**3. Summary and recommendations**

98 The Development and Application of Microwave Heating

altered the physical and chemical properties of the slag.

benefits) is not viable.

2% of that required in previous work.

**2.12. Latest developments in microwave processing of minerals ores** 

comminution and separation processes, is microwave assisted grinding.

The mechanical size reduction of solids is an energy intensive and highly inefficient process. Therefore, there is great incentive to improve the efficiency of size reduction and mineral separation processes. Over several decades, this has promoted significant amounts of research, unfortunately, this has only led to small, incremental improvements in efficiency. One area, which has shown significant promise for improving the efficiency of mineral

Until recently, the majority of test work carried out concerning microwave treatment of minerals utilized standard multi-mode cavities, similar to that found in a conventional kitchen microwave oven. The multimode cavity whilst mechanically simple suffers from poor efficiencies and low electric field strengths, vital to high power adsorption. Whilst the influence of microwave energy from this type of cavity has been shown to have a significant influence on ores and minerals, the inefficiencies of the application method have led to conclusions that at present, microwave treatment of minerals (despite the numerous process

More recent studies have presented studies describing the influence of high electric field strength microwave energy on minerals and ores. It is well known that microwave power density in a material (or volumetric power absorption) is directly proportional to the square of the electric field strength within the material. Therefore, it was shown that if local electric field strength can be magnified energy adsorption or heating rate can be amplified many times without the use of further energy. In turn, this lead to reduced cavity residence times and reductions in the required microwave energy input per ton. Detailed tests at the University of Nottingham have shown that in cavities with high electric field strengths the microwave energy consumption to achieve a desired reduction in strength can be as little as

Investigations have been carried out on several economically important ores utilizing a high electric field strength cavity for microwave treatment. A systematic approach was used in

energy (900 W, 2450 MHz) for the heating a typical EAF dust mixed with powdered carbon for various length of time. Over 90% zinc was volatilized as ZnO (zinc oxide), which was condensed and collected on an alumina plate placed on top of the reaction crucible. The laboratory scale test results demonstrated that zinc removal was rapid and selective. The iron rich residue can be recycled in an iron or steel making furnace. Steel making slag usually contains 20 wt. % iron. To modify the physical characteristics of and to recover iron from the slag. Hatton and Pickles, 199482, Conducted laboratory scale microwave heating tests (1000 W, 2450 MHz). The heating behavior of the steel making slag was investigated with and without the addition of carbon or magnetite. Test results demonstrated that both carbon and magnetite addition increased the heating rate of the slag; 1000℃ with carbon, 800℃ with magnetite, compared to 650℃ without any addition. The amount of iron recovered increased with heating time and reached as high as 90%. Microwave heating

> The information compiled in this chapter demonstrates that microwave energy has the potential for application in mineral treatment and metal recovery processes such as heating, drying, grinding, leaching, roasting, smelting, carbothermic reduction of oxide minerals, pretreatment of refractory gold concentrate or ore, spent carbon regeneration and waste management. Usually, microwave energy is more expensive than electrical energy, mainly due to the low conversion efficiency from electrical energy (50% for 2450 MHz and 85% for 915 MHz). However, the efficiency of microwave heating is often much higher than conventional heating and overcomes the cost of the energy. Generally, mineral processing industries treat a large tonnage of ore or concentrate per day (several thousand to over 30,000 tonnes). Currently, the highest microwave power generator available is 75 kW at 915 MHz. To treat such a large tonnage of ore or concentrate a number of generators would have to be operated in parallel, which may not offer a cost advantage over the conventional process. However, for high value product recovery or low tonnage material treatment microwave energy can offer a cost advantage over the conventional process, for example,

