José L. Nava

Electrochemical degradation of crystal violet with BDD electrodes: Effect of electrochemical parameters and identification of organic by-products

This paper explores the applicability of electrochemical oxidation on a triphenylmethane dye compound model, hexamethylpararosaniline chloride (or crystal violet, CV), using BDD anodes. The effect of the important electrochemical parameters: current density (2.5-15 m A cm(-2)), dye concentration (33-600 mg L(-1)), sodium sulphate concentration (7.1-50.0 g L(-1)) and initial pH (3-11) on the efficiency of the electrochemical process was evaluated. The results indicated that while the current density was lower than the limiting current density, no side products (hydrogen peroxide, peroxodisulphate, ozone and chlorinated oxidizing compounds) were generated and the degradation, through OH radical attack, occurred with high efficiency. Analysis of intermediates using GC-MS investigation identified several products: N-methylaniline, N,N-dimethylaniline, 4-methyl-N,N-dimethylaniline, 4-methyl-N-methylaniline, 4-dimethylaminophenol, 4-dimethylaminobenzoic acid, 4-(N,N-dimethylamino)-4-(N,N-dimethylamino) diphenylmethane, 4-(4-dimethylaminophenyl)-N,N-dimethylaniline, 4-(N,N-dimethylamino)-4-(N,N-dimethylamino) benzophenone. The presence of these aromatic structures showed that the main CV degradation pathway is related to the reaction of CV with the OH radical. Under optimal conditions, practically 100% of the initial substrate and COD were eliminated in approximately 35 min of electrolysis; indicating that the early CV by-products were completely degraded by the electrochemical system.

Arsenic and fluoride removal from groundwater by electrocoagulation using a continuous filter-press reactor.

We investigated simultaneous arsenic and fluoride removal from ground water by electrocoagulation (EC) using aluminum as the sacrificial anode in a continuous filter-press reactor. The groundwater was collected at a depth of 320 m in the Bajío region in Guanajuato Mexico (arsenic 43 µg L(-1), fluoride 2.5 mg L(-1), sulfate 89.6 mg L(-1), phosphate 1.8 mg L(-1), hydrated silica 112.4 mg L(-1), hardness 9.8 mg L(-1), alkalinity 31.3 mg L(-1), pH 7.6 and conductivity 993 µS cm(-1)). EC was performed after arsenite was oxidized to arsenate by addition of 1 mg L(-1) hypochlorite. The EC tests revealed that at current densities of 4, 5 and 6 mA cm(-2) and flow velocities of 0.91 and 1.82 cm s(-1), arsenate was abated and residual fluoride concentration satisfies the WHO standard (CF < 1.5 mg L(-1)). Spectrometric analyses performed on aluminum flocs indicated that these are mainly composed of aluminum-silicates of calcium and magnesium. Arsenate removal by EC involves adsorption on aluminum flocs, while fluoride replaces a hydroxyl group from aluminum aggregates. The best EC was obtained at 4 mA cm(-2) and 1.82 cm s(-1) with electrolytic energy consumption of 0.34 KWh m(-3).

Electrochemical incineration of indigo. A comparative study between 2D (plate) and 3D (mesh) BDD anodes fitted into a filter-press reactor

This paper compares the performance of 2D (plate) and 3D (mesh) boron-doped diamond (BDD) electrodes, fitted into a filter-press reactor, during the electrochemical incineration of indigo textile dye as a model organic compound in chloride medium. The electrolyses were carried out in the FM01-LC reactor at mean fluid velocities between 0.9u2009≤u2009uu2009≤u200910.4 and 1.2u2009≤u2009uu2009≤u200913.9xa0cmxa0s−1 for the 2D BDD and the 3D BDD electrodes, respectively, at current densities of 5.63 and 15xa0mAxa0cm−2. The oxidation of the organic matter was promoted, on the one hand, via the physisorbed hydroxyl radicals (BDD(●OH)) formed from water oxidation at the BDD surface and, on the other hand, via active chlorine formed from the oxidation of chloride ions on BDD. The performance of 2D BDD and 3D BDD electrodes in terms of current efficiency, energy consumption, and charge passage during the treatments is discussed.

