Electrowinning/Electrostripping and Electrodialysis Processes for the Recovery and Recycle of Metals from Plating Rinse Solutions

Abstract

Two electrochemical-based methods have been evaluated to remove heavy metals from a tin/zinc electroplating rinse solution with subsequent recycle of the metals back into the original plating bath. The first method uses electrodialysis to move tin to the anolyte strip solution as an anionic citrato complex while zinc is distributed to both the anolyte and catholyte, showing it exists as both an anionic citrato complex and in free cationic form. Zinc can be recovered by scraping the loose deposit from the cathode and dissolving it in mineral acid.

The second method is a combined electrowinning/ electrostripping technique. The process involves continuously flowing the plating rinse solution through a porous graphite cathode and removing the metal ions via electrodeposition. When a sufficient quantity of metal has been deposited, the electrode is placed in a solution whose chemical composition is similar to that of the original plating bath and the metals ions are stripped from the electrode anodically. The resulting solution is then placed into the original plating bath.

Both methods were used to treat a surrogate rinse solution originally containing 100–300 parts per million of each metal and were successful in reducing the metal-ion concentrations to less than 15 parts per million each. Approximately 70% of the tin and 100% of the zinc are recoverable by either method.     

Electrochemical membrane reactor: In situ separation and recovery of chromic acid and metal ions

An electrochemical membrane reactor with three compartments (anolyte, catholyte and central compartment) based on in-house-prepared cation- and anion-exchange membrane was developed to achieve in situ separation and recovery of chromic acid and metal ions. The physicochemical and electrochemical properties of the ion-exchange membrane under standard operating conditions reveal its suitability for the proposed reactor. Experiments using synthetic solutions of chromate and dichromate of different concentrations were carried out to study the feasibility of the process. Electrochemical reactions occurring at the cathode and anode under operating conditions are proposed. It was observed that metal ion migrated through the cation-exchange membrane from central compartment to catholyte and OH⁻ formation at the cathode leads to the formation of metal hydroxide. Simultaneously, chromate ion migrated through the anion-exchange membrane from central compartment to the anolyte and formed chromic acid by combining H⁺ produced their by oxidative water splitting. Thus a continuous decay in the concentration of chromate and metal ion was observed in the central compartment, which was recovered separately in the anolyte and catholyte, respectively, from their mixed solution. This process was completely optimized in terms of operating conditions such as initial concentration of chromate and metal ions in the central compartment, the applied cell voltage, chromate and metal ion flux, recovery percentage, energy consumption, and current efficiency. It was concluded that chromic acid and metal ions can be recovered efficiently from their mixed solution leaving behind the uncharged organics and can be reused as their corresponding acid and base apart from the purifying water for further applications.     

Preparation and characterization of electroplated amorphous gold-nickel alloy film for electrical contact applications

A process for electroplating amorphous gold-nickel alloy with the atomic ratio of unity was developed. The plating bath was prepared by adding potassium cyanoaurate(I) into a known plating bath which produces amorphous nickel-tungsten alloy. At a sufficiently high gold concentration, the alloy deposit did not contain any tungsten. The amorphous nature of the Au-Ni alloy produced in the new bath was confirmed by using TEM and THEED. Hardness, resistivity, and contact resistance of this new alloy were determined, and the results are discussed for applications as an electrical contact material.     

Separation of nickel from cobalt using electrodialysis in the presence of EDTA

Optimum conditions are determined for the removal of nickel from cobalt solutions by electrodialysis exploiting the greater stability of the EDTA complex with nickel. The Ni–(EDTA)^2– complex and hydrated Co²⁺ ions are transferred from the feed solution to the electrodialysis anolyte and catholyte chambers, respectively. A three compartment cell is required to prevent the transfer of hydrated Ni²⁺ from the anolyte chamber as the EDTA present is destroyed at the anode. Complete removal of nickel from cobalt can be achieved but there is a compromise between cobalt purity and the percentage of cobalt transferred to the catholyte chamber for recovery.     

