- Email: [email protected]
Magnetic tracers
Pergamon 08924375(01)ooo75-9
Minerals Engineering. Vol. 14. No. 7, pp. 797~801.2001 0 2001 Elsevier Science Ltd All rights reserved 0892-6875/011$ - 8ee front matter
TECHNICAL NOTE MAGNETIC TRACERS’
J. DANOCZI The Danoczi Solution, PO Box 489, Wilgeheuwel, 1736, South Africa. E-mail [email protected] (Received 6 November 2000; accepted 24 April 2001)
ABSTRACT Magnetic separation techniques are used extensively in mineral processing operations. Magnetic separators are robust and relatively easy to operate. However, setting up a magnetic separator such that it operates in an optimal manner is dificult involving trial and error techniques and laborious assaying methods. Magnetic tracers are a “tool” that enable magnetic separators to be set up ejjiciently and rapidly. Magnetic tracers are, easily identified, simulant minerals with similar size and density to that of the minerals in the ore body they are simulating. 0 2001 Published by Elsevier Science Ltd. All rights reserved. Keywords
Magnetic Separation; mass balancing; mineral economics
INTRODUCTION
Magnetic separation techniques are used widely both in Industry and in Mining operations. In mineral processing operations, magnetic separators are used for magnetic material beneficiation and for magnetic contaminants removal. Magnetic separators have various forms - Drum, Roll or Induced magnets depending on the required magnetic field strength and magnetic field pattern. Magnetic separators can operate either in dry or wet circuits depending on the requirement of the process. In general, one needs to evaluate the performance of magnetic separators in order to: .
Optimise their separation efficiency by maximising on recovery and maximising the rejection of noneconomical material under a range of operational and environmental conditions.
.
Determine the effectiveness of the magnetic separator when treating various ore bodies for the purpose of assessing the appropriateness of the magnetic separation technology.
* Presented at Minerals Engineering 2000, Cape Town, South Africa, November 2000
797
J. Danoczi
198
.
n
Enable one to select the correct magnetic separator (Neodymium or radial design) when designing a flow sheet for a plant.
Iron Boron or Barium Ferrite; axial
Qualify and quantify design improvements.
Identifying these requirements led to the development of the Magnetic the Author and Batemans Engineering Limited in South Africa.
tracers, which was carried out, by
OBJECTIVES The development
of Magnetic tracers was undertaken
in order to:
.
Develop a method for qualifying and quantifying the appropriateness of magnetic technology in a plant, with ease, under a range of operational and environmental conditions.
.
Develop a technique for comparing magnetic characteristics.
.
Develop a tool that enables one to easily compare the separation efficiency of different magnetic separators or different separation technologies, when selecting equipment for a new plant or upgrading a plant.
.
Develop a technique for comparing different design configurations
.
Develop a tool for quantifying the performance of different design materials used in the manufacture of magnetic separators in order to assess durability.
the efficiency
of separation
separation
of different ore bodies with different
of magnetic separators.
DESCRIPTION OF MAGNETIC TRACERS A Magnetic tracer is an easily identified, simulant mineral, designed to have the same density and size to that of the mineral(s) being recovered or removed in a mineral processing plant. Magnetic tracers have a range of magnetic susceptibilities (magnetic responses) in the region of the mineral of interest. A set of Magnetic tracers comprises of 7 groups of Magnetic tracers, each group containing at least 100 tracers with a prescribed magnetic susceptibility value, giving a total of 700 Magnetic tracers in a set. The recommended magnetic susceptibilities for the 7 groups are as follows: l l
.
3 groups to have magnetic susceptibilities above the desired magnetic cut-point, 3 groups below and 1 group in the region of the desired magnetic cut-point.
