Factors affecting the removal of calcium and magnesium by sea salt
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This post was last edited by sunjl1981 on 2013-1-6 at 21:11. Our factory uses sea salt from Shandong, and the treatment process employed is the Kaimo membrane process. Recently, we have encountered this issue: occasionally, after a batch of sea salt has been processed in the evaporation ponds, the calcium and magnesium levels at the Kaimo membrane outlet are above the acceptable limits (the titration analysis shows values between 5–20 g/l, while the normal level should be 0). The amounts of alkali used are 0.1–0.4 g/l and 0.3–0.5 g/l respectively. The amount of ferric chloride added is sufficient; when imported salt is used, everything returns to normal. The various analytical parameters of the Shandong sea salt are within acceptable limits. What could be causing this problem? These salts that affect calcium and magnesium, when used after being exposed to wind and rain for a month or two, no longer have an impact on calcium and magnesium. Why is that? Is there some chemical component in the salts that influences the chemical reactions involving calcium and magnesium? # + + . hcbbs
1. It’s possible that the calcium and magnesium levels in the raw salt are indeed above the standard; some of the salt samples taken for analysis do not exceed the limit, but it’s impossible to determine the overall level based on these samples alone! 2. After being exposed to rain, the salt is essentially washed naturally, with some of the magnesium chloride and calcium chloride on the surface of the salt particles being washed away by the rain, resulting in a lower calcium and magnesium content. 3. The above are merely my personal opinions; I hope experts can provide an answer.
First, consider whether the sampling and analysis of raw salt are standard. One possibility is that high levels of calcium and magnesium have consumed the sodium hydroxide and sodium carbonate; not all of the calcium and magnesium has been removed, and the analysis of excess alkali is only conducted at regular intervals, so it may not be possible to detect when they have been completely consumed. Another possibility is that the supply of sodium carbonate or sodium hydroxide is interrupted for a period of time.
At our factory, the alkali excess is analyzed once an hour, and the concentration is generally above the specified limit
Based on what the poster has described, I suspect it is caused by calcium and magnesium salts adsorbed on the surface of the new sea salt; at the same time, a large amount of organic matter such as marine organisms on the surface of the salt crystals also affects the removal of calcium and magnesium. During the drying process of sea salt, once sodium chloride precipitates, the concentration of brine becomes very high; as a result, calcium and magnesium salts accumulate or deposit in large quantities on the surface of the sodium chloride crystals, leading to poor removal of calcium and magnesium ions. If the new sea salt is gently rinsed with clean water, it should improve the effect of removing calcium and magnesium.
Is 5~20g/l no longer considered brine? The membrane must be damaged; otherwise, it couldn’t be in such a mess.
Sea salt doesn’t get much exposure to rain, but it becomes usable after being left in the sun for a few days. The specific reason is unclear; it may be that the original ultraviolet rays in sunlight can break down certain organic substances.
The high calcium and magnesium content in the raw salt used by your company is indeed the cause; at the same time, the alkalinity level is low, which results in excessive calcium and magnesium levels in the brine passing through the filter. When the raw salt is washed by rainwater, the calcium chloride and magnesium chloride on its surface are removed, and the brine that passes through the filter then meets the required standards. When using new salt, the amount of excess alkali can be increased appropriately. Our unit uses only sea salt; when new salt is used, the alkalinity level is above 0.7, and the results are good.
Sir upstairs, is a caustic excess of over 0.7 too high? Could it lead to the redissolution of magnesium hydroxide?
All sea salt is used – are the iron and aluminum levels in the secondary brine excessive?