Over the years I have come up with great new ideas, only to find out that I was reinventing the wheel. Reinventing the wheel in its self is not a bad thing. It is how we get better wheels.

Interesting thread but the answer to it is rather detailed and will take some space and time.

So let's start.

If you have access to a handbook on mineral processing they will start with ore handling and continue with the breaking of the ore into a size to release the desired mineral. Larger particles are separated by screening but particles that are too fine to be sorted by screening are usually sorted in water by wet classification bases on how the particles fall in the fluid..

At one time the gains actually "fell" but today the most common classifier is the cyclone. The particles are accelerated into the cone and the denser (larger) keep to the wall exit out the base and the lighter particles are drawn into the over-flow.

Where gravity supplies the acceleration in system such as elutriation there are two main formulas used to calculate the particles fall rate.

(From "Mineral Processing Technology" BA Wills)

1. Newton's Law

If a particle is large (heavy) enough (Mass x Acceleration = Force) the drag force will be largely turbulent resistance.

2. Stokes' Law

If a particle lacks mass to accelerate the drag force will be due to viscous resistance.

In both cases if the particles have the same density the larger one will have the higher terminal velocity.

In both cases if are the same size the denser particle will have the higher terminal velocity.

The formulas for both cases are available for anyone wishing to look them up. However the formula for calculating the size density ratio would be of interest to anyone using gravity separation methods.

Free Fall Ratio

Two mineral particles have densities Da and Db and diameters da and db and fall in a fluid of Df

From Newton's law

da/db =

Db - Df Da - Df

And from stokes law the square root of the above.

For example quartz 2.65 sg and galena 7.5 sg in water

7.5 - 1 2.65 -1

6.5/1.65=

**3.9394 **and the square root of that is

**1.98479**For larger particles that follow Newton's law a particle of quartz 3.94 larger than galena will fall at the same rate.

For small particles that follow Stokes' law the ratio is 1.99.

Newton's Law is valid for particles over 5mm and Stokes' law is valid for particles under 0.05mm and the size in-between

Are in a transition zone.

More to follow: