New insights into the management of hardwater using bentonite: Studying the mechanism via experiments and statistical physics treatment

Abstract Hard water is related to some health issues owned to numerous diseases and economic challenges associated with the calcification of industrial water. Hence, in the present research, the treatment of hard groundwater via adsorption of polyvalent Ca+ 2 and Mg+ 2 ions at different initial concentration using bentonite was investigated. Full characterization of the adsorbent was carried out using different techniques. At all solution temperatures, the formation of a monolayer of these ions was caused by the Ca2+ and Mg2+ hardness–bentonite interaction, and the adsorption process was ascribed to active sites with a homogenous characteristic of the bentonite since Langmuir model fit the Ca2+ and Mg2+ adsorption data (R2 = 0.99). The statistical physics treatment indicated that the advanced monolayer model fitted Ca+ 2 and Mg+ 2 adsorption data at all temperatures. Based on this statical model, mixed (parallel and non-parallel orientations) adsorption geometry was recognized. The density of bentonite active sites (the steric NM parameter) rose from 688 to 1019 mg g− 1 within 25° to 50 ºC and this factor was the main variable influencing the bentonite adsorption capacity. Overall, bentonite is recommended by the current study as a cost-effective and environmentally safe adsorbent to remove TH from groundwater.