The significant role of acid activation in clay modification: a comparative study of activators for bentonite

Abstract Untreated clays often have limited surface area, porosity and surface reactivity, which restricts their diverse applications. Clay activation addresses these limitations by leaching interlayer cations and dissolving mineral impurities, thereby improving their surface properties. In this study, bentonite was activated with 3 M sulfuric (H2SO4), hydrochloric (HCl), nitric (HNO3), acetic (C2H4O2) and phosphoric (H3PO4) acids at 90°C for 20 min. The effectiveness of the acids was systematically evaluated and the resulting physicochemical properties were analysed using Brunauer–Emmett–Teller surface area measurements, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray fluorescence and Fourier transform infrared spectroscopy. The results showed an increase in surface area from 56.8 m2 g−1 for pristine bentonite to a maximum of 232.4 m2 g−1 for H2SO4-activated clay, attributed to the leaching of exchangeable interlayer cations and the removal of impurities. Analyses by TEM and XRD confirmed that the bentonite structure and integrity were largely preserved after activation. TGA demonstrated a 14% reduction in mass loss at high temperatures (500−700°C), attributed to dehydroxylation of structural hydroxyl groups during activation. The acid activation approach successfully enhanced bentonite properties while preserving its structural integrity, making the activated material suitable for advanced applications.