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Suitable Bleaching Agents for Talc (5 replies and 2 comments)
I assume you mean NaHS, sodium hydrosulfide? And yes, you should be concerned if you combine it with acid. It can be done under some circumstances and with the right scrubbers and monitoring equipment in place, but it is not recommended for amateurs.
I also don't know if it would work. I assume you are trying to remove color from the talc that is caused by impurities in the talc. You need to know what these impurities are and their morphology. And obviously, test it in a laboratory and then have someone design a commercial system ... if that is what is needed.
I think that NaHSO3 is the reagent you are thinking about. Instead of it you can inject SO2 gas. Regardless you will have an SO2 atmosphere above the slurry and will need to maintain a closed tank with a caustic scrubbing system. The good thing about caustic scrubbing is that the SO2 you capture can be returned directly to the process tank. SO2 /NaHSO3 are unpredictable oxidizers. They don't always result in oxidation. NaOCl or H2O2 might work.
When you speak about bleaching this is presumably to improve whiteness or brightness. Yes?
What do you know about the origin of the lower whiteness, brightness. I have seen this as due to surface stains of inorganic and organic nature, i.e., iron mineralization and coaly-based contaminants, respectively. The solution differs based on the root cause.
Robert, the bleaching/leaching would be to increase the whiteness of the talc. Currently, the talc is considered to be white or maybe "off-white" in color and my aim is to get it to "brilliant white". Now, these colors should be quantified on a scale (e.g., Hunter) but unfortunately the clients in this part of the world simply use the eye test.
The talc's main gaunge is alumimum oxide at 5%, iron oxide at .7% and calcium oxide at 1%.
I attempted different leaching tests with hydrochloric acid (we may not have enough space to describe it), but suffice to say that at a d97 10 micron particle size, temp. of 55 Celsius, HCL solution of 2 mols, after 4 hours, there was not a noticeable difference in the color of the talc.
Do you know what the minerals corresponding to the aluminium oxide, iron oxide, calcium oxide are? These look like calculated values from chemical analysis to determine Al, Fe, Ca. Yes?
Have you tried to remove the iron mineralization using magnetic separation?
I will send some reference articles with experimental details for leaching if you provide email address.
Robert, thanks for your response. Yes, to your first question. These are the calculated values from a chemical assay.
With respect to magnetic separation, I have not tried it with the samples I currently have, which are d97 10 micron, but I will try it with fresh samples in the 150 to 200 micron range.
My email address is shown on https://www.911metallurgist.com/profile/babygenius76
Thank you so much for your input and help!
Cheers
Look at the following. As part of this searching the patent data bases for US and EU will provide details of process and processing conditions.
Note that understanding whether the discoloration arises from surface coating or discrete mineralization will assist your journey of discovery.
An alternative is hand sorting of the ore. This can work if coarse contaminants may be sorted out adequately. I've seen this done when only a fraction of the production from a GCC operation was going to higher brightness markets.
alternative leaching process
Orthogonal Experiments for Kaolin Bleaching by Using Sodium Dithionite and Sulfuric Acid
Method for removing iron impurities in kaolin
http://color.yanliao.net/youji_1/content/?849.html
Process for the bleaching of pigments
http://www.google.com/patents/US6270564
Handbook of fillers for plastics
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Has anyone looked into this issue? I have heard about adding sodium hydrosulphite is added to an acidic slurry of talc and diluted sulfuric acid. I am concerned about the safety of anything related to sodium hydosulphite. Any suggestions?