The effect of microwave radiation on the processing of Palabora

▲197The Journal of The South African Institute of Mining and Metallurgy MAY/JUNE 2000

Introduction

Microwaves may be defined as that part of theelectromagnetic spectrum that lies between theinfra red and radio frequency withwavelengths between 1 m and 1 mm. Whenmicrowave energy is applied to a material, thecontained material dipoles align and fliparound, at the frequency of the applied energy.Thus, the material heats when the storedinternal energy is converted to heat energy,due to friction. This in situ mode of energyconversion has the attraction of being selectiveto individual mineral phases within a mass(Kelly and Rowson, 1995). Conventionalheating has the disadvantage that the totalmass of material is heated and the radiation isabsorbed into the material by conduction.Overheating and also wasteful heating ofinsulators can occur. These problems arealleviated with microwave radiation whichselectively heats individual phases within amaterial lattice, causing differential expansionat grain boundaries (Mingos, 1991). Selective

heating within mineral lattices has distinctprocess advantages as it can promoteintergranular fracture which reduces requiredgrinding energy and also gives rise toincreased liberation of individual mineralgrains.

Various factors influence the dielectricproperties of a material (or the ability of amaterial to heat). These include the frequencyof the applied field, the temperature of thematerial and material physical properties.

Initial research into the microwavetreatment of minerals commenced in the late1970s when a U.S. patent for thedesulphurization of coal was registered(Zavitsanos, 1978). In 1984 the first extensivestudy into the effects of microwave radiationon minerals was published (Chen et al. 1984).

This paper was qualitative in nature andconcluded that most silicates, carbonates andsulphates were transparent to microwaveradiation; however, most sulphides, arsenides,sulphosalts and sulphoarsenides heatedstrongly, emitting fumes and fusing. Thisinitial study was extended in 1988 when adetailed quantitative study into the microwaveheating characteristics of minerals waspublished (Walkiewicz et al. 1988) Mineralsamples of 25g were irradiated within a 1kW,2.45GHz source and final temperature andrates of heating were determined, as shown inTable I.

Another important observation madeduring this research was that rapid heating ofore minerals in a non heating ganguegenerated thermal stresses that could causeweaknesses in the mineral matrix. Thisobservation has been extended in recent work(Kingman and Rowson, 1998) wheresignificant reductions of up to 90% of thework index were reported for microwavetreated massive Norwegian ilmenite ore inconjunction with increases in concentrategrade and valuable mineral recovery.

The effect of microwave radiation onthe processing of Palabora copper oreby S.W. Kingman, W. Vorster and N.A. Rowson*

SYNOPSIS

The effect of microwave radiation on the processing of Palaboraopen pit ore has been investigated. Significant reductions in Bondwork index are demonstrated for microwave treated samples.Reductions in work index were found to be sensitive to appliedpower level and method of application. After single stage magneticseparation tests, improvements in recovery of FeO were noted.However, these were curtailed by oxidation of the magnetitespecies as a result of continued heating. The effects of microwaveradiation upon the recovery of copper after froth flotation were alsoquantified. Small initial increases in recovery of copper were notedafter microwave treatment. However, with prolonged exposure,recovery was found to decrease. Overall recovery of copper was notaffected except for samples treated for extended duration. Theinfluence of microwave treatment upon the conventional Palaboragrinding circuit has been quantified with the use of USIMPACsoftware. Conclusions are made regarding the economics ofmicrowave treatment for this ore.

Keywords : Microwave; Grinding; Magnetic Separation;Flotation; Economic Analysis

* School of Chemical Engineering, University ofBirmingham, Edgbaston, Birmingham, England.

© The South African Institute of Mining andMetallurgy, 2000. SA ISSN 0038–223X/3.00 +0.00. Paper received May 1999; revised paperreceived Nov. 1999.

The effect of microwave radiation on the processing of Palabora copper ore

Palabora Process Description

Palabora is situated in the north eastern part of South Africa,in close proximity to the Kruger National Park. The Palaboraigneous complex can be described as a “figure of eight”layout, approximately 8 kilometres from north to south and3.2 kilometres from east to west. Copper ore has been minedin the area for many hundreds of years (PMC. Ltd, 1998),although mining did not start commercially until 1956, whena joint venture between Rio Tinto and Newmont MiningCompany formed The Palabora Mining Company (PMC).

