Safety of the water supply is the most important for human health. Sometimes, heavy and toxic metals have been contained in drinking water. In industrial countries, drinking water has been treated with many kinds of technologies and has been supplied to the people. While in developing countries, heavy and toxic metals are contained in drinking water because the developing country does not have a system for water treatment. Heavy and toxic metals have been detected many times, their concentrations are over the standard values for drinking water at the World Health Organization (WHO). The developing countries need a policy as soon as possible.
1)On the other hand, copper, chromium and arsenic (CCA) have been used as an antiseptic for wood around the world. For example, their consumption is approximately 350 thousands ton/year and 20 million ton/year in Japan and in India, respectively. The Waste Study Foundation reported the amount of CCA contained in waste woods in Japan to be 425, 1053 and 460 mg/kg, respectively. The problem concerning wastes has occurred not only Japan but also in many countries and is very important. Their metals are presented in the ash after burning of waste wood and flow from reclaimed ground into seawater. However, large amounts ingested cause adverse reactions such as acute toxicity, nausea, vomiting and diarrhea, and chronic toxic, dermatitis, pigmentation, myelopathy, peripheral neuropathy, jaundice and renal failure.2) The toxicity of inorganic arsenic is higher than that of organic arsenic. Arsenic has been detected over the standard value in the wastewater of factories in Japan. Especially, in Bangladesh, Taiwan, northern China, Mexico, Chile, Argentina and the United States of America, these problems are serious. While activated carbon 3,4) and hydroxyl cerium 5) are famous as adsorbates to remove As(III). In 1993, the WHO decreased from 50 to 10 mg/l the standard value for arsenic concentration in drinking water. Cr(VI) shows a strongly oxidative action, causing inflammation of the throat and mucous membranes of the nose. A high concentration of Cr(VI) causes nasal septal perforation. The carcinogenicity of As(III) and Cr(VI) has been reported in many studies.6-9) It is necessary that the technology for removal of heavy and toxic metals be low cost and easy to use.Aluminum is a perfectly recyclable metal. Gibbsite (GB, Al(OH) 3 ) as well as boehmite (BE, AlOOH) is components of bauxite, and it is well known that GB is cheaper than BE. BE has a high As(III) adsorption ability, 10) the structure of GB changes to that of BE by calcination.11) The adsorption mechanism of As(III) on GB based on model calculations was reported by Oliveira et al. 12) and the specific bonding of arsenate on GB was reported by Weerasooriya et al.13) However, the adsorption ability of As(III) on GB in binary solution system (containing both As(III) and Cr(VI)) has never been reported.In this study, calcined GB was used, and the adsorption ability and adsorption mechanism of both As(III) and Cr(VI) were st...
