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Pre-concentration 

 

Summary

This review looks at the basic concepts of pre-concentration, including its advantages and challenges. It also provides links to important articles and suppliers information.

INTRODUCTION

Pre-concentration is a process where the ore is concentrated mostly at the mine site (especially at underground mines) at a relatively coarser size before dispatching to the processing plant. This is the process where barren/waste rocks are removed from the wanted ore at a coarser particle size without any significant loss in recovery. This can be achieved by hand sorting, screening, or mineral concentrator, or by using advanced sorting instruments. Andrew Bamber (2004) has designed an integrated underground mine and processing system model that is shown in the figure below, taken from his paper entitled Reducing Selectivity in Narrow-Vein Mining through the Integration of Underground Pre-concentration.
Integrated Underground Mining and Processing System

BENEFITS

This technology has many advantages, as listed as below (from Peters et al., 1999, and Scoble et al., 2000):

  • Reduction of surface material handling cost
  • Reduction in backfill unit costs as the waste from pre-concentration be directly used for backfill
  • Reduction in tailings disposal on surface
  • Potential lowering of the cutoff grade and thus significant increase in mining reserve
  • Increase in throughput and thus reduction in unit mining cost
  • Decrease in material lifting cost to the surface from underground mine
  • Increase in mining rate
  • Reduction in milling cost as hard silica gangue is been removed
  • Increase metal production without increase in any process equipment
  • Improving the grade of the ore entering in the processing plant etc.

CHALLENGES

The pre-concentration technology also has some challenges in order to be implemented worldwide (Bamber, 2004):

  • Requirement for large capital-intensive underground excavations to excavate larger throughput for the process plant.
  • Additional footwall development to accommodate pre-concentration plant, material handling system, waste handling system and transportation systems.
  • Shafts and haulages must also be large enough to accommodate the process equipment during construction.
  • Locations must be feasible over the life of mine under consideration, and the location of the pre- concentration facilities with respect to the vertical shaft or decline leading to surface must be considered.
  • The underground environment will substantially affect the design of the underground processing plant.
  • Space constraints, the underground environment will present conditions of heat, humidity, noise, and dust not experienced on surface.
  • Proper ventilation system both for mining and for the pre concentration dust control.
  • In case of wet concentration, water management will also be a deep issue.
  • Also, the design criteria of processing plants arising from geology, mineralogy, geometry, orientation, mining method, ore-body depth, physical ore characteristics, Acid Rock drainage etc.

PRINCIPLES

The feasibility of ore body pre-concentration is tested at bench scale in the lab to check the waste rejection that can be achieved without any significant material loss and also to check the applicability of different techniques. Then a given cutoff grade is selected based on lab results. The rock having a grade lower than that is rejected as waste and used as backfill material, whereas the rock with grade equal or greater than the cutoff grade is accepted as concentrate and hoisted up to the surface and sent to the processing plant for further processing.


SOME PRE-CONCENTRATION TECHNOLOGIES

There are a number of different technologies that are available for pre-concentration that get tested in the lab to check the applicability, such as:

  • screening
  • dense medium cyclone
  • magnetic separation
  • X-Ray Fluorescence sorting
  • X-Ray transmittance sorting
  • conductivity sorting
  • optical sorting (based on color difference)

There are many other sorting techniques available that can be seen in Ore sorting review but they are not significantly used.


FURTHER RECOMMENDED BOOKS AND ARTICLES

There is no book that includes pre-concentration technology specifically as a chapter.

The best article for the detailed information regarding sorting is entitled SORTING: Possibilities, Limitations and Future by H. R. Manouchehri.

Other informative documents are:

  • Pre-concentration of Mill Feeds using Automated ore Sorting processes by AUSIMM
  • An integrated underground mining and processing system for massive sulphides ores by Andrew S Bamber
  • Integrated Mining, pre-concentration and waste disposal system for increased sustainability of hard rock metal mining by Andrew S Bamber
  • Integrated mining and pre-concentration systems for Nickel Sulfide ores by Trent W Weatherwax
  • Integrated mining, processing and waste disposal systems for reduced energy and operating costs at Xstrata Nickel's Sudbury Operations by Andrew Bamber, B Klein, R C Pakalnis and M J Scoble

In addition to this, different conferences regarding mineral processing and technology development and their proceedings are the most useful sources for getting the recent developments in this field. Some of the proceedings include:

  • IMPC proceedings,
  • CIM Bulletins,
  • Industrial Minerals, and
  • APCOM

The following papers and the EduMine live webcast on Mine-Mill Integration also have some good information regarding pre-concentration:

In Canada, the University of British Columbia has an advantage for testing the feasibility for ore pre-concentration.


SUPPLIERS

The suppliers' list for ore sorting devices is very long. Some of them are mentioned below:

More such suppliers can be found on InfoMine's SupplyMine section.


REFERENCES

  • Bamber A. (2004), An integrated underground mining and processing system for massive sulphides ores, MASc Thesis, University of British Columbia.
  • Peters, O., Scoble, M., Schumacher, T. (1999), The technical and economic potential of mineral processing underground, Annual General Meeting, Can. Inst. Min. Metall., Calgary, CD ROM.
  • Scoble, M., Klein, B., Dunbar, W.S. (2000), Mining waste: Transforming mining systems for waste management, 6th Int Conf on Environmental Issues and Mining Production, Calgary, pp 333-340.

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