The ore from Palabora consists primarily of magnetite,carbonate, dolorite, quartz and phoskorite. Copper bearingminerals include chalcopyrite, bornite, cubanite, valleriite,chalcocite, malachite and cuprite. Gold and silver are alsorecovered. Baddeleyite and uranothorianite are importantsecondary minerals.

Approximately 80 000 tonnes of ore are processed daily,26 000 tonnes being milled in the autogenous circuit and thebalance in the conventional circuit. The primary crusherscrush the ore to 100%, passing 180 mm, which is fed directlyto the autogenous mills, which mill to 80% passing 300 µm.In the conventional milling circuit the primary crushingproduct passes through secondary and tertiary crushersbefore being fed to the rod and ball mills, with the finalproduct being 80% passing 300 µm.

The products from the two milling circuits are then fed tothe flotation banks, producing a copper concentrate andtailings. The tailings then undergo magnetic separation toseparate the magnetite and heavy minerals (mainly U andZr). The magnetite is stored on stockpiles or sold for use indense media separation.

Experimental Procedure

Determination of the Effect of Microwave Radiationon Grindability

The effect of microwave radiation upon the grindability ofPalabora ore was quantified by the comparative Berry andBruce method (Berry and Bruce, 1966). This method requiresthe use of an ore of known grindability. The reference ore isground for a certain length of time and the powerconsumption recorded. If an identical weight of test ore isground for the same time period then the power consumption

will be equal to that of the reference ore. Then if r is thereference ore and t the ore under test, from Bonds Equation 1

[1]

Where Wi = Bond work index, P = 80% passing size ofproduct, F = 80% passing size of feed, W =work input pershort ton, it follows:

[2]

Therefore,

[3]

This method has been shown to give accurate values forBond work index for various ores (Yep et al. 1982).Comparative grinding tests were conducted on representative1kg samples of ore. Each sample had an identical sizedistribution. Two microwave heaters were used for theexperimental program. This was done to assess the influenceof applied power level and microwave application methodupon the grindability. The first microwave used was avariable power 2.6kW, 2.45GHz multimode heater. Sampleswere treated at both 1.3kW and 2.6kW. The secondmicrowave used was a 1.5kW, 2.45GHz monomode heaterand samples were treated only at 1.5kW. A multimode cavityis one where the electric field pattern produces successivereflections of the applied wave on the interior cavity of thesystem. Monomode applicators direct the electric field patternstraight at the sample and are often used for cylindricalproducts which are located in the centre of the waveguide. Inthe second microwave unit a nitrogen atmosphere was usedto inhibit oxidation of the ore samples.

To quantify changes in grindability a steel rod mill withdimensions 160 mm x 280 mm, containing five rods withdimensions 25 mm x 265 mm, was used. Grinding wascontinued for 5 minutes at 90rpm. After the requiredgrinding period, the 80% passing size of the ground productwas determined by sieve analysis. Samples were irradiatedfor times varying between 10 and 240 seconds.

Longer exposure times were used for material treated at1.3 and 2.6kW to ascertain any effects of excessivemicrowave heating. Shorter times were used for the 1.5kWtreatment to reduce any likelihood of sample oxidation.

Determination of the Effect of Microwave Radiationon Flotation

The flotation flow sheet used at PMC, Ltd is complex. Itconsists of 8 separate, parallel circuits. Sections 1 to 6 receivefeed from the conventional milling circuit while sections 7and 8 receive their feed from the autogenous mills.

Due to the difficulties involved in accurately simulating aflotation system on laboratory scale, only the initial rougherand scavenger cells have been simulated. This allows for adetailed analysis of the flotation properties of the microwavetreated ore.