pretreatment of refractory gold concentrate, regeneration of CIP spent carbon, roasting or smelting of ore or concentrate for smaller operations. Furthermore, it is possible to apply microwave energy to the leaching of ore or concentrate in slurry or semi-solid mixture (paste) at ambient pressure to yield a metal extraction comparable with pressure leaching. Today's processing industries, including mineral processing, are facing increasing global competition, more stringent environmental regulations, higher overhead costs and shrinking profit margins. The processing industries are addressing these problems in various ways, and their processes are approaching peak product yield as well as performance and productivity efficiency. In the foreseeable future processing industries will be looking for high performance conventional as well as nonconventional processing technology. This is the point at which processes based on microwave energy will get favorable consideration. The continued development of high power microwave generator and precision temperature measuring devices for high temperature operation should have positive impact in the acceptance of microwave assisted mineral treatment process. The current R&D status indicates that microwave energy has the potential to play an important and possibly crucial role in future mineral treatment processes. However, challenges remain to be overcome through a fundamental understanding of microwave interaction with minerals, innovation, R&D investigations and advanced engineering, especially in designing efficient applicators, processes and process control devices.

### **Author details**

S.M. Javad Koleini *Tarbiat Modares University, Iran* 

Kianoush Barani *Lorestan University, Iran* 

#### **4. References**


 [9] Prasher, C.L., 1987, Crushing and Grinding Process Handbook, John Wiley & Sons Limited, Chichester.

100 The Development and Application of Microwave Heating

efficient applicators, processes and process control devices.

**Author details** 

S.M. Javad Koleini

Kianoush Barani *Lorestan University, Iran* 

**4. References** 

*Tarbiat Modares University, Iran* 

(3), 1997, pp. 64-68.

IMM, 28, 1918-1919, pp. 41.

pp. 179-180.

pretreatment of refractory gold concentrate, regeneration of CIP spent carbon, roasting or smelting of ore or concentrate for smaller operations. Furthermore, it is possible to apply microwave energy to the leaching of ore or concentrate in slurry or semi-solid mixture (paste) at ambient pressure to yield a metal extraction comparable with pressure leaching. Today's processing industries, including mineral processing, are facing increasing global competition, more stringent environmental regulations, higher overhead costs and shrinking profit margins. The processing industries are addressing these problems in various ways, and their processes are approaching peak product yield as well as performance and productivity efficiency. In the foreseeable future processing industries will be looking for high performance conventional as well as nonconventional processing technology. This is the point at which processes based on microwave energy will get favorable consideration. The continued development of high power microwave generator and precision temperature measuring devices for high temperature operation should have positive impact in the acceptance of microwave assisted mineral treatment process. The current R&D status indicates that microwave energy has the potential to play an important and possibly crucial role in future mineral treatment processes. However, challenges remain to be overcome through a fundamental understanding of microwave interaction with minerals, innovation, R&D investigations and advanced engineering, especially in designing

[1] Meyer, C., Umm Fawakhir, Bir., 1997, Insights into Ancient Egyptian Mining, JOM, 49

[3] The Tech., Vol. V, Massachusetts Institute of Technology, Boston, April 1, 1886, No. 12,

[5] Fitzgibbon, K.E. and Veasey, T.J., 1990, Thermally Assisted Liberation - A Review,

[6] Yates, A., Effect of Heating and Quenching Cornish Tin Ores before Crushing, Trans

[7] Holman, B.W., 1926, Heat Treatment as an Agent in Rock Breaking, Trans IMM, 26, pp. 219. [8] Myers, W.M., 1925, Calcining as an Aid to Grinding, J. Am. Ceram. Soc., 8, pp. 839.

[2] Oldfather, C.H., 1967, Diodorus of Sicily, Cambridge, Harvard U. Press.

[4] Cowen, R., Exploiting the Earth April, 1999, (online draft copy),

http://www.geology.ucdavis.edu/~cowen/~GEL11.

Minerals Engineering, vol 3, 1/2, pp 181-185.

