Chemical dehydration coupling multi-effect evaporation to treat waste sulfuric acid in titanium dioxide production process

In order to concentrate the diluted sulfuric add from the titanium dioxide (TiO2) production of sulphate process, a new concentration process was proposed by coupling chemical dehydration and multi-effect evaporation. The ferrous sulfate monohydrate (FeSO4 center dot H2O), as the dehydrant, was added to the diluted sulfuric acid to form ferrous sulfate heptahydrate (FeSO4 center dot 7H(2)O) according to the H2SO4-FeSO4-H2O phase diagrams, which partially removes the water. This process was named as Chemical Dehydration Process. The residual water was further removed by two-effect evaporation and finally 70 wt% sulfuric acid was obtained. The FeSO4 center dot H2O can be regenerated through drying and dehydration of FeSO4 center dot 7H(2)O. The results show that FeSO4 center dot H2O is the most suitable dehydrant, the optimal reaction time of chemical dehydration process is 30 min, and low temperature is favorable for the dehydration reaction. 45.17% of the entire removed water can be removed by chemical dehydration from the diluted sulfuric acid. This chemical dehydration process is also energy efficient with 24.76% saving compared with the direct evaporation process. Furthermore, 51.21% of the FeSO4 dissolved originally in the diluted sulfuric add are precipitated out during the chemical dehydration, which greatly reduces the solid precipitation and effectively alleviates the scaling in the subsequent multi-effect evaporation process. (C) 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.