I have to wonder (considering the low value of iron these days), if the need to know the iron percentage in these samples are for a monetary gain or just a mental exercise? Either way, the current separation process and the recommend testing procedure both contain to many errors and misinformation to be of much value. In my experience, being a stickler for the small details often determined the difference between success and failure on a project. :shock:
kjavanb123,
Most black sands will contain several types of iron minerals (i.e. magnetite, hematite, ilmenite and many sulfur bound minerals), but with the exception of magnetite and only very slightly with ilmenite, none of these will respond to a magnetic separation in their natural state. To get a more accurate reading on the total amount of iron in your bulk sample, a pre-treatment is required.
And Rick,
I feel like I’m preaching to the choir here. You must have suffered one of MY frequent brain freezes that seems to happen more often as I get older. You know very well that the 29.16 gram assay is based on 29,166 TROY oz/short ton. As neither iron or any other base metals that I’m aware of are bought or sold using the Troy weight system, the correct assay size would be 32 milligrams for a 32,000 oz/short ton.
But, even that information is of little use if you can’t get the bulk of the iron to separate for testing. As iron is priced by the pound or ton, then it’s better to run tests on larger samples, and I think it can be done at home without expensive equipment or chemicals. To get all the iron minerals to respond to a magnetic separation, all you need is heat.
By slowly heating the black sands to near visible red in a reducing atmosphere, oxygen and many other contaminates are driven off, leaving the iron in a nearly converted ferrite state. Slow heating also prevents any sulfur flash and encapsulating problem which often occurs during rapid high temp roasting.
With some type of fire pit or forge, a big bag of charcoal, a bellows to fan the flame, and a cast iron skillet or large crucible should work. The idea is to generate enough heat (+900 F) to convert the iron. Some charcoal directly on top of the fired test sample will maintain a reduction atmosphere and with occasionally stirring to prevent clumping.
I like working with Goesinto Numbers (Goes-In-To, say it fast like you just sneezed), so a dry pre-weighted 5 or 10 lbs. test sample makes the conversion to a ton easy. After all the charcoal is reduced to ash, do a three drop magnetic separation (more info on this procedure provided if needed), and weigh the difference between magnetics, non-magnetics, compare to original sample weight and extrapolate to one ton. The results of this process will provide a better percentage of available iron and a realistic recovery rate. If iron is the recovery goal? :roll:
Good luck with your project, :mrgreen:
John
