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Offline SO4

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Production of CaSO4
« on: March 04, 2016, 10:35:59 AM »
i'm looking to produce CaSO4 using a high concentration of sulfate water ( about 65-67g/L)
my water is ranging from a pH of 5,5 to 7 . Using NaOH so there is a presence of Na2+ in my solution.My real goal is looking to reduce the sulfate as much as possible and collect a usefull compound and one might be CaSO4


I've used  Ca(OH)2 but as i tought it didnt react alot or maybe not at all whit the SO4 2- , but raised the pH . I realize there wasn't alot of reaction using the quantification of sulfate before/after. This situation could be explain by the low solubility of Ca(OH)2

My question is : Should i used CaO in order to make this reaction : CaO + SO4 2- + H2O = CaSO4 + 2OH-
As CaSO4 isn't highly soluble in water it will precipitate and gives me a powder , mostly made of CaSO4 right? The OH- will of course increase the pH , will it reduce the reaction process/solubility ? Thanks for your time.

Offline Burner

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Re: Production of CaSO4
« Reply #1 on: March 04, 2016, 10:47:36 AM »
I'm looking to produce CaSO4 using a high concentration of sulfate water ( about 65-67g/L)
my water is ranging from a pH of 5,5 to 7 . Using NaOH so there is a presence of Na2+ in my solution.My real goal is looking to reduce the sulfate as much as possible and collect a usefull compound and one might be CaSO4

1. Are you sure you have Na2+??
2. You want to collect CaSO4 by reduction? That isn't nessary. You just need precipitation reaction

I've used  Ca(OH)2 but as i tought it didnt react alot or maybe not at all whit the SO4 2- , but raised the pH . I realize there wasn't alot of reaction using the quantification of sulfate before/after. This situation could be explain by the low solubility of Ca(OH)2

I think so.

My question is : Should i used CaO in order to make this reaction : CaO + SO4 2- + H2O = CaSO4 + 2OH-
As CaSO4 isn't highly soluble in water it will precipitate and gives me a powder , mostly made of CaSO4 right? The OH- will of course increase the pH , will it reduce the reaction process/solubility ? Thanks for your time.

No. CaSO4 will be formed as a solid layer enclosing the CaO solid(CaO is insoluble in water), seals its surface, and prevent further reaction. If you want CaSO4 to precipitate like powder, you need to use other aqueous calcium compounds with a high solubility in water.
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Offline SO4

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Re: Production of CaSO4
« Reply #2 on: March 04, 2016, 11:04:47 AM »
Thanks for your fast reply

Quote
1. Are you sure you have Na2+??
2. You want to collect CaSO4 by reduction? That isn't nessary. You just need precipitation reaction
Well i'm sure they are using NaOH to stabilise the pH so Yes. Also if i drop a few ml of the solution and let it dry it gives a white compound  , i was thinking NaSO4 ,

Quote
No. CaSO4 will be formed as a solid layer enclosing the CaO solid(CaO is insoluble in water), seals its surface, and prevent further reaction. If you want CaSO4 to precipitate like powder, you need to use other aqueous calcium compounds with a high solubility in water.

You mean the produce of the reaction of CaO+ H2O is insoluble? CaO react really strong whit H2O in order to make the Ca(OH)2 so the Ca(OH)2 produced will enclose the CaO and i won't never get Ca2+ in solution to react whit the SO4 2-? I was thinking the high concentration of SO4 might react before whit the Ca2+ and precipitate before the Ca(OH)2 or atleast together .Any suggestion on how  to get Ca2+in solution in order to make the precipitation of CaSO4?

Offline Burner

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Re: Production of CaSO4
« Reply #3 on: March 04, 2016, 11:12:04 AM »
Well i'm sure they are using NaOH to stabilise the pH so Yes. Also if i drop a few ml of the solution and let it dry it gives a white compound  , i was thinking NaSO4 ,
Na2+ hardly exists, so does NaSO4. You can have Na2SO4 though. Also, I don't see any relationship between pH and the reaction.

Quote
You mean the produce of the reaction of CaO+ H2O is insoluble? CaO react really strong whit H2O in order to make the Ca(OH)2 so the Ca(OH)2 produced will enclose the CaO and i won't never get Ca2+ in solution to react whit the SO4 2-? I was thinking the high concentration of SO4 might react before whit the Ca2+ and precipitate before the Ca(OH)2 or atleast together .

CaO reacts with SO42- to form insoluble CaSO4 on its surface. This CaSO4 formed will be in the form of a solid layer sealing the surface of CaO, preventing further contact between CaO and SO42-. So you can only get a little CaSO4 before the reaction stops since no more SO42- can meet the CaO and reacts.

Quote
Any suggestion on how  to get Ca2+in solution in order to make the precipitation of CaSO4?

https://en.wikipedia.org/wiki/Solubility_chart
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Offline SO4

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Re: Production of CaSO4
« Reply #4 on: March 04, 2016, 11:30:13 AM »
sorry , my bad , i ment Na2SO4

Sorry for the lack of explanation, My water comes from a biological reactor capting H2S and converting it into SO4 , H2SO4 makes the pH decrease and they are keeping the pH between 5,5 a 7 by adding NaOH.

