I would be surprised if you find isolated [SiO3]2- ions in such a solution. Wollastonite contains polymeric chains with the composition {[SiO3]2-}n. As Vadim points out, H2SiO3 is also a polymer.

This is why it does not really dissolve in water.

Complete dissolution of silicates is normally achieved using HF. This breaks the Si-O bonds of the polymeric chains (or networks) into pieces, thus allowing complete dissolution. But be careful when using HF !!!

Solubility of CaSiO3 is very low (less than 0.01 % at room temperature). First reaction not take place due to hydrolisys. In my opinion second reaction also is not true.

Correct variant of full hydrolysis:

CaSiO3 + 2H2O -> Ca(OH)2 + H2SiO3

In solution presents product of hydrolisys also - HSiO3-.

This reaction is accelerated when heated, but proceeds very slow anyway.

Dissotiation constants for metasilicon acid (H2SiO3) is: K1 = 1,3•10-10, K2 =1,6•10-12. Metasilicon acid (H2SiO3, as rule is gel) not convert in orthosilicon acid (H4SiO4), but lose water and gave silicon oxide:

H2SiO3 -> SO2 + H2O.

I would be surprised if you find isolated [SiO3]2- ions in such a solution. Wollastonite contains polymeric chains with the composition {[SiO3]2-}n. As Vadim points out, H2SiO3 is also a polymer.

This is why it does not really dissolve in water.

Complete dissolution of silicates is normally achieved using HF. This breaks the Si-O bonds of the polymeric chains (or networks) into pieces, thus allowing complete dissolution. But be careful when using HF !!!

Dear Director Gorshkov and Professor Klein,

Thank you for your replies.

There is no need to worry about my use of HF. I am investigating the effects of carbonic acid on rocks. Moreover, I am confining my investigations to calculations, so I should be perfectly safe :-)

I have discovered a paper:

Sun, H., He, S., Wu, P., Gao, C., Feng, P., Xiao, T., Deng, Y. and Shuai, C. (2016) ‘A novel mgo-cao-sio2 system for fabricating bone scaffolds with improved overall performance’, Materials, vol. 9, no. 4, p. 287.

They quote the reaction as:

CaSiO3 + H2O -> Ca2+ + HSiO3- + OH- (1)

and "the solubility product constant (KSP) of CaSiO3 (2.5 X 10-8)"

I think that equation (1) is in fact two reactions:

CaSiO3 Ca2+ + SiO32- (1a) Kc = KSP

SiO32- + H2O HSiO3- + OH- (1b) Kc = 1/K2

If we add a third reaction ...

HSiO3- + H2O H2SiO3 + OH- (1c) Kc = 1/K1

... and add the left hand sides together , and the right hand sides together, then cancel the common ions we get:

CaSiO3 + 2H2O -> Ca2+ + 2OH- + H2SiO3

which is similar to that suggested by Vadim.

I would prefer to use a more appropriate reference than Sun et al (2016) for the Kc's so if you have any please post them.

Look for references in this article. If this consists of authors compatriot's articles, you have a choise... But, in my opinion, these systems were investigated even in the 1930s - 50s mostly by German researchers. Most likely these articles are not digitized yet.

P.S. Sorry, but I am not a director ... My name is Vadim!

As an inorganic chemist (and a purist :-)) I would prefer to note H2SiO3 and related as {H2SiO3}n or {CaSiO3}n (with subscript n).

Hi Vadim,

You suggest that I look for references in 'this' article ? Do you mean Sun et al. (2016)? They don't give a reference for their value of KSP.

I was hoping someone would point me to a database holding Ksp.s for many (all) minerals. All I have found is the PubChem database https://pubchem.ncbi.nlm.nih.gov/#query=H2CO3 but it does not seem to be much help.

However, I can probably live with the value from Sun et al.

Thanks again.

This was a joke. I saw such articles... Often there is a feeling that science began in 2010 or little bit earlier. You need to go back to the paper library. Start for example, from Preparation of CaSiO3 Powders by Coprecipitation Method and Their Sinterability, J. Ceram. Soc. Japan, December 1991, DOI: 10.2109/jcersj.99.1224.

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