José R. Parga

Electrocoagulation (EC) — science and applications

Although electrocoagulation is an evolving technology that is being effectively applied today for wastewater treatment, the paucity of scientific understanding of the complex chemical and physical processes involved is limiting future design and hindering progress. The objective of this review through a survey of the literature is to bring the chemistry and physical processes involved into perspective and to focus attention on those areas critically needing research.

An XPS and SEM/EDS characterization of leaching effects on lead- and zinc-doped portland cement

Abstract The characterization of leaching effects on portland cement doped with lead and zinc has been carried out by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). Evidence is presented from XPS and SEM/EDS results that the dopant metal ions are preferentially adsorbed on the surface of the cementitious materials. Leaching tests reveal that most of the Zn 2+ ions and some of the Pb 2+ ions are dissolved. A chemical shift with respect to the Si( 2p ) XPS peak occurs due to the increased polymerization of the silicates present in cement. The distribution of the cations before and after leaching is discussed in relation to the XPS and SEM/EDS results.

Oxidation of cyanide in a hydrocyclone reactor by chlorine dioxide

Abstract The greatest amounts of cyanide-containing wastes are produced by precious metals milling operations, the electroplating industry and coal processing or coking effluents processes. Because of high toxicity and to comply with federal and state regulations, the treatment of wastewater is required before safe discharge of cyanide wastes. In this regard, the gas-sparged hydrocyclone (GSH) has been tested as a reactor for the treatment of cyanide solutions for cyanide destruction by oxidation with the use of chlorine dioxide gas (ClO2). The results show oxidation efficiencies of free cyanide approached 99% at all pH values in 5 min. The use of NaCl was also considered for the generation of chlorine dioxide. Excellent performance appears to offer operational and cost advantages over conventional processes.

Passive film breakdown during anodic oxidation of zirconium in pH 8 buffer containing chloride and sulfate

Abstract Metal passivation and passive film breakdown in aqueous systems are complex processes. Zirconium passive films grown in basic solutions containing buffer; chloride and buffer; and chloride, sulfate and buffer have been examined with particular attention to the passive and transpassive regions using cyclic voltammetry (CV). Mechanically polished zirconium electrodes have been oxidized anodically in pH 8 buffer solutions containing 0.021 M chloride, with varying sulfate concentration. The CV curves show that zirconium forms passive layers under these conditions, which are more stable with increasing sulfate concentration. A model is proposed to explain the passive to transpassive transition taking oxygen evolution, crystallization and ohmic behavior into account.

Electrocoagulation treatment of municipal wastewater in Torreon Mexico

Abstract One of the biggest challenges of the twenty-first century is to provide water, primarily potable, to the majority of the world population. This is a critical issue, especially in developing countries. One way to augment that effort is to reuse water. Currently, some emerging wastewater treatment technologies based on electrochemistry (e.g. electrocoagulation (EC), electroflotation, electrodecantation, and electrooxidation) are available that are competitive and advantageous over conventional technologies. Although EC has been known for more than a century, it has not been comprehensively studied. EC has been commercialized for the removal of specific contaminants and wastewater treatment. This work demonstrates EC as an alternative method for the treatment of municipal wastewater in Torreon; Coah, Mexico. COD value for wastewater in Torreon is considered as medium level (245 ppm). Experiments were conducted to determine the optimum operational conditions. Results show a remarkable removal efficie...

Thermodynamic studies of the strontium adsorption on iron species generated by electrocoagulation

Abstract In this research we present and discuss the results of the use of the Electrocoagulation (EC) process for strontium removal from wastewater. The phenomena associated with strontium removal is adsorption on iron magnetic species generated from the dissolution of iron electrodes of the electrolytic cell. With the EC process more than 99 percent of strontium was removed from wastewater without addition of chemical reagents. Sludge generated by EC was characterized by Chemical Analyses, X-Ray Diffraction, Scanning Electron Microscopy and Vibrating Sample Magnetometer (VSM) in order to document the adsorption of strontium on iron-species. The electrogenerated crystalline iron oxides magnetite (Fe3O4) and maghemite (γ-Fe2O3) powders have higher values for saturation magnetization, but lower values for remanent magnetization and coercive fi eld than commercial strontium hexaferrite with micrometric particle size. The experimental data were correlated employing a Langmuir adsorption isotherm. Thermodynam...

