Pins With Nitric Acid

[Tzoax]

Considering this is my first post on this wonderful website, I would like to express my admiring and support to everyone here who is giving their part in making this knowledge base bigger and better. I am from Belgrade, Serbia and i started this hobby several years ago. So far, I've collected only gold foils from fingers using nitric method, this is my first time I tried with pins. So, here is what i did and what my problem is...

First I've collected 100 grams of all kind of gold plated computer pins, I cut every single pin with cutting nippers to remove the part that is not gold plated, so I ended with 100 grams of pure gold plated pins. You can see every step in pictures below.After diluted nitric and filtering I got 7.0 grams on yellowish dust, I repeated process with diluted nitric again and got 2.8 grams of grayish dust with visible gold flakes.

I know that i shouldn't use nitric method with pins because of tin inside the metal base, but I just made this experiment to see what I will get. I found that incinerating and boiling in HCl will remove the tin so I could use AR process normally. But, I am not sure that it is only and best solution for this. So, the question is:
1. What exactly (most probably) i have in this 2.8 grams of dust?
2. What is the best method to use at this point?
3. What would happened if i put this dust directly in Aqua Regia?

 

[butcher]

Tzoax,
From what you posted it looks like you removed the solder (where most of the tin would have been found).

Using nitric acid to remove base metals works very well, even for pins, if you remove the solder, and the pins are not made with an alloy of tin like some of the bronze (copper tin alloys) metals.

Now there could have been some tin from some kinds of base metals as an alloy of the metal like bronze, or they could have been just copper or some ferrous (iron alloy) Kovar, depending on the base metal used to make the pins, they may or may not have had tin involved.

This is where it is very helpful determining what your pins, or other scrap are made of, testing and separating them mechanically, or separating the different types of materials, can help in determining what process may work best for the materials you plan to work with.

A good indication if your material had much tin involved can be determined by how well the solution filtered, when you filtered it, if it just sat there forever it most likely was because of tin, if it filtered fairly easily you most likely did not have much tin involved the alloy of the base metal used in the pins.

Either way, tin or not, at this point incineration, and washing with HCl, can not hurt, and can only help to improve your material for further processing of your material, and can just be beneficial to help improve the material to later processing methods.


Besides aqua regia there are other chemicals you can use to further refine the fine gold powder, like using HCl/NaClO (sodium hypochlorite, bleach), or HCl/Concentrated H2O2. these in many cases can be easier to work with than aqua regia especially if you are not used to working with aqua regia, or understand the process well.

Keep us posted on your progress, with the pictures and this discussion.

 

[Tzoax]

Butcher, thank You for reply. Yes, I removed all solder parts, further more, I cut only gold plated parts to make sure that I got a best material for further treatment. I used pins from hard disk drives, optical drives, modems, IDE pins from motherboards, and some gold plated pins from cellphones and laptops. The basic idea was to see how much gold and optionally other nobel metals would I get by this method with exactly 100.00 grams so I could know some average yields for future processes. The 2.8 grams that I got is non-magnetic (I used neodymium magnet (there was only two thin iron wires that I removed with magnet, one of those could be seen on the last picture that i posted)), so I assume that the problem is the tin. I will try to incinerate the dust, then boil in HCl, then aqua regia, I will post pictures of every step that I take. Since this is a small amount of dust I will try incineration with my heat-gun, maximum heat is 450 degrees Celsius, I was just wondering is it possible and did somebody try to incinerate with a heat gun?
Thank You all very much and thank You again Butcher for helping me.

 

[butcher]

I would try to get the temperature higher, getting the powders to red hot, in air or oxygen to oxidize tin and base metals, and burn off carbonous materials, this can be done with several methods, like over a fire, like with charcoal or wood, if you do not have another method to produce the heat needed.

The heat gun probably will not be worth trying.

A torch, propane stove, electric hot plate...

Eventually you will want to melt the powders back to gold, you can use this heat source for incineration.

