Author(s)

H. Itoh, R. Sasai & T. Itakura

Abstract

Detoxification of polluted water is required in many fields of industrial or agricultural production processes. Not only removal of rare/hazardous elements, but also the recovery and effective use of such elements is essential to increase the resource circulation efficiency. Recycling technology of rare metals and hazardous elements from polluted water would bring about our clean and environmentally benign society. The hydrothermal mineralization process is one of the best candidate techniques to meet the above demand. In the present work, we investigated the consolidation recovery of rare/hazardous inorganic compounds containing B, F, P, Cr, As, Sb, etc. The model wastewaters containing the above elements with various concentrations were treated in autoclave under the hydrothermal temperatures of 100-200oC using Ca(OH)2 or CaCl2 as the mineralizer. Corresponding minerals, such as CaB2O5･H2O, CaF2, Ca5(PO4)3(OH), Ca2CrO4, Ca5(AsO4)3(OH), Ca2(Sb2O7), were consolidated and separated by filtration after the treatments. Solid/liquid separation under hydrothermal equilibrium was found to be very effective for increasing the yield of minerals, because the final concentration in liquid is determined by the solubility of the mineral under the hydrothermal condition. As a result, the concentration of every residual element in liquid decreased below the National Effluent Standard of Japan. The recovered minerals can be supplied as raw materials for the refining process of ordinary minerals. Such a geo-mimetic wastewater treatment method will be applied to the detoxification and recovery of many kinds of rare/hazardous elements in wastewater.

Keywords

hydrothermal mineralization, rare metals, hazardous elements, wastewater, resource recovery