# Problem with dental plasters



## skyos (Apr 3, 2014)

Hi everybody,

It is few months already i read this forum, and read the Hoke s book, very useful.Thanks for all

I try to find some people work already on dental plaster.

I just start to work with some refinner who have some problem with this plasters, he try already cyanuration method and AR method but only a little 10 PERCENT OF THE GOLD DISSOLVE IN THE SOLUTION> (he knows the quantity of gold because he made many analysis already from japan, usa, canada....) and send everytime the "juice" at the spectrophotometry lab for know results.

For the cyanuration :

I looking already about the "Sulfate Calcium" (plasters) and believe maybe the pH of his solution when he had cyanure is acid...but no... he had enough sodium hydroxyde and he can kept the pH very high ( test with pH paper).
Only 10 percents of the gold is dissolved

Try the AR method :

same probleme, only 10 percents of the gold is in the solution


I need to say you he is refinners for more than 15 years already and the cyanuration method and AR method is good for all the other stuff he have to refinn but only plasters make problems...

If somebody used to work on this material and can helping us with some advices, he will be welcome

Thank you to everybody

PS : i want to apologize for my poor english language and for all my mistakes, i m french speaker. Best regards


----------



## nickvc (Apr 3, 2014)

I'm sure one of us can help but I'm at a loss to know what a dental platter is I'm afraid.
Can you post pictures of the material your working with, if so that will help with answering or at least trying to answer your questions.


----------



## skyos (Apr 3, 2014)

Thank you for read my post and try to helping me,

i will post pictures asap, i need to go visit him soon, may be beginning of next week.

He explain me, and i saw it :

it s a hollow mould with the tooth print inside, then they put some fusion metal inside and make turn this mould on itself in order that the metal cover all the face inside the mould.

After, i think the dentist can fix this "false tooth" top of the true tooth ???? 

So, all the stuff come at the factory as split up little cylinders in plaster with the form of the tooth inside.

We make really thin powder of this, and process it with the chemicals.


----------



## skyos (Apr 3, 2014)

i just find this video on youtube : http://www.youtube.com/watch?v=5q_HMeZX3Mg


this is this kind of plasters fragments i have with precious metals inside

Exactly in the same :lol:


----------



## nickvc (Apr 3, 2014)

Is your friend just getting powders or metals or a mix of both?
Has he assayed the incoming metals not just for Au but other values such as Pt and Ag and for any other base metals which can cause problems, the suppliers of the metals should know the alloys they are using so ask them for the make up.
Has he tried inquarting the material to remove any silver and base metals with nitric this should improve his chances of recovering all the gold.


----------



## skyos (Apr 3, 2014)

My friend have several tons of the platter fragments only.

He make analysis of this powder, and the results came back : Inside this powder, they can find, gold , silver, and maybe a few ppm of cadmiun but really a little bit. (I was thinking about the gamma rules in Chemistry about electronegativity of cadmiun and gold but i know the quantity of cadmium is so little front of quantity of gold so that cannot prevent all the reaction)

Everytime, the differents laboratory send back the same results.

He can reffine many other stuff same as gloves, plastic ground, make burning all and reffine the ashes, no have any problems.
In the same for "little link" for make gold platted jewellery inside bath etc... no problems.


He cannot make inquartation, because when he shredd these plasters and make powder, it s look like same plasters..The gold and the silver are "everywhere" in this white powder.

So, i don't know if the probleme comes from the thickness of this powder,or maybe from the chemical composition of the Calcium sulfate.

He tries to make differents thickness 200 microns until 10 microns. Only 10 percents of the stuff cames in the solution.

Only for this plasters, the cyanuration and the aqua regia not working :roll:

I need a fresh look on this because i go round in circles.

Tks


----------



## nickvc (Apr 3, 2014)

I'm going to assume that this is a form of casting powder with small amounts of metal from the casting process, if so gravity separation such as they use in mining might be the way to go, using water and a riffle table to catch the metals and separate the powder. I fear no wet process that I would recommend will work until the majority of the powder has been removed as the powder will hold the value laden solutions so change direction and work out how to remove the powder then you can process the values with much greater success.


----------



## skyos (Apr 3, 2014)

I Will start to study about your idea right now. 
Thank you for answer me so fast.


----------



## g_axelsson (Apr 3, 2014)

Do you mean plaster instead of platter?

I think most investments for the dental industry is made with christobalite as a base, that's a silica based mineral.
Maybe your friend is making a mistake when picking samples for testing. Any remnants of precious metals from the casting should be in the thin surface zone between the melt and the investment, the area turned black by oxidized base metals. The bulk material shouldn't contain any precious metals at all.
To get a representative sample of the bulk material, take a larger sample, grind it and then take the sample to send for testing from the well mixed ground up powder.

Göran


----------



## goldsilverpro (Apr 3, 2014)

This may help.


----------



## g_axelsson (Apr 3, 2014)

Thanks! Very interesting read... now just to find out if there is any larger manufacturer in the area.

Göran


----------



## skyos (Apr 4, 2014)

Thank you Goran ( sorry, it s plaster or gypsum and not platters  )

Thank you Goldsilver pro for the pdf.

I just come back at my factory, i will read this tonight at home ( Bangkok time / Thailand ) and follow our discuss... 

Big thanks to everybody one more time


Just add some pics of the powder he have to process :


----------



## skyos (Apr 4, 2014)

Good read , tks Goldsilverpro

I like the idea to make a "carbonatation" on the gypsum with the (NH4)2CO3, and finally make react the calcium carbonate with HCl for loss weight and smelting all after in the furnace. 

