Followings are a few links for online calculation of saturation index. Also you may read the attached file for further information.

http://www.lenntech.com/calculators/langelier/index/langelier.htm

http://www.aquachek.com/calculators/langelier-saturation-index/

http://www.cleanwaterstore.com/technical/water-treatment-calculations/langlier.php

http://www.aquapure-il.com/Saturation-Index-Calculator.html

http://www.poolandspachemicals.co.uk/waterbalance.htm

Dear Mr. Karbassi, thank you very much. Actually, we were looking for the calculation of SI for geological materials (dolomite, calcite). Finally we used PHREEQC program. 

Sorry, I have no information about this index.

Good discussion, Kindly, could you send me a phreeqc program, please

PHREEQC to download: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/

PHREEQC online running:

https://www.ndsu.edu/webphreeq/webphreeq-input.cgi

Yuliya

I do not know if it is possible to do that online but you can download PHREEQC and it is free and this enable you to work online or offline.

Dear Mr. Karbassi , thank you so much for your guideline. it helped me a lot.

For future reference I can recommend ChemEQL, developed at EAWAG (https://www.eawag.ch/en/department/surf/projects/chemeql/)

I have also used visualMINTEQ and CHEAQS with good results.

I recommend "visualMINTEQ and Aqion", there are very easy to use. But, these software designed for aqueous solutions.

However, the calculation of SI for a co-solvent solution such as Methanol and brine water will be very difficult.

It is well known that the activity coefficient of mineral ions are changed in a co-solvent system, specifically in alcohol solutions. Therefore, I think these kind of software are very limited.

So can anybody advice me which free access software handle co-solvent SI calculations?