Liberate valuable minerals from the waste or gangue!
21 November 2014
Prior to smelting ore the early metallurgists would have removed or sorted waste rock by hand-picking, using the weight and colour to identify the valuable mineral – the first form of pre-concentration or ore sorting. They also used differential specific gravity of minerals and metals to sort mineralised deposits by means of a primitive jig which was made from wood and mounted on a cradle to facilitate rocking – usually on the bank or in a small stream.
Today, on any new mineral beneficiation project, the initial approach to test work is based on information supplied from the geological exploration program, assays and mineralogy. The design metallurgist examines the mineral dressing options to achieve valuable mineral separation from the gangue-waste minerals based on the properties of minerals such as size, specific gravity, magnetic susceptibility, conductivity, colour, floatability and solubility.
The association of the minerals in the ore is of paramount importance to the process consideration in that intimate association and degree of dissemination determine the amount of reduction required by crushing and grinding to achieve liberation.
Pre-concentration methods can be employed to make use of one or a number of these properties and applied to determine pre-concentration potential. Magnets, jigs, dense media and sensor ore sorting are the common methods of pre-concentration. If ores are amenable to pre-concentration at coarse sizes, an opportunity is presented to reject a portion of the crushed ore between the crushing and grinding circuits as a barren fraction, which means the size of all downstream processes will be reduced, or conversely, the overall treatment rate increased, which could be particularly significant in terms of operating cost and product output.
Pre-concentration can add previously uneconomic zones to Ore Reserves and help manage ore blending programs more effectively. They can be applied to selective upgrading of low-grade stockpiles - even waste dumps – to recover value from previously uneconomic material as well as reduce environmental risks and costs, reduce tailings dam or tailings filter size and reduce milling energy requirements adding value to the life of an operation.
Pre-concentration of ore at remote sites reduces haulage costs. Satellite ore bodies can be mined more effectively if pre-concentration scalping is carried out underground or in-pit or close to pit.
Amenability to pre-concentration
For any form of pre-concentration to work, liberation of valuable minerals from the waste or gangue must occur easily during the crushing process. If the valuable mineral is finely disseminated throughout the ore, sorting or other methods of pre-concentration may not be possible as it is necessary to reduce the ore to a size outside the range of coarse pre-concentration devices to liberate the valuable mineral from the gangue.
A variety of sensor sorting technology is available today that can measure some of the aforementioned mineral characteristics at high speeds. The latest technology can merge the information from any combination of sensors and in doing so, gather more data about the particles than a single sensor can. For example, by combining an X-ray transmission (XRT) sensor’s signal with that of a 3D laser scanner, particles can be separated from one another based on both density and the rate of refraction of light within a particular mineral.
STEINERT range includes:-
· X-ray transmission
· Optical-colour and laser
· Induction sensor
Now also available in the new Mobile Sorting Solution