# ph ????



## frosty (Feb 9, 2012)

What should the PH be before you precipitate the gold??????


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## niteliteone (Feb 9, 2012)

Frosty,
Need a little more information.

What type of solution are you talking about?
AR, HCl/Cl, HCl/H2o2 and many more.

Tom C.


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## jeneje (Feb 9, 2012)

Not for sure, but i think it should be above 1 and below 2.5 to drop gold. 
Ken


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## frosty (Feb 9, 2012)

I am using hcI/nitric acid


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## jeneje (Feb 9, 2012)

frosty said:


> forget the first post, I am using hcI/nitric acid


I will try to help here. If you use the search function and search for denox it will give a better answer then i but here goes. To drop your gold you need to remove as much of the HNO3 nitric as you can this is done by Evaporation. Add HCL to your solution 1/3 the volume and heat DO NOT BOIL. As the solution Evaporates down to a syrup add more HCL. When there is no more Brown fumes coming off the HNO3 is gone and you should be able to drop the gold with SMB.

If i am wrong i will be corrected. Hope this helps
Ken

edited,* Do this outside or under a fume hood the vapors are dangerious.*


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## butcher (Feb 9, 2012)

Frosty,

Jeneje, that is good advice. and further reading about evaporation method will help frosty.

You are making aqua regia when you mix these two acids.
When I use this I am not that concerned with pH, it is a very strong combination of acid's. With an ability to dissolve most metals,.

When I use this acid on gold or other very valuable metals to dissolve them, and I wish to be able to precipitate back out a metal from this acid, I am more concerned that I have removed the base metals, oils, trash, from the materials first before I dissolve the gold, these are some of the things that will not let me precipitate my gold back from the solution.

Also I need to eliminate any free nitric from solution, this nitric acid is what oxidizes the gold so that it will form a chloride salt with HCl, this free nitric acid will keep my gold dissolved, so that my chemical reagent will not change gold back to metal and let it precipitate.

I can do this by not using to much nitric when I dissolve the gold (not premixing the acid, using only the amount of nitric needed to get the gold dissolved), and also by eliminating any free nitric acid after my gold is dissolved into solution using the evaporation of solution to remove the more volatile free nitric acid as nitrous oxide fumes, we keep the gold salts acidic and in solution with HCl.

Without this free nitric acid in solution we just have gold chloride salts dissolved in hydrochloric acid, it is still very acidic, and we can now precipitate our gold.


The only time I have even heard of anybody being concerned with pH when precipitating gold was when they were using urea, and they wanted pH> 1, I do not recommend using urea, it adds other trash to your solution, it is almost impossible to tell how much to use and when you have removed free nitric acid, also you can create ammonia in solutions which have the possibility of becoming a very dangerous compounds mixed with gold or other metals in your waste stream, Urea is just too much trouble too dangerous, and not needed in my opinion.


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## 4metals (Feb 9, 2012)

The reality of the situation is you should use as little nitric acid as possible, whereby eliminating the need for the time consuming process of evaporating to syrup to drive off the nitric. 

In production urea is commonly used to react the free nitric acid remaining in solution and eliminate the painstaking process of evaporation. 

Butcher is correct in stating the urea will form ammonia compounds but this is most prevalent in waste treatment when the pH is alkaline to drop the base metals as hydroxides. Then the ammonia can be stripped by aeration. If you treat your waste by cementation on copper, followed by cementation on iron, the iron drops out at an acidic pH and the ammonia is rarely an issue. Still it is in solution and you should add as little as possible to do what you need and no more. 

I think it is time to discuss how urea is used and get all of the opinions aired out all in the spirit of having better informed forum members. To that end, let me say this about urea; 

Urea prills are added to the acid, start slowly and add a small scoop, if there was excessive free nitric the reaction will be noticeable and can double the reaction volume as the solution rises with gas formation and foams up. Wait for the foaming to subside and add a bit more urea. You will notice less and less foaming as you add more urea and finally you will see the prills begin to float to the surface reacting very slowly if at all. That is the sign that the nitric has been consumed and the solution is ready for precipitation. 

I really do not like urea but many refiners use it regularly. Some of the issues are that all of platinum in solution will not be dropped by using ammonium chloride if urea was used and this is true, however the platinum group metals will come down with cementation on copper so it is often a moot point unless you are looking for a lot of platinum in the solution. 

