How to eliminate Sulfates from waste water effluents 3

[22854]

I would like to know which are the most used methods o technologies to eliminate or reduce sulfates contents from industrial waste water to comply with municipal regulations.

Main quantities of sulfates come from neutralizing basin of demin water plant and cooling water tower blow down.

 

[waterexpert]

So on balance, it is worth a little initial investigation to see whether it will be simpler and quicker to change acids, or add one of the simpler sulphate removal techniques.

I'd probably favour lime precipitation and removal by gravity settlement if sulphate removal is needed. Other removal techniques can be considered if space is limited. It's fairly simple to design, and likely to be reliable and cheap to run. It will be far cheaper to build and run than evaporation or membranes.

Seán

http://www.expertise-limited.co.uk

 

[kenvlach]

22854,
Any update?
Does your cation resin mfr. permit use of HCl 5% for regen?

 

[22854]

Thanks to all for this ample discussion.

We studied the option to use HCL to regenerate IX resins but it is not a good option from the economical point of view and have also to change materials and increase storage capacities three times.

The use of RO means that we will still have sulfates (even more concentrated) in the rejected water, so how can we dispose the rejected water?.

We are still thinking in the best solution.

 

[DeltaCascade]

We are back to where we started...
Same problem .. its just concentrated .. perhaps making evaporation to calcium sulphates, etc, more economical .. not necessarily economical .. just more economical as its more concentrated in the RO reject stream ...
(aside: I dont think that lime softening will remove sulfates ... it just removes Ca as CaCO3 ... you may need to add soda-ash .. and SO4 will leave as soluble Na2SO4)

Anyhow, think we answered your questions. when you do your analyses, you may find that repalcing H2SO4 with HCl is the cheapest and most effective option... it wont be "free"..
It will be interesting to see the outcome. Good luck

 

[waterexpert]

I'm not quite sure what you are trying to say, Deltacascade,
but I beleive your submission may contain a factual error.

Adding lime to a concentrated sulphate solution will precipitate calcium as sulphate, not as the carbonate. I understand that there are high sulphate levels here, rather than high carbonate levels. It will additionally precipitate any carbonates present, but I cant see what the problem is with that. CaSO4 has very low solubility in water. That is why its production from sulphates by lime is used for desulphurisation of flue gases at power stations.

As I said before, lime will precipitate an easily thickened calcium sulphate sludge from concentrated sulphate solutions. This is the process used in flue gas desulphurisation, and therefore thoroughly tried and tested.

The relative economics of this compared with evaporation are likely to be good for all but the most concentrated solutions. Heat is effectively free at power stations, but they still use lime precipitation to remove sulphate from flue gas scrubbings.

 

[DeltaCascade]

Yes, agree, and thank you. I am thinking lime-softening of surface waters. And, yeah, we need a waste water analysis ... cant be more than about 2-8max% H2SO4? what with it being demin plant regenerant waste, and thats if it isnt mixed with backwash or (fast, slow or preservice) rinse waters.

One thing for sure, this has been an interestin debate amonst us observers. The calcs for CaSO4 precipitation oughta be interesting.

Best wishes, 22854. Please do let us know how it turns out

Cheers

 

[bimr]

DeltaCascade,

You answer on Nov 30 was the only one that made sense in these threads.

22854,

One additional thought you might try is eliminate the IX system. If you go with an RO/CDI system, you will reduce the amount of chemicals that you are using to produce the product water. IX systems typically use 2x molar concentrations in order to regenerate. So an RO/CDI will have less total ions in the wastewater.

Also, the permitting agency is basically telling you that they want zero discharge. To go zero discharge, you will need to obtain a brine concentrator, which is an evaporator. A brine concentrator recycles about 95+% of distillate that will be the source of your DI water. This is expensive, but is a workable zero discharge system.

 

[RGCook]

In response to the question 22854 posed in the last post....chemical ppt folled by downstream RO is the answer here. Keep your hardness down prior to RO. Next, concentrate up to say 6% brine strength and ppt that AS WELL using chemical ppt. Recycle the effluent back up front.

Net affect, you are constantly removeing the SO4 as CaSO4-2H2O using simple chemical ppt while...at the same time, producing a pretty nice, clean water that should be down around 20-30mmho.

We need some simple flowcharting functionality on these threads, I am dying to map this out! HAHA

Later,

Bob

 

[DeltaCascade]

Thanks, bimr, i needed that
One other option to consider may be adding use of weak acid cation (WAC) resins with the strong acid cation resins that we assume are being used.. WACs are more than twice as efficient in use of sulphuric acid regenerant when calcium is in bicarbonate form ("temporary hardness&quot... and will reduce acid use, but we can't tell if it may be enough without further problem definition.
Cheers, all!//

 

[bimr]

RG Cook,

Chemical precipitation is not used for this application because of the high solubility of calcium sulfate (+2000 mg/l). What can you do with a waste stream with 2,000 mg/l sulfates? Nothing except evaporation, which could you have done without the precipitation step.

RO is also problematic when used on waste streams with high dissolved solids levels.

DeltaCascade has mapped this out for you. If we want to flowchart this thread, just erase everything but his answers.

