solutions of printed circuit boards

Ultrafine copper powders have been recovered from spent etching solutions of printed circuit boards by cementation on helical-form iron scrap chips. The tested solution is an ammoniacal copper solution containing 135 g/l copper with minor impurities. The influences of contact time, temperature, pH, initial copper concentration and Fe stoichiometry on the yield, purity and grain size and shape of the precipitated copper powders were studied. Ultrafine self-assembled copper nanocubes with high purity of about > 99% was obtained at temperature 25 °C, time 20 min, pH 2, Fe stoichiometry 1X and initial copper concentration 20 g/l Cu. It was proposed that the precipitation of copper from the solution involved two main processes: (1) adsorption of copper ions on the surface of the iron chips due to the iron oxides present on it and (2) cementation of copper ions onto the metallic iron contained in the chips. Scrap iron chips is seen to be an effective material for copper powder recovery from spent etching solutions in a pure and fine form.     

Effect of PbO on zinc electrodeposition from zincate solutions

The effect of PhO on zinc electrodeposition on a copper substrate from zincate solutions was investigated using cyclic voltammetry and by polarization measurements as a function of time. It was found that lead deposition caused the zinc deposition potential to cathodically shift by 100 mV in the negative direction. It is suggested that the presence of lead on the copper substrate suppresses hydrogen absorption and consequently inhibits zinc deposition via a path such as

废锂离子电池中锂提取技术研究进展

作为一种关键原材料,锂是生产新能源汽车锂离子电池必需的战略金属。随着新能源汽车产业的快速发展,对锂的需求量持续骤增。然而,我国锂矿石等一次资源储量低,对外依存度目前已高达70%,难以满足快速增长的市场需求,供需矛盾日渐突出。因此,高效清洁提取废锂离子电池中的锂必将成为锂资源的重要补充,对有效避免废锂离子电池对生态环境和人体健康的二次污染风险、保障战略金属锂的安全供给和新能源汽车行业的可持续发展意义重大。鉴于湿法冶金具有回收率高、回收产物纯度高、能耗低等优点,本研究综述了近年来以湿法冶金为主提取废锂离子电池中锂的研究进展,重点分析了废锂离子电池预处理、浸出、锂分离与提取的主要方法及其优缺点,并提出了进一步强化选择性提取锂相关技术研发及废锂离子电池全组分清洁利用的建议,同时对废锂离子电池回收工艺的发展趋势及前景进行了展望。