Cadmium adsorption characteristic of alkali modified sewage sludge

This paper proposed a new biosorbent preparation method by alkali modification of sewage sludge. The cadmium ion (Cd2+) adsorption capacity of alkali modified sewage sludge (AMSS) was evaluated by equilibrium sorption experiments. The amount of released calcium ion (Ca2+) in sorption equilibrium experiment were measured in order to reveal the adsorption mechanism. In addition, Zeta potential, specific surface area and Fourier transform infrared (FTIR) spectra of AMSS were tested. The results showed that the cadmium adsorption isotherms of AMSS fitted well with both Langmuir and Freundlich models, and the maximum adsorption capacities increased by 0.713 mmol g−1. The cadmium adsorption capacity of biosorbent increased with NaOH solution concentration (range from 0.25 to 7.5 mol L−1) for sewage sludge modification. The strong cadmium adsorption of AMSS was attributed to ion exchange effect, electrostatic attraction and complexation. This alkali modified sewage sludge may have a potential for serving as cadmium removal biosorbent.