Uses of raw salt of different qualities
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This post was last edited by sunjl1981 on 2013-1-6 at 21:47. Recently, here we have encountered issues due to significant variations in salt quality – some salts have high levels of magnesium ions while others have high sodium carbonate content – which has resulted in backmixing in the preprocessor. . The salt used recently has a high content of magnesium ions, which causes the sodium hydroxide level in the saltwater to drop to zero when salt is added; this level should be kept between 0.2 and 0.6. When no salt is added, the sodium hydroxide concentration rises sharply to 1.89 g/l. . . Due to backmixing in this preprocessor, the treatment capacity of the Kay membrane decreases, resulting in a reduced load on the electrolyzer. . . Although the flow rate has decreased, the water in the preprocessor is still extremely turbid. . . I would appreciate it if the experts could share their valuable opinions. . . My personal opinion is that the magnesium ions in salt are present in higher amounts than calcium ions; therefore, adding some salt sludge (calcium carbonate) to the pre-reaction tank helps with the precipitation of magnesium hydroxide. . . But I’m afraid there’s also a lot of magnesium hydroxide in the salt mud. # hcbbs
There are many discussions on the quality issues of crude salt in the forum. 1. Why does the solution become turbid again? What you’re experiencing is clearly a problem of excessive magnesium levels. Floatation tanks are not affected by the inversion of calcium and magnesium levels, but the amount of air dissolved in saltwater determines that the magnesium content in the raw salt cannot be unlimitedly high; generally, a level of 0.3% already exceeds the processing capacity of such tanks. 2. Reasons for instability: If the water supply does not keep up with the quality of the raw salt, it can cause instability in the brine system and exacerbate re-sedimentation. 3. How to handle it: First, the raw salt should be tested to determine its calcium and magnesium content. If the magnesium content exceeds 0.25% and is at a high level, it is recommended to wash this batch of salt before using it; this can be done by spraying water on the pile of salt using a high-pressure water gun. If the total amount is not large and there is high-quality raw salt in stock, it can be mixed in; the specific mixing ratio shall be determined based on actual conditions. 4. The brine that has become turbid again must be returned to the desalination system for re-saturation and further treatment. 5. It is not recommended that you add salt mud to aid sedimentation. 6. The turbidity of the water returning to the tank has little to do with flow rate; it is mainly determined by the amount of air dissolved in the water.
First, let me clarify for the original poster: magnesium hydroxide floats in the pre-treater, it does not settle. As mentioned by the poster, the enzyme content in this type of salt is relatively high; such salt needs to be processed through salt washing first: that is, water is sprayed onto the pile of salt, the collected water is mixed with sodium hydroxide and then fed into a sludge tank where it is filtered using a pressure filter. Rinsing it multiple times to reduce the magnesium content in the salt allows it to be used normally. There are many reasons for the back-turbulence in the preprocessor, and the owner needs to conduct thorough analysis to identify the causes and find solutions.
2# Huawei :lol I’m sorry, I have a few questions regarding what you mentioned; could you please explain them? And I’ll explain further in response to your question ； 1. Our raw salt comes from different manufacturers, and the quality parameters are as follows: Sodium chloride: 84.27, 94.95, 91.48, 96.02, 91.62; Calcium ions: 0.17, 0.03, 0.39, 0.26, 0.25; Magnesium ions: 1.30, 0.08, 0.42, 0.1, 0.36; Sulfate ions: 1.72, 1.00, 1.29, 0.67, 0.85. Manufacturers: A, B, C, D, E. The salt used in these past two days was probably from manufacturer A. Indeed, this back-mixing occurred due to excessively high magnesium ion levels. How is the capacity of the pretreater set? What is its relationship with the magnesium ion content? 2. Does \"the water distribution failing to keep up with the salt quality\" refer to the delayed addition of sodium hydroxide? The current situation is that sodium hydroxide is no longer present after adding salt; without salt, the concentration of sodium hydroxide is as high as 1.8 g/l... However, when no salt is used the value is reduced, while it increases when salt is added. Here we are dealing with 400,000 tons per year of ion-exchange membrane caustic soda, and given the large scale of the brine system, this approach isn’t very practical. 3. Regarding the washing with salt piles you mentioned, can magnesium ions be washed away simply using water at the salt pile site? Our salt storage yard is a large salt facility with a capacity of 100,000 tons. It seems like there are great difficulties in doing this. . Hehe, my understanding is too superficial; maybe I misinterpreted what you meant. Please don’t laugh at me! 4. Is re-saturation beneficial for the flotation of magnesium hydroxide? 5. Adding salt sludge should help magnesium hydroxide float or sink, right? 6. The two preprocessors with low flow rates no longer experience backmixing; I keep wondering if there is a relationship between flow rate and this phenomenon Low flow rate and longer residence time in the preprocessor should help magnesium hydroxide to float. Let’s clarify the liquid layer, mud seal, mixed liquid layer, and mud layer inside the preprocessor. . Please give me your guidance! Thank you
Our company should add more sodium polyacrylate as a sedimentation aid, reduce the flow rate of saline, and increase the temperature to speed up the reaction
The design of the preprocessor is based on the quality of the salt; if the levels of calcium and magnesium ions are high, the flow rate of the salt water within the preprocessor must be reduced (that is, the flow rate of the saline solution should be decreased), otherwise insufficient processing time will lead to backmixing； Normal calcium and magnesium levels can increase the flow rate of saline water. Regarding the excess alkali amount, it is possible to increase the amount of sodium hydroxide added during salt addition and decrease it when stopping salt addition.
4# tuya But can salt washing remove magnesium ions? I feel like I can only waste some salt. . There aren’t many of these Type A salts available these days; they can be used for washing, but won’t all of these salts dissolve during the washing process? Now both the saltwater concentration and the quality of the saltwater fed into the tank are within acceptable limits ； What you mean is that a certain volume of saline can dissolve only a certain amount of air at a specific pressure. Therefore, a certain amount of air in the saltwater can only carry away a limited quantity of magnesium ions; the amount of magnesium ions in our saltwater has already exceeded this limit. At present, the pressure inside the pressure vessel is 0.18 MPa, while the pressure of the compressed air is 0.3 MPa. So, is it possible to increase the pressure inside the pressure vessel to 0.28–0.30 MPa? . . Is there any harm in this? I think it should be possible, right? The amount of air that can dissolve in saltwater is high, and therefore the amount of magnesium hydroxide that needs to be processed is also large. . Also, our salt storage area is quite large, and salts of various qualities are stored together. I wonder whether it’s necessary to store raw salts separately according to their quality (the ratio of calcium and magnesium ions). . These are just my personal opinions. . :Lol, please give some advice. .
If the quality of the raw salt varies, it is recommended to use it in combination, adding salt frequently in small amounts each time.