Thoughts on magnesium sulfate wastewater after magnesium oxide desulfurization

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Magnesium oxide desulfurization is favored due to its low investment cost and high desulfurization efficiency. Many manufacturers are using it nowadays. The main component of the wastewater after desulfurization is magnesium sulfate, but it also contains significant amounts of ammonia nitrogen and COD. Not to mention the total amount of salt discharge specified by environmental regulations in some areas, just the huge amounts of sulfate present—tens of thousands or even hundreds of thousands of units—are sufficient to paralyze wastewater treatment plants. So, is it possible to distill magnesium sulfate solution? The answer is no. Since the magnesium oxide used for desulfurization contains a small amount of calcium oxide, calcium oxide also participates in the reaction during desulfurization, and the product formed is calcium sulfate. Calcium sulfate is saturated in the solution. Calcium sulfate is a slightly soluble substance, and its solubility decreases as the temperature rises. Here’s the problem: as soon as heating begins during distillation, calcium sulfate starts to precipitate, which damages the heat exchanger used for distillation and leads to its shutdown. It has also been proven that every device that uses this process fails to operate properly. The second method is relatively simple and crude: it involves reacting concentrated sulfuric acid with magnesium oxide, along with magnesium sulfate solution from desulfurization wastewater. Production of magnesium sulfate heptahydrate. This is also possible as long as you have channels to sell magnesium sulfate. The third method involves reacting magnesium sulfate solution with lime milk to produce magnesium hydroxide and calcium sulfate; the particles of magnesium hydroxide are fine whereas those of calcium sulfate are coarse. Physical methods can be used to separate these two substances; of course, the separation isn’t perfect, but the magnesium hydroxide obtained has a purity high enough to be reused in the desulfurization tower for further desulfurization processes, while calcium sulfate can be sold as a product. After treatment, the sulfate level in the discharged wastewater is reduced to two or three thousand, making it suitable for wastewater treatment.