Bleaching of red clay using Na₂S₂O₄ and NaBH₄ in acidic solution

¹ Faculty of Natural Sciences, Electric Power University, 235 Hoang Quoc Viet, Ha Noi City, Vietnam
² National Institute of Applied Mechanics and Informatics, Vietnam Academy of Science and Technology, 291 Dien Bien Phu, Ho Chi Minh City, Vietnam
³ Faculty of Chemical Engineering, Ho Chi Minh City University of Industry and Trade, Ho Chi Minh City, Vietnam
⁴ Faculty of Natural Sciences Education, SaiGon University, 273 An Duong Vuong St., Ward 3, District 5, Ho Chi Minh City, Vietnam

^* Email: bxvuong@sgu.edu.vn;

Abstract

Bleaching of red clay is carried out by reacting iron-containing clay with the system of two reducing agents Na₂S₂O₄, and NaBH₄, in an acidic environment. The treatment process is performed with the help of ultrasonic equipment, as well as mixing operations performed at high temperature. Several physical-chemical methods such as XRF, XRD, and FTIR were used to evaluate clay samples before and after treatment. The results showed effective iron-removal in red clay. Comparison of whiteness between the processed sample and the original sample is performed by measuring parameters in the CIE L*a*b* color-system. The analysis shows that the whiteness of the treated sample reached 78.72%, showing that the treated clay has clearly improved its whiteness, and can be applied in making high-end ceramic products that require the clay with high whiteness.