Zero emission process for treating titanium chloride slag

Abstract

The invention belongs to the field of post-treatment of titanium dioxide, and particularly discloses a zero emission process for treating titanium chloride slag. The process includes the following steps of (1) alkali leaching; (2) solid-liquid separation; (3) secondary precipitation; (4) micro-filtration / ultra-filtration membrane filtration; (5) primary membrane purification; (6) membrane concentration; and (7) secondary membrane purification. In the process, the purpose is to treat heavy metal ion impurities in the titanium chloride slag and recycle chlorine ions, and solid waste slag is converted to harmless solid to be reused for bricks, tiles, cement and the like of building materials; concentration and purification are performed through a membrane separation integrated process so thatlight salt brine used for the chloro-alkaline industry can be obtained for use; due to implementation of the process, valuable resources in the titanium chloride slag are recycled and utilized, moreimportantly, the titanium chloride slag serious in pollution to environment protecting is completely and thoroughly treated, the bottleneck that the chlorination method solid waste slag is difficult to treat is broken through, a process for producing titanium dioxide in a chlorination method gets one important step in environment protecting direction, and obvious advancement is achieved.

Description

technical field [0001] The invention belongs to the field of chlorination titanium dioxide chemical industry, and in particular relates to a zero-emission process for treating titanium chloride slag. Background technique [0002] At present, the methods for producing titanium dioxide mainly include sulfuric acid method and chloride method. Due to the long process of the sulfuric acid method, serious pollution and poor product quality, it was gradually replaced by the chlorination method. [0003] In the current production of titanium dioxide by chloride method, its main process is: [0004] a. Mix titanium raw material (such as: high titanium slag) and reducing agent (such as: petroleum coke) evenly, then send it into the chlorination furnace, and feed chlorine gas to carry out boiling chlorination at a temperature of 800°C to 1000°C; [0005] b. Separating and purifying the crude titanium tetrachloride obtained after chlorination to remove impurities such as magnesium, ir...

AI Technical Summary

Problems solved by technology

But there are two problems: one is that a large amount of slag is produced after acid dissolution, and the filtration effect is not good due to too strong adhesion and compactness during the press filtration process, and even there is a problem that no water can be pressed; The pH is directly neutralized to above 12 and filtered. Under such high alkaline conditions, amphoteric substances such as aluminum and silicon will dissolve in the lye. With the interception of the nanofiltration membrane, the concentration will become higher and higher and hydrolysis precipitation will occur. On the membrane surface, it affects the smooth progress of the membrane process, and the result of high concentration of aluminum and silicon in the nanofiltration feed will lead to high content of aluminum and silicon in the nanofiltration liquid, which cannot reach the salt water of the chlor-alkali process requirements

However, after careful scrutiny, there are still the following problems: First, a considerable part of the impurity ions remain after neutralization and precipitation. The pH of the neutralization precipitation in this process is 6.5 to 7. Although most of the impurities such as Al, Si, and Fe are precipitated, However, the precipitation of multivalent metal ions such as Zn, Mn, Cu, Ni, Ba, Sr is not complete, and there are still a considerable part of impurity ions remaining in the mixed solution, which will lead to the limitation of reverse osmosis concentration.

The second is that the concentrated brine concentration of the reverse osmosis membrane cannot reach 12%. Due to the problem of neutralizing the pH of the precipitate, a considerable part of impurity ions still exist in the feed water of the reverse osmosis membrane, although there is an ultrafiltration membrane in front of the reverse osmosis membrane. , but the ultrafiltration membrane does not intercept the ions in the solution, so the concentration of multivalent metal ions in the reverse osmosis membrane water does not decrease. Carbonate and sulfate ions form precipitates and precipitate out of the membrane surface, affecting the normal progress of the membrane process, resulting in the concentrated salt concentration not reaching the concentration of 12%.

The third is the problem of membrane technology. One is that the operating pressure of reverse osmosis is 0.6-1 MPa. Such a low pressure cannot offset the osmotic pressure produced by the 12% salt concentration, not to mention the concentrated water. The two are sodium after reverse osmosis. Filtration and nanofiltration process should reduce the salt concentration of nanofiltration effluent, and even if the salt concentration of concentrated liquid after reverse osmosis reaches 12%, the salt concentration after nanofiltration must be lower than 12%

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