钾盐对氰化镀铜溶液性能的影响

研究了钾盐对氰化镀铜溶液性能的影响,结果表明,向镀液中加30～60 g/L的硫酸钾,能够明显提高镀层的光亮度和镀液的覆盖能力,当采用较低质量浓度氰化镀铜溶液时,硫酸钾能够提高镀液的分散能力.生产实践表明:在挂镀氰化镀铜槽中用硫酸钾取代有机光亮剂能够提高镀层与基体之间的结合力.     

Studies on promising cell performance with H2SO4 as the catholyte for electrogeneration of Ag2+ from Ag+ in HNO3 anolyte in mediated electrochemical oxidation process

Electrochemical performance of a divided cell with electrogeneration of Ag²⁺ from Ag⁺ in 6 M HNO₃ anolyte has been studied with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte. This work arose because in mediated electrochemical oxidation (MEO) processes with Ag(II)/Ag(I) redox mediator, HNO₃ is generally used as catholyte, which, however, produces NO _x gases in the cathode compartment. The performance of the cell with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte has been compared in terms of (i) the acid concentration in the cathode compartment, (ii) the Ag⁺ to Ag²⁺ conversion efficiency in the anolyte, (iii) the migration of Ag⁺ from anolyte to catholyte across the membrane separator, and (iv) the cell voltage. Studies with various concentrations of H₂SO₄ catholyte have been carried-out, and the cathode surfaces have been analyzed by SEM and EDXA; similarly, the precipitated material collected in the cathode compartment at higher H₂SO₄ concentrations has been analyzed by XRD to understand the underlying processes. The various beneficial effects in using H₂SO₄ as catholyte have been presented. A simple cathode surface renewal method relatively free from Ag deposit has been suggested.     

Analysis of molar flux and current density in the electrodialytic separation of sulfuric acid from spent liquor using an anion exchange membrane

Separation of sulfuric acid from a dilute solution involved a plate and frame type electrodialysis unit using a commercial anion exchange membrane. Experiments were conducted in batch with catholyte concentrations ranging from 1 to 5 wt%. Effect of applied current density, initial catholyte concentration and initial concentration difference of catholyte and anolyte on the molar flux was studied extensively. The maximum molar flux was estimated to be 10.52×10^-8 mol cm^-2s^-1 at 4.45 wt% catholyte concentration and applied current density of 30 mA cm^-2. Current efficiencies were observed to be 75 to 85% at lower current density, which rose to more than 100% at 20 and 30mA cm^-2, at equal initial concentration of catholyte and anolyte. Diffusive flux and flux due to membrane potential contributed very less compared to total flux in presence of applied electric current. An equation was developed to predict the practical molar fluxes, which fitted satisfactorily with minor standard deviation. Pristine and used membrane specimens were characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM).     

Regeneration of Chromium Electroplating Electrolytes by the Application of Electromembrane Processes

The use of the electromembrane method for the purification of chromium plating electrolytes from cationic impurities (iron, copper, etc.) by three approaches are described. The first variant is based on the removal of these ions during their migration from the solution to be purified into a catholyte through a cationexchange membrane. The second variant is a transfer of chromate anions from a contaminated solution into the anolyte through an anion-exchange membrane. In the third method for the recuperation of chromic acid, accumulated in a recovery bath, it is proposed to use the immersed electrochemical module, combining the processes of concentration and purification from impurities, instead of evaporation.     

紫外-可见分光光度法测定不同电镀液中纳米SiO2的含量

在前期实验研究的基础上,采用紫外-可见光分光光度法测定含有SiO2纳米粉体的瓦特型镀镍液、酸性光亮镀铜液、焦铜液、氯化钾镀锌液中SiO2的含量结果表明,这些体系均存在空白液吸光度很低、工作液吸光度较高的较大的波长区间,是分光光度分析法中理想的测定体系;所对应的标准曲线线性都十分理想,相关系数均大于0．98将此方法与重量分析法进行了对比,表明该方法的平均相对误差(0．044％)远远小于重量分析法(16．2％),且更省时。     

Transport and conductivity properties of an advanced cation exchange membrane in concentrated sodium hydroxide