Flotation tests were carried out on samples treated fortimes of between 10 and 300 seconds. Flotation tests wereconducted in a standard Denver laboratory flotation cell, the

WitFr Pt Ft

=

10 10 10 10Pr

± / ±

Wr Wt WirFr

WitPt Ft

= =

=

10 10 10 10Pr

± ±

WWi

P

Wi

F=

10 10±

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198 MAY/JUNE 2000 The Journal of The South African Institute of Mining and Metallurgy

Table I

Summary of mineral heating rates (afterWalkiewicz, 1988)

Mineral Chemical Max Temp Time EnergyComposition Achieved (°C) (min) Input

(kWh/t)

Chalcopyrite CuFeS2 920 1 667

Galena PbS 956 7 4667

Magnetite Fe3O4 1258 2.75 1833

Orthoclase KAlSiO3O8 67 6 4000

Pyrite FeS2 1019 6.75 4500

Quartz SiO2 79 7 4667

Sphalarite ZnS 88 7 4667

feed for all tests being 80% passing 300µm as is plantpractice. A 3-litre glass cell was used in all cases with aconstant impeller speed of 2000 rpm.

25g/t Sodium IsoButyl Xanthate (SIBX) was used ascollector and 35 g/t Senfroth to stabilise the froth.

The ore was added to 2.5 litres of water and 2 min wasallowed for conditioning to ensure total wetting of theparticles before collector addition. A further 2 min wasallowed for conditioning before frother addition. A final 30 swas allowed for final conditioning.

Aeration was started and the froth collected for 1 min.Froth was then collected in a separate receptacle for a furtherminute. Changing receptacles again, the froth was collectedfor a further 3 min, at which point the air flow was turned offand 35 g/t collector added and 2 min allowed for conditioningbefore addition of 35 g/t frother. A further 30 s was allowedfor conditioning.

Flotation was then continued for 15 min. Each flotationconcentrate was filtered, dried and the copper contentdetermined by atomic absorption spectroscopy. Allexperiments were carried out in duplicate and the valuesfound to be within ±2% of each other.

Determination of the Effect of Microwave Radiationon Magnetic Separation

Palabora Mining Company, Ltd distinguishes between high-and low-titanium content magnetite. This distinction isnecessary as low-titanium magnetite is sold for use in densemedia separation in coal cleaning plants. As the completemagnetic separation flow sheet at PMC, Ltd is complex, singlestage magnetic separation tests have been used to assess theeffect of microwave radiation on magnetite recovery.

Using a spinning riffle, 100g representative samples ofthe untreated and treated material were obtained for use inlaboratory scale magnetic separation trials.

The magnetic separation trials were conducted using asingle pass Boxmag Rapid (BHW) wet magnetic separatoroperating with a peak field intensity of 1200 gauss. Theferrous iron content (FeO) of each sample was determined induplicate by titration with potassium dichromate afterdecomposition in a sealed tube.

Results

Grindability Study

Figure 1 shows the effects of varying power 2.45GHzmicrowave radiation on the Bond Work Index of ore fromPalabora open pit.

Figure 1 clearly shows that microwave treatment has hada significant effect upon the work index of this ore. The mostspectacular influence has been in the initial treatment periodwhere the work index is shown to reduce from 13.06 kWh/tto 9.2 kWh/t after 10 seconds’ irradiation. A similarreduction is shown for the same time period for materialtreated at 1.3kW. Ore treated for 10 seconds in themonomode 1.5kW microwave heater shows a decrease from13.06kWh/t to 7.7kWh/t. The reason for this larger decreasein work index, despite lower applied power level (than the2.6kW samples), is the mode of application of energy. Ingeneral, monomode systems, due to the nature of thepresentation of the energy to the sample are more efficient

(Kingman, 1999). This is indicated by the results obtained.As exposure time was increased for the samples treated at2.6kW, significant further decreases in the values of workindex were noted. After 30 seconds’ treatment, a value of4.2kWh/t was obtained for material treated at 2.6kW. Thesame time of exposure at 1.3kW gave a value of 8kWh/t. Theapplied power level of microwave radiation is therefore seento have an effect on the degree of reduction in work index.

