Gravity beneficiation

1. What is gravity beneficiation?

Gravity separation, known as gravity beneficiation, is a mineral processing method that separates minerals according to their different densities. In addition to various gravity concentration equipment, there must be a medium (air, water, heavy liquid or heavy suspension) when conducting gravity separation. In the gravity concentration process, mineral particles will be applied force by gravity (if in the centrifugal force field is mainly centrifugal force), the mechanical force exerted by the equipment and the force of the medium, the proper combination of these forces will make the different density of the particles produce different movement speed and trajectory, and ultimately they can be separated from each other.

2. What are the characteristics and applications of gravity beneficiation?

Gravity separation method has the characteristics of simple equipment structure and low operating cost, so it can widely be used when the conditions are suitable. The main applications of gravity concentration are,
1. The separation of gold, platinum and other precious metals.
2. Sorting of tungsten and tin ores.
3. In the treatment of rare metal elements containing minerals in the sand ore is very common, such as zirconium, titanium minerals containing the separation of the seashore sand ore;
4. Hematite, limonite separation
5. Separation of manganese ore.
6. Separation of fine coal and gangue in coal processing plant.
7. Separation of some non-metallic minerals and veinstones, such as the separation of asbestos, mica, kaolin, seafoam and diamond, etc.
8. For non-ferrous metal ores such as copper, lead and zinc, which are mainly treated by flotation, preenrichment by gravity concentration is also a common method.
9. Gravity concentration by particle size sorting process such as classification, desliming, etc., almost in all mineral processing plants are indispensable operations.
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Gravity Separation

1. Introduction

Separation by density difference is a process that is as old as recorded history. Separation of gold by density difference dates back to at least 3000 BC as depicted in writings from ancient Egypt. The principle employed in gravity separation goes back further in time to the formation and weathering of the rocks and the releasing of the minerals they contain and the transport of the mineral grains by heavy rains. It is the driving force for the formation of the alluvial deposits of precious metals and gemstones that have been worked since beyond recorded history as they still are today. Archaeological excavations have discovered mineral concentration activities such as the lead–silver concentrating plant in Attica, Greece, dating from 300 to 400 BC. So gravity separation has a long history as a mineral concentration process.

Not all mineral combinations are amenable to this type of concentration technique. To determine the suitability of gravity separation processes to a particular ore type, a concentration criterion is commonly used. A concentration criterion (CC) can be defined as

where SG = specific gravity (or density), and the fluid is typically water or air.
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Separation and Concentration Techniques

The separation and concentration of the valuable mineral can take place after the ore is crushed, ground, and classified into the required particle size distribution. There a number of different techniques are employed in concentrating the valuable minerals. These techniques exploit differences in physical or chemical properties of the valuable and gangue minerals.

Basically, there are four kinds of separation and concentration techniques:

i. Sorting – based on appearance, colour, texture, optical properties and radioactivity

ii. Gravity and Dense-Medium Separation – Separation based on specific gravity of the valuable mineral relative to the gangue and the carrying medium such as water. In dense-medium separation, the a carrying medium is a mixture of water, magnetite, or ferrosilicon. The paramagnetic properties of the medium allow it to either remain in suspension at a predetermined slurry density or to be separated from water for cleaning and reuse.

iii. Magnetic Separation – separation based upon natural or induced differences in magnetic susceptibility of the minerals within the ore.

iv. Froth Flotation – separations based on the surface chemistry properties of a mineral. The natural or modified surface property of the mineral determines its ability to attach to an air bubble and float to the surface.