denmark1982 said:
Topher_osAUrus"
said:
How many fingers? about 1 pound ( dont how much in gold foils in gram)
How much nitric?
1 part(coffe cup) nitric acid 53 % and hydrochloric acid 35% 3 parts ( those at coffe cups i mean)
How much smb? i used about 3 teaspoon
All details that are needed before any good responses can be given.
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If I understand the above right you used 1 (coffee cup) of 53% nitric along with 3 (coffee cups) of 35% HCl to dissolve the metal from 1 pound of fingers - meaning you put the whole fingers in the AR (nitric plus HCl) & not just foils that had been removed/recovered from the finger
In ether case (whole fingers - or just gold foils) you used
WAY to much nitric & I do mean WAY to much nitric :!:
The result is that you still have
a LOT of "free nitric" in your solution
Free nitric means nitric that has not been used up dissolving metal - which means the nitric (that is not used up & therefore still free) has the power to keep dissolving metal
The result of this is that when you go to drop (or precipitate) you gold - it will not do so - because the free nitric keeps the gold dissolved thereby preventing it from dropping out of solution
Therefore - in order to get your gold to drop --- you MUST get rid of (use up) the free nitric BEFORE trying to drop the gold
If there is just a "little" bit of free nitric - when you try to drop the gold - it "may" precipitate - at first - but then the gold will start dissolving again because of the "little" bit of free nitric
If you have a LOT of free nitric (as in your case) it simply will NOT drop -
at all - because there is so much free nitric that the SMB does not have the power to overcome the "large" amount of free nitric keeping the gold dissolved
Therefore - to get your gold to drop - you have to get rid of &/or use up the free nitric FIRST (we refer to getting rid of the free nitric as de-noxing)
There are a number of different ways to get rid of the free nitric - with out going into a lot of detail the different ways are ---
1) an evaporation method - this is best used if you only have a "little" bit of free nitric
2) de-noxing with chemicals like sulfamic acid (preferred) or urea (not preferred) - how much chemical you need to de-nox depends on how much free nitric you have --- so though you can do it this way if you have a lot of free nitric it will result in increasing the amount of chemical waste you create --- so again this method works best if you only have a little bit of free nitric
3) or you can dissolve more metal to use up the free nitric - you could dissolve more gold - or more copper - or even some other metal like iron or zinc - this is the method I would use
First you need to understand how acids work at dissolving metals --- when dissolving gold with AR it takes "
about" 1 ml of 70% nitric to dissolve 1 gram of gold ( I say about - because depending on conditions - it may take less - or it may take more) --- BUT it will take "about" 4 ml of 70% nitric to dissolve 1 gram of base metals
In other words - using 70% nitric --- it takes "about" 4 times more nitric to dissolve 1 gram of base metals then it takes to dissolve 1 gram of gold
Now then - I know that the nitric you used was 53% --- I am not going to take the time to do the math to figure out how much metal 1 ml of 53% will dissolve - in stead I am going to use the 70% nitric as an "example" to explain this
So using 70% nitric as the example - IF - your coffee cup is the same size as a "measuring" cup we use here in the U.S.A. that would be 236.58 ml of 70% nitric (used in your AR) that is enough to dissolve "about" (more or less depending on conditions) 236.5 grams of gold --- so you could use up the free nitric by dissolving that much more gold --- but that is a LOT of gold
However - because it takes about 4 time more acid (nitric) to dissolve the same amount of base metal - that means you can use about 4 times less base metal to use up the free nitric - copper is the best base metal to us in this case
That means you only need "about" 59 grams of copper to us up the nitric
BUT - here is the added benefit to using copper to use up the free nitric --- copper is more reactive to the acid then gold - therefor the acid likes to dissolve the copper more then it likes to dissolve the gold - BUT - because you already have gold dissolved in the acid - when the free nitric is used up dissolving the copper - the nitric that was already used to dissolve the gold is also going to work at trying to dissolve more copper & the reason for that is that the copper is more reactive to the acid then the gold --- so - the result is that as the nitric that originally got used to dissolve gold & is now trying to dissolve copper - causes the gold to be forced out of the solution as the "extra" copper goes into solution
We call this "cementing" your gold out of solution by using a "more" reactive metal to "displace" the less reactive back out of the solution
In other words it is a metal ion "exchange" that takes place with the more reactive metal going into solution - which in turn "forces" the less reactive metal "back out" of solution
It is based on the reactive series of metals which you will find here :arrow: https://en.wikipedia.org/wiki/Reactivity_series
How it works is that more reactive metals will cause less reactive metals to be forced out of solution - even though ALL the acid was used up to dissolve the original less reactive metal
In other words - say you have 10 grams of gold dissolved in AR - AND - there is NO acid left to dissolve more gold because ALL the acid has been used dissolving gold --- if you put copper in the solution - the copper will start replacing the gold - thereby forcing the gold out --- then when all the gold has been forced out - & the solution is now loaded with copper (instead of gold) you can then put iron in the solution & the iron will go into solution - & force the copper back out
So - you can use a piece of copper to not only use up the free nitric - BUT - also to "cement" any gold in solution back out of solution --- you want to use a heavy piece of copper like a piece of copper pipe rather then using tine copper like copper wire - & you want to be sure the copper is fully submerged in the solution with no copper sticking out of the top of the solution
the other option would be to dissolve more gold plated items like gold plated pins so that the base metals help to use up the free nitric plus adding the extra gold to your recovery
Kurt