So my water contain some Na+, i gave this useless info and did not introduce it.Sorry

If i use CaO as powder and procure a high agitation i might still get CaSO4 right? Of course , as you said, i will not get a 100% convertion ratio but i might get a convertion ratio that might be interesting , atleast to try it in lab?
Thanks for your help sir

Offline Burner

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Re: Production of CaSO4
« Reply #5 on: March 04, 2016, 08:57:15 PM »
sorry , my bad , i ment Na2SO4

Sorry for the lack of explanation, My water comes from a biological reactor capting H2S and converting it into SO4 , H2SO4 makes the pH decrease and they are keeping the pH between 5,5 a 7 by adding NaOH.

So my water contain some Na+, i gave this useless info and did not introduce it.Sorry

Na+ has no effect in production of CaSO4.

Quote
If i use CaO as powder and procure a high agitation i might still get CaSO4 right? Of course , as you said, i will not get a 100% convertion ratio but i might get a convertion ratio that might be interesting , atleast to try it in lab?
Thanks for your help sir

Yes, you can still get CaSO4 from the surface of CaO, and if your CaO powder is fine enough you can get a significant proportion of it. However, why do you want CaSO4? If you need it for other experiments, you may need to separate the CaSO4 from the CaO(and I am not sure how to do so). But if you purpose is just making CaSO4 and nothing else, then it is still ok.

Quote
Thanks for your help sir

I am a high school student only.
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Offline Borek

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Re: Production of CaSO4
« Reply #6 on: March 05, 2016, 03:37:36 AM »
CaO reacts with water fast enough that for most practical purposes if you deal with water solutions it shouldn't matter whether you add Ca(OH)2 or CaO. I would check which one is cheaper and easier to dose to decide which one to use.

I wonder if you can't kill two birds with one stone, by using CaO (or Ca(OH)2) for pH control (instead of NaOH).
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Offline Burner

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Re: Production of CaSO4
« Reply #7 on: March 05, 2016, 05:32:52 AM »
Brainfarted, I forgot CaO can react with water to form aqueous solution. Sorry for that.

I would still recommend other soluble calcium compounds such as Ca(NO3)2 and Ca(HCO3)2. The latter is an alkaline salt if I am not mistaken.
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Offline Arkcon

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Re: Production of CaSO4
« Reply #8 on: March 05, 2016, 08:55:41 AM »
There is some debate whether or not calcium bicarbonate exists.  https://en.wikipedia.org/wiki/Calcium_bicarbonate

Briefly, many laboratories, from university undergraduate labs to advanced biotech labs, send their aqueous waste through a lime pit.  The CaO becomes CaOH, and the high pH destroys some organics, but more significantly, precipitates heavy metals.  I don't know how the spent CaO is dealt with, probably as hazardous waste.

I understand the chemistry behind converting sulfated water into CaSO4, but really doubt anyone would pay enough for something that's easily mined in bulk, to make all the fluid handling you'd need to install worthwhile.

Other chemical engineers, on this board, often talk about waste remediation, and may be able to help more.
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Offline SO4

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Re: Production of CaSO4
« Reply #9 on: March 05, 2016, 11:16:37 AM »
I'm agreed whit you , CaSO4 is not rare at all and unexpensive. The neutralisation H2SO4  whit a calcium source gives CaSO4 industries tend to do this in order to increase the pH and reduce the sulfate concentration before landing it back into the environnement. My goal is not to make CaSO4, it's to use the SO4 and tend to make it *harmless* to environnement and in same time maybe make this process costless. My main problem here is my  water/waste is already *neutralised*. I was hoping to make (NH4)2SO4 or Al2(SO4)3 (another topic !). But i'll still try to make the CaO reaction and try to see how much sulfate do i used.
« Last Edit: March 05, 2016, 09:34:30 PM by Arkcon »

Offline Burner

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Re: Production of CaSO4
« Reply #10 on: March 05, 2016, 08:25:44 PM »
I'm agreed whit you , CaSO4 is not rare at all and unexpensive. The neutralisation H2SO4  whit a calcium source gives CaSO4 industries tend to do this in order to increase the pH and reduce the sulfate concentration before landing it back into the environnement. My goal is not to make CaSO4, it's to use the SO4 and tend to make it *harmless* to environnement and in same time maybe make this process costless. My main problem here is my  water/waste is already *neutralised*. I was hoping to make (NH4)2SO4 or Al2(SO4)3 (another topic !). But i'll still try to make the CaO reaction and try to see how much sulfate do i used.

(NH4)2SO4 and Al2(SO4)3 are soluble in water. There are some other insoluble sulphates for example PbSO4(of cause lead contamination is another issue), BaSO4 and SrSO4
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