How to do regeneration of defluorinating activated alumina

- Nov 10, 2020-

Activated alumina is a kind of adsorbent with high aluminum content. Activated alumina can be used as adsorbent, desiccant, defluorinating agent, etc. The specifications of activated alumina are 1-2mm, 1-3mm, 3-5mm, 5-7mm, and the particle size of activated alumina used in different fields is different. 

Today we will introduce the regeneration of defluorinating activated alumina and the matters needing attention during regeneration. When the fluorine content of the effluent reaches the terminal fluorine content value, the activated alumina should undergo regeneration treatment. Sodium hydroxide solution should be used as the regenerating solution, and aluminum sulfate solution can also be used. When sodium hydroxide is used for regeneration, the regeneration process can be divided into four stages: recoil, regeneration, secondary recoil (or leaching) and neutralization. When aluminum sulfate is used for regeneration, the aforementioned neutralization stage can be omitted. The expansion rate of the backwash filter layer can be 30%-50%, and the backwash time can be 10-15min. The washing intensity depends on the size of the filter material, generally 12-16L/m2·s. The regeneration solution should pass through the filter layer from top to bottom; the flow rate, concentration and dosage of the regeneration solution can be adopted according to the following regulations:

 1. Sodium hydroxide regeneration: NaOH solution with a concentration of 0.75% to 1% can be used, and the consumption of sodium hydroxide can be calculated based on the need for 8-10g of solid sodium hydroxide to remove 1g of fluoride. The volume of the regeneration solution is 3-6 times the volume of the filter particles, the regeneration time is 1-2h, and the flow rate of the regeneration solution is 3-10m/h. Aluminum sulfate regeneration: the concentration is 2% to 3%, and the consumption of aluminum sulfate can be calculated based on the 60-80g solid aluminum sulfate {AL2(sO4)3·18h2O} needed to remove 1g of fluoride. The regeneration time can be 2~3h, and the flow rate can be 1~2.5m/h. After regeneration, the regeneration solution in the filter must be emptied.

  2.The secondary recoil intensity can be 3~5L/m2s, the flow direction passes through the filter layer from bottom to top, and the recoil time can be 1~3h. For leaching, raw water is used at 1/2 of the normal filtration flow rate, and the filter particles are rinsed from the upper part. The rinse time is 0.5h and the rinse time is 0.5h. Using aluminum sulfate as the regenerant, the pH value of the effluent at the end of the secondary backwash should be greater than 6.5, and the fluorine content should be less than 1mg/L. Sodium hydroxide is used as the regenerating agent, and neutralization should be carried out after the second recoil (or leaching). For neutralization, 1% sulfuric acid solution can be used to adjust the pH of the inlet water to about 3. The flow rate of the inlet water is the same as the normal defluoridation process, and the neutralization time is 1 to 2 hours until the pH of the outlet water drops to 8-9. Regardless of the number of times of washing, washing and preparation of regeneration solution, raw water can be used. The effluent of washing and neutralization is strictly prohibited for drinking and must be discarded.

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