Effect of Mechanochemical Processing on Adsorptive Properties of Blast Furnace Slag

Mechanochemistry is of greater interest at present because of its application in the transformation of waste. In this study, an innovative application is proposed, namely to mechanochemically treat blast furnace slag so that it can be recycled into a low-cost adsorbent. In particular, the way this industrial waste adsorbs methylene blue present in aqueous solutions has been dealt with in detail. To this end, the slag was treated in a planetary mill at different charge ratios, rotational speeds and milling times, and then characterized by laser granulometry, porosimetric, X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses. These investigations shed light on the interrelationships between milling conditions and the physico-chemical characteristics of the slag. Next, the most interesting samples to submit to the following adsorption equilibrium and kinetic tests were chosen. These runs were conducted at different dye initial concentrations and adsorption times, and the results were interpreted according to the previously analyzed characteristics of the slag. Furthermore, adsorption data was postprocessed to obtain values for the equilibrium and kinetic constants, the separation factor, the removal efficiency, the initial adsorption rate, and the characteristic adsorption times.