Process Parameters Optimal Investigation on the Na2so4 Fractional Crystallization from Coal Chemical Industry High-saline Wastewater

Abstract

The fractional crystallization process of high-saline wastewater is important for the sustainable development of coal chemical industry. This study mainly focused on the process investigation of Na₂SO₄ crystallization separation. The effects of heating temperature and stirring rate on the particle size distribution of anhydrous sodium sulphate (Na₂SO₄) crystals were investigated by batch-evaporation crystallization. Taking into account the product performance and the operating costs, the optimal operating conditions were determined to be 130 °C and 300 rpm. Granular Na₂SO₄ crystals with a purity higher than 99.0% were obtained. And the corresponding D_0.10 was 309 µm. Moreover, the effects of impurity ions and organic matter on the preparation of Na₂SO₄ were discussed. The experimental results reveal that the addition of impurity, whether ions or organic matter, can lead to a decrease of D_0.10. Specially, D_0.10 increases with the increasing wt.%(K⁺), while D_0.10 gradually decreases as wt.%(F^-) increases. Furthermore, the influence level of organic matter on D_0.10 was ranked as tributyl phosphate> 4-methyl-2-pentanone> dodecane> p-nitrophenol. The corresponding SEM images show that the addition of 10 mM of these four substances have little effect on the crystal morphology.