Laboratory-scale Electrolytic Cell Research Articles

Electrochemical Separation of Pb-Ag-Sb Alloys in the KCl-PbCl2 Melt

Abstract Anode dissolution of lead, silver, antimony, and liquid lead-bismuth-antimony alloys has been studied by the polarization method depending on the alloy composition in the molten KCl-PbCl2 eutectic. Lead was found to dissolve and to form Pb2+ ions within the whole range of anode current densities in the Pb-Ag-Sb (49.0-28.0-23.0) and Pb-Ag-Sb (11.0-55.0-34.0) melts. The limiting diffusion current of lead dissolution was observed at the anode current density of 0.34 А/cm2 in the Pb-Ag-Sb (5.0-65.0-30.0) alloy. At the anode current densities exceeding these values the antimony dissolution was observed. To define a mechanism of metals electro dissolution, the number of electrons participating in the electrode reactions was calculated. Based on the polarization curves analysis the regime of electrochemical separation of lead alloys was selected. Metallic lead and the remaining Ag-Sb-Pb alloy with the valuable components concentration exceeding 90 wt.% were obtained in the laboratory-scale electrolytic cell.

Electrochemical Production of Bismuth in the KCl-PbCl2 Melt.

An anode dissolution of binary metallic lead–bismuth alloys with different concentrations of components has been studied in the KCl–PbCl2 molten eutectic. The dissolution of lead is found to be a basic process for the alloys of Pb–Bi (59.3–40.7), Pb–Bi (32.5–67.5), Pb–Bi (7.0–93.0) compositions in the whole interval of studied anode current densities. A limiting diffusion current of lead dissolution was observed at 2 A/cm2 and 0.1 A/cm2 for the alloys of Pb–Bi (5.0–95.0) and Pb–Bi (3.0–97.0) compositions, respectively. The dissolution of bismuth takes place at the anode current densities exceeding the mentioned values. The number of electrons participating in the electrode reactions is detected for each mechanism. Based on the theoretical analysis, the experimental electrolysis of bismuth was performed in the laboratory-scale electrolytic cell with a porous ceramic diaphragm. The final product contained pure bismuth with a lead concentration of 3.5 wt.%.

Electrolyte viscosity and solid phase formation during aluminium electrolysis

This paper presents experimental data on the dependence on alumina and calcium fluoride concentrations of the viscosity of the industrial electrolytes NaF-AlF3-CaF2-Al2O3 with cryolite ratios (CR) of 2.1, 2.3, 2.5 in the temperature range 1243–1293 K. The temperature dependence of the formation of a solid phase on the graphite crucible wall in cryolite-alumina electrolyte during aluminium electrolysis was studied in a laboratory-scale electrolytic cell. The viscosity of the industrial electrolytes was found to depend more on the temperature and cryolite ratio than on the alumina concentration in the melt. A long period of electrolysis with controlled solid phase formation on the cell wall was carried out, with a constant electrolyte composition (CR = 2.4), a calcium fluoride concentration of 5 wt% and an alumina content of 4.0 wt%. The formation of a stable solid phase layer on the graphite crucible wall was found to depend on the electrolysis temperature. A correlation was observed between the formation of a solid under the influence of temperature and the viscosity of the melt.

Electrochemical Removal Cyanide in Wastewater by Ti/RuO<sub>2</sub>-Pt Electrodes

A laboratory-scale electrolytic cell with a Ti/RuO2-Pt anode and a Ti cathode was developed to treat high concentration cyanide-contained wastewater. The effects of the different electrode distances, concentration of chlorine anion and current densities, on the CN- removal were investigated. The results shown the too short and long electrode distance resulted in high energy consumption and low current, the appropriate electrode distance was essential. The CN- removal was very significant at the electrode distance was 9 cm, and the removal efficiency reached 99.2%. The removal CN- electrochemical oxidation was mainly attributed the success to in direct oxidation effect of chlorine /hypo-chlorite produced during the electrochemical reaction process. The CN- removal efficiency increased with increasing the concentration of chloride ion and operating current density. The optimum experimental condition was set at the electrode distance of 9 cm, NaCl dosage of 0.5 g/L, the current density of 10 mA/cm2, and pH of 12. At the optimum experimental condition, the CN- concentration in the solution decreased from 150.33 mg/L to 1.20 mg/L, and the CN- removal efficiency reached 99.2%.

