Treatment of industrial wastewater containing high fluoride levels
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This post was last edited by tcs1789@163.com on 2009-9-23 at 15:56. Our company is currently facing the problem of treating industrial wastewater with high fluoride content; the fluoride ion concentration can sometimes reach 3000 mg/L. We use lime precipitation and coagulation treatment, but the fluoride concentration in the wastewater after treatment remains above 100 mg/L. To meet the wastewater discharge standards, we have to dilute the water further, which increases the volume of wastewater to be discharged – a really troublesome situation. I hope those with more experience can offer some good suggestions@
The removal rate for first-order reactions has reached 99.6%, which is very good. I think an additional stage of sedimentation + coagulation can be added; with proper pH control, 99% removal can be achieved, resulting in an effluent concentration of 10 ppm. For safety reasons, a slight dilution is sufficient to meet the emission standards.
You can add calcium hydroxide and calcium chloride. The lime you use is probably calcium oxide; the hydrolysis of lime releases heat, which is not conducive to the precipitation of calcium fluoride. Temperature has a significant impact on the ionization constant of calcium fluoride. You should use slaked lime, which is calcium hydroxide, as it does not release heat, can help regulate the pH value, and can also bind fluoride ions. Adding calcium chloride here takes advantage of the common-ion effect to promote more complete precipitation of calcium fluoride. Additionally, calcium chloride is a neutral salt, so there is no need to add acid later for neutralization, and it also increases the concentration of calcium ions, thereby reducing the ionization constant of calcium fluoride. Finally, phosphoric acid is added to adjust the pH of the water, which facilitates the further formation of calcium fluorophosphate precipitate. This will achieve **emission standards of ≤10PPM**. Floculants such as ferric chloride or polyaluminum chloride can also be added; this will ensure compliant discharge, but it is best to carry out a secondary reaction followed by secondary sedimentation. For reference only.
Membrane separation technology can be used to address the issue of unstable fluoride levels in the effluent, ensuring that these levels remain below 1 mg/l; in this way, the water can meet the standards for reuse! Reduce emissions! !
It’s so suitable for use as cryolite... sweat
The precipitation method cannot remove all fluoride; what you’ve achieved is already sufficient. In fact, if the amount of wastewater is large, such as 3000 mg/H, it’s more appropriate to use a closed-loop system for producing cryolite. Moreover, the market for cryolite is currently quite good
I just saw a product that can treat industrial fluorine wastewater to levels below 2 ppm; I’d like to discuss it with you. I’m not sure if tcs1789@163.com is your email address? I’ll give it a try, hehe.
3# tcs1789@163.com Thank you~
Actually, I think you could consider a different approach: concentrate this liquid and sell it to fluorine chemical manufacturers as raw material. However, I assume you are working with semiconductor factories or crystalline silicon factories; there are many environmental protection companies that can provide comprehensive solutions for fluoride-containing wastewater.
Personally, I think it should be relatively easy to remove F ions; if one stage isn’t sufficient, multiple stages can be used. This allows water that does not meet the standards to be recycled, thereby increasing the efficiency of the chemicals used. By controlling the amount of chemicals added and the pH level, it should be possible to ensure that the F ion levels are within the acceptable range.