Characterization of the Corrosion Layers Electrochemically Formed on the Lead–Silver/ H2SO4 + Mn ( II ) Interface

The corrosion layers electrochemically formed on the lead-silver/H 2 SO 4 + Mn(II) interface were studied through open-circuit potential monitoring, cyclic voltammetry, and chronoamperometry and were characterized by cyclic voltammetry, X-ray diffraction, and scanning electron microscope coupled to an energy dispersive spectrometer to analyze microregions. Mn(II) oxidation reactions take place in the range of 1 60 min, the formation of δ-MnO 2 predominates, transforming the crystalline surface into an amorphous and nonelectroactive one. Furthermore, the anodic layer is broken, liberating Pb 2+ and exposing metallic lead, which is oxidized to PbO 2 . The Pb 2+ released forms PbMn 8 O 16 on the electrode surface and PbSO 4 in the bulk.

Electrochemical combustion of indigo at ternary oxide coated titanium anodes

The film of iridium and tin dioxides doped with antimony (IrO2-SnO2–Sb2O5) deposited on a Ti substrate (mesh) obtained by Pechini method was used for the formation of uf0b7 OH radicals by water discharge. Detection of uf0b7 OH radicals was followed by the use of the N,N-dimethyl-p-nitrosoaniline (RNO) as a spin trap. The electrode surface morphology and composition was characterized by SEM-EDS. The ternary oxide coating was used for the electrochemical combustion of indigo textile dye as a model organic compound in chloride medium. Bulk electrolyses were then carried out at different volumetric flow rates under galvanostatic conditions using a filteruf02dpress flow cell. The galvanostatic tests using RNO confirmed that Ti/IrO2-SnO2-Sb2O5 favor the hydroxyl radical formation at current densities between 5 and 7 mA cm uf02d2 , while at current density of 10 mA cm uf02d2 the oxygen evolution reaction occurs. The indigo was totally decolorized and mineralized via reactive oxygen species, such as ( uf0b7 OH, H2O2, O3 and active chlorine) formed in-situ at the Ti/IrO2-SnO2-Sb2O5 surface at volumetric flow rates between 0.1uf02d0.4 L min -1 and at fixed current density of 7 mA cm -2 . The mineralization of indigo carried out at 0.2 L min -1 achieved values of 100 %, with current efficiencies of 80 % and energy consumption of 1.78 KWh m -3 .

The use of a rotating cylinder electrode to recover zinc from rinse water generated by the electroplating industry.

This work concerns the application of a laboratory scale rotating cylinder electrode (RCE) to recover zinc from rinse water generated by the electrolytic zinc process (initially 1,300, 4,400, 50, 20 mg L(-1) of Zn(II), Fe(III), Ag(I) and Cr(VI), respectively, at pH 2), although it is also applicable to other electroplating industries. Experimental results demonstrated the convenience of the removal of ferric ions, as (Fe(OH)(3(s))) by a pH adjustment to 4, before zinc electro recovery on the RCE. The generation of smooth zinc deposits on the RCE was obtained at Reynolds numbers within the range of 15,000 ≤ Re ≤ 124,000 and limiting current densities (J(L)) in the interval of -4.8 to -13 mA cm(-2). The zinc recovery reached a conversion of 67% in 90 min of electrolysis for Re = 124,000 and J = -13 mA cm(-2), 21% current efficiency, and energy consumption of 9.5 kWh m(-3). The treated solution can be recycled back through the same rinsing process.

