Sulphuric Acid Activation of a Calcium Bentonite

Abstract

The objective of this work was to determine the changes of thermal and surface properties of a bentonite from Çankιrι after activation using different concentrations of H₂SO₄ solutions (0.5–4 M). XRD, FTIR, DTA, and TG analyses of the samples were performed to examine the structural changes of the bentonite before and after acid activation. DTA peaks showed an exothermic change in the temperature region 900–1000°C. Changes at low acid concentrations resulted from cation exchange (exchangeable cations with H ions) and removal of impurities from the bentonite. Differences of surface properties and thermal properties at higher acid concentrations (2–4 M H₂SO₄) were caused by structural changes and partial decomposition of the samples. Surface area measurements showed that with the increase of concentration of H₂SO₄ solution the total BET surface area increased, while the maximum value of specific surface area (240.9 m²/g) was attained by the sample activated with 2 M H₂SO₄. Activation with higher concentrations (3–4 M) caused a decrease in the surface area. The particle size distributions of the original and acid-activated samples showed that the acid activation strongly affected the particle sizes of the particles. While 97.8% of the original bentonite sample is less than 10 µm in size, 97.8% of the activated samples with 0.5 M acid and 92% of the activated sample with 4 M acid are less than 28.25 µm in size.

Keywords:

• bentonite
• acid activation
• surface properties
• thermal analysis
• pore diameter