If the mineral has a specific shape oddity associated with it (elongated designed so as to simulate these shape features.
or flat), the magnetic
tracer can be
The Magnetic tracers are shape and colour coded according to the magnitude of their magnetic susceptibility. Magnetic tracers used for testwork on the Neodymium Iron Boron (NdFeB) magnetic separator have low magnetic susceptibilities (weak magnetic attraction forces) and are generally cubic. The Magnetic tracers used for testwork on the Barium Ferrite (BaFe) magnetic separator have high magnetic susceptibilities (strong magnetic attraction forces) and are generally diamond shaped. The Magnetic tracers are then processed over the magnetic separator once collection boxes are positioned on each fraction (magnetic and non-magnetic fraction) of the magnetic separator. The Magnetic tracers are then collected and audited. From the results of this test, the magnetic partition curve is drawn as demonstrated in Figure 1.
Magnetic tracers
THE USES OF MAGNETIC
799
TRACERS
Magnetic tracers provide a number of metallurgical benefits to a plant that incorporates magnetic separation processes.
Magnetic Partition Curve
,_-____
f---
:A Fig. 1 The magnetic partition curve for a magnetic cut-pointof 60 magnetic susceptibility units,
Magnetic partition curve
Magnetic tracers provide a tool for generating magnetic partition curves from which the following information can be evaluated: a l l l
The The The The
magnetic cut-point. sharpness .of the cut. quantity of foreign material reporting with the concentrate. expected loss of concentrate material.
Valuable information gathered from magnetic partition curves is used to characterise the performance of the magnetic separator for a variety of operational parameters, environmental conditions and to determine its operational limits. Quantify the efficiency of the magnetic separation process
Magnetic tracers are ideally suited to quantify the efficiency of a magnetic separation process. First, the ore body and the minerals of interest have to be character&d for their magnetic characteristics. The magnetic characterisation measurements conducted on the minerals are carried out in a kappa bridge (magnetic susceptibility meter). This instrument measures the magnitude of the magnetic response of a mineral to an external magnetic field and if necessary, any magnetic anisotropy. This information is then used to select the set of Magnetic tracers needed for the tests.
J.
800
Danoczi
Tests are then conducted with the Magnetic tracers and the magnetic partition curves are drawn. The results are then analysed with respect to the magnetic characteristics of the mineral of interest. Information on the performance of the magnetic separation process can be directly extracted from the magnetic partition curve. Optimisation
of the magnetic cut-point
The optimum magnetic cut-point required from a magnetic separator is determined by first carrying out magnetic characterisation tests on the ore body and on the minerals of interest with a magnetic susceptibility meter. Minerals usually have a range of magnetic properties depending on the degree of inclusions and contamination in the minerals. The optimum magnetic cut-point is often an economic decision and is a function of the revenue value of the mineral Characteristics and the metallurgical processing costs. When optimising a magnetic separator, first the correct speed of the unit has to be determined. Magnetic tracers are then passed over the Drum or Roll while the splitter plate is moved into position to provide the desired magnetic cut-point. Evaluation
of the appropriateness
of the magnetic separation technology
The appropriateness of the magnetic separation technology can be evaluated and quantified to determine from an economic base, if the technology needs upgrading or if alternative technologies are necessary. Magnetic characterisation studies are first carried out on the feed and on the minerals of interest that report to the magnetic separator. From testwork with Magnetic tracers one can assess:
l
If the correct magnetic scalping has occurred upfront of the magnetic separator by ensuring that no Magnetic material adheres to the magnetic separator.
l
If the rotational velocity of the magnetic separator is adequate by ensuring that no Magnetic tracers are adhering to the magnetic separator.
l
If a stronger or weaker magnetic field strength is required from analysis of the steepness of the magnetic partition curve.
l
If the diameter of the magnetic separator needs increasing by assessing the trajectories of the particles and the magnitude of the centrifugal force.
l
If the magnetic field gradient is correct for the range of particle sizes by quantifying the efficiency of the magnetic cut-point for different sized Magnetic tracers.
This information enables one to assess if the operational parameters are correct, if the magnetic separator needs servicing, upgrading or replacing and whether the technology is appropriate for treating the ore body. Technical audits
To carry out technical audits on magnetic separators, the efficiency of the magnetic separation process has to be quantified. This can now be achieved effectively with Magnetic tracers and then plotting magnetic partition curves. CONCLUSIONS
Magnetic separation processes are used extensively in the mineral processing industry and with the development of Magnetic tracers, the benefits from optimised magnetic separation processes can be realised.
