Cyclical cadmium adsorption and desorption by activated sludge immobilized on alginate carriers

This paper concerns cadmium desorption in subsequent cycles of adsorption/desorption by chemical sorbents such as 2% sodium alginate, sodium alginate with the addition of poly(vinyl) alcohol (PVA) in the following proportions: 1.5% alginate and 0.5% PVA, 2% alginate and 2% PVA, 2% alginate and 5% PVA, and two kinds of activated sludge immobilized on alginate sorbents. It was proved that adsorption by alginate and alginate with PVA obeys a second-order rate law. The higher the PVA amount in alginate, the lower the reaction rate. Mineral acids such as hydrochloric and sulphuric acids were used as desorption agents. It was observed that all sorbents tested remove cadmium with high and almost constant efficiency from the solution containing 50 mgCd/dm3, whereas desorption effectiveness depended on the kind of sorbents and desorbing agents.