Titanium Gypsum Purification: Study on the Oxalic Acid-Sulfuric Acid Composite Acid Leaching Treatment of Titanium Gypsum

Abstract

gypsum is identified as an industrial by-product discharged by enterprises engaged in the production of titanium dioxide. The presence of high levels of iron impurities results in inferior physical properties, which hinders its extensive application in the field of building materials. This study focuses on titanium gypsum, investigating the impact of oxalic acid leaching and the combined leaching process of oxalic acid and sulfuric acid on the iron removal rate of titanium gypsum. Additionally, the study seeks to explore the underlying mechanisms that influence these processes, with the aim of enhancing the potential for titanium gypsum to be utilised effectively in the building materials sector. The findings of this study reveal that the application of oxalic acid leaching is highly effective in eliminating Fe(OH)3 impurities from titanium gypsum. The leaching process is predominantly governed by diffusion dynamics, ensuring a thorough and efficient purification of the material. The study's outcomes demonstrate that elevating the temperature or prolonging the duration of the leaching process significantly enhances the leaching efficacy. The optimal conditions for the process have been identified as a 6% mass fraction of oxalic acid, a liquid-to-solid ratio of 8 g/g, a leaching temperature set at 90°C, and a leaching time of 110 minutes. Under these parameters, the iron leaching rate can achieve an impressive 84%; The most effective combination ratio has been determined to be an equal blend of 50% oxalic acid and 50% sulfuric acid. This mixture can boost the iron leaching rate to an impressive 95%, indicating that it is an efficient method for purifying titanium gypsum. In the process of treating titanium gypsum with a composite acid leaching solution of oxalic and sulfuric acids, the synergistic effect of H+ ions, which dissolve Fe(OH)3 impurities, and C2O42- ions, which complex with Fe3+, results in a substantial removal of the flocculent Fe(OH)3 impurities from the gypsum crystal surface. This action effectively exposes the crystal surface to an environment rich in C2O42-, H+, and SO42- ions, facilitating a more direct and thorough interaction that enhances the leaching process; An excess of C2O42- ions initially complexes with the gypsum surface, leading to the formation of CaC2O4•H2O. Following this, within the acidic leaching environment maintained at 90°C, and under the influence of H+ and SO42- ions, CaC2O4•H2O undergoes a transformation into CaSO4•2H2O. This compound then recrystallizes on the gypsum crystal surface. This recrystallization not only prevents the formation of calcium oxalate impurities but also significantly elevates the quality of the titanium gypsum post-acid leaching treatment.

Keywords: Titanium gypsum, Oxalic acid leaching treatment, Oxalic acid-sulfuric acid composite acid leaching treatment