Efficient Cadmium Removal from Aqueous Environments Using a Composite Produced by Coal Fly Ash and Rhamnolipid Biosurfactants

A novel bio-composite produced from coal fly ash accompanied by rhamnolipid biosurfactants was produced and used as an efficient adsorbent for the removal of cadmium from aqueous solution. Effects of initial solution pH (3-11) and absorbent to cadmium ratio (40-200) on cadmium removal, as process response, were studied and optimized using a central composite type response surface methodology. Results showed that both factors significantly affect the removal efficiency. Optimum adsorption conditions, resulting in over 99% cadmium removal, were achieved at pH 10 and absorbent to cadmium ratio of 40. Time-wise studies revealed that a maximum removal can be achieved following a classic first order model with a rate of 548.57 min-1. The cadmium adsorption on activated fly ash was also found to follow the Langmuir isotherm model with monolayer adsorption mechanism. Moreover, the bio-composite yielded a maximum adsorptive capacity of 67.11 mg/g. The selectivity study in bimetal aqueous systems using copper, lead and zinc metals also confirmed the high adsorption capacity of bio-composite. This study demonstrated that rhamnolipid-fly ash bio-composite could be considered as a promising efficient, low-cost resource material for the treatment of heavy metal polluted wastewaters.