Samples exposed at 2.6kW for time periods greater than60 seconds showed some evidence of partial melting. Thispartial melting was found to give rise to some extremely lowvalues of work index. After 180 seconds treatment valuesbelow 1kWh/t were obtained. For an ore of this type partialmelting and/or oxidation of the contained valuables is notdesirable.

Ore treated using the monomode waveguide system at1.5kW gave the most significant results, as considerablereduction in work index were obtained without melting oroxidising the ore (to the extent of air treated samples). After90 seconds’ treatment at 1.5kW in a nitrogen atmosphere, awork index value of 2kWh/t was obtained. This is asignificant decrease when compared with untreated ore andwould certainly reduce the amount of energy required forgrinding.

The explanation for the reductions in work index aftermicrowave treatment are two fold. The major mechanism islikely to be the differential heating and, therefore, expansionof the minerals within the mineral matrix. All mineralsrespond to the application of dielectric fields in differentways, which lead to different heating rates, causingdifferential expansion in the mineral lattice. This differentialexpansion causes significant fracture around grainboundaries. This can have several benefits: firstly, grindingenergy can be reduced and secondly, heightened liberation ofwhole mineral grains can give rise to increases in recovery ofvaluable mineral. The second explanation for the significantreductions in work index for microwave treated ore isillustrated by a false colour SEM backscattered image shownin Figure 2. The image shows a former dolorite grain that hasbeen subjected to significant temperature increase and hasdecomposed to form calcium hydroxide and calcium ferritespecies. The altered microwave products are shown to be



Figure 1—Effect of microwave radiation upon Bond Work Index (kWh/t)


highly porous and therefore weaker than before treatment.Dolorite has been shown to cause particular problems in thegrinding circuit at Palabora mine as it has a high value ofwork index (~30kWh/t) so this decomposition is veryimportant.

Flotation Study

Figure 3 shows the effect of microwave radiation uponPalabora ore treated in air.

It can be seen from Figure 3 that microwave treatmenthas had a significant effect upon the froth flotation of thisore. If the recoveries after 5 minutes’ total flotation time arecompared, it can be seen that for all samples, except thattreated for 10 seconds, recovery has fallen. Recovery for the10 second treated sample is 69.7% after 5 minutes’ flotation,compared with 68.75% for the untreated sample. The reasonfor this increase is possibly liberation of the copper sulphideminerals away from the gangue, and other minerals in thematrix. However, it is important to note that that themicrowaves have caused no detrimental effect to the flotationof the sulphide species (for low exposure times). This isshown in Figure 4. The explanation for the reduction incopper recovery for samples exposed for longer than 10seconds is oxidation of the copper sulphide species. SIBX willnot form stable products with oxidized copper sulphidespecies, therefore the recovery falls. An interestingobservation from Figure 3 is, however, that after the finalscavenge float the total recovery of copper is not affecteduntil after 90 seconds’ microwave treatment. Figure 5 showsa back scattered SEM micrograph which illustrates thedevelopment of partial melt products after 120 seconds’microwave treatment at 2.6kW. The formation of thesepartial melt products will obviously affect the flotation of theore (particularly if copper sulphide species are involved as inFigure 5) The copper recovery for ore treated at 2.6kW for 4minutes is 77.7%, compared with 86.94% for untreatedmaterial.

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Figure 2—False colour SEM micrograph of 180 seconds treated oresample (2.6kW, 2.45GHz)

Figure 3—Effect of microwave radiation upon flotation (air treated)Figure 4—Liberation of copper species from magnetite after microwavetreatment for 10 secs at 2.6kW

Figure 6 shows the effect of microwave treatmentutilising an inert nitrogen atmosphere upon the flotation ofthis ore. If the recoveries after 5 minutes are compared, it canbe seen that after 10 seconds’ and 30 seconds’ treatmentslight increases in recovery occur when compared withuntreated material. The recovery after 10 seconds’ treatmentand 5 minutes’ flotation being 72.7% and for 30 seconds’treatment and 5 minutes’ flotation 70.8%. This increase,

again, can be explained by the phenomenon of thermallyassisted liberation, as illustrated in Figure 4. The untreatedrecovery after 5 minutes’ flotation was 68.7%. After 30seconds’ microwave exposure recovery fell with increasingexposure time. The final recoveries for all samples treated ina nitrogen atmosphere are similar, indicating that the overallflotation process was not affected by the nitrogen treatment.

