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Microwave in Minerals Processing and Metallurgy (8 replies)
e2V Technologies have so far come closest with their ProWave microwave vermiculite exfoliation system. Other than that, Rio Tinto are cooperating closely with Nottingham University (UK), and I am aware of ongoing research at Stellenbosch in South Africa.
My understanding is on a lab scale results look promising, but the material transport (i.e. making a continuous feed) is one of the main complicating factors that has kept it from industrialisation.
Certain minerals heat up in a microwave field, others do not. I have explored this for the last 10 years, funded by Barrick Gold H.O. Group, which was interested in distinguishing between gold bearing sulphides and pregnant robbing carbon. The emphasis was on selective machine sorting, using as little MW energy as allowed by sensitive IR sensors. Undesirable rocks would be blown of the belt employing standard sorting technology. Even that, I decided, was too costly for sulphide ore upgrading; the savings in the Mill are just not large enough. So, in semi-retirement, I had the fortune of my grandson joining me in trying to bring the costs further down by doing away with IR sensors and air blasting. The rocks again go through a MW field, the mixture of warm and cold rocks still falls on a belt, but this belt is surfaced with a layer of thermosensitive adhesive. The warm rocks stick, cold ones don't, resulting in different belt discharge trajectories for the two.
I waited for a positive response from you knowing you were investigating the MW some time now.
I did work with a Russian type x-ray unit called RADO- it scanned screened crush ore for the minerals one selects- Cu, Fe, S, Au and then used a similar air blast - it calculated the speed of the belt and the time from observance to position of blast and then blew it off with an air blast.
We found however that the x-ray was not that effective deeper into the ore- so it meant smaller sizing and better crushing to start with it worked pretty well selecting minerals visible on the surface and its recovery went quite well only real drawback was if you had encapsulated free gold, it would not show. Back to the MW, what were the power requirements per KW per ton equivalent to get the temp up to your experiment level? Surely that also is a function of particle size and heat capacity for that ore specific? My experience was MW on huge scale was too costly on power and that was for high carbon volumes- not even ore where moisture also played a role for sure.
My second knowledge of MV was from us bureau of mines. In paper 1989 was declared the influence MV on the several minerals. Was showed, that sulphides was warm, other (quartz, calcite etc.) was cold.
I see a comment really to show that it is possible to push the limits of mining in general and mineral "dressing" in particular, even with modest means, by stepping outside our "silo". In this work, my first objective was to enrich my grandson's study experience, maybe get him interested in mining? My longer term vision is to couple ore sorting to, say a Wirtgen mining machine and leave waste in the pit. That way the cut-off grade can be lowered, old pits even revisited by mining marginal ore? This kind of thrifty thinking has disappeared in the last 20 years, time for the cycle to reverse as it always does in mining.
Regarding your kWatt/tonne question, I can't answer that (yet). In theory, the system only draws energy for the valuable rocks. Mark and I are searching for low temperature melting glues (the low cost glues used for gluing cartons all require 110 C rocks). The machine Mark is building is intended to explore this summer the variables of glue, T, t, pressure with artificial and real rocks. For the latter we prefer drill core. To sell the investigative program, we will use drill core obtained from a defined ore block which will be re-drilled, say three equidistant cores (27 mm), and cut into 2" length, XRF assayed and then evaluated on Mark's machine. This way we know the geometry at identical weight, eliminating some variables for now and likely showing how arbitrary (incorrect) the current block model is for planning.
Additional work on this subject was done by CANMET: Kazi E. Haque, Int.J.Miner. Process. 57 (1999) 1-24, and by me: G.Van Weert, P.Kondos and O. Wang, CIM Journal Vol 2, No. 3, 2011, 117 - 124. The inconvenient truth is that all of it only scratches the surface of this subject. With the Bureau of Mines and CANMET gone, maybe the Chinese will fill the gap; they are very active exploring non-traditional microwave applications.
Microwave energy is too expensive to use for making lime. It is successfully used for curing rubber tires, speeding up the production of organic compounds, etc., materials that sell for > $1/kg, one order of magnitude more than lime.
After two month we treated rocks sulphides (from refractory gold ore). During the treatment from quartz-box (inside the box was sulphides) output the sulphur liquid. After we had two product- liquid sulphur & calcine. To calcine we provide leaching test. The gold recovery was 90%.
I looked at that for floating activated carbon fines (for regeneration) out of filter-cake, without much success. The concept was that activated carbon would absorb the MW energy preferentially over other substances present and generate bubbles on its surface. At Delft U of Technology we even tried solutions saturated in CO2
The use of microwaves for carbon activation was invented in the 1980's and it earned my privilege to study metallurgy. The issue is that it is cost prohibitive and the name MICRO exactly spells out the problem.
It worked fantastic in small laboratory volumes - the carbon was far less damaged and with the correct amount of moisture actually resulted in a very high absorbance carbon- used coconut shell at the time and the same carbon through a resistivity furnace was less active.
What would you want to do with the idea elsewise- roasting ore?
Unlikely- energy again cost prohibitive-
Solar heating again is finding interest in the treatment of water where the beams are collected through a lens like a magnifying glass and with the heat and energy released destroys chemicals like cyanide - more studies on costing is required, but I can see it take off.