Problem of salt waste caking
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Dear experts, our company’s evaporation and salt separation workshop is treating wastewater from one of the production units. This wastewater mainly contains sodium chloride, with a pH level of 12–13; it is then adjusted to around 10. After triple-effect evaporation, the filter cake resulting from filtration tends to compact into hard masses that are difficult to remove. Could this be due to an excessively high alkalinity, with a large amount of sodium hydroxide present, causing such compaction? However, the workshop claims that the pH has been adjusted to around 10, which should mean there is little sodium hydroxide left in the solution. So why does this problem still occur? I wonder if you’ve encountered this issue: can adjusting the pH alone solve the problem of salt caking? Thank you, reward_7ree
PH=12~13, still need to modulate below 10. The content and types of metal ions also need to be analyzed; if there are many transparent or colored crystals, it becomes more difficult to handle them.
PH is set at 12~13, and then adjusted to around 10; however, the workshop claims that the PH has already been adjusted to around 10. There must be a basis for adjusting the PH to around 10 – one cannot rely solely on what is said.
The crystals that precipitate upon the evaporation of NaOH are very small, have a large specific surface area, and experience strong interfacial forces between them, which makes caking likely; that’s what I guess. NaOH pellets also tend to clump together when dissolved; you can try pouring the NaOH powder into a beaker all at once, and clumps will easily form at the bottom of the beaker. It takes a long time of stirring with a glass rod for it to dissolve.
Could there be caking issues caused by other substances in the workshop?
It is estimated that the caking phenomenon is caused by the high content of organic matter in the wastewater; front-end pretreatment steps before evaporation can be considered, and large-pore adsorption resins represent one such method, as they are not affected by salt content.
Thank you. Well, later the workshop reported that after using a filter for filtration, the problem of clumping of waste salt became less noticeable
Well, it’s possible; there are impurities present in the wastewater tank
If you have by-product salt, feel free to contact me; we can handle that salt. Those interested can discuss it further