Post by growingtedium on Apr 10, 2012 15:08:18 GMT -5
I have a bit of data on tumbling pyrite, that may be useful to someone.
I was tumbling 2-10mm sized pieces of pyrite in a Covington 2 barrel, 6lb tumbler. In each load I had a few larger pieces of jasper to keep things moving. The barrels were approximately half full. My goal was not to get shiny round samples - just to eliminate the platy and needle shaped grains which were created during the crushing.
The grinding process released both iron and sulfur, and the sulfur was easy to smell. I assume the black black slurry that forms is partially small grains of pyrite and partially iron that's been released. Adding a magnet to the load may help control the black mess. The mixture reacted chemically with the aluminum end cap of the Convington tumbler and took a wire brush to get cleaned up.
Initially I tumbled with some 120 grit and that worked fairly well, but it did dull the surface of the pyrite. The surface under a microscope was visibly pitted/dented by the grit. The jasper pieces were plated with a fine layer of pyrite and took a gold color.
A second load was tumbled without grit, just allowing the pyrite sand/gravel to self abrade. After a month with occasional removal of the sludge, there was some rounding of the larger grains, little change in the smaller grains, significant grain size reduction overall due to cleaving and the jasper was again coated with a thin layer of pyrite. If the slurry had been removed, the coating on the jasper would wear away on the corners until the slurry built up again. The surface of the pyrite did not have a dull pitted appearance, but progress was much slower.
The black slurry material is nasty stuff. It sticks to everything and is water repellant, but can be removed with dish soap. I found the best way to clean the pyrite in the end was to repeatedly rinse the grains with fresh water, to add some dish soap to the barrel and to let it tumble for a few minutes. Repeat until the water after tumbling remains clear. I had too many grains to wash each by hand.
Good luck.
I was tumbling 2-10mm sized pieces of pyrite in a Covington 2 barrel, 6lb tumbler. In each load I had a few larger pieces of jasper to keep things moving. The barrels were approximately half full. My goal was not to get shiny round samples - just to eliminate the platy and needle shaped grains which were created during the crushing.
The grinding process released both iron and sulfur, and the sulfur was easy to smell. I assume the black black slurry that forms is partially small grains of pyrite and partially iron that's been released. Adding a magnet to the load may help control the black mess. The mixture reacted chemically with the aluminum end cap of the Convington tumbler and took a wire brush to get cleaned up.
Initially I tumbled with some 120 grit and that worked fairly well, but it did dull the surface of the pyrite. The surface under a microscope was visibly pitted/dented by the grit. The jasper pieces were plated with a fine layer of pyrite and took a gold color.
A second load was tumbled without grit, just allowing the pyrite sand/gravel to self abrade. After a month with occasional removal of the sludge, there was some rounding of the larger grains, little change in the smaller grains, significant grain size reduction overall due to cleaving and the jasper was again coated with a thin layer of pyrite. If the slurry had been removed, the coating on the jasper would wear away on the corners until the slurry built up again. The surface of the pyrite did not have a dull pitted appearance, but progress was much slower.
The black slurry material is nasty stuff. It sticks to everything and is water repellant, but can be removed with dish soap. I found the best way to clean the pyrite in the end was to repeatedly rinse the grains with fresh water, to add some dish soap to the barrel and to let it tumble for a few minutes. Repeat until the water after tumbling remains clear. I had too many grains to wash each by hand.
Good luck.