was recently at Harmony Mine at Fochville ( deepest gold mine in the world ) in the North Western Cape training a whole bunch of Site Incident Response Training Teams where I met Jon Tweedt from Iowa in my guest house . Very interesting guy : over a cup of coffee he certainly opened my horizons . I thought the micro-wave in the corner of the kitchen was where I warmed up my supper . I never thought it comes from the invention of radar in the Second World War and what its uses are today .

It ' s an ongoing process but developing micro-wave technology is making big inroads into mining productivity throughout the world , and it is good to see that we are also embracing it in South Africa . This is not one of my normal articles but read on and , according to Jon , see where they are using the principles these days .

Thermal processing of ore minerals has been understood to improve processing rates in mining operations for some time .

Inducing a thermal shock causes microfracturing to occur within ore samples , reducing the total amount of energy required to pulverise the material into a fine enough powder for further chemical processing which removes precious metals from the ore mineral . Conventional heating techniques are costly and time-consuming , and do not yield sufficient energy reductions to justify their use . Microwave heating , however , is capable of rapidly super-heating only the target mineral while leaving the surrounding gangue material almost entirely unprocessed .

This rapid heating causes very fast thermal expansion of the target mineral , which increases the internal stresses in ore samples and can cause fracturing on both a micro- and macro-scale . Increased mineral content in certain ores contributes to this phenomenon , and it has been tested and proven by applying microwave power in the range of hundreds of kilowatts up to over

a megawatt . Larger sample sizes obviously require increased power to produce comparable results .

The magnetron tube – which converts standard DC power to microwave power – is limited to a maximum of 100kW at 915MHz . This functions as a cavity resonator which was developed by British scientists and physicists during World War II for use in radar systems . This technology was later applied to industrial thermal processing and remained the standard for nearly 80 years . Research into the optimal ISM frequency band at which to apply microwaves is ongoing , with possibilities including 2450MHz , 915MHz , and 400MHz . Industrialscale microwave generators capable of producing upwards of 100kW within the allowable frequency band of 900-930MHz have been unavailable until recently .

In the meantime , transistor technology became ubiquitous and subsequently replaced vacuum tube technology in nearly

Andrew Perks is a subject expert in ammonia refrigeration . Since undertaking his apprenticeship in Glasgow in the 1960s he has held positions of contracts engineer , project engineer , refrigeration design engineer , company director for a refrigeration contracting company and eventually owning his own contracting company and low temperature cold store . He is now involved in adding skills to the ammonia industry , is merSETA accredited and has written a variety of unit standards for SAQA that define the levels to be achieved in training in our industry .