Study on Adsorption of Heavy Metals by Rice Husk and Extraction of Heavy Metals Adsorbed in Rice Husk

Abstract

Heavy metals with strong toxicity are often contained in mine drainage from the suspended or abandoned mines where mining activities were once conducted. The mine drainage continues to flow semipermanently. Thus the treatment of mine drainage must be continued. As the current treatment method for the mine drainage treatment, the neutralization treatment process utilizing alkali chemicals is mainly conducted. However, few alkali chemicals satisfy both low cost and high neutralizing ability. In addition, regarding the neutralized deposits generated during the treatment of mine drainage, it is difficult to secure the disposal sites. Moreover, in recent years, the metal demand has increased in IC chips and parts for electric vehicles. Thus, focusing on the rice husk which is an industrial waste, the purposes of this study are to verify the adsorption performance of rice husks for heavy metals and to verify whether the extraction of heavy metals from rice husks to which heavy metals are adsorbed is possible or not. In this study, the following two tests are carried out: The adsorption test of rice husk for heavy metals and the extraction test with acid from the rice husk which absorbs the heavy metals. From the test results, the adsorption isotherms of Zn, Cu and Cd on the rice husks are described from the adsorption tests, and the adsorption states of Zn, Cu and Cd on the rice husks are discussed. Furthermore, it is proved to be possible to extract them from the rice husks which adsorbs such heavy metals.