[mehc]

Calcium carbonate is coated with stearic acid to increase hydrophobic properties. Stearic acid is chemically and physically absorbed on calcium carbonate particle surface.

In literature I cannot find any standard chemical method to decoat calcium carbonate to determine percentage of stearic acid coating.

However, it is possible to decoat calcium carbonate by treatment with HCl, stearic acid layer floats on top.

Can anyone suggest any other method to decoat calcium carbonate.

Thanks.

[Hunter2]

Are sure you have a coating or a compound: Calciumstearate. Stearic acid reacts with calciumcarbonate to lime soap normally.

[mehc]

Yes, its only coating, a surface modification.

[Arkcon]

Actually, I'd only heard of the plasticizers being used for very hygroscopic salts, such as calcium chloride or calcium nitrate.  Since calcium carbonate is mostly insoluble in water, I don't think it needs a coating.   Often what's done is the sample is dissolved, and the top layer of scum is skimmed off.

[gjuhasz]

I wonder how big CaCO3 particles are we talking about, ie what are the approximate amount of coating vs particle. It significantly influence what is the right tool.

Since the Ca salts of acids are rather stable and less soluble compared to Na or K salts, I see why such a system would be stable. But cannot just wash it down / rinse eg with a concentrated solution of some soluble Ca salt or other cation? Mechanical stiring, ultrasound etc may be very important if you go this way.

Also, are these separation methods the best way to approach the problem? Your acid is a really dirty material in water, hard to make nice reactions with it, produce foamish surfaces, may stick on your glass etc. So in short I wouldn't bother with taking it down and trying to measure it. Have you though about something simple like gravimetery / TG?

[mehc]

Actually, I'd only heard of the plasticizers being used for very hygroscopic salts, such as calcium chloride or calcium nitrate.  Since calcium carbonate is mostly insoluble in water, I don't think it needs a coating.   Often what's done is the sample is dissolved, and the top layer of scum is skimmed off.

Calcium carbonate is used as filler with polymers like PVC etc. For that application the surface of calcium carbonate should be hydrophobic which is otherwise hydrophyllic. That's the reason that it is coated.

Currently I am using the same method, treating with HCl and filter the stearic acid. But I was searching for a more efficient method. Air drying stearic acid takes more time as it cannot be dried in oven due to 69.8 degree C melting point.

[mehc]

I wonder how big CaCO3 particles are we talking about, ie what are the approximate amount of coating vs particle. It significantly influence what is the right tool.

Since the Ca salts of acids are rather stable and less soluble compared to Na or K salts, I see why such a system would be stable. But cannot just wash it down / rinse eg with a concentrated solution of some soluble Ca salt or other cation? Mechanical stiring, ultrasound etc may be very important if you go this way.

Also, are these separation methods the best way to approach the problem? Your acid is a really dirty material in water, hard to make nice reactions with it, produce foamish surfaces, may stick on your glass etc. So in short I wouldn't bother with taking it down and trying to measure it. Have you though about something simple like gravimetery / TG?

The ratio of coating is about 3 % stearic acid.

Percentage coating has to be determined as quality control test for coating. TG etc are not accessible, the only possible option is chemical treatment.
Treating with soluble calcium salt may work, i think. But soluble calcium salt will form insoluble calcium stearate. Separating the newly formed calcium stearate and decoated calcium carbonate will be difficult. However I will try it. Thanks for this idea.