MX2007013111A - Solar energy-assisted process for treating effluents polluted with hexavalent chromium. - Google Patents

Abstract

Described is a global process for treating effluents polluted with hexavalent chromium, which is based on the use of copper electrodes (cathodes) and photovoltaic energy for an integral handling of the process. The copper cathodes present a quick kinetics for reducing the hexavalent chromium (reacting in a spontaneous manner), and are cathodically protected by the electrode polarization in order to avoid wear. Furthermore, copper is a material useful both as two-dimensional plates and as meshes for the construction of three-dimensional electrodes, which improve the mass transference and therefore the process efficiency. The general principle of the process refers to the reduction of hexavalent chromium (a species highly toxic, corrosive and difficult to remove from an aqueous medium) into trivalent chromium (a species less toxic, essential for life and easily removed by precipitation). On the basis of fundamental studies, copper is an electrode material that presents high kinetics for the Cr (VI) electro-reduction, low voltage electrolysis (minimization of the power consumption) and ease of machining. The electrode is integrated to a parallel plate reactor, which has a size-stable anode that is operated by a centrifugal pump and a plurality of flow regulating valves. With regard to the global process, the operation of the pump represents more than 90% of the required electric power, thus the photovoltaic power use being an attractive alternative for recovering the investment used to implement the process for treating effluents, since the commercial electric power is not required. The filter-press type reactor allows the process to be adapted to different volumes and concentrations of the solutions to be treated, since it enables the reactors to be stacked in parallel, as well as the use of three-dimensional electrodes for improving the mass transference and an easy upgrading thereof by geometric similitude. The control of the process performed by an electric power control device and the FIA device allows the operation of the same to be performed with a minimum human intervention, thus determining the moment at which the effluent reaches the required concentration, generally established by environmental standards; the total removal of chrome from the effluent may be achieved by precipitating the trivalent chromium and decanting the precipitated material in order to be subsequently confined or valued.