My solution is solid mass of crystals

Hello,

I need a little expert knowledge as to what I have done wrong. First off I am dissolving gold from older circuit boards, I used an aqua regina consisting of muratic acid and sodium nitrate. After all the metal dissolved I used a urea nitrogen to neutralize the acids. My next step is to follow Hoke's step of evaporating out the solution and then boil with muratic acid. Then use metasulfite to drop the gold.

Here is the problem while trying to get the solution into a syrupy form I ended up with a very large block of crystallized salts, (blueish green in color). I have searched this forum but do not find where anyone else has had this issue. I am 100% positive that I have gold in the solution or crystals at this point. My question is how do I dissolve these crystals and get back to a liquid form to drop the gold?

This is just my guess,

Blue is possibly copper sulfate, green possibly copper chloride,if silver it would also form sulfates and chlorides, this could be a mix of many metal chloride and sulfate salts, it does not sound like you removed base metals before trying to dissolve the gold, and I suspect you will have tin in this mix a bad combination to have when you have gold in solution.

I think I would add some acid and get it back up into solution filter if you can (if you have trouble filtering then suspect gold and tin formed the dreaded gold colloidal solution) and cement values from on copper, you may have powders that will not dissolve into acid (silver sulfate, possible un-dissolved gold or precipitated gold lead chlorides and so on, the lead chloride is soluble in boiling hot water, the other powders can be added to anything in your filter, and if you did have tin and formed a gold colloidal solution then evaporate it to almost dry rinse in NaOH till neutral pH, rinse out salts with hot water, dry and incinerate, boil in HCl add just a tiny amount of water and decant base metal solution from settled powders, repeat this and hot water rinses till solution has removed as much base metals as possible (dark brown or green solution indicates copper still being removed from solution. this should help to remove tin and other troubles from the gold (or silver chloride) powders.

I think you should also spend a little more time removing base metals from your materials, also look into separating material as much as possible before any acid treatment, removing certain parts cleaning them of solder even before trying to dissolve the copper, removing base metals before dissolving your gold.

A little more time with those books (Hoke's) and reading the forum is always helpful.

Sjeepboy said:

Hello,

I need a little expert knowledge as to what I have done wrong. First off I am dissolving gold from older circuit boards, I used an aqua regina consisting of muratic acid and sodium nitrate. After all the metal dissolved I used a urea nitrogen to neutralize the acids. My next step is to follow Hoke's step of evaporating out the solution and then boil with muratic acid. Then use metasulfite to drop the gold.

Here is the problem while trying to get the solution into a syrupy form I ended up with a very large block of crystallized salts, (blueish green in color). I have searched this forum but do not find where anyone else has had this issue. I am 100% positive that I have gold in the solution or crystals at this point. My question is how do I dissolve these crystals and get back to a liquid form to drop the gold?

Click to expand...

First, did you depoplate the boards or put them in whole? Second did you remove all the base metals first with HNO3? Third why did you use Urea and evaporate the solution down to a syrup. Forth when evaporating AR you should not BOIL boiling will cause loss of values. The blueish green crystals i think is copper. If i'm wrong i will be corrected.
Ken

add some hcl and warm gently to rehydrate the crystals and test with stannous chloride.

I am just starting out and was trying to work with the directions from Shor International subzero package originally. That is why I was using urea. I have a heap of old HP products from the 50's - 70's and this was basically the pin connecters and various other external parts. This is my first batch prior to this forum or reading Hoke. There are probably countless mistakes made, however I want to make adjustments now prior to doing more recovery.

To answer some of the questions I did not dissolve the base metals entirely. I dropped everything directly into my AR solution. I also disposed of the leftover metals out of ignorance. However I did not introduce urea until after I filtered out the solution, so I hope that much gold cemented onto the remaining metals.

Obviously gold refining is much more in depth than the 2 page directions from Shor.

My solution is very green, when in liquid form it almost appears black.

I have not placed any of the boards into AR. Basically what I have used are the items from depopulating the boards. These are older boards and have lots of gold bearring items on the top of them.

After reading Hoke this last week I will definitely change my process. However I do want to try and salvage this batch.

Thank you for your posts and advice.

too bad, sorry to hear about that. im afraid you may not have any gold left to work with. when you dissolve mixed metals (gold and base metals together) in AR the electromotive series comes into play. i wont try to explain as it would take too long. study the electromotive series of metals to understand why you have no gold in solution.

from answers.com

electromotive series, list of metals whose order indicates the relative tendency to be oxidized, or to give up electrons (see oxidation and reduction); the list also includes the gas hydrogen. The electromotive series begins with the metal most easily oxidized, i.e., the metal with the greatest electron-donating tendency, and ends with the metal least easily oxidized. The tendency to be oxidized is not an absolute quantity; it can only be compared with the tendency of some other substance to be oxidized. In practice, the tendency to be oxidized, called the oxidation potential and expressed in volts, is measured relative to a standard hydrogen electrode, which is arbitrarily assigned an oxidation potential of zero. The oxidation potential measures the tendency of the half reaction M → M+n + ne− to occur, in which some metal M loses n electrons, e−, and acquires a positive charge of +n. The more positive the oxidation potential, the more readily oxidation takes place. The electromotive series is thus a list of the metals in the order of their tendency to undergo the half reaction. The series is also called the replacement series, since it indicates which metals replace, or are replaced by, other metals (or hydrogen) in compounds. In general, a metal will replace any other metal lower in the series and will be replaced by any metal higher in the series. The order of some common metals in the electromotive series, starting with the most easily oxidized, is: lithium, potassium, calcium, sodium, magnesium, aluminum, zinc, chromium, iron, cobalt, nickel, lead, hydrogen, copper, mercury, silver, platinum, and gold. A list arranged according to oxidation potential and including not only metals but also all other elements and ions is called the electrochemical series.

Read more: http://www.answers.com/topic/electromotive-series#ixzz23FTXi4tx

Quick question, when I add ammonia to some of the crystals, they instantly dissolve and I get a cloudy blue solution. Is there anything to this, can I percipitate gold from this blue solution. Just confused, I hate to just throw out the whole batch and start over.

Don't throw anything away. Redissolve the crystals, then read Hoke and treat as you would a stock pot.

sjeepboy,

If I were in your position, I would stay away from ammonia.

First, follow Geo's advice and add hot water to re-dissolve crystals. It may be necessary to add small amounts of hydrochloric acid, but not too much.

Once crystals dissolve, filter to remove any residue, save the filter as it may contain precious metals.

Check the solution for precious metals using stannous chloride. If positive for precious metals, the easiest way to recover them is by cementing out with a piece of copper inserted into the solution. However, this will generate of residue of mixed precious metals which will need to be refined and separated further.

The filter may contain precious metals, so incinerate the filter and residue then start again to recover precious metals values.

I believe Geo said to add HCL and not water to rehydrate the crystals. 8)

You are correct, Geo did say to add HCl.

I would probably stay away from concentrated HCl and add hot water first then add small amounts of HCl to keep the solution acidified.

My guess is all the crystals are mostly sodium nitrate with some base metal hydroxides. Hot water should dissolve the sodium nitrate and the small amounts of HCl will help dissolve the base metal hydroxides.

Thanks for the advice, I will give it a shot over the next couple of days.