Optimal operational conditions for the electrochemical regeneration of a soil washing EDTA solution

The present research deals with the optimization of the operating parameters (cathode replacement time, hydraulic retention time, current intensity and pH) of an electrochemical process aimed at the regeneration of a soil washing EDTA solution used for heavy metal extraction from a natural contaminated soil (excavated from Bellolampo, Palermo, Italy), which was vastly polluted with Cu (59 261.0 mg kg(-1)), Pb (14 178.1 mg kg(-1)) and Zn (14 084.9 mg kg(-1)). The electrolytic regeneration of the exhausted washing solution was performed in a laboratory scale electrolytic cell with 50 ml each cathodic and anodic chambers divided by a cation exchange membrane. Experiments II and III showed maximum Cu and Zn removal efficiencies from the EDTA solution, of 99.2+/-0.2 and 31.5+/-9.3%, respectively, when a current intensity of 0.25 A and a hydraulic retention time of 60 min were applied to the electrolytic cell, while the maximum Pb removal efficiency of 70.9+/-4.6% was obtained with a current intensity of 1.25 A and a hydraulic retention time of 60 min. During Experiment I the overall heavy metals removal efficiency was stable and close to 90% up to 20 h, while decreased to values lower than 80% after 40 h, indicating the occurrence of a significant saturation of the cathode graphite bed between 20 and 40 h. The capability of the regenerated EDTA solution to treat heavy metals polluted soils was tested in further experiments applying both a single and a multi-step washing treatment procedure. In particular, the latter showed the feasibility to increase heavy metal soil extractions over subsequent washing steps with Cu, Pb and Zn total removal efficiencies of 52.6, 100.0 and 41.3%, respectively.

Numerical Simulation of Transient Natural Convection along Vertical Plane Electrodes Caused by Electrolytic Current Modulation

A transient natural convection develops along vertical plane Cu electrodes during modulation of the electrolytic current in the copper refining process. The electrolysis modes of “Current On,” “Current Off,” and “Current Reverse” are frequently encountered in industrial electrolysis. The time variation of both the concentration profile of ion and the velocity profile in a aqueous electrolyte confined between both vertical electrodes had been reported in a laboratory-scale electrolytic cell. The mass transfer rate of ion as well as the natural convective fluid motion is now numerically analyzed under the presumption of uniform current density distribution along electrode height. Calculated transient concentration and velocity profiles accompanied with various switching modes of the electrolytic process quantitatively agree well with the measurements.

Copper recovery and cyanide oxidation by electrowinning from a spent copper-cyanide electroplating electrolyte

Copper-cyanide bleed streams arise from contaminated baths from industrial electroplating processes due to the buildup of impurities during continuous operation. These streams present an elevated concentration of carbonate, cyanide and copper, constituting a heavy hazard, which has to be treated for cyanide destruction and heavy metals removal, according to the local environmental laws. In the Brazilian Mint, bleed streams are treated with sodium hypochlorite, to destroy cyanide and precipitate copper hydroxide, a solid hazardous waste that has to be disposed properly in a landfill or treated for metal recovery. In this paper, a laboratory-scale electrolytic cell was developed to remove the copper from the bleed stream of the electroplating unit of the Brazilian Mint, permitting its reutilization in the plant and decreasing the amount of sludge to waste. Under favorable conditions copper recoveries around 99.9% were achieved, with an energy consumption of about 11 kWh/kg, after a 5-h electrolysis of a bath containing copper and total cyanide concentrations of 26 and 27 g/L, respectively. Additionally, a substantial reduction of the cyanide concentration was also achieved, decreasing the pollution load and final treatment costs.

