Fundamentals, present and future perspectives of electrocoagulation.

Electrocoagulation is an electrochemical wastewater treatment technology that is currently experiencing both increased popularity and considerable technical improvements. There has been relatively little effort to better understand the fundamental mechanisms of the processes, particularly those that could provide design parameters to optimize the performances of this relatively simple and inexpensive technique. In a research programme to delineate the mechanisms of the fundamental processes involved in, the authors have realized that the technology has been insufficiently reviewed with emphasis on the fundamentals and their relationship to the performance of this technology. This paper presents an in-depth discussion and consideration of the factors that need to be addressed for optimum performance of this technology. Recent improvements of this technique and the theoretical model studies are also reviewed.

Treatment of orange II azo-dye by electrocoagulation (EC) technique in a continuous flow cell using sacrificial iron electrodes.

This paper describes the EC treatment of orange II dye solution in a flow cell using sodium chloride as an internal electrolyte. In this technique dye solutions were passed through a flow-through EC apparatus consisting of a flow-through cell, the electrode assembly, the feed pump and the DC power supply unit. The cell contained five parallel iron electrodes, which form four parallel cells. Experiments were run at 25 degrees C under various electrolyte concentrations, dye concentrations, current density, flow rate of the solution, and pH at dc current range of 2-5A. Various number of recycles of the treated dye solution were also performed at the same dc current range. Optimum conditions to get high removal efficiency were experimentally determined. It was found that 98.5% of the dye was removed from the solution under the optimum conditions. The residue from a blank run (pH = 7.3) and a dye added run (pH = 8.5) were collected by vacuum filtration and analyzed by XRD after drying in a vacuum desiccator. The XRD data indicated the presence of mainly maghemite (gamma-Fe2O3) and magnetite (Fe3O4) in the residue. However, there is not much difference between the X-ray diffractograms of the blank sample and the dye-containing residue to warrant any conclusions therefrom with regard to the interactions between the oxides and the dye molecules.

An X-ray diffraction (XRD) and Fourier transform infrared spectroscopic (FT-IR) investigation of the long-term effect on the solidification/stabilization (S/S) of arsenic(V) in Portland cement type-V.

The long-term effects on solidification/stabilization (S/S) of As5+-bearing oxyanions (AsO4(3)-) in Portland cement type-V (OPC) have been investigated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopic (FT-IR) techniques. The results of this study confirm our previous results that the early hydration of cement is inhibited by the presence of AsO4(3)-, and that the inhibition is mainly caused by the formation of highly insoluble Ca3(AsO4)2 on the surface of hydrating cement particles. Arsenate analog of ettringite [Ca6(Al2O6)(SO4)3 x 32H2O] was identified in the early stages of hydration of pure Portland cement and As(V)-treated Portland cement [OPC-As(V)], but not in 10-year-old similar samples. The XRD and FT-IR results indicated interactions of oxyanions and cement particles to produce minor quantities of As5+-bearing compounds in fresh as well as in 10-year-old samples. New As5+-bearing phases, NaCaAsO4 x 7.5H2O and Ca5(AsO4)3OH were identified in the 10-year-old OPC-As(V) samples by XRD analyses. Based on these results it is concluded that Portland cement may be considered as a potential matrix to immobilize As5+-bearing wastes.