determination of gold content frm kt gold dissolved solution
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Besides instrumental analysis (AA, etc), the only universal method I know of is to dry or incinerate the liquid sample and then fire assay it. Chemical methods are usually chosen based on the solution matrix. For example, different chemical methods are required for cyanide solutions than for acid chloride solutions.
I once had a recurring situation where I was doing smallish stone removal lots and dropping small individual lots of gold. I've always been able to drop higher purity gold from larger lots so I wanted to come up with a way to quantify the gold in solution in a refinery without instrumentation.
I weighed the filtered clean pregnant aqua regia (to 0.01 grams) and subtracted out the tare to get a solution weight. Then I added exactly 100 ml of the solution to a tared 100 ml volumetric flask and weighed it on an analytical balance. Some simple math and I knew an exact volume for the lot.
Next I pipetted 10 ml of solution into a plastic baggie filled with flux and fused the bag, flux, and adsorbed liquid in an assay fusion. Cupelling the resultant bead, which was very pure, told me how much gold was in 10 ml and hence in the entire lot.
I did the procedure on dozens of lots but dropped the gold individually to convince myself of the validity of the method. It is very accurate.
Then we were able to batch lots until we had 500 oz of fine content and drop it together. Less labor and purer end product.
I weighed the filtered clean pregnant aqua regia (to 0.01 grams) and subtracted out the tare to get a solution weight. Then I added exactly 100 ml of the solution to a tared 100 ml volumetric flask and weighed it on an analytical balance. Some simple math and I knew an exact volume for the lot.
Next I pipetted 10 ml of solution into a plastic baggie filled with flux and fused the bag, flux, and adsorbed liquid in an assay fusion. Cupelling the resultant bead, which was very pure, told me how much gold was in 10 ml and hence in the entire lot.
I did the procedure on dozens of lots but dropped the gold individually to convince myself of the validity of the method. It is very accurate.
Then we were able to batch lots until we had 500 oz of fine content and drop it together. Less labor and purer end product.
4metals said:
The last time I brought this up, some people thought I was nuts, so I didn't mention it this time. However, since 4metals did something very similar, I'll go over it again.
An old method for gold in cyanide solutions is to make a boat from lead foil, pipet a sample of the solution into the boat, evaporate the solution over very slow heat, put everything in a crucible along with flux, and run a fusion. However, if the cyanide solution contains a lot of NaOH, it will eat through the lead during the drying. Acid chloride solutions will also eat through the lead. So, I tried drying the samples (usually 5 ml) in a watch glass or petri dish over VERY low heat. This worked, but it was hard to get all the residue from the watch glass into the crucible. There were always traces stuck to the glass.
Then, I tried adding half of the mixed flux to the crucible, pipetting the sample (no matter what the matrix) directly onto this flux, adding the rest of the flux, and, quickly (didn't want the liquid to soak into the crucible), I put it into the furnace and ran the fusion as normal. As 4metals did, I compared the assays to the recovery results, and, walla, they were always right on. I've been using this method for liquids ever since.
samuel-a
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goldsilverpro said:
Iv'e seen this before, but can't find the website where it was published.
It was very detailed process with pictures, and he assayed Pt,Pd,Ag and Au, same you mentioned.
I really hope i could find this website again and share.
I used a standard flux but added extra soda ash, it's been a while but to determine the amount of soda ash, just weigh a pile of soad ash and slowly add to a 10 ml aliqout until it is close to neutral pH, then re-weigh the pile and you know how much soda ash to add to your standard flux portion. Use the same soda ash addition for all fusions.
By putting all of the flux in a thin plastic sandwich bag, it adsorbed into the flux without fear of soaking into the assay crucible. The bag burns off and there's no urgency to do anything quickly.
I too used lead boats, and hated them!
By putting all of the flux in a thin plastic sandwich bag, it adsorbed into the flux without fear of soaking into the assay crucible. The bag burns off and there's no urgency to do anything quickly.
I too used lead boats, and hated them!
Join the club!
I assume you reduced the sugar or flour (or lees, maybe) because of the carbon produced by the bag.
Considering a 10 ml sample can contain over 1 gram of fine gold, vs a sweeps sample (which my flux was designed for) which can contain 1/4 of that (for good sweeps) I never lowered the reducing power of the flux because of the plastic.
Or maybe I never lowered it because I didn't think of it, but I had excellent results.
Considering the gold chloride content is so high, over doing it with carbon doesn't seem to pose too much of a problem.
Or maybe I never lowered it because I didn't think of it, but I had excellent results.
Considering the gold chloride content is so high, over doing it with carbon doesn't seem to pose too much of a problem.
bhupesh17 said:
Possibly, in a pure system. In the real world, with varying amounts of other metals and acids present, I can't see how you could get acceptable accuracy.
eeTHr
Well-known member
I'm just curious as to why the exact amount of Au in a solution is necessary. Are you buying or selling just the solution, or trying to determine how much percipitent to use, or what?
In a commercial refinery it is always desirable to know what is in solution. Stone removal is a process where the ability to quantify the gold before dissolution is not possible so you do not know how much gold is in it until you precipitate it. The process detailed above is used so you can batch multiple lots together and still pay the customer accurately. It is a labor saving technique made possible by accurate weighing and assaying.
samuel-a said:
Fire assay, by far, is the best, most reliable method of assaying ores. The flux given in the link is but one flux mixture. Every ore is at least somewhat different and, for best results, each usually requires at least a somewhat different flux mixture. For example, various ores are either acidic, basic, or neutral and each requires a flux adjustment. Preliminary assays can be run to determine the flux needed. I have 5 of the top assay texts and they all tell you how to go about this. To be good at assaying ores requires a lot of study. The guy in the link says:
That is very true, in general. However, if that refers to making no adjustments to the flux formula he gives, that is total BS. There is certainly no one formula that works for everything.
