BIOSORPTION OF CADMIUM BY ALGAL BIOMASS - ADSORPTION AND DESORPTION CHARACTERISTICS

The adsorption and desorption characteristics of a biosorption process comprising the biomass of the marine alga Sargassum baccularia, cadmi um ions and desorbing agents hydrochloric acid and ethylenediaminetetr aacetic acid (EDTA) were investigated using a batch reactor system. Bo th desorbents were effective in stripping adsorbed cadmium from the bi omass. It was found that HCl at pH 2 could desorb 80% of the cadmium i nitially loaded onto the biomass. Almost complete recovery of cadmium was achieved by a 3.24 mM EDTA solution. The reusability of the biomas s was tested in five consecutive adsorption-desorption cycles. The qua ntity of cadmium desorbed over the five cycles with either HCl or EDTA as desorbent corresponded well to the quantity loaded, indicating tha t complete desorption was readily achieved. However, the cadmium uptak e capacity of the biomass deteriorated with repeated use of HCl or EDT A. HCl was found to have reduced cadmium uptake by 56% while the reduc tion for EDTA was nearly 40% over the five adsorption-desorption cycle s. EDTA thus emerged as a slightly better desorbing agent compared wit h HCl. After completion of the five cycles it was found that 30% of th e original biomass weight had been lost with HCl as the desorbent. EDT A exhibited desorption behaviour similar to that of HCl by causing a b iomass loss of 16%. The loss of biomass indicates that some dissolutio n of biomass components containing cadmium binding sites apparently oc curred, reducing the cadmium uptake capacity of the biomass in multipl e cycles of adsorption-desorption. (C) 1997 IAWQ. Published by Elsevie r Science Ltd.