New Technology for Recovery of Gold and Silver by Pressure Cyanidation Leaching and Electrocoagulation

The present chapter describes a new technology of pressure oxidation/cyanidation leaching for the dissolution of gold and silver and the recovery of the precious metals by using the electrochemical process of Electrocoagulation (EC). The novel method demonstrates that the oxidation and dissolution of gold and silver in alkaline cyanide solution can be conducted simultaneously in the same reactor in less than 90 minutes with a recovery that exceeds 96%. Then, the pregnant cyanide solution with gold and silver is sent for recovery of precious metals by using a very promising electrochemical technique (EC) that does not require high concentrations of silver and gold in cyanide solutions.

Detoxification of cyanide using titanium dioxide and hydrocyclone sparger with chlorine dioxide

Abstract The extraction of gold and silver from minerals and concentrates with cyanide is an important hydrometallurgy process that has been studied for more than 120 years. This technology, which consists of the dissolutions of the precious metals in cyanide solutions, followed by the recovery of the values by cementation, activated carbon or ion exchange resin. Most of the wastes in the industrial effluents’ milling are known to contain high contents of free cyanide as well as metallic cyanide complexes, which give them a high degree of toxicity. Appropriate methods for the treatment of cyanide solutions include cyanide destruction by oxidation using a photoelectrocatalytic detoxification technique with titanium dioxide microelectrodes. This is one of the most innovative ways for the treatment of wastewater containing cyanide. Another is the use of chlorine dioxide (ClO2) with a gas-sparged hydrocyclone as the reactor. The results show that photodegradation of cyanide was 93% in 30 minutes using a 450 W halogen lamp, and in the case of ClO2 the destruction of cyanides was 99% in 1 minute. In both cases, excellent performances can be achieved with the high capacity of these technologies.

Plasma oxidation as a tool to design oxide films at low temperatures

Interfacial oxidation, an established approach to produce surface thin films for catalysts, corrosion, ware protective coatings and electronic structures is currently performed by thermal, anodic, and plasma methods. Fundamental physical-chemical models that can allow film design, particularly on alloys are lacking and plasma oxidation is the least studied of these methods. In this work, plasma oxidation of three CuZr alloys (CuZr2, CuZr, and Cu51Zr14) has been studied using x-ray photoelectron spectroscopy and depth profiling methods. The dependence of the resulting oxide film on alloy composition and sample temperature during plasma oxidation is investigated. In contrast to thermal and electrochemical oxidation which lead to the formation of a zirconium oxide film, plasma oxidation leads to the formation of a copper oxide or metallic copper overlayer depending on temperature and copper concentration in the bulk. It is shown that plasma oxidation can be used to design oxide films at room temperature, whi...

Synthesis and characterisation of strontium hexaferrite using an electrocoagulation by-product

Strontium ferrite (SrFe12O19) was synthesised in a solid phase reaction by applying the conventional ceramic method. The precursor powder, containing magnetic iron species generated by the electrocoagulation technique, was allowed to react with strontium carbonate in the solid phase. The molar ratio of the precursor to strontium carbonate was maintained at 12:1 (Fe:Sr), yielding strontium ferrite (SrFe12O19). The electrocoagulation sludge generated was characterised by X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. The strontium ferrite obtained was characterised by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis, differential thermal analysis and vibrating sample magnetometry. The combined results of these analyses showed that the strontium ferrite obtained was of excellent quality with excellent magnetic properties.