AuMINIMayhem said:
Harold or Steve.. I like using the "AR then Urea then SMB" method. Is there a reason for using the differing precipitants in AR?
According to Hoke, there are instances where something may persist in following gold through the precipitation process when using any single reagent. By using more than one (not simultaneously, but upon a second refining), it's assumed that the substance may not be dragged down, or otherwise precipitated along with the gold.
I guess what I'm asking is in what cases would I use Zinc powder, copperas, ferrous sulfate, oxalic acid, etc instead of SMB.. or would I use them in addition to SMB to recover gold that may not have dropped out?..
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Gold, unlike the platinum group metals, will precipitate totally form solution if you have done your work properly. There should be no gold left behind, regardless of the precipitant of choice. If you're having that problem, you should look at your procedure and make any necessary changes so it isn't happening.
Unless you're working with cyanide, I can't think of any instance when you'd use zinc for precipitating gold------for it precipitates virtually everything that may be in solution. Zinc can be used for recovery, but not for purification, in other words. As far as your choice in precipitants, pick your poison and go with it! I'm not convinced that any one is better than another-----although there may be small differences that play a role under given circumstances.
SMB is nothing more than SO2, but in a solid form instead of a gas. My choice was to use SO2 in a cylinder. It is fast, easy, and very convenient the way I was set up. I had plumbed a line to my lab, so the bottle wasn't in the room with me. At the end of the line there was a hose barb and valve, located at the mouth of my fume hood. It took but seconds to apply the short length of vinyl hose to the barb, and attach the 3/8" glass tube I used for precipitation. It was all supported by a clamp that was fastened to the opening of the hood, so the setup was readily adjustable, and was completely out of the way when not in use, with the components stored in a drawer beneath the hood.
I do not contend that my method is the best-----but it was the best for me. How you work, and the nature of your objective will dictate what is best for you. My endeavor was no longer a hobby---I had to work efficiently, for I was working many hours each day, and had to make every minute count in order to keep up with the work.
So you'll know, ferrous sulfate and copperas are one and the same. Chemicals had strange names at one point in time (think sal ammoniac, which, if I'm not mistaken, is soda ash), then there was some attempt at organizing and standardizing chemical names. Why ferrous sulfate was called copperas is very strange-----for it is a salt of iron, not copper. It's been years since I last worried about these matters---- so I stand to be corrected if I recall it improperly.
Harold