801
Magnetic tracers
Previously, the benefits of magnetic separation techniques have not been fully realised due to limited measurement techniques available. The development of Magnetic tracers and the ability to accurately characterise ore bodies and minerals for their magnetic properties with the use of the Kappa bridge (magnetic susceptibility meter), provide the tools to make the necessary measurements. Optimised magnetic separators can now offer benefits to: l
Marginal deposits.
l
The processing of dump material to provide a new source of revenue.
l
The treatment of deposits where magnetic differences are small or on deposits where magnetic differences have not been realised. RECOMMENDATIONS
Magnetic tracers should be used to optimise magnetic separation equipment in order to maximise on the benefits from magnetic separation processes. When evaluating a new deposit for its ore resources and its economic benefits, characterisation tests on the ore body should include magnetic susceptibility measurements. These results will then enable one to assess if magnetic separation is a viable option for inclusion in the new plant design. When assessing the need to upgrade a plant, ore characterisation tests should be conducted on the ore body to determine if any recent developments in technology can be used advantageously. When auditing the operational efficiency and effectiveness of magnetic separators, three items of information are required. 1.
The magnetic characteristics of the ore body and minerals of interest.
2.
The static magnetic field measurements on the Drum or Roll magnetic separator.
3.
The magnetic partition curve derived from testwork using Magnetic tracers.
SOURCE OF MAGNETIC TRACERS Magnetic tracers can be obtained through the Author whose contact details are provided or by contacting Batemans Engineering Ltd in South Africa directly.
ACKNOWLEDGEMENTS The author would like to thank Bateman Engineering Limited for facilitating the development and production of the Magnetic tracers and a special thanks to Peter Cook the Laboratory Manager of Batemans for his contributions in the research and the final manufacturing of the Magnetic tracers.
Correspondence on papers published bwills@min-engcom
in Minerals Engineering
is invited by e-mail to
Minerals Engineering. Vol. 14. No. 7, pp. 797~801.2001 0 2001 Elsevier Science Ltd All rights reserved 0892-6875/011$ - 8ee front matter
TECHNICAL NOTE MAGNETIC TRACERS’
J. DANOCZI The Danoczi Solution, PO Box 489, Wilgeheuwel, 1736, South Africa. E-mail [email protected] (Received 6 November 2000; accepted 24 April 2001)
ABSTRACT Magnetic separation techniques are used extensively in mineral processing operations. Magnetic separators are robust and relatively easy to operate. However, setting up a magnetic separator such that it operates in an optimal manner is dificult involving trial and error techniques and laborious assaying methods. Magnetic tracers are a “tool” that enable magnetic separators to be set up ejjiciently and rapidly. Magnetic tracers are, easily identified, simulant minerals with similar size and density to that of the minerals in the ore body they are simulating. 0 2001 Published by Elsevier Science Ltd. All rights reserved. Keywords
Magnetic Separation; mass balancing; mineral economics
INTRODUCTION
Magnetic separation techniques are used widely both in Industry and in Mining operations. In mineral processing operations, magnetic separators are used for magnetic material beneficiation and for magnetic contaminants removal. Magnetic separators have various forms - Drum, Roll or Induced magnets depending on the required magnetic field strength and magnetic field pattern. Magnetic separators can operate either in dry or wet circuits depending on the requirement of the process. In general, one needs to evaluate the performance of magnetic separators in order to: .
Optimise their separation efficiency by maximising on recovery and maximising the rejection of noneconomical material under a range of operational and environmental conditions.
.
Determine the effectiveness of the magnetic separator when treating various ore bodies for the purpose of assessing the appropriateness of the magnetic separation technology.
* Presented at Minerals Engineering 2000, Cape Town, South Africa, November 2000
797
J. Danoczi
198
.
n
Enable one to select the correct magnetic separator (Neodymium or radial design) when designing a flow sheet for a plant.
