Can sulfates be removed by chemical precipitation?
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There is wastewater containing 9,000 ppm of sulfates. Can chemical precipitation be used to remove some of the sulfate ions? How much can be removed approximately? I’m not sure if universities have any experience in this area.
I’ll take the lead on this; I hope everyone can offer their guidance.
For the removal of sulfate ions, do you plan to use barium sulfate or calcium sulfate for that purpose? The problem with barium ions: they are highly toxic. Properties of calcium sulfate: Slightly soluble.
In principle, if the calcium ion concentration in the wastewater is not high, nanofiltration can be considered to remove sulfate ions. For example, the nanofiltration membrane used in our company has a rejection rate of 98.8% for sodium sulfate, allowing it to concentrate sodium sulfate to over 10%. However, the calcium ion concentration in the wastewater cannot be high, and the impact of other impurities in the wastewater on the nanofiltration membrane must also be taken into account. Essentially, this involves preprocessing. This requires an understanding of the details of wastewater. What is your purpose for removing sulfate ions? What kind of wastewater is this?
This sulfate-containing wastewater is generated during the production process; the volume of this wastewater is 600 tons per day, with 1.2 tons of sulfate ions present, as well as some starch-like substances. After passing through the wastewater treatment system, the sulfate concentration is 4000 mg/L, which does not meet the discharge standards; therefore, treatment is required.
It should be sodium sulfate; the sulfate ions here are difficult to remove. Some people say that adding lime can help remove them by converting them into calcium sulfate precipitate, but in reality this does not work – the reaction does not take place. The conventional methods for removing sulfates are concentration followed by evaporation crystallization, or dilution by adding low-concentration water.
Evaporation crystallization is costly; NF can be used to remove sulfate ions
As mentioned on floor 7, nanofiltration can retain sulfate ions (sodium sulfate), but the calcium ion concentration in the wastewater must be very low, and advanced pretreatment is required. The sodium sulfate concentration in the nanofiltration concentrate can reach 10%. The nanofiltration membranes we produce ourselves have a rejection rate of over 98% for sodium sulfate. What is the COD value of the wastewater? What else is there besides starch?
If it contains a high amount of organic matter and inorganic impurities (SS), cannot this method be used?
May I ask what conditions need to be met and what preprocessing is required if NF is to be used?
It is mainly necessary to know the COD value and calcium ion content of the wastewater. As a pretreatment, micro-ultrafiltration is generally used.