Efficient removal of Cu(II) from aqueous solution using activated carbon modified by rhamnolipid biosurfactant

One of the environmental challenges of various industries is the removal of heavy metals from aquatic environments. Nowadays, the use of adsorption method is considered as an efficient method to overcome this challenge. Although, the physical and chemical characteristics of the sorbent are of particular importance. In this research, the efficiency of an activated carbon sample modified with rhamnolipid biosurfactants was evaluated in order to remove copper ions from the aqueous environment.

For this purpose, the effect of some operational parameters including the ratio of adsorbent to metal (50 to 200), initial solution pH (4 to 10) and stirring speed (100 to 300 rpm) on copper removal efficiency in the form of a central composite experimental design was investigated. The results of experimental studies were evaluated using statistical modeling and analysis of variance.

The statistical analysis of the results revealed that the effect of all parameters on the adsorption efficiency was significant, so That the efficiency increased with the increase of the ratio of adsorbent to metal and pH, and with the decrease of the stirring speed. As a result of optimizing the process, the removal efficiency of more than 99% was achieved under the ratio of adsorbent to metal of 200, pH of 7 and stirring speed of 100 rpm. Additional studies under optimal conditions showed that the process follows pseudo-second-order kinetics and the Freundlich isothermal adsorption model. Moreover, thermodynamics and multistep adsorption studies showed that the adsorption of copper on the modified adsorbent is a two-step process including a high-rate primary chemical adsorption followed by a slow physical secondary adsorption, likely precipitation. The evaluation of absorption selectivity also indicated substantially adverse effect of other metals on the absorption rate of copper ions.

The results of this research showed that activated carbon improved with rhamnolipid biosurfactants can be used as a promising and efficient sorbent for the treatment of wastewater contaminated with heavy metals.