It is possible that the effects of thermally assistedliberation could be exploited for higher exposure times bychanging to a different collector. SIBX is a very selectivecollector, the use of Sodium Iso Propyl Xanthate (lessselective) may mean higher initial recoveries, even forsamples that have undergone oxidation. However,considerations of grade would have to be made.

Magnetic Separation Tests

Figure 7 shows the effect of varying power microwaveradiation upon single stage magnetic separation tests. It canbe seen that microwave treatment has had a considerableeffect on the recovery of FeO. For material treated at 2.6kWthe most significant change occurs within the first 10seconds of treatment. After this time a recovery of 77% isobserved, compared with 72% for non-treated material. After10 seconds the recovery of FeO falls to 74.5%, which is stillhigher than untreated ore. A similar figure is obtained formaterial treated for 60 seconds. If tests had been carried outon material exposed to 2.6kW radiation for longer, reductionsin recovery below that of untreated material would have beenseen. This is due to the partial melting and magnetiteoxidation that is shown in Figure 6 and also Figure 8. Itappears that for material exposed to an applied power level of2.6kW any more than 10 seconds’ treatment is causingmineralogical changes within the sample. Figure 7 alsoshows the effects of 1.3kW microwave radiation uponrecovery of FeO. In general, the recovery remains fairlysteady until after 90 seconds’ treatment, where a recovery of76.5% compares with a non-treated value of 72%.

The effects of 1.5kW microwave treatment upon themagnetic separation of this ore are also presented.Microwave exposure of this material was carried out in aninert N2 gas atmosphere. Oxidation of the containedmagnetite could therefore not happen. The microwavegeneration device used also supplied energy to the samples



Figure 5—Partial melting of copper/magnetite species after 120seconds microwave treatment at 2.6kW

Figure 6—Effect of microwave radiation upon flotation (nitrogen treated)Figure 7—Effect of varying power microwave radiation upon recovery ofFerrous Fe


using the more efficient monomode-type waveguide. Afterthe first 10 seconds microwave treatment, the recovery canbe seen to have increased from 72% for non-treated materialto 79%. For the next 50 seconds’ exposure, the recoverystays constant (there is no sign of reduced recovery due tooxidation). After 90 seconds’ total treatment the recoveryincreases further from 79% after 60 seconds to 83%. Furtherexposure times were not investigated.

The probable reason for the increase in recovery formicrowave-treated samples is similar to that for the increasesin recovery after flotation. Microwave treatment inducesdifferential heating in the ore matrix. This differentialheating leads to differential expansion at grain boundariescausing the propagation of intergranular fracture.Intergranular fracture leads to the liberation of whole mineralparticles and therefore possible increases in recovery. Whererecovery has fallen (particularly in the samples treated at2.6kW) partial melting or oxidation of the magnetic specieshas occurred, lowering the magnetic susceptibility of the ore;thus FeO recovery is lower.

Economic Analysis of Microwave Treatment

USIMPAC software supplied by BRGM, France, wasdeveloped to allow the modelling of mineral processingflowsheets. The effects of altering variables on any givenflowsheets can easily be quantified. It is useful to have actualplant data to configure and test the models, prior to runningiterations. More information regarding the models used foreach individual piece of equipment is given in the literature(Anon, 1999). The software was used to model the PalaboraMining Company, Ltd conventional grinding flowsheet. Thisflowsheet consists of an open circuit rod and ball mill,

followed by a close circuit ball mill.For each mill in the circuit the following information wassupplied.

➤ Diameter and length➤ % Critical Speed➤ Volumetric loading of rods/balls➤ Rod/ball SG➤ Work Index of Material. (kWh/t)

For cyclones the following data were required

➤ Cut point (µm)➤ % Solids in underflow

The streams entering the primary rod mill above weredescribed, using the size distribution from all grinding tests.The d80 of this stream was approximately 16 mm. However,the d80 of the rod mill feed at Palabora mine is slightlysmaller at 11.2 mm. The model was run using actual plantdata from Palabora mine (Henderson, 1980) (except d80 ofthe feed). The model was tested by comparing predicted andtrue values of circulating load. The model predicted thecirculating load to be 277%, assuming a d80 input size of16mm. The actual circulating load on plant is approximately250% for a feed with a d80 of 11.2 mm. From this it wasassumed that the model was a reasonably accuratereplication of the plant.