	- [30] Marland, S., Han, B., Merchant, A., Rowson, N., 2000, The Effect of Microwave Radiation on Coal Grindability, Fuel, 79, pp. 1283-1288.
	- [31] Kingman, S.W.; Vorster, W.; Rowson, N.A., 2000, The Influence of Mineralogy on Microwave Assisted Grinding, Minerals Engineering, 13 (3), 313-327.
	- [32] Wang, Y., Forssberg, E., 2000, Microwave Assisted Comminution and Liberation of Minerals, Mineral Processing on the Verge of the 21st Century, Özbayoğlu et al. (eds), Balkema, Rotterdam.
	- [33] Vorster, W.; Rowson, N.A.; Kingman, S.W., 2001, The Effect of Microwave Radiation Upon the Processing of Neves Corvo Copper Ore, Int. J. Miner. Process., vol. 63, pp 29-44.
	- [34] Kingman, S.W., Jackson, K., Cumbane, A., Bradshaw, S.M., Rowson, N.A., Greenwood, R., 2004, Recent Developments in Microwave-Assisted Comminution, Int. J. Miner. Process, 74, pp. 71-83.
	- [35] Amankwah, R.K., Khan, A.U., Pickles, C.A., Yen, W.T., 2005, Improved Grindability and Gold Liberation by Microwave Pretreatment of a Free-milling Gold Ore, Trans. Inst. Min. Metall. C., Vol. 114, pp. C30-C36.
	- [36] Koleini, S.M.J., Barani, K., 2008, The effect of microwave radiation upon grinding energy of an iron ore, Microwave Technology Conference, Cape town, South Africa.
	- [37] Barani. K., Koleini., S.M.J., 2010, The effect of microwave treatment upon an iron Ore comminution, international mining congress, Tehran, Iran.
	- [38] Koleini, S.M.J., Barani, K., Rezaei, B., 2012, The effect of microwave treatment upon dry grinding kinetics of an iron ore, Mineral Processing and Extractive Metallurgy Review Journal, vol. 33 (2), pp.159-169.
	- [39] Salsman, J.B.; Williamson, R.L.; Tolley, W.K.; Rice, D.A., 1996, Short-Pulse Microwave Treatment of Disseminated Sulfide Ores, Minerals Engineering, vol 9, no.1, pp 43-54.
	- [40] Whittles, D.N., Kingman, S.W., Reddish, D.J., 2003, Application of Numerical Modelling for Prediction of the Influence of Power Density on Microwave Assisted Grinding, Int. J. Min. Proc., 68, pp. 71-91.
	- [41] Jones, D.A., Kingman, S.W., Whittles, D.N., Lowndes, I.S., 2005, Understanding Microwave Assisted Breakage, Minerals Engineering, 18, pp. 659-669.
	- [42] Florek, I., Lovas, M., Murova, I., 1996, The effect of microwave radiation on magnetic properties of grained iron containing minerals, in: Proceedings of the 31st International Microwave Power Symposium, Boston, USA.
	- [43] Kingman, S.W., Corfield, G.M., Rowson, N.A., 1999, Effect of microwave radiation upon the mineralogy and magnetic processing of amassive Norwegian ilmenite ore, Magn. Electrical, No. 9. pp.131–148.
	- [44] Kingman, S.W., Rowson, N.A., 2000, The effect of microwave radiation on the magnetic properties of minerals, J. Microwave Power Electromagn. Energy 35 () 144–150.
	- [45] Cui, Z., Liu, Q., Etsell, T.H., 2002, Magnetic properties of illmenite, hematite and oilsand mineral after roasting, Miner. Eng. Vol. 15 pp.1121–1129.
	- [46] Sahyoun, C., Kingman, S.W., Rowson, N.A., 2003, The effect of heat treatment on chalcopyrite, Phys. Sep. Sci. Eng. 12 pp.23–30.
	- [47] Uslu, T., Ataly,U., Arol, A.I., 2003, Effect of microwave heating on magnetic separa- tion of pyrite, Colloid Surf. A: Physicochem. Eng. Aspects 225, (2003), 161– 167.

 [48] Znamenackova, I., Lovas, M., 2005, Modification of magnetic properties of siderite ore by microwave energy, Sep. Purif. Technol. 43 (2005), 169– 174.

102 The Development and Application of Microwave Heating

Balkema, Rotterdam.

