This review looks at the basic concepts of ore sorting, including principles and different methods. It also provides links to important books, articles and suppliers information.
Ore sorting is the basic mineral concentration process where individual ore particles are separated from the unwanted material based on some physical properties. This process has been used over a thousand years. Visual inspection and some basic physical properties such as density and hardness was used by workers for hand picking and removing the unwanted gangue. With the increase in the capacity of plants, new technologies were developed, including electronic sorters.
Based on the physical properties of the ore, electronic ore sorters where developed. Depending upon the type of ore, various properties are used, such as:
- Reflectance and color in visible light for Magnesite, limestone, base metals, gold ore, phosphates, talc, coal
- Reflectance and color in ultraviolet ray for Scheelite
- Natural Gamma radiation for uranium ore
- Magnetic properties for iron ore
- Conductivity for Sulphides
- X-Ray luminescence for diamonds
For a better view about the detailed sorting process scope and usages, click here.
Infrared, Raman, and microwave attenuation have also been tested for some ore types.
The working principle for an electronic sorter is to use these properties and determine the value of it, and then eject the particles that have the value lower than a given threshold value as gangue or concentrate.
For example, in case of photometric sorters, a laser light source and sensitive photomultiplier are used. The photomultiplier detects the light reflected from the surface of rocks passing through the sorting zone. Electronic circuits analyze the photomultiplier signals, which change with the intensity of the reflected light and produces control signals to activate the appropriate valves of an air-blast rejection device to remove certain particles selected by means of the analyzing process, as shown here:
Different stages of the ore-sorting device can be sorted as:
- A method for feeding
- Method for sensing
- Method for comprehending and utilizing the information achieved from sensing zone
- A method for separating one mineral from another
General configuration of a sorting machine can be sketched as:
General configuration of a sorting machine (Source: Sorting: Possibilities, Limitations and Future, H.R. Manouchehri)
Common sensing methods for sorting and related sensing devices are shown in figure below:
(Source: Sorting: Possibilities, Limitations and Future, H.R. Manouchehri)
ADVANTAGES OF ORE SORTING
lists some very important advantages:
- Pre-concentrate mill feed into high grade and low grade fraction
- Sort high grade out of the low grade stockpile and waste dumps
- Reduce environmental risks and costs
- Optimize multiple process streams
- Pre-concentrate ore underground or at remote site
- Monitor the composition of the mill feed
PROBLEMS AND CHALLENGES IN ORE SORTING
Despite of several advantages, ore sorting has some problems related to it. Here are some:
- Ore loss as sometimes the mineral is finely disseminated in the rock and the sorter not able to pick it and regard it as waste.
- Sorters throughput is not very high.
- The rock should not be fine as more fine means more number of particle and since sorters analyze individual particles, So its sensitivity.
- The particle surface must be properly washed before sorting or the sorter effectiveness will not be high.
- The feed need to undergo preliminary sizing to feed monolayer to the sorter to improve its effectiveness.
There are a number of different sorters available in the market. Some of them are mentioned below:
- Gunson's sorter MP80 was the first sorter to use microprocessor technology.
- RTZ ore sorters Model 16 photometric sorter established in 1976.
- UltraSort UFS120 is a modern photometric sorter used for magnesite, feldspar, limestone and talc.
- X-ray sorters are used in the diamond industry.
- Radiometric sorting is used in uranium ore in South Africa, Namibia, Australia and Canada.
- Neutron absorption separation is being used in the sorting of boron minerals.
- Photoneutron separation is recommended for the sorting of beryllium minerals.
- RTZ Ore sorter Model 19 sorter is based on conductivity and magnetic property, and has been used in sulfides, oxides and native minerals.
- Outokumpu developed the "Precon" sorter and installed it in Hammaslahti Copper Mine that used gamma scattering analysis.
- Microwave attenuation was used to sort diamond bearing kimberlite.
- For sorting of asbestos ore sorters were developed that use low thermal conductivity of asbestos fibres.
- Ultraviolet radiation sorter was developed for sorting of scheelite.
RECOMMENDED BOOKS & ARTICLES
The most important book for understanding the basics of the ore sorting is Mineral Processing Technology
by B. A. Wills and T. J. Napier-Munn.
The best article for the detailed information regarding sorting is Sorting: Possibilities, Limitations and Future by H R Manouchehri. Other important books and articles can be listed as:
In addition of this, different conferences regarding mineral processing and technology development and their proceedings are the most useful source for getting the recent developments in this field. The proceedings includes:
The suppliers' list for ore sorting devices is very long and some of them is mentioned below:
Manouchehri, H.R. (2006), Sorting: Possibilities, Limitations and Future
Wills, B.A.; Napier-Munn, T.J. (2006), Wills' Mineral Processing Technology: An introduction to the practical aspects of ore treatment and mineral recovery. Elsevier Science & Technology Books, pp. 373-377
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