I prefer to use sulfamic acid for neutralizing the excess nitric, it is a stoichiometric relationship to nitric content but in lieu of rather complicated analysis to determine the free nitric content it is a learning curve to determine how much to add. Depending on your dissolving conditions I have been able to make some assumptions of how much nitric remains and add sulfamic accordingly. I have had success with testing for the completeness of the reaction using a few prills of urea and looking for the floaters. 

I know that GSP has used sulfamic to kill off rather large quantities of nitric and liked the way it worked. Perhaps he will comment on his feelings of using it in lieu of urea or evaporation.


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## samuel-a (Feb 9, 2012)

4metals said:


> it is a stoichiometric relationship to nitric content but in lieu of rather complicated analysis to determine the free nitric content it is a learning curve to determine how much to add. Depending on your dissolving conditions I have been able to make some assumptions of how much nitric remains and add sulfamic accordingly.



Isn't ORP meter used in such situation?


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## 4metals (Feb 9, 2012)

Yes ORP is one option but most refiners will not use it. 

I go into refineries who are complaining about red fumes coming out of their scrubbers.

I ask, When did you last calibrate the pH probe? 

Calawho? What's that do, I've got red fumes!

Would you try and explain Oxidation Reduction Potential to them?


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## butcher (Feb 9, 2012)

4metals,
Thank you, for the information it is very good, I do not say urea will not work, I used it when I first began, what I did not like about it, was I used fertilizer grade urea, it did add some impurity's to my solutions. I could really never get the hang of exactly when enough was enough, it seemed temperature of the solution played a big role, in how much the prill would react or fizz, also many times in recovery processes I may neutralize and incinerate my gold powders, and I do not wish to take any chances.

Since my first attempts at recovery and refining I have change my Ideas of how to do things, learning from GSP to use minimum amount of nitric acid needed when dissolving gold, and proper evaporation processes from Harold, and eliminated the trouble-some use of urea, my results showed me these methods worked, and worked well, I had no use for urea but to fertilize my grass, (and maybe a few prills for testing purposes).

Also I try to Help the new-members who thinks he can just dump a bunch of dirty old circuit boards in a bucket, pour in a whole lot of these two acids (or a fertilizer and an acid) making up ma batch aqua regia, then dump in a bunch of urea fertilizer, stir it up and then add sodium metabisulfate till more white salts fall out of solution into the bottom of the bucket, and wonder where the gold is,.

How do I know what there waste buckets will hold? Should I advise them to neutralize the powders with NaOH and roast them? What if the urea could make ammonium compounds in these? 

I do not know.

I just feel better about telling them Urea is not needed, learn to use the nitric acid in better proportions, learn the proper evaporation procedures, forget the urea, and put it on the grass where it was meant to go.

Be sides maybe for testing I see no reason for urea in recovery and refining, urea will make my grass green.

If I do not use too much acid I do not have to waste it in evaporation, (or add fertilizer to try and destroy my expensive, and hard to get nitric acid), the evaporation process for me has become easy, yes it takes time (time I have), and the gold salts are cleaner, precipitation has become easier for me.

I am as thick sculled as an ole mule, it is hard to change my thinking, today this is my thinking, and my opinion, and I am sticking to it, (your gonna need a big, big two by four to get me pointed in another direction on this issue).

Your friend Butcher


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## steyr223 (Feb 9, 2012)

Nice !!!


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## 4metals (Feb 9, 2012)

Butcher,

At the level of refining where I make a living, the material is high grade and turn around is critical. That is why I think like I do. I also do not like urea. But when you're refining 1000 + ounce lots of karat gold you want it in, up, dropped and out ASAP. Things weren't as critical in the $200-300 gold price range but today with refiners advancing to get their work in, they need it to be sold quickly. They advance close to a million dollars a day and work on a fraction of a percent, they can't risk the market dropping. They lock in their delivery for the next day and have to deliver. 

Most of these guys digest in aqua regia and add according to a standard chart ounces on one side and liters of hydrochloric and nitric on the other. They need as complete a digestion as possible in the least amount of time. So obviously a triple evaporation is out of the question. 

Considering thousands of ounces of karat scrap is refined daily using urea, I felt it is something our members need to know. Seeing how the other half lives so to speak. I would prefer all refining be done with as little excess nitric as possible (preferably none but that's been covered) but that involves a technical step up for the average mid sized refiner. 

But no matter how you feel about this we'll pass on the two by four approach!

Just an after-thought but I think urea will turn your grass brown, it's too hot for fertilizer as prills.


