Removal of reactive dyes from aqueous solutions using combined coagulation/flocculation and adsorption on activated carbon

The removal of two reactive dyes (Black 5 and Orange 16) was investigated. The objective of this study was to investigate the removal of reactive dyes through a combined treatment process with coagulation/adsorption on activated carbon. Activated carbon derived from coconut shells was used as the adsorbent and aluminum chloride was used as the coagulant. In order to obtain the best conditions for the removal of the dyes, the influence of the following parameters was verified: coagulant and alkalizer dosage, aqueous solution pH, temperature of the mixture and salt addition (sodium chloride). Spectrophotometry was the analysis technique used to measure the concentration of dye remaining in the fluid phase. The results for the adsorption of the reactive dyes were fitted to the models of the Langmuir, Freundlich and Radke-Prausnitz isotherms and showed good correlation. The removal efficiencies were approximately 90% and 84% for the Black 5 and Orange 16, respectively. In order to evaluate the final effluent obtained after the coagulation and adsorption process, acute toxicity tests were carried out with Artemia salina and Daphnia magna, which verified that the effluent was atoxic. The combined coagulation/adsorption process was shown to be an excellent option for the removal of reactive dyes.