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This study investigated the electrogeneration of Ce(IV) and its application on the destruction of polyvinyl alcohol (PVA) in an undivided electrochemical cell. The effects of electric current, concentration of nitric acid, and temperature on PVA destruction efficiency were investigated and the corresponding specific energy consumptions (SEC) were also evaluated. The experimental results indicate that the PVA destruction increased with increasing the applied current, the concentration of nitric acid, and decreasing the temperature. When considering the PVA destruction efficiency and the corresponding SEC simultaneously, the best operating condition was found by 92% at the optimal applied current 0.1 A, concentration of nitric acid 0.5 M, and temperature 323 K, respectively. A pseudo-first-order kinetic model provided a good fit to the experimental results at various temperatures. The activation energy was calculated to be 78.27 kJ mol−1, based on pseudo-first-order rate constants from the Arrhenius equation. [ABSTRACT FROM PUBLISHER]

This study evaluates the performance of an innovative paired photoelectrochemical oxidative system fabricated in our laboratory to determine the removal efficiency of polyvinyl alcohol (PVA) in aqueous solutions. An innovative paired photoelectrochemical oxidative system employed metal redox mediators with high redox potential for anodic oxidation (MEO process) and UV assisted photoelectrochemical oxidation (PEO process) for cathodic oxidation in a divided electrochemical cell. Several parameters were investigated to characterize the removal efficiency of PVA, such as the current density, initial Ce(III) concentration, nitric acid concentration, oxygen flow rate, and UV irradiation intensity. The effects of these parameters on the specific energy consumption were also investigated. Additionally, the conversion yield of Ce(IV) concentration and the electrogeneration of H2O2 were calculated in this study. The optimum current density, initial Ce(III) concentration, nitric acid concentration, oxygen flow rate, and UV irradiation intensity were found to be 3 mA cm−2, 0.01 M, 0.3 M, 500 cm3 min−1, and 1.2 mW cm−2, respectively. The synergistic effect of combination process of MEO and PEO would be as a promising alternative for the removal efficiency of PVA. [ABSTRACT FROM AUTHOR]

This study investigates the effectiveness of using the activated carbon fiber (ACF) cloth electrodes for the reduction of the conductivity from the water with a low NaCl content. The ACF cloth can not reduce the conductivity of the solution by pure adsorption, but shows good effectiveness while charging. Findings show the effectiveness of the ACF electrode does not change significantly after at least ten repeated charging/discharging cycles. The highest reduction degree of conductivity is about 60 %, and the recovery degrees approach almost 100 % in this work. The reduction degree of conductivity increases with increasing the applied voltage and the initial NaCl concentration below 200 ppm. The ACF electrode treated by HNO3 of different concentrations and treatment time possess a lower desalination degree, which decreases with increasing the treatment time and the concentration of HNO3. [ABSTRACT FROM AUTHOR]

Feasibility of salicylic acid removal from an aqueous solution was investigated in an electrochemical cell equipped with either aluminum or iron plates by using electrocoagulation (EC). Several parameters, including electrode materials, solution pH variation, applied voltage, and solution temperature, were investigated. In addition, effects of applied voltage and solution temperature on electric energy consumption and time needed to reach 90% removal were investigated. Experimental results indicated that the Al/Al electrode pair was the most efficient choice of the two electrode pairs tested in terms of salicylic acid removal efficiency. In terms of pH variation during EC, generation of coagulant metal hydroxides for the Al/Al electrode pair was greater than that for the Fe/Fe electrode pair, which also enhanced the removal efficiency. The optimum applied voltage and solution temperature were found to be 20 V and 308 K, respectively. A pseudo-second-order kinetic model provided a good fit to the experimental results at various applied voltages and solution temperatures. In addition, the activation energy was calculated as 20.21 J mole−1 based on pseudo-second-order rate constants from the Arrhenius equation, indicating that salicylic acid precipitation in an aqueous solution was attributable to the EC process. [ABSTRACT FROM AUTHOR]

Abstract: The removal of salicylic acid from aqueous solutions was investigated in an electrochemical cell equipped with aluminum plates by using electrocoagulation (EC). Metal hydroxides generated during EC were used to remove salicylic acid from aqueous solution, and the effects of varying current density and solution temperature on salicylic acid adsorption characteristics were evaluated. The findings indicated that complete salicylic acid removal could be achieved within reasonable removal efficiency and with relatively low electrical energy consumption. The optimum current density and temperature were found to be 1.2mAcm−2 and 298K, respectively. Thermodynamic parameters, including the Gibbs free energy, enthalpy, and entropy, indicated that the salicylic acid adsorption of aqueous solutions on metal hydroxides was feasible, spontaneous and endothermic in the temperature range of 288K to 318K. The experimental data were fitted with several adsorption isotherm models to describe the EC process. The adsorption of salicylic acid preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. In addition, the adsorption kinetic studies showed that the EC process was best described using the pseudo-second-order kinetic model at the various current densities and temperatures. [Copyright &y& Elsevier]