An electrochemical concentrator for application to the chlorine-caustic industry is currently under development. In it 30 to 35 wt % NaOH enters the anolyte and catholyte chambers and exits at 20 and 50 wt %, respectively. Consequently, in support of the electrochemical concentrator development, the conductance and transport properties of advanced cation exchange membranes in concentrated sodium hydroxide, are being investigated. The membrane voltage drop, sodium ion transport and water flux of these membranes in 20 to 35 wt % sodium hydroxide anolyte and 30 to 50 wt % sodium hydroxide catholyte at 75°C are presented. To better understand the behaviour of these membranes, electrolyte sorption measurements were conducted in the anolyte/catholyte environment appropriate for the electrochemical concentrator. The water uptake data appear to correlate well with the conductance data and the combined NaOH and water sorption data are consistent with the sodium ion transport data.     

Dual solution-type HCHO fuel cell systems using an anion exchange resin membrane with electroless-plated Cu or Pd anode

Loading characteristics of a prototype HCHO fuel cell systems with an anion exchange membrane which separates the anolyte from the catholyte were investigated. Electrodes of Cu or Pd, deposited by an electroless-plating technique onto the membrane, showed high electrocatalytic activity to the anodic oxidation of HCHO in 1 M NaOH solution. The system with Cu anode and 1 M NaOH for both anolyte and catholyte showed high loading characteristics but poor durability, whereas that with 1 M K₂CO₃ showed low characteristics because of lowered pH of the anolyte. It was shown that a dual solution-type cell with 1 M K₂CO₃ anolyte and 1 M NaOH catholyte yielded improved characteristics as compared with the simple K₂CO₃ system. The output level was, however, at an unsatisfactory level owing to poor membrane conductance. The temperature dependence of the output performance was studied in the range 7–55°C.     

镍-铁合金镀液中硼酸的分析

利用传统方法分析镍-铁合金镀液中的硼酸,镀液中亚铁离子会严重影响测定结果。介绍了一种方法,用过硫酸钠氧化镀液中的亚铁离子和络合剂,再用氢氧化钠沉淀出铁离子和镍离子,过滤后用硫酸酸化试液,以甲基红为指示剂,用碱中和过量的硫酸。最后用甘露醇与硼酸反应生成较强的络合酸,以酚酞作指示剂,用氢氧化钠标准溶液滴定。这种方法分析结果较准确,能够满足监控镀液中硼酸的要求。     

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.     

Ion transport in a two membrane electrowinning cell for the production of hydrochloric acid

A three-compartment electrowinning cell has been evaluated for the regeneration of HCl from metal chloride catholyte. By segregating the catholyte with an anion exchange membrane, and the anolyte with a cation exchange membrane from the middle electrolyte(ampholyte) compartment, HCl could be produced in the ampholyte electrochemically up to one molality. The anolyte consisted of sulphuric acid. Successful operation of such a double membrane cell depends on controlling ion transport through the membrane, especially chloride migration into the anolyte. Results of electrowinning and self-diffusion experiments for three types of cation exchange membrane are presented and discussed.     

Chromium hexacyanoferrate as a cathode material in microbial fuel cells

In this work, it has been demonstrated that the disadvantages associated with the use of the potassium ferricyanide solution as the catholyte in a microbial fuel cell (MFC) were overcome by using a graphite cathode electrochemically modified with chromium hexacyanoferrate (CrHCF) film. The existing use of potassium ferricyanide solution as the catholyte is limited by the need to replace the catholyte every week and it cannot be used in a sustained manner. The present work evaluates the suitability of the CrHCF modified film as a suitable cathode material in a prototype of a MFC wherein Hansenula anomala is used as the biocatalyst in the anode compartment. The CrHCF film was prepared in the presence of the dopant camphor sulphonic acid to improve the reversibility of the film in phosphate buffer.     