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## butcher (Feb 9, 2012)

4metals,
I was all bunkered down for that two by four between and right above the eye's, glad I didn't catch it. 
Many here are going to do their work how they see fit, no matter my opinion.

I do think us discussing this also helps them decide how they may choose to work.

I am just trying to learn the chemistry of some of this, and the thought of some of the possibility’s of mixtures of metal salts and these chemicals can be a little scary, especially if we do not completely understand what we are making sometimes, and my waste stream, get to be a real variable mix of components, and many times the powders from this goes back into my recovery stages, for these reasons I try to keep anything that has come into contact with ammonia, separate (even after acidifying) and also anything that may cause ammonium salts out also, at least until I understand the chemistry better.

Thanks for the good discussion.


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## 4metals (Feb 10, 2012)

> Many here are going to do their work how they see fit, no matter my opinion.



Good point! There are lots of members running karat gold and in their case the urea isn't as big an issue, especially if you take care and don't over do it with the nitric. You process many different components and it is a wise idea to keep your waste "soup" from getting too exotic. When I had a shop and ran all different types of material, I kept stock pots separate for every type of processing done and never mixed the precips until they were dried and incinerated. 

Another point about urea, it is always important to leave room for the solution to rise when reacting. As a minimum never fill a vessel more than half full. I've seen many large tanks of acid foaming up right to the top before the big bubbles form and collapse to drop the level. That's nerve wracking! I always like to keep a hose handy to give a fine spray to those bubbles when they get close to the top. 

Just last week I was refining with an Italian refining machine and the acid was pumped over to their "cementation tank" where the urea and SMB are added. The load was about 60 gallons with rinse water and it took a 5 gallon pail of urea to kill it. To get a jump on the urea addition, they recommend adding a few scoops of urea to the dry tank, as the acid pumps in it reacts quickly with little rise and the subsequent additions do not react as violently. Again, karat gold, fast turn over, and the gold assayed in excess of .9995. This particular plant operates cold with tumbling so I am cutting back the nitric in the formula. I am used to heated reactions with a good heat at the end to drive off a good amount of the excess nitric as the reaction is driven towards completion.


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## frosty (Feb 10, 2012)

Jeneje: Thank you for all the replys, I had already used urea, do I still have to do the evap/ to kill the hno3 ? the soultion is geen and on the bottom of the flask are white crystals what are they???? So should I still do the eavp. ???? as you can see I am new to this. I order from shor on the net. All so what is the best AR to use instead of using Hno3??? I like to do things right. :lol:


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## nickvc (Feb 10, 2012)

For a start dump Shor all you need to know is all here and for free, including where to buy your chemicals at reasonable cost and most processes needed to refine virtually all forms of scrap.
Have you read Hoke? 
If not do so, it details in plain language all the basics of refining although e scraps is omitted as it was written back in the 1930s.
If your not sure what your doing stop and cover your solution, put it some where safe, and do the necessary reading and research, it will save you much frustration and from possible losses of values.
We are here to help but learn as much as possible to give yourself a head start and so you will understand the advice given.


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## Dr. Poe (Feb 10, 2012)

I address this only to the newbies that want an easy answer to dropping gold at the proper pH.
Once the nitric is dispelled, raise the pH to 1.5 if you were working scrap gold or to 3pH if you are working mine concentrates that contain other oxidants like selenium, tellurium, arsenic, or manganese dioxide. The drop from mine concentrates will need to be refined again, but you will get your gold. Use soda ash (Na2CO3) and allow complete digestion after each spoonful or you will go too high. Reagents like SMB (sodium meta-bisulfate) have sodium in their formula and so raise the pH slightly when used. Dr. Poe


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## butcher (Feb 10, 2012)

Frosty,
Follow Nickvc's advice, you can only profit from it. You are not profiting going in the direction you are taking now. 

I will add put a thick bar of copper in that bucket also, I would also not have a lid that would not let gases escape, aqua regia could build pressure if gases cannot escape. Do not store where it could corrode other metal things like tools in your shed.


Dr. Poe is there a chemistry of these oxidants in ore that change by having the pH less acidic, (their oxidation power diminished) or (they chemically change state)?


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## Dr. Poe (Feb 10, 2012)

butcher said:


> Frosty,
> Follow Nickvc's advice, you can only profit from it. You are not profiting going in the direction you are taking now.
> 
> I will add put a thick bar of copper in that bucket also, I would also not have a lid that would not let gases escape, aqua regia could build pressure if gases cannot escape. Do not store where it could corrode other metal things like tools in your shed.
> ...



