Classification and Concentrating

Metallurgy

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Classification and Concentrating

Postby Philski » Thu Feb 13, 2014 6:39 pm

Classification and Concentrating

Classification is the condition that favors separation by size and not density.

Classification is also method of separating minerals into two or more products based on there different velocities under the effects of gravity in a viscous medium that offers some resistance. Air, water or any other fluid that offers resistance can be equated. under vacuum and under constant acceleration it has an infinite rate of acceleration.

For instance In a vertical tube with a constant stream of resistance moving upwards the lighter particles will float upwards and the heavier will drop or remain stationary in the fluid/air. Could be a new sluice design right here.

Larger particles >5mm do create turbulence and are calculated differently because of the turbulent flow they create.
Stokes law which takes into consideration the viscosity of the fluid, speed of gravity, particle size and density of the fluid is used to calculate the smooth flow of small particles and the laminar flow the generally produce. Image

in a working plant this is used on particles that could not be efficiently screened and the hydrocyclone that operates under centrifugal force and is typically used today. hydraulic that operates under gravity. similar to a sluice box

The hydro uses mixed ore with water (Generally 40%) and the lighter fraction is shot up and out while the heavier minerals hit the wall and directed down towards the bottom. The biggest advantage with the hydrocyclone is the centrifugal forces are much higher than gravity alone forcing the particles to settle out at a faster rate.

Concentration of minerals is by means of one or more of the minerals characteristics. For gold its specific gravity. Mineral concentration by gravity, flotation, electrostatic, and magnetism.

The 3 factors that describe the extent of concentration are Recovery, Grade and Ratio of concentration.

Recovery is mass of valuable in product stream divided by mass of valuable in input stream x 100

Grade
is mass of valuable in stream divided by mass of valuable in stream AND waste in stream x 100

Ratio of concentration mass of feed stream divided by mass of concentrate.

for example a flotation test on Galena Pb (lead)

Head 1500 kg @ 8.55%Pb
cons 220 kg @ 57% Pb
Tailings 0.2% Pb
Ratio of Concentration 1500 / 220 = 6.82

The recovery is a trade off between grinding the nano size for a high con % or hand picking pure ore from the heap at a loss of recovery rate. You can not end up with more than 100% of what is in the feed, Nothing can be created or destroyed. Any loss will be in the tailings. This is all material balancing. And a science type may call it the conservation of matter. Product in = product out.

Gravity Separation This is one we all know. A pan, sluice box etc. Others include spirals, shaker table and an extreme one is the use of Mercury (Hg) to "float away" the light material because of its high SG and allow the gold to settle out while the the light rock floats away. Similar to oil floating on water, because oil is the lighter.

Image
Image taken from: creative commons

I will add more info and calculations (arnt they fun) as time permits.

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