The effects of microwave treatment upon the ore wereinvestigated by changing the parameter of Bond work indexand calculating the circulating load. The values of Bondwork index used for the tests were obtained from Figure 2from exposure times of 10, 30 and 90 seconds.

The values of work index were input into the model foreach mill and the model run as for the configuration test.Figure 9 shows a plot of circulating load versus Bond workindex. The effect of changing the grindability of the ore onthe circulating load can clearly be seen. As Bond work indexis decreased so does the Circulating load. In fact if the workindex is reduced as far as 2kWh/t (as is indicated possible bythe experimental tests) the circulating load is totallyremoved. This obviously has significant implications for theenergy requirements for the processing of this ore. Thepractical implication of reducing the Bond Work Index of theore as low as 2kWh/t is (according to the simulation) toallow the same product size distribution at the same plant

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Figure 8—Reflected light image of magnetite particle after 60 secondstreatment at 2.6kW. Note oxidation on grain margins

Figure 9—Variation of calculated circulating load with BWI

throughput with just a closed circuit rod mill. In practice,reducing the Bond Work Index of the ore will significantlyincrease the plant throughput for a set flowsheet.

Electrical energy consumed by comminution processeshas been shown to account for approximately 3% of the totalworld energy consumption (Schwechten et al. 1990). Thisobviously justifies investigations into methods to reduceenergy input for size reduction. This paper has demonstratedthat microwave energy can have a significant effect on thegrindability and downstream processing of Palabora ore.

Accurate prediction of process energy requirements forlaboratory microwave treatment is difficult. Reasons for thisinclude scale factors, (surface to volume ratio and heat losseffects), difficulties in calibration of power sensors, non-optimal applicator designs with high reflected powers andlow magnetron efficiency. Based upon the results of thefollowing tests it can be seen that to reduce the work index ofthe ore from 13.1kWh/t to 2kWh/t takes irradiation at 2.6kWfor 180 seconds. Therefore, it can be shown that for a 1kgsample of ore:

2.6 x 180/ (3600 x 0.001) = 130kWh/t. For 10 seconds’exposure this energy input is reduced to 7.2kWh/t for areduction in Bond work index of 4.1kWh/t. It is clear fromthese figure and also the mineralogical investigation that toexpose ore for 180 seconds is pointless as the micro-structure and mineralogy is destroyed (admittedly givinglarge reductions in Work Index). Ten seconds’ exposure,however, gives a reduction in required grinding energy of4.1kWh/t for an energy input of 7.2kWh/t. The benefits ofmicrowave treatment of ores do not extend solely toreductions in required grinding energy. As has beendemonstrated in this paper, consideration must be given toincreases in grade and recovery of valuable minerals,increases in plant throughput, liberation of valuable mineralsat higher grind sizes, therefore reducing slimes production,and also reductions in plant wear (particularly media andliner). In carrying out a full techno-economic, however, thefollowing points must also be considered. This test work wascarried out using laboratory scale equipment. Suchequipment is unlikely to have an energy efficiency of muchabove 40%, for the reasons stated above. Industrial scalemicrowave systems have the advantage that they operate at915MHz, with typical magnetron efficiencies of 85%.Penetration depths at 915MHz are also superior to those at2.45GHz, which would also provide greater flexibility in thedesign of the system. It has been previously stated that anefficiency of up to 70% on an industrial scale is generallyaccepted (Metaxas, 1991).