Iron Boron or Barium Ferrite; axial
Qualify and quantify design improvements.
Identifying these requirements led to the development of the Magnetic the Author and Batemans Engineering Limited in South Africa.
tracers, which was carried out, by
OBJECTIVES The development
of Magnetic tracers was undertaken
in order to:
.
Develop a method for qualifying and quantifying the appropriateness of magnetic technology in a plant, with ease, under a range of operational and environmental conditions.
.
Develop a technique for comparing magnetic characteristics.
.
Develop a tool that enables one to easily compare the separation efficiency of different magnetic separators or different separation technologies, when selecting equipment for a new plant or upgrading a plant.
.
Develop a technique for comparing different design configurations
.
Develop a tool for quantifying the performance of different design materials used in the manufacture of magnetic separators in order to assess durability.
the efficiency
of separation
separation
of different ore bodies with different
of magnetic separators.
DESCRIPTION OF MAGNETIC TRACERS A Magnetic tracer is an easily identified, simulant mineral, designed to have the same density and size to that of the mineral(s) being recovered or removed in a mineral processing plant. Magnetic tracers have a range of magnetic susceptibilities (magnetic responses) in the region of the mineral of interest. A set of Magnetic tracers comprises of 7 groups of Magnetic tracers, each group containing at least 100 tracers with a prescribed magnetic susceptibility value, giving a total of 700 Magnetic tracers in a set. The recommended magnetic susceptibilities for the 7 groups are as follows: l l
.
3 groups to have magnetic susceptibilities above the desired magnetic cut-point, 3 groups below and 1 group in the region of the desired magnetic cut-point.
If the mineral has a specific shape oddity associated with it (elongated designed so as to simulate these shape features.
or flat), the magnetic
tracer can be
The Magnetic tracers are shape and colour coded according to the magnitude of their magnetic susceptibility. Magnetic tracers used for testwork on the Neodymium Iron Boron (NdFeB) magnetic separator have low magnetic susceptibilities (weak magnetic attraction forces) and are generally cubic. The Magnetic tracers used for testwork on the Barium Ferrite (BaFe) magnetic separator have high magnetic susceptibilities (strong magnetic attraction forces) and are generally diamond shaped. The Magnetic tracers are then processed over the magnetic separator once collection boxes are positioned on each fraction (magnetic and non-magnetic fraction) of the magnetic separator. The Magnetic tracers are then collected and audited. From the results of this test, the magnetic partition curve is drawn as demonstrated in Figure 1.
Magnetic tracers
THE USES OF MAGNETIC
799
TRACERS
Magnetic tracers provide a number of metallurgical benefits to a plant that incorporates magnetic separation processes.
Magnetic Partition Curve
,_-____
f---
:A Fig. 1 The magnetic partition curve for a magnetic cut-pointof 60 magnetic susceptibility units,
Magnetic partition curve
Magnetic tracers provide a tool for generating magnetic partition curves from which the following information can be evaluated: a l l l
The The The The
magnetic cut-point. sharpness .of the cut. quantity of foreign material reporting with the concentrate. expected loss of concentrate material.
Valuable information gathered from magnetic partition curves is used to characterise the performance of the magnetic separator for a variety of operational parameters, environmental conditions and to determine its operational limits. Quantify the efficiency of the magnetic separation process
Magnetic tracers are ideally suited to quantify the efficiency of a magnetic separation process. First, the ore body and the minerals of interest have to be character&d for their magnetic characteristics. The magnetic characterisation measurements conducted on the minerals are carried out in a kappa bridge (magnetic susceptibility meter). This instrument measures the magnitude of the magnetic response of a mineral to an external magnetic field and if necessary, any magnetic anisotropy. This information is then used to select the set of Magnetic tracers needed for the tests.
J.
