Radiometric Concentration

(also radiometric dressing), the separation of useful minerals from gangue through the use of methods based on the properties of some minerals to emit radiation (emission-radiometric methods) or attenuate radiation (absorption-radiometric methods). Emission-radiometric methods make use of the natural radioactivity or luminescence of minerals, and absorption-radiometric methods make use of X-radiation and neutron and gamma radiation.

Figure 1. Radiometric separator for naturally radioactive ores: (1) conveyor belt, (2) screen, (3) radiometer detector, (4) gate valve, (5) electromagnet, (6) radiometer, (Re, S) switch relay, and (V) power source

Radiometric concentration is done by means of radiometric separators (Figure 1). First, a detector registers the radiation and converts it into electric pulses. The pulses then proceed from the detector to a radiometer, in which the pulse frequency is compared with a previously given threshold value. If the frequency exceeds threshold levels, a command is given to the unit to separate the useful mineral into dressed product and wastes (tailings, or tails).

There are three methods of radiometric separation: (1) the separate chunk method, in which the radiation of individual ore chunks is recorded, (2) the batch method, in which the radiation of batches consisting of several chunks is recorded, and (3) the flow method, in which the radiation of a continuous flow of ore is recorded. Of these, the separate chunk method is the most efficient but the least productive.

Radiometric concentration has become a common method in the treatment of uranium ores and is the major way of concentrating this type of raw material. In addition, it is used in the treatment of beryllium ores (photoneutron process), gold-bearing ores and nonmetallic minerals (photometric process), diamond-bearing ores (luminescence process), iron ores (gamma-absorption process), and boron ores (neutron-absorption process).

Figure 2. Radiometric control station: (1) radiometer detectors, (2) radiometers, and (3) scale

A variant of radiometric concentration is radiometric sorting, in which railroad cars, motor vehicles, skips, or other ore-laden vehicles are sorted by a radiometric control station (Figure 2). Although the station operates at a high efficiency, the coefficient of ore concentration is low. This method is therefore used mainly for separating and removing the poorest part of an ore sample from a rock mass.