 

[RGCook]

bimr,

I understand your point; however, the solubility of CaSO4-2H2O (not SO42-) is about 2,000-2,200 mg/L. Also, RO can be applied to concentrate streams like this in a zero-liquid discharge application. You seem to have missed the implication that Ca must be removed prior to RO or, as you say, it will not be very effective concentrating, because it will likely salt out. Yeah...ok... Remove the Ca hardness using NaCO3, essentially dropping the Ca as CaCO3 up front using NaOH, to elevate pH. This leaves you with a Na2SO4 salt going to RO that is effectively concentrated very will up to about 6% by weight. In a ZLD facility I was involved in, it is true that we evaporate in a forced circulation crystallizer to drop the salt. However, if one was to recycle the concentrated NaSO4 solution and ppt with lime, it is something that, in my opinion, should at least be explored. It may be conceivable to get creative and at least minimize the load on the downstream crystallizer.

Don't be so quick to dismiss ideas. That is the point of the thread. And with all due respect, you seem to have missed the chemistry.

 

[waterexpert]

faq164-544 covers this area.

 

[bimr]

RGCook,

What am I missing? I agree that RO has been used at some zld facilities. My point was that the use of RO for zld has been problematic. It is not just the salts that you have to worry about. You have to be concerned with organics, suspended matter, barium, pH, chlorine, etc. With enough pretreatment, RO can be made to work in almost any application, but it not necessarily economical. If I had a choice between an RO unit or a brine concentrator, I would go to a brine concentrator. Most of the successful zld facilities use evaporators.

Again, I agree with you that you can knock down the calcium, thereby minimizing the potential scaling of calcium sulfate. But, how are you going to do that? For high levels of calcium (greater than 300 mg/l) there is nothing that is economical. The relative cost of removing calcium noncarbonate hardness with precipitation is 5 times the cost of removing bicarbonate hardness. The relative cost of removing sulfates with lime or soda ash is probably worse.

22854 wanted to know which are the most used methods or technologies to eliminate or reduce sulfates contents from industrial waste water to comply with municipal regulations. I don't see that he was looking for someone to be creative.

 

[nareshiitr]

It will be removed by wet air oxidation..if u want any info please go to google.com

 

[bimr]

nareshiitr: Glad to see that you know about google.com. Maybe you can use it to improve your posts.

In this thread, we have calcium sulfate salts which 22854 would like to remove from wastewater.

I would agree that sulfides can be oxidized to sulfates. But generally, no significant quantity of sulfides are present present in wastewater. Unless you are a tannery.

 

[25362]

Sulfates' elimination is indeed a difficult problem to solve.

It is strange that a limitation of 100 ppm of sulfates in water going to the sea has been imposed since the average content of sea water is near 900 ppm S as Ca, Mg and K sulphates. This is probably the result of a waiver on the content of other contaminants.

Anyway, when speaking of precipitating sulfates I recall that analytical chemists actually use Ba salts to measure-gravimetrically- sulfates in body fluids by weighing the precipitated BaSO₄. Its solubility product K_sp=10^-10, resulting in a solubility of less than 30 ppm at 25-30^oC. Could this fact be used in 22854's case without becoming too "creative" as bimr implies? BTW, it is CaSO₃ that has a very low solubility in water (less than 60 ppm at ambient temperatures).

Ba salts are toxic, therefore their addition, if at all, should be done with utmost care in a manner that their presence is less than stoichiometric, and, even better, a cation exchange resin should be used, after the separation of BaSO₄ has taken place, to ensure no Ba ions escape with the effluent. This salt should precipitate quite easily having a density of 4.5 times that of water. Because of its low solubility BaSO₄ can be "safely" used to X-ray the digestive tracts of humans.

Would a lab trial be practical? I wonder.

 

[kenvlach]

Re sulfate limit: this may be due to sulfate attack of concrete.

Re Barium toxicity: Barium is actually pretty non-toxic, see MSDS at

https://fscimage.fishersci.com/msds/02510.htm

An isotope is used for medical imaging.

Presume that barium is little used for sulfate precipitation due to cost and because using BaCl₂ or Ba(NO₃)₂ would just substitute chloride or nitrate ions.

 

[25362]

To kenvlach, the website you mention refers to Ba sulfate (barite) which I already said is non toxic because it precipitates, and it is widely used in medicine as an X-ray contrast medium, as a filler in paints, plastics, rubber, the ceramic industry, and in drilling muds.

Barium metal and most barium compounds, with the exception of barium sulfate, are extremely poisonous, regardless of price. See, for example,

http://www.jtbaker.com/msds/englishhtml/b0372.htm

http://physchem.ox.ac.uk/MSDS/BA/barium_chloride_anhydrous.html

 

[22854]

Dear Friends,

Thank you all for your help and assesment. Regarding the limits of 100 ppm of sulfates going to the sea, by the time I asked my first question we sent a reclamation to the authorities to study and reestablish new limits for this and other parameteres of contaminants in the effluent waters going to the sea. Last week we have received a still non-official notification from the government that is changing the requested parameters. Specifically for sulfates they are changing from 100 ppm to Not Specified. This means that no controls will be done on this until a new limit is stablished.

 

[JaccoH]

Dear all

There appear to be two threads on the same topic. Have a look at thread thread164-47948. It has some alternative technologies.

Greetings,

Jacco