Analysis of electrochemical degradation products of sulphonated azo dyes using high‐performance liquid chromatography/tandem mass spectrometry

Electrochemical treatment of wastewaters containing azo dyes in the textile industry is a promising approach for their degradation. The monitoring of the course of the decomposition of azo dyes in wastewaters is essential due to the environmental impact of their degradation products. In this work, aqueous solutions of a simple azo dye with a low molecular weight (C.I. Acid Yellow 9) and more complex commercial dye (C.I. Reactive Black 5) were electrochemically treated in a laboratory-scale electrolytic cell in sodium chloride or ammonium acetate as supporting electrolytes. Ion-pairing reversed-phase high-performance liquid chromatography coupled with negative-ion electrospray ionization mass spectrometry is applied for the identification of electrochemical degradation products. In addition to simple inorganic salts, the formation of aromatic degradation products obtained due to the cleavage of azo bonds and further degradation reactions is shown, as well as chlorination where sodium chloride is the supporting electrolyte. Degradation mechanisms are suggested for the treatment with sodium chloride as the supporting electrolyte.

Analysis of sulphonated azodyes and their degradation products in aqueous solutions treated with a new electrochemical method

Aqueous solutions of four sulphonated azodyes, Reactive Orange 91, Reactive Red 184, Reactive Blue 182 and Reactive Black 5, containing 0.2 mol/L of electrolyte were treated in a laboratory scale electrolytic cell with a new electrochemical method intended for the textile wastewater treatment. The electrochemical process was monitored by means of absorbance of UV-Vis light and chemical oxygen demand values. Carbon fleece was used as a cathode, and platinated titanium was used as an anode. Reversed-phase high-performance liquid chromatography coupled with photodiode array and mass spectrometric detectors was applied for the analysis of dyes, their impurities and degradation products after the electrochemical treatment. Dihexylammonium and triethylammonium acetate as ion-pairing reagents, or alternatively ammonium acetate as an ion-exclusion suppressing reagent, were used to improve the separation.

Design, construction and operation of a laboratory scale electrolytic cell for sodium production using a β″-alumina based low-temperature process

Sodium metal can be produced at low temperatures (∼523 K) by electrolysis of sodium tetrachloroaluminate (NaAlCl4) in a cell, which employs sodium ion conducting beta-alumina as diaphragm. A laboratory-scale electrolytic cell and associated systems were designed and constructed to study the various aspects of the energy efficient process. Graphite/reticulated vitreous carbon (RVC) was used as the anode and molten sodium as the cathode. Electrolysis was carried out at ∼523 K with currents in the range 1–10 A (10–125 mA cm−2). The cathodic current efficiency was close to 100%, but the anodic current efficiency was very low (20–30%), probably due to the consumption of chlorine in the intercalation reaction of graphite and aluminium chloride. The sodium metal was analysed by AAS and found to have 5N purity. On prolonged electrolysis, the graphite anode disintegrated due to the formation of ‘graphite intercalation compounds’. RVC behaved as a better chlorine-evolving anode in the initial period of electrolysis, but its ability for chlorine evolution decreased on continuous electrolysis. The study indicated the need for effective stirring of the electrolyte with excess NaCl to avoid build up of aluminium chloride and the resultant complications in the cell.

Organochlorine formation in magnesium electrowinning cells

The formation of organochlorines during the electrolytic production of magnesium was investigated using a laboratory-scale electrolytic cell having a graphite anode, a liquid aluminium alloy cathode, and a molten chloride electrolyte. The cell was operated at current densities ranging from 3000 to 10,000 A m −2 and at temperatures ranging from 660°C to 750°C. Organochlorines were adsorbed from the cell off-gases onto silica gel, extracted with hexane, and determined by gas chromatography. All compounds identified were fully chlorinated aliphatic and aromatic compounds, the major components being hexachlorobutadiene, hexachlorobenzene, hexachloroethylene, and octachlorostyrene. The total amount of organochlorines per tonne of magnesium produced decreased with electrolysis time and with current density and increased with operating temperature; it was also dependent on the type of graphite employed. The output of organochlorines varied from 5 to 20 g t −1 of magnesium.