help required with aqua regia

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Anonymous

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i had 22lbs(10kgs) of mixed sd-ram stock.i used 6ltrs of aqua regia(4.8 ltrs 37% HCl and 1.2 ltrs C.P. HNO3) to dissolve the various metals and gold.i kept it overnight and the next morning i diluted the aqua regia solution to 10 ltrs and then i used approximately 80-100 gms urea to nuetralize the nitric acid at room temperature till there was no visible fizzing.then i filtered the solution to remove the undissolved impurities with a filter bag.then i used approximately 80-90 gms of SMB in aqua regia(sodium metabisulfite)to drop the gold (i used more SMB bec i cud see fizzing on immersing the SMB in the aqua regia solution).
i kept it fr a night and the next mworning i filtered it using a vacuum filter and a filter cloth.but the yield was quite low.it was 1/10 of the expected/calculated value .
what possible mistakes cud have occured ? can anyone help me out with this.
 
Sounds like you used way too much solution. Always remove your fingers and process them serperatley from the rest of the ram stick. That way you do not have to deal with the possible lead and other contaminents. When you add your urea it would be a good idea to warm up your solution it will remove the nitric easier. Even when you see no reaction from adding the urea it might help to add a little more to make sure there is definetly no nitric left. Did you test your solution with stannous after you used your SMB to see if you still have gold in your solution?
 
thanks mate,

well the ram had gold plated on it on its fingers n also on the other remaining portion.so i wud hav lost a ceratin quantity of gold if i were to jus trim the fingers off the ram.my basic calculation for aqua regia was based on assuming 20% of the ram weight to be it s metallic content weight (which is still a lot) n hence for 10 kgs of ram i hav 2kgs of metal content which accordin to certain blogs n threads require 6ltrs to 8ltrs of aqua regia.n i checked the filtrate fr gold by stannous chloride test n it did giv a positive output stating the prsence of gold.i tried dissolving urea in warm water n then nuetralizing it but it wudnt help me much.can u help me out with the nuetralization part.i guess tats where i m messing it all up
 
That is understood. If you want to run he whole board in solution here is my suggestion. Remove the chips from the board. Soak the baord in hot HCL to remove the solder. Remove the boards from the solution and wash them in water to remove any residue of lead or other contaminent. Then run them in AP or you can use AR with the calculation on the yield return's found on the forum posted bt Steve and other's. Him and Catfish have a good thread on this on the forum. Use the required amount of chemical's according to those yields with a little less nitric that what is required. After that is accomplished the boards need to be incinerated and run thru a ball mill and crushed up to a fine powder. At that point you can either take the powder and put into a crucible with the desired mix of flux and heated till the metals coagulate and then cornflake the metal and run in AR. Filter the solution and test for PM content. If you have PM in solution drop with SMB or copperas. Let the solution settle for 24hrs and siphon off the solution and your gold will be in the bottom of your container. Then follow the prescribed washing procedure as described on the forum and then reprocess you gold for a 2nd time. Be sure and check your filter and if you have any residue process it for possible PM's.
 
thanks fr ur advice.it s rly helpful
but out of curiosity i want to know the best method for nuetralization of nitric acid.
there is the vaporize ..add HCl ..vaporize..HCl till syrupy method and another alternate wud b adding dissolved urea in warm water
if u can help me out with the urea nuetralization part bec a lot of my stock solution is in aqua regia and i hav to recover gold from this stock.
and since i hav used nitric in excess i need to tackle this problem.
also if u cud guide me with the proper usage of hydrazine hydrate fr pptn of gold from aqua regia
thanking u
sohail gupta
 
You have one option of using a base like soda ash and raising the PH and dropping everything out. Or you can take some copper plate or pipe and put it in the solution and let the copper cement out the PM's and then reprocess what settles. I would use the copper myself. You might consider adding some more urea to your solution. How much solution do you have that you are working with?
 
well as of now i have around 10 ltrs of solution.i did not discard my filtrate.and i have recovered 1 gm of gold already.but since the stannous chloride test is positive fr gold i wud like to recover the rest of it properly.i did consider of adding more urea but it wud not show any fizzing.and when i added SMB to it there was no visible precipitation (but there was fizzing on addition of SMB).so i took a small batch out of it( 500ml) and i added hydrazine hydrate(12ml) to it to c a blackish powder ppt. i added HCl to c if the powder wud dissolve in it but it did not.
i m still unsure abt the nuetralization part.
 
sohailsgupta said:
well as of now i have around 10 ltrs of solution.i did not discard my filtrate.and i have recovered 1 gm of gold already.but since the stannous chloride test is positive fr gold i wud like to recover the rest of it properly.i did consider of adding more urea but it wud not show any fizzing.and when i added SMB to it there was no visible precipitation (but there was fizzing on addition of SMB).so i took a small batch out of it( 500ml) and i added hydrazine hydrate(12ml) to it to c a blackish powder ppt. i added HCl to c if the powder wud dissolve in it but it did not.
i m still unsure abt the nuetralization part.
Click to expand...

If you have 10 liters I would warm up the solution and add 100g of urea and let it set for a little bit after stirring, take you a 5-10 ml sample and put it on a plate and add a few specks of SMB and see if the gold drops. If it does andthen redissolves add you another 50g of urea and then repeat till the gold that drops on the plate does not redissolve and then add another 100g of urea let it set and then use your SMB on your 10 liters of solution.
 

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