A new mesoporous activated carbon as potential adsorbent for effective indium removal from aqueous solutions

Abstract

In this work, a new mesoporous activated carbon (MC01) suitable for the adsorption of indium from aqueous solutions has been synthetized; with the final aim of pre-concentrating this ion metal. The new material was synthesized by replica method using sucrose and silica gel as raw materials, and adjusting both carbonization time and temperature to obtain a material whose surface is mainly constituted by phenolic groups. This way, its pH value in aqueous suspensions makes it suitable for indium adsorption. The mesoporous carbon is able to remove around 96% of the indium, attaining equilibrium in less than 15 min. The study of the adsorption conditions indicates that the adsorbent dosage has a large impact on the process, being 10.0 mg/g the optimum dosage. On the contrary, the process is highly pH dependent since the adsorption capacity decreases by a 68% if the pH is lowered from 3.5 to 2; however, buffered media slightly affect the process, with a decrease of the indium adsorption capacity around 5%, due to the presence of foreign ions. The recovery of the adsorbed indium was carried out employing HNO3 and HF solutions, proving that low pH values promote this phenomenon, reaching a recovery rate of 82% with a pH = 0.5 HNO3 solution. Additionally, the pre-concentration of indium was analyzed by diminishing the volume of regenerative solution. The results indicated that, when the volume of regenerative solution was decreased by one-eight part, the indium concentration increased six fold. Thus, adsorption is suitable for the pre-concentration of metallic indium ions in water solutions to be further recovered by any other technique, such as extraction.