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Electronic Ore Sorting - an introduction

 

Electronic Ore Sorting – an introduction

 

Ore sorting is the original concentration process, having probably been used by the earliest metal workers several thousand years ago. It involves the appraisal of individual ore particles and the rejection of those particles that do not warrant further treatment.

Hand sorting has declined in importance due to the need to treat large quantities of low-grade ore which requires extremely fine grinding. Hand sorting of some kind, however, is still practised at some mines, even though it may only be the removal of large pieces of timber, tramp iron, etc. from the run-of-mine ore. Electronic ore-sorting equipment was first produced in the late 1940s, and although its application is fairly limited, it is an important technique for the processing of certain minerals (Sassos, 1985; Salter and Wyatt, 1991; Sivamohan and Forssberg, 1991; Collins and Bonney, 1998; Arvidson, 2002).

 

 

 

Electronic sorting principles

 

Sorting can be applied to pre-concentration, in which barren waste is eliminated to reduce the tonnage reporting to the downstream concentration processes, such as in uranium or gold ore sorting, or to the production of a final product, such as in limestone or diamond sorting. The ore must be sufficiently liberated at a coarse size to allow barren waste to be discarded without significant loss of value. Pre-concentration by sorting is seen as a method of improving the sustainability of mineral processing operations by reducing the consumption of energy and water in grinding and concentration, and achieving more benign tailings disposal (Cutmore and Ebehardt, 2002). Many rock properties have been used as the basis of electronic sorting, including reflectance and colour in visible light (magnesite, limestone, base metal and gold ores, phosphates, talc, coal), ultraviolet (scheelite), natural gamma radiation (uranium ore), magnetism (iron ore), conductivity (sulphides), and X-Ray luminescence (diamonds).

Infrared, Raman, microwave attenuation, and other properties have also been tested.

Electronic sorters inspect the particles to determine the value of some property (e.g. light reflectance) and then eject those particles which meet some criterion (e.g. light vs dark rocks). Either valuables or waste may be selected for ejection. It is essential, therefore, that a distinct difference in the required physical property is apparent between the valuable minerals and the gangue.

The particle surfaces must be thoroughly washed before sorting, so that blurring of the signal does not occur and, as it is not practical to attempt to feed very wide rock size ranges to a single machine, the feed must undergo preliminary sizing. The ore must be fed in a monolayer, as display of individual particles to the sorting device must be effected. Photometric sorting is the mechanised form of hand-sorting, in which the ore is divided into components of differing value by visual examination (Arvidson, 2002).

The basis of the photometric sorter (Figure 1) is a laser light source and sensitive photomultiplier, used in a scanning system to detect light reflected from the surfaces of rocks passing through the sorting zone (Figure 2). Electronic circuitry analyses the photomultiplier signal, which changes with the intensity of the reflected light and produces control signals to actuate the appropriate valves of an air-blast rejection device to remove certain particles selected by means of the analysing process. The sorter is fully automatic and can be attended by one operator on a part-time basis.

 

Figure 1

Figure 2

 

We at Dynamic Machinery invite you to visit our factory and see first-hand how we can benefit your company with the products that we build and supply. We have extensive knowledge in the electronic mineral sorting field and request you to put us to the test.  

 

 

References

Arvidson, B. (2002). Photometric ore sorting, in Mineral Processing Plant Design, Practice and Control, ed. A.L. Mular, D.N. Halbe, and D.J. Barratt, 1033-1048 (SME).

Collins, D.N. and Bonney, C.F. (1998). Separation of coarse particles (over 1 mm), Int. Min. Miner., 1, 2(Apr.), 104-112.

Cutmore, N.G. and Ebehardt, J.E. (2002). The future of ore sorting in sustainable processing, Proc. Green Processing, Cairns, May, 287-289 (Aus. IMM).

Salter, J.D. and Wyatt, N.P.G. (1991). Sorting in the minerals industry: Past, present and future, Minerals Engng., 4(7-11), 779.

Sassos, M.P. (1985). Mineral sorters, Engng. Min. J., 185(Jun.), 68.

Sivamohan, R. and Forssberg, E. (1991). Electronic sorting and other pre-concentration methods, Minerals Engng., 4(7-11), 797.

Wills, BA and Napier-Munn, TJ (2006). Mineral Processing Technology - An Introduction to the Practical Aspects of Ore Treatment and Mineral, 373-374.

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