Utilization of Waste and Renewable Material‐HCM as an Efficient Adsorbent for Heavy Metal Ions Removal: A Study of Adsorption Isotherms and Kinetics**

Abstract

This work describes the method of extraction and characterization of hardness causing materials (HCM) from boiling tap water via distillation assembly. The obtained white colored powered material was then calcined at different temperatures. It was revealed that powder residue was mainly consisted of calcium carbonate at room temperature and decomposed majorly to CaO, confirmed using XRD, when calcined at 900 °C for about 4 h. Moreover, thermogravimetric analysis (TGA) showed single‐step decomposition in case of HCM‐900 °C whereas two‐step decomposition was observed for both HCM‐400 °C and HCM without calcination which can attributed to release of CO2 from CaCO3 and then decomposition of CaO in later cases. The SEM images showed crumbled type structure, flaked structure and disintegrated small‐sized round shaped agglomerated particles for HCM‐25 °C, HCM‐400 °C and HCM‐900 °C. In addition, the impact of adsorption of different heavy metal ions (Mn7+, Cr6+ and Ni2+) over HCM with different time intervals was studied. The Langmuir adsorption isotherm is the best fit adsorption isotherm for this work. The kinetics studies follow the second order reaction. The results revealed that the Mn7+ adsorbs at higher efficiency among all the metal ions at negatively charged surface of HCM‐ 900°C due to higher oxidation state of Mn7+.