Hello Nouha,

Do you have the same turbid solution if you mixed only with DI water. It might be a chemical reaction between this solution and the KCl/ZnCl2. I don't know the chemistry of the naphthalene, but you might try to perform this easy experiment. 

I found this paper, 

http://link.springer.com/article/10.1007%2Fs11743-000-0140-1

Let me know if you can get a copy.

Good luck.

 Dear Nouha Loukil,

If Chlorides are not required for your final product then you can remove them by washing or rinsing with DI water on filtration system( if your desired compound is not soluble in water). It may take time to remove all the chloride. You can test the presence of  Chlorides in filtrate solution by a single drop of 0.01N AgNO3 solution. 

Regards.

Muhammad Imran

Hi Nouha Loukil

The material is said to be soluble in water. Not soluble in aromatic and polar solvents. (www.rhodia.com/product-literature-download.action?...SUPRAGIL+WP).

My guess is that the presence of Zn++ divalent salt at high concentration convert some of the sodium water soluble salt into Zn insoluble salt. I guess with Ca++ the problem to be harder. If you can turn to monovalent cation I guess problem will diminish.

Meir Stern 08/02/17