The pH value of the effluent from the ion exchanger used to treat nickel-containing wastewater is too high after regeneration
Thread Content
The ion exchangers used to treat nickel-containing wastewater have a pH level of the effluent that is too high after regeneration, reaching as high as 12. The regeneration solution is HCl, which is then neutralized with NaOH. The water production cycle was originally 45 hours, but it has now been increased to 70 hours; however, the pH of the output water remains too high. I’d like to ask everyone what the reason is?
What is the pH of the incoming water? Do you have any test reports for it? What resin is being used?
Two ion exchangers are used in series; when Resin No. 1 becomes saturated or after reaching a predetermined water production cycle, it is regenerated and then used at Position 2, while Resin No. 2 is used at Position 1. The pH of the inlet water is 6-7, and its concentration is unstable, ranging around 100 mg/l; it can exceed 200 mg/l at times. Strong acid cation exchange is used, with the outlet water standard for the ion exchanger being 0.5 mg/l. The regeneration process involves first regenerating with HCL, then rinsing, followed by neutralization with NaOH, and again rinsing. After regeneration, it will be used in the second position; the pH of the water produced by ion exchange in the first position is normal, around 7. The pH of the water output from the second location (i.e., the resin that has just been regenerated) was extremely high, at 12. As discussed earlier and simultaneously, it was believed that the amount of Ni retained by the ion exchanger was too small and unevenly distributed, which resulted in poor regeneration efficiency. Then we increased the preset water production cycle from 45 hours to 70 hours, but the water output at position two was still high. Moreover, the concentration of the water released after each regeneration exceeds the limit for several hours. I’m not sure if it’s related to the concentration and amount of the regeneration solution, or to the rinsing time after regeneration?
Two ion exchangers are used in series; when Resin No. 1 becomes saturated or after reaching a predetermined water production cycle, it is regenerated and then used at Position 2, while Resin No. 2 is used at Position 1. The pH of the inlet water is 6-7, and its concentration is unstable, ranging around 100 mg/l; it can exceed 200 mg/l at times. Strong acid cation exchange is used, with the outlet water standard for the ion exchanger being 0.5 mg/l. The regeneration process involves first regenerating with HCL, then rinsing, followed by neutralization with NaOH, and again rinsing. After regeneration, it will be used in the second position; the pH of the water produced by ion exchange in the first position is normal, around 7. The pH of the water output from the second location (i.e., the resin that has just been regenerated) was extremely high, at 12. As discussed earlier and simultaneously, it was believed that the amount of Ni retained by the ion exchanger was too small and unevenly distributed, which resulted in poor regeneration efficiency. Then we increased the preset water production cycle from 45 hours to 70 hours, but the water output at position two was still high. Moreover, the concentration of the water released after each regeneration exceeds the limit for several hours. I’m not sure if it’s related to the concentration and amount of the regeneration solution, or to the rinsing time after regeneration?
This is because the alkali wasn’t washed out properly. It’s clearly not a strong-acid cation resin, but rather a chelating resin; it’s very difficult to wash away alkali from chelating resins. I suggest that first, you reduce the concentration of the alkali, and second, increase the amount of water used for washing away the alkali