 

[Tzoax]

Thanks Butcher, I used electric hot plate to incinerate. After incinerating 2.8 grams of material, I ended with 1.7 grams of material, here are some pictures.
Next, I will boil in HCl and I will post the results.

 

[butcher]

Try to find one of these Corning Pyro Ceram dishes, or the amber Vision ware skillets (dish), they can come in handy in the lab, tough enough to incinerate powders in, and you can do the acid washes after cooling it down, you can even do most of the rest of the refining in that dish (the less you transfer the powders the less gold you leave behind).

It looks like you may have used aluminum foil, hard for me to tell from the picture, you could use stainless steel to do the incineration of the gold powders, but I would not use other metals to incinerate the gold powders in, (aluminum can give us trouble in refining), aluminum foil at the temperatures I incinerate at would not hold up well at all, As when I incinerate on a hotplate, even with the hot plate on high heat I would be running my torch over the top of the powders, the Corning dish ( or vision ware dish can handle the heat) as I heat the powders till they glow red hot, the dish adds no contaminates to my powders, and I can proceed to the further steps of a process in the dish as it is acid resistant and can act as a lab dish (like lab glass ware) to do the acid work in.

Note if you do use stainless steel, do not use your acids in stainless steel, they are corrosion resistant not acid proof, the will dissolve.
I do not use stainless for heating metal that can have salts like chlorides involved, that can also attack the iron in the stainless steel, especially at high heat.

keep studying the forum, it is full of useful information, and some really great tips of the trade.

 

[Tzoax]

Thanks for the tips Butcher, next time I will be well prepared for this. Yes i used aluminum foil. Wright now I am boiling the 1.7g of dust in HCl. Here is the picture. I noticed the gray sedimentation at the bottom of the dish, do I have to boil until the gray stuff disappear or that gray substance could be gold or some other precious metal. I mean, how could I know when to stop boiling, is there any indicator?

 

[butcher]

If you only use HCl, it will not react to dissolve your gold, but it will dissolve many of the base metals making them soluble chlorides, you do not have to heat the acid for very long, if the solution is strongly colored (usually from copper) you may need to do a couple of washes.

I will normally bring solution up to a boil and turn down the heat, giving plenty of time for all of the insoluble gold powders to settle, decanting the soluble base metal solution while still warm (more metals are soluble in the warm solutions).
If the solution is strongly colored I will repeat this process again with fresh acid and a little water.

The boiling water washes that follow I will also decant hot, after the gold has time to settle, where lead chlorides are much more soluble (lead chloride is not soluble in the cold water, but is pretty soluble in boiling hot water, so here cooling the soluble lead chloride will crystallize back out as clear to whitish needle like crystal salts of lead chlorides.

Even though you are most like not dealing with silver here. I thought I would add this, as it may be helpful at a later date:
Some metal chlorides like the white fluffy insoluble silver chloride powders need longer time to settle in solution as the fluffy cottage cheese seems to want to float around in solution longer than many of the other insoluble powders.
Silver chloride and lead chloride can be separated using boiling hot water, where lead chloride become much more soluble and silver chloride stays insoluble, giving time for the silver powders to settle before decanting the clear lead chloride water solution, the lead chloride after decanting if cooled will again form the insoluble lead chloride crystals

The yellow color rusty looking color of your powders in the filter above, and this yellow color in HCl make me think you have iron mixed with these gold powders, the colors of solutions can be indicators of what may be in solution, but testing the solutions is the only way to know for sure.

Tin as a chloride is clear and gives no real color to the HCl solution.
Aluminum can look milky and or form a gelatinous hydroxide.

Iron chlorides can be soluble in several forms, they can color solutions green yellow or brown, depending on state of oxidations and conditions of solutions, if boiled for a prolonged time can form an insoluble red powder of iron oxides (rust) which is not too much of a problem because it is pretty hard to dissolve even in the acids you dissolve gold in. Iron in solution can resemble gold in solution sometimes difficult to tell the difference from color or looks alone, here is where testing of solutions can solve the mystery (see Hokes book check out page 100).

