Microwaving rocks can save you money on your next mining project!
Of course, we are talking about our new microwave mineral testing (please don’t run off to your kitchen microwave). Microwave treatment can reduce ore competency and improve mineral liberation leading to a coarser grind compared to untreated ores. Not only can this coarser grind size improve downstream processes such as gravity concentration, but it can also increase plant throughput and reduce energy consumption by up to 50%!
With the help of Dr. Erin Bobicki, we have compiled a handy list of answers to your frequently asked questions about microwave mineral testing below! For more information about the many benefits of adding microwave mineral treatment to your project, don’t hesitate to contact our mineral laboratory with your additional questions.
1) What Are Microwaves?
Microwaves are a form of electromagnetic radiation similar to visible light or radio waves. They are generally large with wavelengths between one millimeter and one meter with corresponding frequencies of 300 gigahertz to 300 megahertz. Microwaves are used in everything from your household microwave to military radars and, of course, our microwave mineral testing.
2) How Do Microwaves Heat Things?
Microwave heating occurs primarily by two mechanisms. The first is dipolar rotation—this is what happens in your microwave at home when you’re cooking things. Water is a polar molecule, so when excited the water will try to align itself in the electric field which results in friction and heating. The other mechanism is by ionic or electron conduction, in this case, it’s resistive heating. The ions are moving in the field and that movement causes resistance and Joule heating. That’s what we see in rocks as opposed to dipolar rotation because rocks generally contain very little water.
3) What Happens When You Microwave Rocks?
Rocks are composed of different minerals and different minerals have different microwave responsive properties. When exposed to microwaves, differential heating results in cracking across grain boundaries and improvements in ore liberation after grinding.
4) Do Different Rocks Respond Differently To Microwaves?
Sulfides and different metal oxides tend to heat very well in response to microwaves, whereas silicates, carbonates, and other typical gangue minerals do not. This means that the ores that contain these minerals such as chalcopyrite, pentlandite, galena, pyrite, pyrrhotite, magnetite, etc., heat in response to microwave exposure. Ore texture is also important; ores with a more coarse texture, such as a veiny texture, tend to respond well to microwave-assisted sorting.
5) Why Microwave Ores?
Microwave treatment of ores can result in fractures across grain boundaries which improves mineral liberation and decreases ore competency. We can also use thermal signatures for ore sorting to reject barren rocks prior to grinding.
6) How Much Energy Is Required?
In the pilot plant, we typically aim for less than two kilowatt-hours per tonne of electrical energy.
7) How Energy Efficient is Microwave Treatment?
One of the benefits of microwave treatment is its energy efficiency compared to other heating techniques. The conversion of electricity to microwave energy at the industrial frequency of 915 megahertz is about 90%. For high microwave absorbing material, you can expect about 90% of the energy to be absorbed. If you consider the conversion of electricity to microwave energy, and then microwave energy to heat in a material, you can expect above 80% efficiency during the microwave treatment processes.
8) Is Microwave Mineral Testing Safe?
Microwaves are safe as the wavelengths are long and very easy to contain. Microwave technology is also mature and used extensively in many other industries.
9) What Are The Economic Benefits Of Microwave Treatment Of Ore?
The economic benefits of microwave treatment include energy savings, increased plant throughput, enhanced recovery, improved concentrate grade, and a reduction in tailings production (which means a lower amount to pump and manage).
10) What Is The Throughput Limit Of A Microwave System Of Ore Treatment?
In terms of pure microwave treatment, we are easily able to scale up to 1000 tonnes per hour or more.
11) Which Ore Particle Sizes Should Be Treated By Microwaves?
In terms of particle size, we’re not generally limited in terms of microwave penetration depth. We can treat crushing product, such as primary grind feed, but for smaller sizes we’re primarily limited by what we can efficiently sort.
12) What Are the Environmental Benefits Of Microwave Treatment of Ore?
The environmental benefits of microwave treatment include reduced energy use in grinding and in downstream processing, reduced greenhouse gas emissions that can directly result from the reduced energy use, the generation of fewer tailings, and reductions in water and reagent use.
13) What Happens When There Is Water In The Ore?
If there are low concentrations of interstitial water, exposure to microwaves can actually enhance the heating and fracture.