Due to the widespread use of cyanide in mining operations, its recovery and destruction is important for both the environmental aspects of wastewater and its treatment, and the economic aspects associated with the high consumption of chemicals by the process itself. A photoelectrocatalytic detoxification technique with titanium dioxide microelectrodes is one of the most innovative ways for the treatment of wastewater containing cyanide. However, this technique has a disadvantage for industrial application in that the separation of titanium dioxide after the photocatalytic degradation of cyanide is rather difficult due to the fineness of the particles, and therefore, the reuse of the titanium dioxide has not been attained for the treatment of cyanide-containing wastewater. To overcome this weak point, an electrocoagulation (EC) technique is used to recover the titanium dioxide from its aqueous suspensions. The results show that photodegradation of cyanide is 93 % in 30 min using a 450 W halogen lamp. The recovery of anatase with the EC process is 98 %. The results indicate that this technique has the potential to serve as a reliable and economical method because sunlight can be used efficiently as the power source. The Langmuir isotherm is used to obtain the thermodynamic parameters, i.e., free energy, enthalpy and entropy. The evaluation of these parameters, i.e., DG°= -37 kJ/mol, DH°= -54 kJ/mol and DS°= 0.524 kJ/mol K, indicates the spontaneous and exothermic nature of the adsorption of the anatase particles on the iron species.

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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 (ClO 2 ) 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 ClO 2, the destruction of cyanides was 99% in 1 minute. In both cases, excellent performances can be achieved with the high capacity of these technologies.

The protection of the global environment and in particular, the provision of a sustainable source of clean water is a necessity for human survival. Specifically, large quantities of chromium containing compounds are being discharged into the environment. This study has been carried out to determine the feasibility of chromium adsorption on iron species by an Electrocoagulation (EC) process using the Langmuir Isotherm. The full potential of EC with air injection as an alternative wastewater treatment technique to remove chromium from well water shows more than 99 % removal without the addition of any chemical reagents. In this study, X-Ray Diffraction, Scanning Electron Microscopy, Mössbauer Spectroscopy and Fourier Transform Infrared Spectroscopy are used to characterize the solid products that reveal the expected crystalline iron oxides, i.e., lepidocrocite, magnetite, gohetite, and iron oxide.

Protection of global environment and sustainable sources of clean water are a necessity for human survival. The wide use of heavy metals by modern industries has generated heavy metals containing wastes and by-products. Specifically, large quantities of arsenic compounds are being discharged into the environment. The full potential of Electrocoagulation (EC) with air injection as an alternative wastewater treatment technique to remove arsenic from water showed more than 99 percent of removal without adding any chemicals. This study has been carried out to determine the feasibility of arsenic adsorption on iron species by EC process using the Langmuir's Isotherm. Thermodynamic parameters such as ΔH• , ΔS • , and ΔG • were calculated. It was found that the adsorption process is exothermic and spontaneous. Some experiments were conducted to determine the optimum operating conditions such as current density, pH, and residence time. Also in this study, X-Ray Diffraction, Scanning Electron Microscopy, Mössbauer Spectroscopy, and Fourier Transform infrared spectroscopy were used to characterize the EC solid products that revealed the expected crystalline iron oxides (lepidocrocite, magnetite, gohetite, and iron oxide).