Yes, their oxidation power is decreased @ pH 3. Since they form similar oxy-acids to the thionates, often only cementation
will recover the gold. Even more strange is that they can hold silver chloride in solution along with gold so oxalic acid should only be used for the final refining. On a positive note, titration is often possible (The precipitation of single elements by slow addition of reducing agents like powdered zinc or copper. Hydrogen works well, but is too dangerous for a newbie. A newbie's best bet is to cement all values, roast the precipitate, then re-refine. Dr. Poe 8)


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## qst42know (Feb 10, 2012)

4metals

I have used sulfamic once but had very little excess nitric. I used it hot and it bubbled some but large bubbles similar to boiling water. 

Do you have the same foaming issues with sulfamic acid when used in quantity?


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## frosty (Feb 10, 2012)

hi all , yes I read hokes book, This is want I did, I got some e gold. then i put it in a flask with hn03 and heated to remove the base metals, then I used urea to neutralize the solutions and filtered and dumped the solution. I than used hcI and did the same thing, then i used smb to drop the gold, but nothing happen??? the solution is green, I know gold is in the solution. 
so what did do wrong.????? Thank you for the replys.


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## Geo (Feb 10, 2012)

frosty, 

normally i would have already posted a reply but i was waiting to see what you were going to say about testing. you did test with stannous chloride to make sure you had gold in solution, right?

what did the test look like? you said you know you have gold in solution so the test must have been a strong positive?

find the formula for making stannous chloride test solution. make some. test your solution. let us know what the results are and then we will be able to help you.


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## steyr223 (Feb 10, 2012)

wow! hu? wait... what did i miss

frosty wrote

" I got some e gold. then i put it in a flask with hn03 and heated to remove the base metals, then I used urea to neutralize the solutions and filtered and dumped the solution. I than used hcI and did the same thing, then i used smb to drop the gold, but nothing happen??? "

i dont see any hci and nitric together or acidl/bleach when u dumped your solution after filtering did you put the hcl into that solution or just by itself

can you nutrralize / denox only nitric? wouldn't that make it not no3?? then when combining with hcl it would not form A/R???

when you say dumped solution what do you mean mind you i am very neww so please forgive me if i really did miss something. :lol:


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## steyr223 (Feb 10, 2012)

hay geo 
i might be reading this wrong but i think in solution to some one new means theres gold flakes in your a/p solution or nitric.

it took me a while to stop saying this that way

unless he tested but i dont belive he did and i would guess your question means you dont either
:roll:


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## Geo (Feb 10, 2012)

steyr223 said:


> hay geo
> i might be reading this wrong but i think in solution to some one new means theres gold flakes in your a/p solution or nitric.
> 
> it took me a while to stop saying this that way
> ...



he tried to dissolve everything in AR and now he has metal solids still in solution wondering how to get the gold out of his solution that isnt in solution because it plated out on un-dissolved base metal. (assumption on my part) but what im trying to pass along is he is assuming he has gold in solution even though he says there was still metal un-dissolved. he didnt test to see if there was gold in solution and now has a big discussion going and wants to know how to get his gold back. when he figures out that the solution is barren then we can help him find his missing gold.


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## Harold_V (Feb 11, 2012)

frosty said:


> hi all , yes I read hokes book, This is want I did, I got some e gold. then i put it in a flask with hn03 and heated to remove the base metals,


Did you inquart? If not, was the gold greater than 10K, which would be marginal at best, for that type of treatment. 



> then I used urea to neutralize the solutions and filtered and dumped the solution.


Blink! Blink!

Can you tell us why you did that?



> I than used hcI and did the same thing,


Same question. Can you tell us why you did that?



> then i used smb to drop the gold, but nothing happen???


What did you expect to happen?

At this point, you have treated the gold improperly in every possible way. 



> the solution is green, I know gold is in the solution.
> so what did do wrong.????? Thank you for the replys.



Can you tell us how you "know" the gold is in solution? Did you test with stannous chloride? If so, what was the result of your test? Can you describe what you witnessed?
When you had finished with your work, did you have any solids remaining? If so, can you describe what you saw?

It is my opinion that you may have gone through Hoke's book, but you learned almost nothing. Please go back to the book and read with the idea of retaining what she teaches. Read it as many times as it takes for you to understand what she's teaching you. You didn't get one thing right.

