South African Journal of Chemical Engineering (Oct 2022)
Studies towards the adsorption of sulphate ions from acid mine drainage by modified attapulgite clays
Abstract
The lack of access to safe drinking water has been a global crisis for the longest time, which has encouraged researchers to improve existing technologies or create new strategies to address issues associated with water pollution from both inorganic and organic pollutants. Adsorption and photodegradation are amongst the simple, cost-effective and environmentally durable methods applied in wastewater treatment. The chemistry and applications attapulgite clays receive ongoing attention in removal of contaminants from water due to their fascinating unique remarkable adsorption properties as well as their economic appeal, attapulgite clays have been extensively studied for the adsorption of various contaminants in aqueous media. In this study, the removal of sulphate ions from Acid Mine Drainage (AMD) using modified attapulgite by electrolyte (BaCl2) and two surfactants viz., hexadecyltrimethylammonium bromide (HDTMA), and trimethyldecylammonium bromide (TDTMA) was investigated. The study is the first to investigate and compare all three modified attapulgite by electrolyte (BaCl2) and two surfactants viz., hexadecyltrimethylammonium bromide (HDTMA), and trimethyldecylammonium bromide (TDTMA) and the factors that affecting removal of sulphate from AMD. A scanning electron microscope (SEM), X-ray diffraction (XRD) patterns, and a Fourier Transform Infrared (FTIR) spectrometer were used to analyse and validate the modified attapulgite clays. Batch adsorption studies were then carried out using the modified attapulgite clays, and the influence of various parameters influencing sulphate ion recovery, such as contact time, temperature, and solids loading, was investigated. At 25 °C, sulphate ion removal rates of 75% were obtained using BaCl2-modified attapulgite at a solid loading of 10% (m/v).TDTMA and HDTMA-modified attapulgites followed, with ion recovery of 69 and 16%, respectively, at a solid loading of 200% (m/v). These results suggest that BaCl2 was the most effective ionic surfactant when used to modify attapulgite clay for sulphate ion removal, and was therefore chosen for downstream studies. When the reaction temperature was increased to 35 °C and 45 °C to investigate the influence of temperature, it was discovered that the removals of sulphate ions were reduced to 66 and 64%, respectively. These results demonstrated that increasing the temperature has a negative impact on the removal of sulphate ions. The Temkin adsorption isotherm and the second-order kinetic model were found to have a very significant correlation with the results, implying that they best describe the experimental data. The activation energy of 23.7 kJ/mol clearly showed that chemisorption was the primary sulphate removal method. The results of this investigation demonstrated that BaCl2-modified attapulgite clay was a good adsorbent for the efficient adsorption of sulphate ions from AMD.
