Chelating resin regeneration
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It is well known that there are various methods for treating wastewater generated from the regeneration of chelating resins. But they all have advantages and disadvantages. Discharging wastewater is costly, adjusting the pH of saltwater is troublesome, and the storage capacity of saltwater is also an issue. There is also the use of sodium hypochlorite in water preparation, and the amount available for this purpose is limited. Are there any other ways to use these chemicals in other products (this is not a mainstream option, so it won’t be considered), or are there methods that can significantly reduce emissions to solve this issue? Is this solution feasible or has it already been used by someone? Additionally, separate acid and alkali regeneration tanks should be built. The first 10 m3 (the figure is merely illustrative) before acid regeneration are sent to wastewater or elsewhere, while the remaining amount along with the acid is discharged into the acid regeneration tank. The acid is adjusted to 4–10% based on the remaining acidity (usually 7%), and is then used directly in the acid regeneration feed circulation. Alkalis also follow a similar approach. (Piping; operation is not considered here, as it’s not a challenging aspect.) This can significantly reduce the amount of waste discharged. Reduce the use of pure water and acids/bases. Significantly reduces the pressure of wastewater and primary brine. Possible problems. Circular acids contain heavy metals such as calcium and magnesium, while recycled circular alkalis contain salts; does this have an impact on the recycling process? Because the initial liquid is discharged, substances such as calcium and magnesium chloride do not continue to accumulate, but a certain concentration is maintained over time.
During the regeneration process, acids and bases are stored separately for use in the dechlorination tower, which helps to address the issue of wastewater discharge.
It will create pressure in the brine inventory, and it’s not much different from directly adjusting the pH value to restore the brine.
Under normal circumstances, there’s no pressure on the amount of brine available, unless all the water in the plant is used for brine production. Here, all the wastewater from the resin towers is used for that purpose, and sometimes additional water needs to be added; there’s no problem at all.
I’ve heard that a few factories have already done this, but I haven’t found out which ones are doing it.
I haven’t seen that company using this method. I’ve seen a company do it this way: there’s a large pond next to the resin tower; all the wastewater from acid and base regeneration flows into this pond. Then, process gas is used to stir and mix the waste liquid. The treated regenerated water is subsequently supplied to other users.
These are the operations carried out by our company at present; the amount of alkali used for internal purposes can be reduced to some extent, and there have been no fluctuations in the secondary brine.
The hydrochloric acid concentration during regeneration is 7% and the alkali concentration is 5% – can this be used directly in the dechlorination system?
How big are your two pools? What are the acid and base concentrations after mixing is complete at the end of regeneration? What are the precautions when adding acids or bases to the dechlorination tower? How do you operate?
The wastewater resulting from resin regeneration in our factory is discharged into the adjacent wastewater tank; after the pH level is adjusted to the appropriate value, it is sent to the sewage treatment plant for further processing. But there are also problems now: the wastewater tanks are too small, resulting in uneven mixing, which often affects the regeneration of the resin columns.
After neutralization, it can be recovered and reused as primary brine; there is no problem with this.