On mechanical activation of glauconite: Physicochemical changes, alterations in cation exchange capacity and mechanisms

Abstract

Mechanical activation (MA) of glauconite [(K,Na,Ca)(Fe3+,Al,Mg,Fe2+)2(Si,Al)4O10(OH)2] has been investigated to improve its cation exchange capacity (CEC), an impediment for its direct use as nutrients (agro-mineral), notably potassium. Glauconite is mechanically activated using planetary ball milling for varying lengths of time up to 240 min. Milling induces time dependent physicochemical changes in terms of particulate characteristics (morphology, particles size distribution, geometrical and BET specific surface area), structure (crystallite size and strain; –OH/H2O bonding) and surface charge (zeta potential). It is possible to tailor the CEC of glauconite with MA. A remarkable improvement (30-fold!) in the CEC of K+ ions is possible. The effect of milling time on the exchange behaviour is ion-specific. Plausible mechanisms of cation exchange are presented in terms of the chemical nature of the ions involved and the physicochemical changes. Lastly, MA approach is compared with reported methods of potassium recovery; its superiority as a green option is underlined.