Adsorption of Congo Red by surfactant-impregnated bentonite clay

Due to an ever-changing climate and invasive foreign plant species increase, South Africa struggles with limited water resources. Water is important for the sustenance of all living organisms and it has to be protected. The development of different water treatment techniques becomes more popular to achieve efficient and cost-effective ways of removing contaminants from water. In this study, the property of bentonite clay was altered through impregnation with surfactants such as benzyltrimethylammonium chloride (BTMA), hexadecyltrimethylammonium bromide (HDTM) and tris(hydroxymethyl)aminomethane (THMA) and then used for the removal of the anionic dye, Congo Red (CR), from solutions. The characterization of the different clay samples was done with the use of X-ray diffractometer, X-ray fluorometer and FTIR spectroscopy. To determine the bentonite adsorption affinity the pseudo-first- and second-order kinetic models were used as well as the Langmuir- and Freundlich isotherm models. Other influencing factors that were tested include the effects of adsorbent dosage, initial dye concentration and contact time. The natural bentonite (NB) and bentonite impregnated with BTMA or THMA only adsorbed CR to a certain extent with an adsorption affinity of qe = 5.00 mg/g, qe = 1.87 mg/g and qe = 2.76 mg/g, respectively. The HDTM-impregnated bentonite performed very well in adsorbing CR with an adsorption affinity of qe = 16.04 mg/g. Evaluation of thermodynamic parameters such as ΔG° and ΔH° indicated that the adsorption process was thermodynamically favourable and endothermic in nature. HDTM can therefore be considered to improve the adsorption capacity of natural bentonite clay for the removal of an anionic dye such as C