[cruzbye]

Hello, I work for an electronic firm (Semiconductor) in search of some information. We are ISO 14000 certified (an Environmental Waste Reduction Participant). We strip gold in a solution called Aqua Regia (HCL and Nitric Acid) Yes this is the very same chemical people in the forum is searching for. I have several questions from bloggs I have read on this site.

1) We strip Gold in a chemical called Aqua Regia because I tried Potassium Iodide/Iodine solution and the crystals are very expensive for the yield of gold stripped. The problem with Aqua Regia is that it is hazardous waste and shipping is very expensive. We tried storing the chemical in a poly (Plastic) Bottle which degrades after about 1 year caused by the Nitric Acid. Nitric comes in glass bottles for that very reason. Is there another container other than glass or Teflon that Nitric can safely be stored in? The exothermic reaction is completed because we use the chemical for 6 months continuously stripping gold, so I should not have to worry about pressure build up.

2) I have read several bloggs about plating gold out of the chemical, by dilution with water and using an iron rod and a gold rod, and as the iron dissolves into solution the gold attaches to the gold rod. Is this true, no external power source is needed? How do I know when the gold has completed its plating? How long does it take to complete the plating?

3) Getting rid of the acid is easy for us because we have an (AWN) Acid Waste neutralizer to neutralize the acid before sending to city waste, but are there an issues with iron going down the drain to city?

Hope someone can help?

[Borek]

We strip Gold in a chemical called Aqua Regia because I tried Potassium Iodide/Iodine solution and the crystals are very expensive for the yield of gold stripped.

Au can be dissolved in cyanides solution without other oxidant than air oxygen. Sorry, no idea about the reaction speed/reagent cost. Also replacing concentrated acids with cyanides solution can be not a wise idea - but that's a possibility.

using an iron rod and a gold rod, and as the iron dissolves into solution the gold attaches to the gold rod. Is this true, no external power source is needed?

Iron dissolution provides energy needed. However, if your solution is acidic (sure it is, you have used excess aqua regia) it will dissolve iron. This can make whole process hard to controll, but I am just wild guessing here.

Getting rid of the acid is easy for us because we have an (AWN) Acid Waste neutralizer to neutralize the acid before sending to city waste, but are there an issues with iron going down the drain to city?

Amount of iron dissolved when recovering gold won't be high - about 1g of iron per 4 grams of Au (not including iron dissolved by acids). However, when you start to neutralize acids you rise pH of the solution - and Fe(OH)₃ will precipitate. Depending on the way AWN operates it can be - or can be not - a problem.

[cruzbye]

The pH of the acid is less than 1, very acidic, what is the recomendation of the pH to plate gold out of solution?

Is there a wire connected from the Iron Rod to the Gold Rod?

Can the process be accelerated with a battery?

If a battery or power source is used does the chemical need to be diluted?

Thank you all for your *delete me*!

[Borek]

Is there a wire connected from the Iron Rod to the Gold Rod?

That's the only place where the answer is easy: YES!

No idea about pH details, although I would try to rise it to slow down iron dissolution in acid, at the same time not going high enough to start precipitation. As for battery - it will be necessary if the other electrode is not iron. Google for gold electroplating, although you will be probably presented mostly with cyanide solutions.

Selection of correct parameters for plating can be difficult, but these things were done before and I am sure they can be found in literature; sorry I can't be of more help here.