It could be said that rather than pre-treating ore withmicrowave radiation (to increase grindability and produceincreases in recovery of valuable mineral) it would be betterjust to grind for longer and increase the fineness of grind andhence improve the metallurgical characteristics by increasingliberation. Therefore, addition of microwave radiation is atbest simply application of energy in a different form.Grinding minerals for extended time periods has thedisadvantage, however, of causing the production of slimesand therefore losses in downstream processing (magneticseparation and froth flotation being particularly sensitive tothe presence of slimes). Microwave pre-treatment of the orehas the effect of causing liberation at a higher particle d80

therefore giving rise to less slimes production. It is importantto note that increases in recovery after microwave treatmentare not solely due to the enhanced liberation of particles butalso to liberation at a higher particle d80. Increased grindingtimes would also give rise to lower plant throughput (for thesame flowsheet) and increases in wear to mill, media andliner. All these items are significant operating costs in anymineral processing plant.

Industrial scale microwave equipment is available thatwill produce about 70kW in continuous operation. Clearly, fora plant like PMC, Ltd, many generators would be required.The capital cost of industrial microwave equipment has beenestimated at $1200 per kW for high power systems (VanWyk, 1997) and the capital cost of such systems willundoubtedly be significant. It will be vital that energy inputto the system be minimised and therefore work is currentlybeing undertaken at the University of Birminghamconcerning the application of ultra high electric field strengthmicrowaves to minerals and ores on a continuous basis.When this data is available, a full techno-economic analysisof the application of microwave radiation to PMC, Ltd ore willbe possible. Work is also underway at the University ofBirmingham to optimise the application of energy to thesample. It has been concluded by other workers (Stein et al.1994) that failed applications of microwave energy weremainly due to the poor design of the application equipment.This should be remembered when applicator design is carriedout for any process which requires microwave energy.

Conclusions

This study has clearly demonstrated the effects of microwaveradiation upon the processing of ore from Palabora mine andthe influence of significant reductions in work index havebeen demonstrated upon a part of the grinding circuit. Asenergy is being added to the process, however, a full techno-economic analysis is required to prove the benefits ofmicrowave treatment for ores of this type. The reductions inwork index, coupled with increases in recovery of valuablemineral, in addition to other benefits such as less mill wearand higher plant throughputs, must be balanced against boththe capital and operating costs of this technology.

Acknowledgements

The authors would like to thank the Engineering andPhysical Science Research Council, the School of ChemicalEngineering at the University of Birmingham and Rio TintoTechnology Development Ltd, for funding this work.Palabora Mining Company, Ltd are thanked for the supply ofsamples and plant information. Dr. I M. Reynolds of RioTinto Technology Development is also thanked for his help inproducing the mineralogical investigation.

References

ANON. USIMPAC Software manual, BRGM, France, (1999)BERRY, T.F. AND BRUCE, R.W. A Simple Method of Determining the Grindability

or Ores, Canadian Mining Journal, 1966, 6(6), pp. 63–65. CHEN, T.T. DUTRIZAC, J.E., HAQUE, K.E., WYSLOUZIL, W., and KASHYAP, S. Relative

transparency of minerals to microwave radiation, Canadian MetallurgicalQuarterly, 1984, 23(3), pp. 349–351.




HENDERSON, K. Milling and Concentrating Palabora Mining Company Ltd, 1990.KELLY, R.M. Microwave reduction of oxidised ilmenite concentrates Ph.D.

Thesis (Unpublished), 1996. University of Birmingham.KINGMAN, S.W. The Effect of Microwave Radiation upon the Comminution and

Beneficiation of Minerals, 1999, Ph.D. Thesis, (Unpublished), Universityof Birmingham, England.

KINGMAN, S.W. and ROWSON, N.A. Application of Microwave Energy to EnhancePerformance of Mineral Separation Processes, in Innovation in PhysicalSeparation Technologies, (ed.). R.A. Williams et al. Inst Min. Metal. 1998.

Mingos, D.M.P. Applications of Microwave Heating Effects to SyntheticChemistry, Chem. Soc. Rev. 1991. 20. pp. 1–47.

SCHWECHTEN, D. and MILBURN, G.H. Experiences in Dry Grinding with HighCompression Roller Mills for end Product Quality Below 20 Microns.