Process, 74, pp. 71-83.

Inst. Min. Metall. C., Vol. 114, pp. C30-C36.

Microwave Power Symposium, Boston, USA.

copyrite, Phys. Sep. Sci. Eng. 12 pp.23–30.

mineral after roasting, Miner. Eng. Vol. 15 pp.1121–1129.

Journal, vol. 33 (2), pp.159-169.

Min. Proc., 68, pp. 71-91.

Electrical, No. 9. pp.131–148.

comminution, international mining congress, Tehran, Iran.

Radiation on Coal Grindability, Fuel, 79, pp. 1283-1288.

Microwave Assisted Grinding, Minerals Engineering, 13 (3), 313-327.

[30] Marland, S., Han, B., Merchant, A., Rowson, N., 2000, The Effect of Microwave

[31] Kingman, S.W.; Vorster, W.; Rowson, N.A., 2000, The Influence of Mineralogy on

[32] Wang, Y., Forssberg, E., 2000, Microwave Assisted Comminution and Liberation of Minerals, Mineral Processing on the Verge of the 21st Century, Özbayoğlu et al. (eds),

[33] Vorster, W.; Rowson, N.A.; Kingman, S.W., 2001, The Effect of Microwave Radiation Upon the Processing of Neves Corvo Copper Ore, Int. J. Miner. Process., vol. 63, pp 29-44. [34] Kingman, S.W., Jackson, K., Cumbane, A., Bradshaw, S.M., Rowson, N.A., Greenwood, R., 2004, Recent Developments in Microwave-Assisted Comminution, Int. J. Miner.

[35] Amankwah, R.K., Khan, A.U., Pickles, C.A., Yen, W.T., 2005, Improved Grindability and Gold Liberation by Microwave Pretreatment of a Free-milling Gold Ore, Trans.

[36] Koleini, S.M.J., Barani, K., 2008, The effect of microwave radiation upon grinding energy of an iron ore, Microwave Technology Conference, Cape town, South Africa. [37] Barani. K., Koleini., S.M.J., 2010, The effect of microwave treatment upon an iron Ore

[38] Koleini, S.M.J., Barani, K., Rezaei, B., 2012, The effect of microwave treatment upon dry grinding kinetics of an iron ore, Mineral Processing and Extractive Metallurgy Review

[39] Salsman, J.B.; Williamson, R.L.; Tolley, W.K.; Rice, D.A., 1996, Short-Pulse Microwave Treatment of Disseminated Sulfide Ores, Minerals Engineering, vol 9, no.1, pp 43-54. [40] Whittles, D.N., Kingman, S.W., Reddish, D.J., 2003, Application of Numerical Modelling for Prediction of the Influence of Power Density on Microwave Assisted Grinding, Int. J.

[41] Jones, D.A., Kingman, S.W., Whittles, D.N., Lowndes, I.S., 2005, Understanding

[42] Florek, I., Lovas, M., Murova, I., 1996, The effect of microwave radiation on magnetic properties of grained iron containing minerals, in: Proceedings of the 31st International

[43] Kingman, S.W., Corfield, G.M., Rowson, N.A., 1999, Effect of microwave radiation upon the mineralogy and magnetic processing of amassive Norwegian ilmenite ore, Magn.

[44] Kingman, S.W., Rowson, N.A., 2000, The effect of microwave radiation on the magnetic properties of minerals, J. Microwave Power Electromagn. Energy 35 () 144–150. [45] Cui, Z., Liu, Q., Etsell, T.H., 2002, Magnetic properties of illmenite, hematite and oilsand

[46] Sahyoun, C., Kingman, S.W., Rowson, N.A., 2003, The effect of heat treatment on chal-

[47] Uslu, T., Ataly,U., Arol, A.I., 2003, Effect of microwave heating on magnetic separa- tion

of pyrite, Colloid Surf. A: Physicochem. Eng. Aspects 225, (2003), 161– 167.

Microwave Assisted Breakage, Minerals Engineering, 18, pp. 659-669.


**Section 2** 