If you haven’t read Hokes book you will be wandering in the dark trying to learn this art, her book will open your eyes.

Doing the experiments listed in Hoke’s book will help you tremendously to understand many of the points we discuss here.

 

[Tzoax]

I boiled the 2.7 grams of material three times in HCl and decanted after material settled, decanted liquid is on the first image. Then I boiled three times with destilled water, decanted it and filtered it. The final product so far is weighted 0.5 grams. The second image is material in filter still wet, the third image is material in filter dried out. I noticed the gray-white material beside golden foils, the color of that material was gray when it was wet, and silver-white when it was dried out. The fourth and fifth image is the same material, I made a dust of it and stretched it for better view. Sorry if I made a couple of grammar mistakes, my english is not quite well.

Can You suppose what gray-white material is?
What would be the best step for now on? Do I have to repeat HCl boiling or I can continue with aqua regia? (I have everything-urea, SMB, HCl, HNO3)
What is the average yields of pure gold of the same gold plated pins (only gold plated parts, no solder) that I used per 100 grams in Your experience and in Your opinion?

I have Hoke's book, I started to read and learn one month ago, I will study it very closely, thank You Butcher. I think I have some basic knowledge, but there is a still a lot to learn and to practice.

 

[butcher]

Spend a little time understanding how to use aqua regia, using a little excess HCl and limiting the nitric acid to only the amount needed (no more) by adding it in small amounts, using heat and giving time for the nitric to react and oxidize the gold and be consumed in the reaction, so that after gold is in solution you have little, or no free nitric acid to give you troubles with precipitation by re-oxidizing the gold as you try to reduce it.

It takes approximately 3.8ml HCl and 0.95ml HNO3 to dissolve a gram of gold.

You can add the amount of HCl calculated for the amount of gold you plan to dissolve, (excess HCl is not a problem), heat the solution, measure out the figured amount of nitric acid needed in another container, and add it in small quantities to react with the gold, giving it time to react, observing the reaction between additions, so as not to add more nitric than needed, you may not need all of the measure HNO3 to get the gold dissolved.

There are several methods to remove excess nitric acid if you happen to overuse nitric in your reaction.
Urea, being the worst of these methods to choose from,(in my opinion), potentially dangerous, and problem causing in certain situations.

Limit the amount of nitric used to consume it. (GSP's trick).
Use a gold button to consume free nitric acid. (Harold's trick).
Leaving some gold undissolved. ( a form of the above method)
Three-evaporation method. (Procedure found in Hoke's book).
Sulfamic acid to remove free nitric acid.

I like to use combinations of these methods.

How aqua regia is used can be a big problem, along with de-NOxing of the solution prior to precipitation of gold, this is where most people have problems, a little education can save you a lot of those problems, your gold will not run away while you take some time to study.

 

[Tzoax]

Thank You Butcher, i will do that, I will study a Hoke's book more and I will come back here to finish this process, just tell me please do I have to process all of this material (including gray/white dust) with aqua regia or I have to get back to HCl boil? I boiled it three times until the liquid was clear, what do You advice?

 

[butcher]

At this point I am not sure what the gray or white dust may be.
I would most likely follow through with the process, at this point and see what happens.

Maybe another member has a clue.

 

[Tzoax]

First I made a stannous chloride by heating 0.3 grams of solder tin and 5 grams of HCl until dissolved (picture 1).
I put 0.5 of material in container, then I mixed it with 4 grams of HCl, then heated up and added 3 drops of HNO3 at a time, I added total 9 drops of NHO3.
Then I added little urea at a time until urea stopped dissolving. I washed container and filtered yellow liquid, and tested with stannous chloride, the test is positive for gold (picture 2). The yellow liquid is on the picture no. 3. Again, in the filter was a gray/white dust (about 0.25 grams), it is shown on picture 4 and 5. Does anybody know what it might be?

