Application of response surface method for removal of Cr(VI) from aqueous solutions using foam fractionation process

Discharge of heavy metals into the environment by wastewater from production and application processes is nowadays getting more and more serious due to the rapid development of such processes. Produced water during oil production and wastewater form metal plating and ore dressing are few examples to mention. In this research, removal of chromium ions from aqueous solutions has been studied by foam fractionation process using cetyl trimethyl ammonium bromide as surfactant. Effect of processing time, gas flow rate, initial surfactant concentration, and initial pH on removal efficiency has been investigated. Preliminary screening tests were performed, and initial surfactant concentration and processing time were recognized as the variables with a significant effect on removal efficiency. Response surface methodology based on central composite design as a design of experiment method was employed to design experiments to study the effect of important variables more precisely. Five levels for each significant variable were considered and design of experiment. An accurate correlative model is developed for the estimation of removal efficiency under different operating conditions in foam fractionation process with a maximum relative error of 1.674%. Four sets of validation tests were also conducted, and the results of validation tests were shown to be in accordance with those obtained on tests dictated by design of experiment. Optimum operating conditions were found to be with an initial surfactant concentration of 175 ppm and 45 min of processing time that yielded 97.74% removal of Cr(VI) from a solution of 10 ppm initial concentration.