Harold


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## freechemist (Feb 17, 2012)

Hi 4metals,

Among a lot of other important statements on the use of urea you wrote:

_"I think it is time to discuss how urea is used and get all of the opinions aired out all in the spirit of having better informed forum members."_

I dislike urea, too, especially for destroying/neutralizing excess nitric acid, simply because I think it doesn't do this job. But still, urea has become a valuable tool for me as an easy to handle, precisely weighable source of ammonia, be it for neutralization of excess acid as a base, or to prepare some important PGM-ammine compounds in a simple, well controlled manner. To me, use of urea is an important theme, and so I propose, to discuss it in a new, separate thread.

Regards, freechemist


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## freechemist (Feb 17, 2012)

Hi Dr. Poe,

In your reply you wrote:

_"I address this only to the newbies that want an easy answer to dropping gold at the proper pH.
Once the nitric is dispelled, raise the pH to 1.5 if you were working scrap gold or to 3pH if you are working mine concentrates...."_

Especially for newbies, this is false information, which may mislead them into futile and frustrating neutralization-attempts. It is not necessary to raise the pH-value, in order to precipitate gold with SMB. In my own lab- and production-practice this functioned always well, without exception, with solutions containing an average of 50-60 grams of free HCl (about 1.5 moles) per liter, which corresponds theoretically to a negative pH-value, that
means, a value below 0.

Regards, freechemist


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## Harold_V (Feb 17, 2012)

freechemist said:


> Hi Dr. Poe,
> 
> In your reply you wrote:
> 
> ...


I'm afraid I have to agree. In all of my years of refining, I don't recall ever having to adjust pH before precipitating gold, and I know my solutions always had a serious excess of HCl, so much so that, on some occasions, I'd experience filter failure. I don't recall even one instance of experiencing any difficulties in achieving a complete recovery of values. 

Harold


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## 4metals (Feb 17, 2012)

I have never adjusted pH before adding urea. In fact the only time I've measured pH of the solution was after the gold was dropped and the barren solution was treated for precipitation of base metals as hydroxides. 

Even at this stage of the game the pH starts out at a reading of zero before caustic additions begin.


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## 4metals (Feb 17, 2012)

At the request of Freechemist, I have started a thread on the use of urea in the Chemicals
section.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=48&t=13102


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## butcher (Feb 17, 2012)

I was under the impression that adding urea raised the pH in the reaction with aqua regia, 
(I never measured the pH, or tried it so I cannot say for sure this happens).

some how I posted this by mistake (double post),on the new topic 4 metals started, on the subject of useing urea.


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## samuel-a (Feb 17, 2012)

butcher said:


> I was under the impression that adding urea raised the pH in the reaction with aqua regia,
> (I never measured the pH, or tried it so I cannot say for sure this happens).
> 
> some how I posted this by mistake (double post),on the new topic 4 metals started, on the subject of useing urea.




Urea combat the nitric by producing urea nitrate, which is oddly enough an ionic bonded compound and is electrically stable (neutralized) much like any other salt.
I won't even try and pretend i understand in full the chemisty behind this reaction, this info is out of Wiki and this is my understanding of it.

Were you to have only nitric acid solution, obviously, pH will shift up upon adding Urea, but AR, in most cases contain excess of HCl. As long as the free HCl is maintined above 1M, the pH of AR will not budge from zero.

-------

I too never adjust pH for gold precipitation, i guess now the good Dr. will send us all back to the classroom...


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## Skip55 (Feb 18, 2012)

Im new to leaching,but I believe I have a good leach.After leaching,I poured off the liquid and I didnt change the PH I used a small amount of zinc and dropped all the other metals.I cut off thin zinc foil with a sissors into the leach and let it sit a short while to separate. Then I poured off the cleared solution that was left from the dropped pgms, silver, and then brought the ph to as close to 7 ph as possible and dropped the gold separately. (added zinc also.) The gold dropped out quickly. Was very simple and was quick to drop.I have not seen the leach I used published anywhere,and it worked on ore that had gold silver,copper produced a green color in the leach.Some of the leach tests on other ore I had was brown with less acid but I found that more acid was needed,wasnt strong enough on cons that were course ground,can see a little gold in my microscope.It well take practice to know how much acid on cons.Skip


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## Harold_V (Feb 18, 2012)

Skip,
I'm having more than a little trouble with the idea that you managed to precipitate silver with zinc, all the while leaving gold in solution. 

Are you positive that was the results you achieved?

If so, perhaps someone can explain why it worked as you suggested.

Harold


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