 

[Tzoax]

Anyway, after that I mixed 6.5 grams of SMB and 24 ml of destilled water and slowly poured in the AuCl3 solution. The stannous cholide test was now negative for gold. The yellow liquid instantly changed color from yellow to cloudy white, here is the picture. I expected a brown/black color, i assume the white color is because there is so little gold, does anybody know is this true or there is some other reason for this white color?
At the bottom of dish is forming a really fine dust, I will wait 24 hours and see what will happen. I am just curious about this white color, why isn't it black?

 

[lazersteve]

There are a few ways to identify your unknown powder.

The best would be to XRF the powder. Some universities, local gold buyers, or scrap yards will do this for you for free.

Steve

 

[Tzoax]

Thank You Lazersteve, I will collect all remaining materials like this in a jar and when I collect larger amount I will mix it and send to analyse. I found a firm near me that do exactly that - they have EDX880 Universal Precious Metals Analyser, one test costs 10 euros, here is the link of that firm http://www.plemmet.com
When i analyse it I will post results here.
The gold dust settled at the bottom, I will decant it and let it dry out. I have one question - when the golden dust dries out, what is the best way to remove it from the glass, I guess the dust will be sticked to the glass.

 

[necromancer]

there is no need to use so much SMB, 0.5 g would have been enough

rule of thumb: 1g smb will drop 1g of gold, a "little" extra never hurts, fine tuning your process will save money even if its 2 cents at a time

 

[jtechian]

I have a question maybe someone has the answer on processing pins for gold. Would it be good to dissolve all metals other then gold using sulfuric acid as it eats the copper rather then hydrochloric which does not directly eat copper, then filter out the gold flake to further process with nitric after neutralizing the sulfuric and rinsing? I was just wanting to rid the pins of all other metals as a first step, or am I trying to over simplify it?

 

[butcher]

Copper metal is not a very reactive metal, this is why it is placed just above the more noble metals in the reactivity series of metals, there it is below hydrogen in this list of reactivity of the metals, because it is not easily attacked by hydrogen from acids (like HCl or H2SO4), copper will not dissolve in dilute sulfuric acid, just like HCl it would need an oxidizer, you can dissolve it in concentrated Hot sulfuric acid where SO2 gas is being formed, but that is just way too dangerous and complicated.

You can add an oxidizer, but at that point I would just use HCl, or even CuCl2, or better yet ferrous chloride, or (the old used "acid peroxide" we normally have lots of waiting to be treated as waste) in a heated reaction this Copper/Iron chloride solution can consume lot of copper, it does take some understanding as to how the copper and iron chloride reacts, to be able to use this to recover the gold, and to separate the copper and iron from this to reuse the copper, as copper chloride, I have made a few posts that may help if someone wishes to try it.

If using sulfuric acid with pins the concentrated sulfuric acid electrolytic cell would be one of the best choices

 

[Tzoax]

there is no need to use so much SMB, 0.5 g would have been enough

rule of thumb: 1g smb will drop 1g of gold, a "little" extra never hurts, fine tuning your process will save money even if its 2 cents at a time

Thank You Necromancer, I will keep that on mind. This is my first time dealing with aqua regia, I am doing this test to prepare my self refining 5 grams of golden foils from fingers that I collected so far. So far i am satisfied, everything works well, also I am doing this test to get familiar with processing pins. So far i concluded that my first mistake was mixing all kind of pins, for now on, I will class them and process separately depending of the alloy of the base metals in pins. My second mistake was (maybe it is not a mistake, I was just experimenting) is that i cut every single pin to remove all solder and all parts of pins that is not gold plated. I found out that is very time consuming and that there is not really need for that considering that boiling in HCl will remove all tin. My third mistake was that I used nitric acid at a first place. I found that even I cut all non gold plated parts there is a lot of metals inside the base metal alloys contains tin or some other metal that nitric won't dissolve, so anyway I think that I had first to boil it with HCl, then HCl + H2O2, I think that if I did that in this case I'd get better results.