Recovery of rare metal by biosorption using algae and environmental improvement

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1. Adsorption and elution of metal ion using packed column with algal powderMetal cations such as Cu, Ni, Co and Cd are adsorbed by packed algal layr at pH5-7, and eluted at pH 2. Therefore, aqueous solution with elevated metal ion concentration e.g. above 1000 ppm can be got from very dilute aqueous solution (e. g. 12ppm) via biosorption and elution. From this concentrated aqueous solution, metal can be electro-deposited through electrowinning.When powder of undaria pinnatifida or laminaria sp. is used for adsorption operations in packed column, aqueous solution cannot flow through the column because of the viscosity of the bulk. To oversome this trouble, aqueous paste of mixture of algal powder and a small amount of alginate salt powder is extruded into CaCl_2 aqueous solution through a nozzle. Whtn the noodle-like coagulated algal powder is packed in a column, the bulk has little viscosity, so the aqueous solution flows very well.The adsorbents made of algal powders exhibit excellent properties especially in elution oprtation. Therefore, amount of acidic reagent for elution can be reduced compared to the case of using ion exchange resin.2. Metal ion adsorption by algae and FTIR spectraBy FTIR spectra algae can be classified into two classes,(1) Algae which contain cellulose or alginate,(2) Algae which contain protein.When algal powder of class (1) above is contacted with acid aqueous solution at pH about 2 as pretreatment, IR absorbance of 1730 cm^<-1> is observed. This absorbance is considered to be the sign of the change in COOR partial structure in the algal powder.