800
Danoczi
Tests are then conducted with the Magnetic tracers and the magnetic partition curves are drawn. The results are then analysed with respect to the magnetic characteristics of the mineral of interest. Information on the performance of the magnetic separation process can be directly extracted from the magnetic partition curve. Optimisation
of the magnetic cut-point
The optimum magnetic cut-point required from a magnetic separator is determined by first carrying out magnetic characterisation tests on the ore body and on the minerals of interest with a magnetic susceptibility meter. Minerals usually have a range of magnetic properties depending on the degree of inclusions and contamination in the minerals. The optimum magnetic cut-point is often an economic decision and is a function of the revenue value of the mineral Characteristics and the metallurgical processing costs. When optimising a magnetic separator, first the correct speed of the unit has to be determined. Magnetic tracers are then passed over the Drum or Roll while the splitter plate is moved into position to provide the desired magnetic cut-point. Evaluation
of the appropriateness
of the magnetic separation technology
The appropriateness of the magnetic separation technology can be evaluated and quantified to determine from an economic base, if the technology needs upgrading or if alternative technologies are necessary. Magnetic characterisation studies are first carried out on the feed and on the minerals of interest that report to the magnetic separator. From testwork with Magnetic tracers one can assess:
l
If the correct magnetic scalping has occurred upfront of the magnetic separator by ensuring that no Magnetic material adheres to the magnetic separator.
l
If the rotational velocity of the magnetic separator is adequate by ensuring that no Magnetic tracers are adhering to the magnetic separator.
l
If a stronger or weaker magnetic field strength is required from analysis of the steepness of the magnetic partition curve.
l
If the diameter of the magnetic separator needs increasing by assessing the trajectories of the particles and the magnitude of the centrifugal force.
l
If the magnetic field gradient is correct for the range of particle sizes by quantifying the efficiency of the magnetic cut-point for different sized Magnetic tracers.
This information enables one to assess if the operational parameters are correct, if the magnetic separator needs servicing, upgrading or replacing and whether the technology is appropriate for treating the ore body. Technical audits
To carry out technical audits on magnetic separators, the efficiency of the magnetic separation process has to be quantified. This can now be achieved effectively with Magnetic tracers and then plotting magnetic partition curves. CONCLUSIONS
Magnetic separation processes are used extensively in the mineral processing industry and with the development of Magnetic tracers, the benefits from optimised magnetic separation processes can be realised.
801
Magnetic tracers
Previously, the benefits of magnetic separation techniques have not been fully realised due to limited measurement techniques available. The development of Magnetic tracers and the ability to accurately characterise ore bodies and minerals for their magnetic properties with the use of the Kappa bridge (magnetic susceptibility meter), provide the tools to make the necessary measurements. Optimised magnetic separators can now offer benefits to: l
Marginal deposits.
l
The processing of dump material to provide a new source of revenue.
l
The treatment of deposits where magnetic differences are small or on deposits where magnetic differences have not been realised. RECOMMENDATIONS
Magnetic tracers should be used to optimise magnetic separation equipment in order to maximise on the benefits from magnetic separation processes. When evaluating a new deposit for its ore resources and its economic benefits, characterisation tests on the ore body should include magnetic susceptibility measurements. These results will then enable one to assess if magnetic separation is a viable option for inclusion in the new plant design. When assessing the need to upgrade a plant, ore characterisation tests should be conducted on the ore body to determine if any recent developments in technology can be used advantageously. When auditing the operational efficiency and effectiveness of magnetic separators, three items of information are required. 1.
The magnetic characteristics of the ore body and minerals of interest.
2.
The static magnetic field measurements on the Drum or Roll magnetic separator.
3.
The magnetic partition curve derived from testwork using Magnetic tracers.
SOURCE OF MAGNETIC TRACERS Magnetic tracers can be obtained through the Author whose contact details are provided or by contacting Batemans Engineering Ltd in South Africa directly.
ACKNOWLEDGEMENTS The author would like to thank Bateman Engineering Limited for facilitating the development and production of the Magnetic tracers and a special thanks to Peter Cook the Laboratory Manager of Batemans for his contributions in the research and the final manufacturing of the Magnetic tracers.
Correspondence on papers published bwills@min-engcom
in Minerals Engineering
is invited by e-mail to