The effect of electro-osmosis on the synthesis of lead and tin fluoroborates

Pronounced electro-osmosis phenomena were observed during the anodic dissolution of lead and tin in fluoroboric acid with an anionic exchange membrane separating the anode compartment from the cathode compartment. The consequent volumetric increment of anolyte was influenced by the current density and the initial volume and concentration of catholyte. The selectivities (S _i) of the given membrane were found to be $$\begin{gathered} 50\% Sn(BF_4 )_2 solution: S_{BF^{4 - } } = 0.952; S_{Sn^{2 + } } = 0.048 \hfill \\ 50\% Pb(BF_4 )_2 solution: S_{BF^{4 - } } = 0.887; S_{Pb^{2 + } } = 0.113 \hfill \\\end{gathered}$$      

一次氯化钾滚镀锌故障处理

对一次氯化钾滚镀锌故障进行了分析,并提出了处理方法。在目前的滚镀生产线上,基本上是用稳流器将镀槽的施镀电流控制在某一固定值附近,通过调整滚桶装载量的方式进行生产。由于氯化钾镀锌液中含有较多吸附性较强的大分子有机物添加剂,在电镀过程中这些添加剂在镀件表面脱附较慢。当电流密度较大时,镀层中就容易夹杂较多的有机物。在滚镀比表面积较小的零部件时,如果采用与电镀比表面积较大的零部件同样的施镀电流,则会产生不良镀层。因此,在氯化钾滚镀锌的生产中,除了调整滚桶装载量外,还需根据镀件比表面积调整施镀电流。通过改进传统的操作方法,排除了这次氯化钾滚镀锌的故障。     

Composition controlling of Co-Ni and Fe-Co alloys using pulse-reverse electroplating through means of experimental strategies

The optimal plating settings in the pulse-reverse electroplating mode for the non-anomalous plating of Co-Ni deposits (i.e., the metal composition of deposits is equal to that of the plating solutions) from chloride solutions were approached by using experimental strategies including fractional factorial design (FFD), path of steepest ascent and central composite design (CCD) coupled with the response surface methodology (RSM). The potentials and time period of pulse-plating were the key factors affecting the composition of Co-Ni deposits in the FFD study. The two variables were the path of the steepest ascent investigation to approach the optimal conditions for non-anomalous plating of Co-Ni deposits. The effects of pulse-plating potential and pulse-plating time on the compositions of Co-Ni deposits were further examined using a regression model in the CCD study.The variable Ni contents of Co-Ni deposits are caused by metal hydroxide on the deposit surface. After anodic dissolution process, the increasing pulse-plating time and lower pulse-plating potential can remove metal hydroxide and improve Ni ion deposition ratio on the fresh deposit.All Fe-Co deposits were equal to the composition metal ratio of plating bath while pulse-reverse-plating potential included the anodic dissolution process.     

镍钨合金电沉积的电流效率和镀层显微硬度

通过调节镀液中不同的Ｎｉ／Ｗ比例、温度和沉积电流密度,研究在焦磷酸盐体系中镍钨合金电沉积的电流效率、沉积层和组成和显微硬度。实验结果表明：合金共沉积的电流效率不高。为了尽量提高合金的沉积电流效率,主要途径宜增大镀液中硫酸镍和钨酸钠的浓度;提高合金沉积电流密度,降低镀液中［Ｎｉ］／［Ｗ］比例,则镀层中的钨含量增大;合金沉积层的显微硬度随镀层中的Ｗ含量提高而增大。     

Adsorption off Lauryl Sulfate from Electrolyte Solutions on Cobalt Hydroxide

Abstract

The adsorption of lauryl sulfate on cobalt(II) hydroxide from solutions of inorganic salts has been found to change as follows: without salt ≥ chloride ≥ bromide ≥ nitrate ≥ sulfate ≥ phosphate Adsorption in the presence of acids increases in the following series: without acid ≥ hydrochloric ≥ sulfuric ≥ phosphoric, and is higher than in the presence of salts. The surface concentration of lauryl sulfate adsorbed from a suspension without electrolyte is about 0.9 (μmol/ m². The surface coverage of hydroxide by lauryl sulfate is about 1/5 of a monolayer, but it decreases in the presence of electrolyte. The law of mass action was applied to characterize the effect of solution composition on the adsorption of lauryl sulfate on cobalt(II) hydroxide.