Hydrochloric versus sulfuric acid activation of krantau bentonite: From structural transformation to oil bleaching efficiency
نویسندگان
1 Institute of General and Inorganic Chemistry, Academy of Sciences of Republic of Uzbekistan, 77a M. Ulugbek, P. O. Box: 100170, Tashkent, Uzbekistan.
2 Urgench State University, Khorezm Region, Urgench, Uzbekistan.
3 Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent, Uzbekistan.
4 Fergana State Polytechnic University, Fergana, Uzbekistan.
5 Namangan State Technical University, Namangan, Uzbekistan.
6 Mamun University, Khorezm, Uzbekistan.
7 Namangan State Technical University, Namangan, Uzbekistan.
8 Urgench State University, Khorezm Region, Urgench, Uzbekistan.
9 Institute of General and Inorganic Chemistry, Academy of Sciences of Republic of Uzbekistan, 77a M. Ulugbek, P. O. Box: 100170, Tashkent, Uzbekistan.
10 Department of Environmental Engineering and Life Safety, Termez State University of Engineering and Agrotechnologies, Islam Karimov Street, 288A, P. O. Box: 190100, Termez, Uzbekistan.
11 Tashkent Institute of Chemical Technology, Tashkent, Uzbekistan.
12 Institute of General and Inorganic Chemistry, Academy of Sciences of Republic of Uzbekistan, 77a M. Ulugbek, P. O. Box: 100170, Tashkent, Uzbekistan.
doi
10.22034/crl.2026.573229.1782چکیده
Acid activation is an effective route to enhance the surface and sorption properties of natural clays. In this study, Ca-type bentonite from the Krantau deposit (Karakalpakstan, Uzbekistan) was beneficiated by elutriation and Na2CO3 treatment and then activated with HCl or H2SO4 (5–15 wt.%) at 95–100 °C for 2–6 h (solid/liquid = 1:6). FTIR and XRD indicated that calcite dissolution and cation exchange occur mainly within 2 h; with H2SO4, residual CaSO4 (gypsum) reflections appear. Chemical analysis confirmed a stronger decalcification by HCl (CaO decreased from 21.25 to 1.75 wt.%) than by H2SO4 (to 7.36 wt.%). Nitrogen adsorption at 77 K gave type IV isotherms, consistent with predominantly mesoporous structures. The specific surface area increased from 40.27 m2/g for the initial bentonite to 64.22 m2/g after 15% H2SO4 and to 101.6 m2/g after 15% HCl; micropore volume rose from 0.0099 to 0.043 cm3/g, and the mean pore radius shifted from 57.5 to 54.6 Å. SEM/EDS confirmed structural rearrangement and a strong drop in Ca (from 12.4 to 0.76 mass%). Performance was evaluated in sunflower-oil bleaching (0.5–1.0 wt.% adsorbent): the HCl-activated sample significantly lowered oil color and acid value (to 0.4 mg KOH/g) and reached 95% β-carotene removal within 40 min at 70 °C. Overall, HCl activation under these conditions yields the most effective bentonite adsorbent for edible-oil refining.