Minerals Engineering 1990. 3(1/2). pp. 23–34.STEIN, D.F., EDGAR, R.H., ISKANDER, M.F., JOHNSON, D.F., JOHNSON, S.M., LOB, C.G.,

SHAW, J.M., SUTTON, W.H., TEIN, P.K. and MUNNS, T.E. Microwaveprocessing—an emerging industrial technology, Microwave processing ofMaterials IV, Materials Research Society Symposium Proceedings.Materials Research Society, Pittsburgh, 347, 1994. pp. 3–8.

VAN WYK, E.J. Microwave regeneration of activated carbon, M.Eng. Thesis,University of Stellenbosch, Stellenbosch, South Africa. 1997.

WALKIEWICZ, J.W. KAZONICH, G. MCGILL, S.L. Microwave heating characteristics ofminerals and compounds, Minerals and Metallurgical Processing, Feb.1988. pp. 39–42.

ZAVITZANOS P.D. Coal Desulphurisation using Microwave Energy, US Patent NoEPA-600/7-78-089 (1978). ◆

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With the concurrence of its member institutes, the decisionwas taken at a meeting on 2 March 2000 of the CentralCommittee of the Environmental Planning Professionals’Interdisciplinary Committee (EPPIC) to wind up its affairsforthwith. The balance of any funds remaining would bedistributed among member institutes in good financialstanding. The future of the prestigious EPPIC Awardsremains open.

The demise of EPPIC was brought about by diminishingfinancial and direct support for this umbrella body whichrepresented the responsibilities and interests of a number ofprofessional institutes towards the environment.

One feels ambivalent about the situation, but it isprobably fair to say that EPPIC had accomplished its Missionand should now retire with dignity and pride.

EPPIC was formed in 1974 in response to a generalcriticism of the disregard of environmental factors by theplanning professions, expressed in 1973 at a conferencearranged by the South African Institution of Civil Engineers(SAICE) on Transportation and the Environment.

SAICE played a leading role in the formation of EPPIC inrequesting Mr E J Hall, then President of SAICE, to convenea meeting of concerned professional institutes of thoseprofessions which commonly initiate, plan or act as theprinciple agent in the planning and execution ofdevelopments which could have significant impacts on theenvironment.

The SAIMM joined EPPIC shortly after its inception andwas represented on its Central Committee by Peter Harris.He was succeeded in the mid 1980s by John Freer, who in1988 recommended to Council the formation of a Committeefor the Environment within the administrative structure ofthe Institute. This was done the following year with a viewto integrating environmental issues into the work of allrelevant committees of the Institute, such as the TechnicalProgramme Committees and the Journal, Education and

Awards Committees, while the Chairman represented theInstitute on EPPIC’s Central Committee and reported toCouncil. The SAIMM was probably the only memberinstitute of EPPIC to adopt this ideal model wherebyenvironmental matters were thoroughly integrated into itsmanagement structure. Had all member institutes donelikewise, support for EPPIC would have been unequivocaland the reflection of the execution of EPPIC’s mission by allmembers of all its member institutes that much morecomplete and lasting.

Be that as it may, the facts of the matter are that, in theabsence of relevant legislation, EPPIC was formed toencourage the professional planning institutes, and throughthem their members, to take environmental factors intoaccount proactively and voluntarily during the planning,execution, operation and closure of all their projects.Members can look back with pride regarding the progressmade in this regard over the last 25 years.

Today legislation is in place to enforce good practice inenvironmental management in the form of the NationalEnvironmental Management Act (NEMA) (1998) whichincorporates aspects of the repealed EnvironmentalManagement Act (1989) and its regulations, as well as,more specifically for the mining industry, the EMPrequirements of the Minerals Act (1990).

Hopefully, EPPIC’s influence will continue to pervade theminds of the members of this institute, encouraging them tobe proactive towards the early identification of those aspectsof their activities that could have a significant impact on theenvironment, eliminating those that they can and amelio-rating the rest, while seeking continual improvement in thisregard. ◆

* Issued by: John Freer, <[email protected]>

The demise of EPPIC*

The effect of microwave radiation on the processing of Palabora

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Transcript of The effect of microwave radiation on the processing of Palabora