Adsorptive Study on a Sample Fly Ash Composited by Rhamnolipid Biosurfactants

A sample fly ash obtained from reject product of a drying furnace was activated by rhamnolipid biosurfactant from Pseudomonas aeruginosa MA01 strain and used as an efficient adsorbent for the removal of cadmium from aqueous solution. The absorbent was characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscope (SEM) methods. The effects of three factors, namely, initial solution pH, absorbent to lead ratio, initial metal concentration and contact time, on cadmium removal were studied and optimized using a fractional factorial design. The adsorption rates were analyzed by using atomic adsorption spectrometer (AAS). Statistical analyses showed that all factors significantly affect the cadmium removal. Process optimization resulted in maximum cadmium removal of 99.38% at initial solution pH of 10, absorbent to metal ratio of 40 and 120 min equilibrium contact time, and 99.08% removal after about 20 min. Kinetic studies revealed that cadmium adsorption follows the first order model with the rate constant of 548.57 h-1. The cadmium adsorption on activated coal tailings was also found to follows the Langmuir isotherm model compared with Freundlich, Temkin and Jovanoic models. The Langmuir isotherm shows that the metal adsorbs onto a homogenous surface as a monolayer. The model assumes that distribution of adsorption energies over the adsorbent surface is uniform. The maximum adsorption capacity (qmax) of absorbent for cadmium adsorption was 48.08 mg/g at ambient temperature. This study demonstrates that rhamnolipid-fly ash composite could be considered as a promising efficient, low-cost, and easily available adsorbent for the treatment of heavy metal polluted wastewaters.