Rethinking Black Sand Concentrates (Part 2)
(Fine gold recovery is not always easy.)
Black sand concentrates containing fine gold can be a hassle to process but the gold they contain may be well worth the effort. Here's some more info on black sands that I think you'll find useful:
Past analyses performed by mining engineers have revealed that most black sands are composed primarily of magnetite (Fe3O4), ilmenite, and hematite with small residues of monazite and oxidized lead, tin, and silver. Magnetite's specific gravity is around 5.18 while gold's is nearly four times heavier at 19.3.
Interestingly enough, magnetite tends to form a protective shell of sorts around gold particles which changes the overall weight of these fine particles (I call them "microdots"). Because of this, most fine gold recovery systems use this weight difference as the basis for how they operate. This is both good and bad. Although very efficient overall, common fine gold recovery systems can lose some gold particles that remain stuck to their magnetite "shells."
Squeezing the Last Drop of Gold
As you can see here, there's more to fine gold particle recovery from black sands than meets the eye. There's obviously a science as well as an art to fine gold recovery and I'm learning this right along with you. I guess my problem in this regard is that over the course of 33 plus years as a small-scale gold miner I simply focused on the art aspect...not the science. Perhaps this is true of you as well.
(Although not foolproof by any means, spiral wheel concentrators can be very effective fine gold recovery systems.)
However, the fact that magnetite is (surprise, surprise) highly magnetic and ilmenite slightly so makes the fine gold recovery problem easier to solve. But how do you separate the magnetic shell from those minute gold particles? Therein lies the heart of the matter if you want to squeeze the very last drop of gold from your black sand concentrates.
Consider Ourselves Lucky
Here's the good news. This magnetite "shell" bonding can be overcome because it's based on physical parameters and NOT chemical factors. When chemical bonds predominate in gold mining it's a whole different ballgame in terms of how gold-bearing materials are processed, and gold recovery of any sort becomes problematic in the strictest sense.
So I guess we have to consider ourselves lucky that magnetite has only a physical grip on fine gold particles in black sand concentrates. Otherwise we'd all be wearing lab aprons and face shields and working under chemical fume hoods. (Not to mention the potential risk of being arrested for running what some might think a secret meth lab!)
There's more to come on black sands, so stay tuned.
Good luck to one and all.
If you liked this post, you may want to read: "Canadian Placer Gold: Southern Quebec Province (Part 1)"
(c) Jim Rocha (J.R.) 2013
Questions? E-mail me at firstname.lastname@example.org