Reactor Design for Advanced Oxidation Processes

Electrochemical reactor design for oxidation processes follows similar engineering principles used for typical electrosynthesis reactors and include considerations of the components materials, electrode and cell geometries, mass transport conditions, rate of reactions, space–time yield calculations, selectivity, modeling, and energy efficiencies. It is common practice to optimize these characteristics at laboratory scale level followed by more practical considerations to build a larger reactor able to accomplish a required performance that can be easily assembled and requires low maintenance and monitoring. The scaling-up process should involve testing a variety of electrode configurations and cell designs to maximize the degradation of a particular pollutant. In this chapter, we describe the general principles of reactor design and list the most typical reactor configurations and performance followed by some recent advances in modeling and further developments.

Electrochemical oxidation of cyanide on 3D Ti–RuO2 anode using a filter-press electrolyzer

The novelty of this communication lies in the use of a Ti-RuO2 anode which has not been tested for the oxidation of free cyanide in alkaline media at concentrations similar to those found in wastewater from the Merrill Crowe process (100xa0mgxa0L-1 KCN and pH 11), which is typically used for the recovery of gold and silver. The anode was prepared by the Pechini method and characterized by SEM. Linear sweep voltammetries on a Ti-RuO2 rotating disk electrode (RDE) confirmed that cyanide is oxidized at 0.45xa0<xa0Exa0<xa01.0xa0V vs SHE, while significant oxygen evolution reaction (OER) occurred. Bulk oxidation of free cyanide was investigated on Ti-RuO2 meshes fitted into a filter-press electrolyzer. Bulk electrolyzes were performed at constant potentials of 0.85xa0V and 0.95xa0V and at different mean linear flow rates ranging between 1.2 and 4.9xa0cmxa0s-1. The bulk anodic oxidation of cyanide at 0.85xa0V and 3.7xa0cmxa0s-1 achieved a degradation of 94%, with current efficiencies of 38% and an energy consumption of 24.6xa0kWh m-3. Moreover, the degradation sequence of cyanide was also examined by HPLC.

Electrochemical Study of a Flotation Zinc Concentrate in Sulfuric Acid: Galvanic Interactions Affecting the Rate of Dissolution of Sphalerite

The anodic dissolution of a flotation zinc concentrate (63.4 % sphalerite (ZnS), 20.1 % pyrite (FeS 2 ), 5 % chalcopyrite (CuFeS 2 ), 0.33% galena (PbS), 0.45 % terahedrite (Cu 12 Sb 4 S 13 ) and 0.4 % arsenopyrite (FeAsS)) was studied in 1.7 M H 2 SO 4 . An electrochemical strategy (based on common electrochemical techniques) was proposed to find the potential range at which each mineral species can be oxidized. Anodic potential pulses were applied to carbon paste electrodes prepared with zinc concentrate (CPE-zinc concentrate). The resulting solutions were analysed by anodic stripping voltammetry (ASV). In addition, the surface of each modified CPE-zinc concentrate was characterized by cyclic voltammetry (CV). The sphalerite is oxidized in the range of 0 ≤ E < 600 mV vs SSE with slow kinetics; similarly, galena dissolution takes place in the same range. The dissolution of sphalerite is galvanically protected, while dissolution of chalcopyrite is favored.

Simulations of a Single-Phase Flow in a Compound Parabolic Concentrator Reactor

This paper deals with the analysis and interpretation of flow visualization and residence time distribution (RTD) in a compound parabolic concentrator (CPC) reactor using computational fluid dynamics (CFD). CFD was calculated under turbulent flow conditions solving the Reynolds averaged Navier–Stokes (RANS) equation expressed in terms of turbulent viscosity and the standard k−e turbulent model in 3D. A 3D diffusion-convection model was implemented in the CPC reactor to determine the RTD. The fluid flow visualization and RTD were validated with experimental results. The CFD showed that the magnitude of the velocity field remains almost uniform in most of the bulk reactor, although near and inside the 90° connectors and the union segments, the velocity presented low- and high-speed zones. Comparisons of theoretical and experimental RTD curves showed that the k−e model is appropriate to simulate the nonideal flow inside the CPC reactor under turbulent flow conditions.