Ageo308 said:
Hi Harold, a couple of questions I have:
* When you evaporate, what happens if you let it evaporate right down till there is minimal liquid?
When you take the solution too far, elemental gold will begin to precipitate. That's a sure sign that you have eliminated the nitric. Depending on how clean the solution is, it is usually a dark red, leaning on red/brown/black when that happens, and it's very obvious. The solution, assuming you've kept if hot, will appear to have metal flakes ----much like aluminum or bronze paint. Hoke has a procedure to recover from the condition, but it has risks. I simply would add a drop of nitric, along with a few drops of HCl, and watch to see the gold dissolve.
Using an added button of pure gold during the evaporation process pretty much eliminates the need to evaporate to that point. I evaporated until I knew the nitric was gone, then I'd evaporate a little more if I had excess HCl present, but only to guarantee no filter failure. Excess HCl does no harm otherwise. Once evaporated properly, the solution would be taken up with tap water to dilute it well. A target volume is 3 ounces of gold per liter before precipitation, although I didn't follow that rule. I also precipitated with SO
2 gas, and iced my gold chloride before precipitating.
Would you be evaporating gold? The reason I ask is because my fans are yellow in colour and I can only think that's some from of metal chloride staining it (hopefully not gold).
That's not a good sign. Get some sunlight on the fans. If it's gold, they'll turn purple. You can also test with stannous chloride. If you don't see a color develop, you are seeing something else, but you may still be evaporating too quickly. Your solution should never boil unless it's covered with a watch glass. You must not hurry evaporation. Might pay you to read Hoke on that subject. Also----when you're dissolving your values, keep them covered with a watch glass. It's not a novelty--it's mandatory. The gasses that are evolved come off with considerable energy and carry droplets with them. A watch glass will collect the values and return them to the beaker.
Also how much precipitant would you allow for? And is too much no good or it does no harm? The reason I ask is because if I fall short then you need to wait another night for it to drop.
A rule of thumb is that an ounce of ferrous sulfate will precipitate an ounce of gold, but as Hoke suggests, an excess is a good idea. You might consider setting your sights on 1¼ ounces/ounce.
There is no need to wait for gold to settle when precipitating. Test your solution immediately after introducing the precipitant. The reaction should be instantaneous. If, after you've mixed your precipitant with the gold chloride solution, you still show values when testing with stannous chloride, you can immediately introduce more precipitant. I used to mix what I expected I'd need, then hold back on a small percentage. Mix, test, then either discard the extra, or introduce it to complete the precipitation. That way you wait only once for the gold to settle.
What you add may not be harmful----depends on the precipitant. Ferrous sulfate will wash out quite well, so I wouldn't be too concerned about using too much. Just insure that you follow the guidelines I set forth for washing. They work, and work very well.
From this you can conclude that there are benefits to using SO
2 from a cylinder. You test constantly as the gold precipitates, and stop introducing the gas when it's all down. It pays to stir the bottom when you have an abundance of gold, for gold chloride gets dragged down with the gold that comes down first if there is not a complete precipitation (assuming it settles quickly-----which is often the case).
Harold
