Talk:Calcium sulfate

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From gypsum

A growing source of gypsum is from Flue gas desulfurization which scrubs the sulfur emissions from fossil fuel burning power stations. This is done by using finely ground limestone which reacts with the sulfur dioxide to produce high purity gypsum as a by-product. This is now the main source for calcium sulfate. Schould this be mentioned here? Stone 16:49, 2 February 2006 (UTC)

Density error?[edit]

This density (~22g/cm^3), about that of Ir, seems to me to be in error. Drywall doesn't strike me as that heavy. Should this be verified? --Oreo Priest 03:10, 10 August 2006 (UTC)

This value is correct (checked the Merck index). I should note though, that this is for the anhydrous form. The hydrated form which is in drywall has a density of 2.32g/cc. In addition, I think this would be the density of one solid crystal not of light powder which has a lot of free space between particles. Finally if you compare the value to magnesium sulfate (d 2.66), it seems to make sense. —Preceding unsigned comment added by (talk) 06:47, 2 December 2007 (UTC)
The article had been vandalized (see Special:Contributions/, and the arror was discovered and reverted about a month after it was introduced into the article. The correct value is 2.96, not 22.96. - Mike Rosoft (talk) 18:27, 6 September 2008 (UTC)

Need to break up this article[edit]

The chaotic nature of the chembox data is because the article refers to multiple minerals. Suggest change this to a short disambiguation page, pointing to separate articles for each hydration state. This is justified because the different hydrates are all high-volume minerals with very different applications, etc. LinguisticDemographer 01:44, 11 February 2007 (UTC)

This will create sevaral stub articles with less use. Better would be to write a chapter about every of the compounds in this article.--Stone 09:17, 12 February 2007 (UTC)

Does this mean we can multiple databoxes in one article? LinguisticDemographer 16:17, 12 February 2007 (UTC) I think this might be possible.--Stone 16:57, 12 February 2007 (UTC)

Re-write production[edit]

Re-wrote section to refer to calcium sulfate rather than "gypsum", in chemist's language. Remove unsubstantiated (since 25 Jan 2007) and POV content. . . . LinguisticDemographer 19:19, 5 August 2007 (UTC)

Drierite mention added.[edit]

I've added a sentence on Drierite, as Drierite redirects to this article, but had no mention anywhere in the article. I'm of the belief that when a term is redirected, it should be mentioned somewhere in the target article. Otherwise, someone looking up info on blue/pink Drierite who reaches this article and sees CaSO4 is a white compound will be confused. I also took this opportunity to integrate the orphan sentence about the compound's color into the first paragraph. Kel - Ex-web.god 22:27, 10 October 2007 (UTC)

Qualitative analysis[edit]

How to differentiate between calcium sulfate and calcium hydroxide? They both have low solubility in water.--Tohyf (talk) 10:10, 30 November 2007 (UTC)

The hydroxide is a fairly strong base despite its low solubility. You could identify it using pH paper, for example. --Itub 10:43, 3 December 2007 (UTC)

contradictory articles[edit]

This article says that anhydrite will not react with water even over geological timescales, while the anhydrite article says it will react readily. Which one is correct? —Preceding unsigned comment added by (talk) 22:20, 1 July 2008 (UTC)

Can someone address this? It's a fairly pervasive myth/confusion, mention of how to re-hydrate it in a lab demo would be enough to clear things up. — Preceding unsigned comment added by (talk) 21:03, 22 November 2017 (UTC)

Environmental impact[edit]

Seeing that this CaSO4/CaSO3 is a waste product of many a industrial process , can some one add on comment regarding waste disposal as the pH is >12 it is classified as corrosive and need to be dumped at a special waste disposal site?? —Preceding unsigned comment added by (talk) 06:47, 4 November 2008 (UTC)

You try only to produce CaSO4 xH2O and then the stuff is normaly sold as Drywall or gypsum or plaster. --Stone (talk) 10:24, 4 November 2008 (UTC)

Superscript text

calcarea sulphurica is used as a homeopathic[edit]

Calcarea sulphurica is used as a homeophathic to treat acne. The claim that it will dry up pustules from the inside out therefore clearing up the acne. I want to know how is this possible. What is the chemical reaction that allows this homeopathic to inhibit or dry up puss filled pimples,ect. Does anyone know? —Preceding unsigned comment added by (talk) 06:50, 5 February 2010 (UTC)

Solubility product constant, Ksp[edit]

For calcium sulphate hemihydrate, CaSO4*0,5H2O in this article is indicated Ksp = 3,1*10^-7, but in my Handbook of Chem. and Physic, 84th edition, 2003-2004, this Ksp is for a sulphite, namely for calcium sulphite hemihydrate, CaSO3.0,5 H2O. There is no value Ksp for CaCO4*0,5 H2O in this handbook. I made the same mistake myself and thought it was for the sulphate. I have not corrected it in the article. — Preceding unsigned comment added by (talk) 14:33, 16 April 2012 (UTC)

Good catch, I think. I checked the CRC handbook and it appears you are 100% right. Best regards, Stan J. Klimas (talk) 00:42, 17 April 2012 (UTC)

Solubility from solubility product[edit]

The article currently contains the following remark:

Note that the solubility of the calcium sulphate in the figure results about 10 times higher than that which is calculated with the solubility product of 0.0000493 given in same page. The value of Ksp is given also in Note also that different values in the same order of magnitude but smaller are given in

In my opinion, this is misleading and should be removed. The calculation of solubility from solubility product for calcium sulfate needs to consider activity coefficients. The author of this remark seems to have forgotten about it. E.g., see here, p.1379. Stan J. Klimas (talk) 02:05, 17 April 2012 (UTC)

Stripped out Ksp References[edit]

I stripped these out of the text, someone may be able to put them to some use, but they weren't particularly useful for what was being said in the article.

They all are sort of short of any references anyway.JSR (talk) 17:29, 30 September 2012 (UTC)