Abstract: This study investigated the color removal efficiency of Acid Orange 7 by electrochemical oxidation. The operating variables, such as the applied current density, the pH of solution, the temperature of solution, and the concentration of electrolytes, were investigated. Five materials were used to compare their efficiencies for removing the Acid Orange 7. The removal efficiency follows the order: ACF c>ACF b>ACF a>Pt/Ti>graphite. The color removal percentage increased when increasing the applied current density up to 10.0mA/cm2, at which point the color removal rate began to be controlled by mass transfer. Experimental results showed that higher pH and temperature of the solution were beneficial for the removal of Acid Orange 7 and that the Na2SO4 electrolyte concentration did not significantly affect the removal rate. The energy consumption was in the range of 1.178 to 10.44kWh/moldm3, depending on the applied current density. The adsorption and electrooxidation were found to follow first-order kinetics. The best overall rate constant for ACF a was found to be 0.16min−1 at an initial pH of 9.7. The regeneration of ACF anode surface was observed after a 30-min treatment using 10.0mA/cm2. [ABSTRACT FROM AUTHOR]

Abstract: The removal of total organic carbon (TOC) from aqueous solution containing polyvinyl alcohol (PVA) using iron electrocoagulation (EC) was investigated. Iron hydroxides generated during EC were used to remove PVA and TOC from the aqueous solution, and the effects of varying current density and solution temperature on PVA and TOC adsorption characteristics were evaluated. The findings indicated that complete PVA removal accompanied by TOC removal of an aqueous PVA solution could be achieved within a reasonable electrolysis time and with relatively low electrical energy consumption. A pseudo-first-order kinetic model provided a good fit to the experimental results at various current densities and solution temperatures. In addition, the experimental data were fitted with several adsorption isotherm models to describe the EC process. The predictions of the Freundlich adsorption isotherm model satisfactorily matched the experimental observations. Thermodynamic parameters, including the Gibbs free energy, enthalpy, and entropy, indicated that the TOC adsorption of the aqueous solution containing PVA on metal hydroxides was feasible, spontaneous and endothermic in the temperature range of 288K to 318K. [Copyright &y& Elsevier]

Abstract: This study investigated the efficiency of COD removal from real dyeing wastewater by using Fe2+ in combination with electrogenerated hydrogen peroxide at the PAN (polyacrylonitrile) based activated carbon fiber cloth cathode. A systematic study of COD removal percentage was carried out at different oxygen sparging rates, applied current densities, Fe2+ concentrations, solution pHs and temperatures. The electro-Fenton technology can successfully remove COD from the complex real dyeing wastewater. Over 70% of COD can be removed after 240min of treatment. The COD removal efficiency increased significantly with the oxygen sparging rates up to 150cm3/min. The highest COD removal efficiency, 75.2%, was achieved at an applied current density of 3.2mA/cm2; COD removal efficiency deteriorated at higher current densities because the rates of side reactions increased. The results showed that the optimal solution pH was 3. Increasing the solution pH rapidly decreased COD removal efficiency. Conversely, COD removal efficiency increased with increasing Fe2+ concentrations up to 2mM. Temperature had a slightly negative effect on COD removal efficiency. [Copyright &y& Elsevier]

Abstract: The feasibility of polyvinyl alcohol (PVA) removal from aqueous solution was investigated using iron electrocoagulation. Several parameters, including type of electrode pair, applied voltage, supporting electrolytes, and solution temperature were investigated. The effects of applied voltage, supporting electrolyte, and solution temperature on PVA removal efficiency and specific energy consumption were also investigated. Experimental results indicated that a Fe/Al electrode pair was the most efficient choice of the four electrode pairs tested in terms of PVA removal efficiency. The optimum applied voltage, supporting electrolyte concentration, and solution temperature were found to be 10V, 100mg L−1 NaCl, and 298K, respectively. A pseudo-second-order kinetic model provided a good fit to experimental results at various applied voltages and solution temperatures. In addition, the activation energy was calculated to be 49.45J mol−1 based on pseudo-second-order rate constants from the Arrhenius equation, indicating that PVA precipitation in aqueous solution was attributable to the electrocoagulation process. [Copyright &y& Elsevier]

