Methods for removing calcium and magnesium and co-producing water and salt by low-cost process during sea water desalination

Abstract

The invention discloses methods for removing calcium and magnesium and co-producing water and salt by a low-cost process during sea water desalination. By the methods, on the basis of removing the calcium and magnesium in the sea water desalination industry, water and salt producing processes can be integrated, so that fresh water can be produced when the crude salt is produced; sea water is treated by a low-cost method for removing calcium and magnesium ions, so that the sea water cannot be scaled, and the sea water desalination and vacuum salt production are linked; the sea water is refined by a lime-mirabilite-carbon dioxide method, and the used raw materials are lime, mirabilite and carbon dioxide which are cheap and readily available; the process comprises the following steps of removing magnesium, namely adding a proper amount of mirabilite into the sea water, adding lime milk, and reacting the magnesium ions to form magnesium hydroxide precipitations so as to remove the magnesium; causticizing, namely causticizing superfluous calcium hydroxide and sodium sulfate to form calcium hydroxide and sodium sulfate precipitations, and separating the produced sodium sulfate precipitation; removing calcium, namely introducing flue gas into concentrated sea water subjected to magnesium removal and causticizing, reacting the calcium hydroxide and the carbon dioxide to form sodium carbonate, reacting the sodium carbonate and the calcium ions to form calcium carbonate so as to remove calcium.

Description

Technical field [0001] The invention relates to the problem of removing calcium and magnesium in the seawater desalination industry. On the basis of this, the integration of industrial water production and salt production processes can be realized, and refined raw salt can be obtained while fresh water is produced. [0002] The invention uses the lime-glauber's salt-carbon dioxide method to refine the concentrated seawater containing calcium and magnesium ions in the seawater desalination process, so as to solve the problem of scaling in the subsequent processing process. In the early stage of the process, due to the low concentration of seawater, the reverse osmosis method with low energy consumption is adopted; in the middle stage of the process, low-temperature multiple-effect or high-temperature multiple-effect or similar thermal methods that can adapt to medium concentrations are used; in the latter stage of the process, vacuum salt production is used The process obtains ...

AI Technical Summary

Problems solved by technology

However, the lime soda ash method and caustic soda ash method used to refine brine are used to refine calcium and magnesium, the refining cost is huge for water, and the seawater desalination industry with high calcium and magnesium content cannot bear the cost pressure.

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