It s mean i will probably have a button with Au, Ag and Ca ???? and the glass top of this button ?

Or maybe the Calcium salt CaCl2 will move in the rinse water ? :roll: :roll: :roll: 

Will try this soon and say you more about the results.


----------



## skyos (Apr 7, 2014)

Just order some kilos of (NH4)2CO3 from China.

Will process this material around 22nd or 23rd of this month.

Pics will follows after process and results.

We expect 150 to 200 grammes (Au) /tons (if can have some Ag with the nitric, it is welcome  )... Will say you if everything cames out with this method or only a few percentage and sum up the cost and the benefit per tons.

Best regards to all the GRF .


----------



## skyos (May 29, 2014)

just receive the ammonium carbonate yesterday from the chinese supplier....
Results soon

Have a good day


----------



## skyos (Jun 12, 2014)

So little update, 2 days ago , afer 2 months of problems with chinese suppliers and thai border custom, we finally receive the ammonium carbonate....

So we let it overnight inside a big plastic container with some homemade rotor, (10 kg ammonia carbonnate and 50 kilos of plasters 200 microns, demineralised water)....

The following days , we put inside filter and clean with water several times.

Then next, add some HCl, some strong reaction happend ( foam and bubbles) but it s a little bit dissapointing . We not loss so much weight. i will add fews pitures :









After filtering and add some Hcl >>>





That is what we can see after the process >>>













Most of the black particule stuck on some neodymium magnet from HDD. Still have the brown one, maybe the metal ???
The remaining probleme , it s is not enough concentrate for smelting ...

If somebody have some advices or ideas, you are welcome 

Best regards


----------



## skyos (Jun 25, 2014)

Hi, nobody used to process this king of "waste" ?


----------



## Digitaria (Jun 25, 2014)

It sounds like a lot of work for an small return, but you are learning a lot and overcoming problems as you go, which is invaluable but for me, this would not be worth it, but everyone finds their own speciality. 

I hope all this perseverance pays off for you.


----------



## glondor (Jun 25, 2014)

Skyos, If you are still working on this project, please re-read the "size reduction" section of the pdf posted by Goldsilverpro. 

The information in that section is VERY useful to you. The implication is any size under 200 mesh contains almost 0% gold when wet screened. To me, this implies, with careful milling, the gold particulate does not break down to smaller than 200 mesh. There for, you can wash/ screen the plaster away. The information also states that the silver WILL break down to smaller than 200 mesh, and most will be lost.

Try washing the plaster away through a 200 mesh screen from your ammonium carbonate size reduction method. See what you get!

The ammonium carbonate method might even save the silver as it is not being pulverized in a mill.

*edit to add more thoughts*


----------



## skyos (Jun 26, 2014)

Hi Digitaria and Glondor,

first thank you for your precious help and comments,

i m agree with you Digitaria, the return is not so big ( only 200/1000 Au) but it s look like big money when you know that my friend keep 40 or 50 tons of this plaster for more than 10 years ago....It s between 8 and 10 kg of gold...
It is good pension for his retirement but , i agree with you all, it s hard work...

Glondor, i am very confused about the size and the form we can find the precious metal after we process it.
I forget to explain you something :

my friend believed so much in the potential money in can have with this plaster, so he decided to buy this kind of gravity concentrator fron Knelson Cie. The price is around 14 000 USD. It can accelerate the particule maybe at "200 G"

http://www.knelsongravitysolutions.com/

He never can find anything inside the collection cone. At Knelson, they say it s maybe because the particule are too little...

That s why i try to ask you on this forum and try to aask if somebody use to process this kind of plaster because i have no idea already about what look like the material i will find ?

So maybe it s only this plaster canno t be proccess, but it s look like so dissapointing because you know have some stuff inside but canno't make it go outside....

In all the case, thank you for your time and for make this forum live... Very instructive


----------



## Digitaria (Jun 26, 2014)

That is a nice nest egg :mrgreen:


----------



## glondor (Jun 26, 2014)

I am just working on intuition here, but I see careful milling as breaking up the plaster to smaller than 200 mesh, while perhaps flattening any gold content to a larger size. (gold is very malleable) I would think, washing through various size mesh would wash away the smaller plaster slurry, while leaving the malleable metal content behind. I would say, based on GSP's pdf that it is well worth the investigation. If i recall correctly 99.7% of the gold present was caught @ the 200 mesh level.


----------



## skyos (Jun 26, 2014)

I m agree with you Digitaria, but the nest is too big and we cann t find the eggs 

Hi glondor, I m 100% agree with you and I read and my friend read the GSP PDF many times ...but.... (I m sorry for the but) even we screen until 50 microns with water for helping, and make analysis , the gold is everywhere. I understand the nuggets effect , the problem is that the analysis from 3 differents labs from 3 differents country came back with the same results of 200/1000 for above and below 50 microns ( 275 meshs I think)...


----------



## skyos (Jul 3, 2014)

Hi everybody, i d like to apologize , i make a little mistake because i misunderstood what my friend say....

The result was pretty good : for sure the PMs are everywhere BUT yesterday, my friends say me he can concentrate 75 % of the PM inside 5 kilos and let 25 % in 45 kilogrammes.

I think he could be better but for the beginning is quiet effective. 

Sorry Glondor, and thank you GSP for your pdf....

So, now,it will have a long time for try to concentrate the maximun and after , he will try to melt this....

When i will have more information about this, i will keep you update...

Have a nice day.


----------

