New insights into the management of hard water using bentonite: experimental and statistical physics treatment

ABSTRACT Hard water along with the calcification of industrial water has been related to certain health issues causing numerous diseases and economic challenges. Hence, in the present research, the treatment of hard groundwater via adsorption of polyvalent Ca2+ and Mg2+ ions at different initial concentrations 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 Ca2+ and Mg2+ adsorption data at all temperatures. Based on this statistical 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 1,019 mg g−1 within 25–50 °C 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 total hardness from groundwater.