Farmers want it. Miners do not. The disputed item is element 15 on the periodic table – phosphorus.
Essential for healthy crops, but a ‘killer’ in the iron and steel industry.
In Western Australia, home to big cereal-growing areas and iron ore mining, the phosphorus issue is profound.
Farmers’ soils need a generous dose of phosphorus rich fertiliser to make up for a natural deficiency. But travel 1000 kilometres north from WA’s wheatbelt and you will find a different story – iron ore miners who would pay handsomely to have phosphorus removed because ores with high phosphorus will not be accepted by steel mills, or can only be sold at a hefty discount.
This is where the CSIRO’s Minerals Down Under Flagship is working to make a difference, taking up the phosphorus challenge at a number of levels, including the hunt for a cost-effective method of lowering phosphorus levels in iron ore, and looking for a quicker and better way to identify phosphorus in an orebody.
A key to the identification challenge is the use of electron microscopy to peer deep inside a mineral assemblage to determine not just how much phosphorus there is, but precisely where is it located so a method of removal, or lowering of phosphorus levels, can be developed.
Phosphorus in iron ore is just one of many uses of a variety of electron microscopes used by CSIRO.
Similar work has been carried out on problems with ilmenite, nickel and uranium ores where understanding the distribution of impurities within grains can yield rich rewards.
However, none of the work undertaken so far has the potential to yield as big a reward as solving the problem of high phosphorus, widely regarded as the ‘holy grail’ of iron ore mining with a prize valued in the billions of dollars.
One estimate is that up to eight billion tonnes of ‘high-phos’ ores are located close to rail and port facilities in WA’s Pilbara region, but are undeveloped because they grade more than 0.1 per cent phosphorus, enough to turn steel brittle and unusable in some applications if not removed.
Several attempts have been made to find a commercial solution to the problem of high-phosphorus ores, but the most successful approach so far has been to blend high and low-phosphorus ores to achieve a level satisfactory to customers, generally less than 0.08 per cent phosphorus.
In this article, we speak with Colin MacRae, manager of CSIRO’s MicroBeam Laboratory and a researcher in advanced x-ray microanalysis of large areas at the nanometre scale.
Treadgold: How big an issue is phosphorus for the iron ore industry?
Colin MacRae: It is a major challenge.
We see a large number of iron ore deposits that are phosphorus affected.
The best deposits of high-grade ore are depleting and it is becoming increasingly difficult to find low phosphorus ores.
T: How is the issue being tackled by CSIRO?
CM: There are two groups involved.
The microscopy group is identifying the different occurrences of phosphorus within iron ore, while another group has developed a number of methods to remove it, including one that is being trialled on ores to see which of the phosphorus types it removes.
T: This answer indicates that the phosphorus occurs in a number of ways?
CM: It does, and what we’re doing is surveying a number of orebodies.
We start by looking at the material before it has had any work done on it, and then at various stages of the process to see how it behaves so we can fine-tune the process.
The key to what we’re doing is the pursuit of a cost effective method of phosphorus removal.
T: What tools are you using to see and measure phosphorus?
CM: The key tool is a very high-resolution electron microprobe which allows the fine-scale dissemination of the different phosphorus phases, which is critical to understanding its deportment of iron ore, particularly an ore type known as goethite.
T: By phases, do you mean the dissemination changes over time?
CM: There are certainly different forms of phosphorus depending on whether it has been exposed to groundwater and altered from a haematitic to a goethitic type of deposit, a process that enables the phosphorus to move from one part of an iron oxide structure to another.
T: Has this type of work been done before?
CM: It has, but what hasn’t been done is to follow selectively the removal of the phosphorus.
One of the skills we’re bringing to this challenge is to work hand-in-hand with the group that is developing the technique, and help fine-tune it.
That’s a skill we’ve been able to apply on a number of projects.
We’ve done something very similar when we worked on the removal of radiogenic elements from ilmenite.
T: The value you bring is to use the tools at your disposal to aid the group designing a process?
CM: Yes. With a better understanding of what’s happening at a nano-scale we can optimise the process far faster than could be normally achieved.
T: Presumably phosphorus in iron ore is just one project?
CM: It is. We’re also working on nickel in laterites, which is a similar issue to phosphorus in iron ore, except in this case nickel is not a contaminant but a valuable element we wish to recover.
The nickel deportment is at the hundreds-of-nanometre scale so it requires very high end microanalysis, and a similar problem involves a major uranium deposit.
T: Some of the equipment you’re using must be rather sophisticated?
CM: We were the first group in the Southern Hemisphere to get a field emission electron microprobe, and we’re in the unique position of helping the company that makes them with the development of the device.
We work closely to develop new capabilities that are then on-sold around the world, which means we have a research and commercialisation agreement.
T: How does the device work?
CM: A normal electron microprobe has a hairpin tungsten filament which heats white-hot with electrons boiled off it.
That’s good, but high-resolution work effectively needs a single crystal that has a zirconia coating over it.
The surface is again white-hot, but it’s a very small surface and the electrons are driven off in a field emission effect.
Basically it’s a way of giving us a very small electron spot and that means we can do our mapping and analysis at a very high resolution, much higher than a traditional electron source.
T: And that means you can identify the microscopic composition of the material being analysed?
CM: Yes, but it also means we can identify the phases in which the element of interest is occurring, and see whether that element can be targeted or removed through the process we’re looking at, and then re-survey to see how successful the process has been.
T: Is the phosphorus work a pure CSIRO project?
CM: It is a research project primarily funded by CSIRO, but as it gets closer to commercialisation it is being looked at by a number of iron ore companies.
It’s really moving into a new phase, moving out of the small-scale and scoping out its overall applicability.
T: You’re using more tools than the electron microprobe, can you talk about that?
CM: Well, the other one worth mentioning is the work being done at high temperature with an environmental scanning electron microscope, which is being used in a new titanium process that is being developed by the Light Metals Flagship.
It’s a similar story using a different instrument in which the group is developing a technique for titanium production. In that case we can actually mimic the process at high temperature inside an electron microscope.
That is a pretty fast way of optimising a process because you can see what’s happening in real time.
T: Your work seems to be looking at ways to solve mineral processing problems: wouldn’t it be better to become involved before, rather than after, the event?
CM: There’s no doubt that it’s a huge advantage to understand the initial mineralogy of an orebody and then understand what your process is doing to it, because if the mineralogy changes slightly you have a very good idea what will happen in your process.
T: What you’re saying is understand the science first and then design the process, not the other way around?
CM: Quite often processes are very successful when the ore is consistent.
When it changes you have to reassess what you’re doing.
It’s always our desire to work at the start of a process, but quite often we come in late and have to try and understand why the efficiency of a process has fallen away.
*This article originally appeared in the October issue of CSIRO’s Process magazine.
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