Characterization of Hydrochloric Acid Activated Natural Kaolin and its application as adsorbent for Mg2+

Abstract

Hard water can form deposits (scale) on pipe walls and operating units in industrial machines. One way to soften hard water is by using adsorbents to reduce the number of ions causing hardness, one of which is Mg2+. Kaolin is a natural mineral which has potential as an adsorbent. The ability of kaolin as an adsorbent can be enhanced utilizing activation. In this study, kaolin was chemically activated using HCl solution with varying concentrations, namely 4, 5, and 6 M. The activation was carried out by stirring kaolin with the activator solution for 24 hours. The adsorbent characterization was performed by the infrared spectrophotometer (FTIR) and the gravimetric method. The adsorption test for Mg2+ by activated kaolin was determined by adding 1g of adsorbent to 25 mL of 10 ppm Mg2+ solution with stirring rate 150 rpm. Furthermore, the adsorption contact time was varied, namely 30, 90, 150, and 180 minutes. The concentration of Mg2+was determined by a titration method using ethylenediaminetetraacetate (EDTA). The percentage of Mg2+ adsorbed was calculated as the concentration of Mg2+ adsorbed against the initial concentration. The results showed that kaolin activated by 6 M HCl could adsorb 68.9% of Mg2+ at the optimum contact time of 150 minutes. Activation of kaolin with HCl 6M can release organic impurities present in natural kaolin, which is thought to affect increasing its adsorption capacity for Mg2+.