The removal efficiency of COD in the treatment of simulated laundry wastewater using electrocoagulation/electroflotation technology is described. The experimental results showed that the removal efficiency was better, reaching to about 62%, when applying ultrasound to the electrocoagulation cell. The solution pH approached neutrality in all experimental runs. The optimal removal efficiency of COD was obtained by using the applied voltage of 5V when considering the energy efficiency and the acceptable removal efficiency simultaneously. The Cl− concentration of less than 2500ppm had a positive effect on the removal efficiency. The performance of the monopolar connection of electrodes was better than that of the bipolar connection in this work. In addition, the removal efficiency of using Al electrodes was higher in comparison with using Fe electrodes in the study. The highest COD removal amount per joule was found to be 999mgdm−3 kWh−1 while using two Al electrodes, although the removal efficiency increased with the number of Al plates. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to explore the feasibility of removing silica particles and reducing turbidity from oxide chemical mechanical polishing (oxide-CMP) wastewater. Based on the dynamic characteristics of batch electrocoagulation, three operating stages (lag, reactive, and stabilizing) are proposed to identify the relationships among the zeta potential of the silica particles, solution turbidity, and the corresponding mean particle size of the silica. Experimental results show that the silica particles were destabilized and settled at the critical mean particle size, which was estimated to be above 520nm after 10min, and the corresponding turbidity removal mostly occurred during the reactive stage. Furthermore, the corresponding mean particle size varied from 520 to 1900nm as the treatment time progressed from 10 to 20min, which also occurred during the reactive stage. Several parameters, including different electrode pairs, electrolyte concentration, applied voltage, and the optimum condition of power input were investigated. Experimental results indicate that a Fe/Al electrode pair is the most efficient choice of the four electrode pair combinations in terms of energy consumption. The optimum electrolyte concentration and applied voltage were found to be 200ppm NaCl and 30V, respectively. [Copyright &y& Elsevier]

Abstract: Supercritical carbon dioxide extraction, which is a feasible “green” alternative, was applied in this study as a sample pretreatment step for the removal of gallium (III) ions from acidic aqueous solution. The effect of various process parameters, including various chelating agents, extraction pressure and temperature, dimensionless CO2 volume, the concentration of the chelating agent, and the pH of the solution, governing the efficiency and throughput of the procedure were systematically investigated. The performance of the various chelating agents from different studies indicated that the extraction efficiency of supercritical CO2 was in the order: thiopyridine (PySH)>thenoyltrifluoroacetone (TTAH)>acetylacetone (AcAcH). The optimal extraction pressure and temperature for the supercritical CO2 extraction of gallium (III) with chelating agent PySH were found to be 70°C and 3000psi, respectively. The optimum concentration of the chelating agent was found to be 50ppm. A value of 7.5 was selected as the optimum dimensionless CO2 volume. The optimum pH of the solution for supercritical CO2 extraction should fall in the range of 2.0–3.0. [Copyright &y& Elsevier]

Abstract: Indium and its compounds have numerous industrial applications in the manufacture of liquid crystal displays and semiconductors. Indium compounds are considered hazardous materials that can be carcinogenic. Supercritical fluid extraction using carbon dioxide was utilized in this research as a sample pretreatment step for extraction of indium(III) ions from the synthetic etching wastewater of the semiconductor and optoelectronic industries. Several parameters, including various chelating agents, pH of solution, molar ratio of chelating agent to indium(III) ions, temperature and pressure were systematically investigated. Indium(III) ions were extracted by supercritical CO2 combined with several various types of chelating agents including β-diketone (AcAcH), fluorinated β-diketone (TTAH), thiopyridine (PySH), and piperidinyldithiocarbamic acid (NCS2H) to extract the ions from acidic aqueous solution. The performance of the various chelating agents from different studies indicated that the extraction efficiency by the supercritical CO2 was in the order: NCS2H≧PySH>TTAH≫AcAcH. The optimum pH for supercritical CO2 extraction should fall in the range from 2.0 to 3.0. The optimum molar ratio of chelating agents to indium(III) ions was found to be a ratio of 10:1. It was also revealed that the optimal extraction pressure and temperature for the supercritical CO2 extraction of indium(III) with various chelating agents AcAcH, PySH and NCS2H were 70°C 2000psi, 60°C 2000psi, and 60°C 2000psi, respectively. [Copyright &y& Elsevier]

In this study, the removals of the mercury and methyl mercury by applying an electric field have been investigated. The experimental results show that the non-uniform distributions of the pH, conductivity and potential gradient would be formed during the treatment. These unexpected distributions would slow down the removal of contaminants. Sothe mercury and methyl mercury could be only reduced t about 73.6% and 59.4% utter 100-day treatment, respectively. Thus, the enhancementby sing buffer solutions or canon exchange membranes was conducted to avoid the backing anon of the OH- generated at the cathode. The results show that the removal efficiencies of the mercury could attain 88% or more and that of the methyl mercury could reach to 4% or more after only 60-day treatments by using either buffer solutions or cation exchange a membranes. [ABSTRACT FROM AUTHOR]

This work investigates the removal of color from wastewater that contains low dyestuff concentrations by the Electro-Fenton process. The color was removed by in situ electrogenerated hydrogen peroxides at a three-dimensional graphite cathode with added ferrous sulfates. Experimental runs were conducted to evaluate the effect of the operating parameters, such as the oxygen contact mode, the oxygen sparging rate, the applied current density, the concentration of ferrous ions, the solution temperature and the pH among others, on the removal of color. The removal efficiency of the color in the cathodic chamber reached 70.6% under specified operation conditions in 150min. The removal efficiency was controlled by the mass transfer when the oxygen-sparging rate was less than 0.3dm3/min for the reactor configuration herein. The optimal applied current density was 68A/m2 when the energy consumption was considered. The highest removal efficiency was obtained by adding 20mM Fe(II) to the solution. The optimal solution pH was 3 in this work. The temperature negatively affected color removal. [Copyright &y& Elsevier]