Biosorption of cadmium by algal biomass: Adsorption and desorption characteristics

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Abstract
The adsorption and desorption characteristics of a biosorption process comprising the biomass of the marine alga Sargassum baccularia, cadmium ions and desorbing agents hydrochloric acid and ethylenediaminetetraacetic acid (EDTA) were investigated using a batch reactor system. Both desorbents were effective in stripping adsorbed cadmium from the biomass. It was found that HCl at pH 2 could desorb 80% of the cadmium initially loaded onto the biomass. Almost complete recovery of cadmium was achieved by a 3.24 mM EDTA solution. The reusability of the biomass was tested in five consecutive adsorption-desorption cycles. The quantity of cadmium desorbed over the five cycles with either HCl or EDTA as desorbent corresponded well to the quantity loaded, indicating that complete desorption was readily achieved. However, the cadmium uptake capacity of the biomass deteriorated with repeated use of HCl or EDTA. HCl was found to have reduced cadmium uptake by 56% while the reduction for EDTA was nearly 40% over the five adsorption-desorption cycles. EDTA thus emerged as a slightly better desorbing agent compared with HCl. After completion of the five cycles it was found that 30% of the original biomass weight had been lost with HCl as the desorbent. EDTA exhibited desorption behaviour similar to that of HCl by causing a biomass loss of 16%. The loss of biomass indicates that some dissolution of biomass components containing cadmium binding sites apparently occurred, reducing the cadmium uptake capacity of the biomass in multiple cycles of adsorption-desorption.

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