Does low grade ore mean low performance?
by Keith Vining
Understand your ore to maximise its value
If you’re a ‘low grade’ ore producer, does that really mean your ore will suffer from low performance?
In my previous blog, I outlined the lump ore characteristics of major hematite-goethite ore components. It highlighted the fact that no single ore component has optimum properties across the board.
The same is true for fine ores (nominally -6.3mm). A fine ore is an assemblage of components with complementary properties; and a high-performing ore or blend is a balanced assemblage — our goal is to work with you to understand how to achieve the best possible balance.
So, if beneficiation is not economically feasible for you, then all hope is not lost. It is possible to work towards optimising fine ore performance by fully understanding your material and how to blend it — in order to maximise performance and minimise deleterious effects.
What defines ideal sinter?
Sintering is the major utilisation route for fine ore. Essentially, an ‘ideal’ sinter should be physically strong to resist breakdown. It should also have sufficient macro-/micro-porosity to allow ready reduction in the blast furnace.
Sinter mineralogy and structure strongly influence these properties. These are in turn determined by:
- -1mm ore chemistry — with the right proportions of reactive hematite, alumina and silica in the granule-adhering fines layer. These maximise SFCA formation and minimise the proportion of glassy phases
- particle size distribution — sufficient coarse particles with low reactivity (e.g. dense hematite, hematite-goethite) to form stable sinter nuclei and the right amount of reactive fines to melt and form strong inter-granule bonds. Too much melt formation and flow can result in filling pores and channels, resulting in high strength, but low productivity
- granulation properties — nuclei with surface micro-roughness to enhance adhesion and ‘keying’ of the adhering particles, and ‘sticky’ adhering ultrafines promote bed permeability (e.g. ochreous goethite is effective as a granulation binder).
Understanding a material, how it blends, and what other materials it works well with can be crucial to its value-in-use and sintering performance.
As an example, the addition of magnetite or hematite concentrate to sinter blends can be a way to ‘sweeten’ the mix and increase Fe grade.
But these concentrates are typically of low reactivity, which affects sinter melt formation. Their uniform sizing also affects granulation and bed permeability.
It is therefore important to understand the limitations to concentrate addition in fine ore blends — this is an area of ongoing collaborative research for our Carbon Steel Futures team.
Work towards ideal sinter performance, even with a low grade ore
If you understand the properties of your ore, and what you can and can’t do with it, then you can optimise performance.
Key to this is to avoid making an immediate value judgement — on the basis of chemistry — that the presence of certain impurities will have a negative impact on your ore.
An example of this is alumina; is it always bad?
Despite the widely held perception that higher alumina levels will always have a negative impact on the properties and behaviour of ore, our research tells us that this isn’t necessarily the case. Reactive alumina is necessary to form the bonding phases that result in high quality sinter.
It’s true that too much alumina in a sinter blend can have undesirable effects on melt properties — mainly, the reduction of fluidity and an increase in the temperature and fuel rate needed to achieve balanced sintering.
But we have also been able to demonstrate that Al-bearing goethite coarse particles can form stable granule nuclei and therefore minimise undesirable effects of higher alumina levels on the sinter melt.
From this example we can see that it is possible for an ore to ‘perform above its weight’, especially when you consider the compatibility of materials.
It’s therefore important not to simply accept your ore as ‘low performance’, where instead there could be potential to prove its value-in-use beyond the chemically-determined grade.
Better understand your ore with a Compact Sintering Test
If you want to know the true effects that alumina and other impurities will have on the performance of your ore, then understanding your product — beyond its chemistry — is vital.
To understand this, the Carbon Steel Futures group has developed a Compact Sintering Test methodology.
This includes laboratory-scale tests to evaluate fundamental sintering properties. I’ve discussed these tests previously in regards to TI strength vs temperature — which is used to evaluate -1mm matrix-forming particles — and assimilation — used to evaluate coarser, nucleus-forming ore particles.
These small-scale sinter experiment tests complement our pilot-scale sintering capability, and mesh seamlessly with our textural classification scheme. Combined, these techniques allow you to determine the value-in-use of your ore beyond chemical composition and, due to the low sample size requirement, can also be used to evaluate exploration samples and provide an early indication of potential ore performance.
These tests mean that you don’t have to just accept your chemical-composition defined ore price. If you find out your ore properties, and understand what can be done with them, then you can support sales and product acceptance with technical marketing data.
This in turn will allow you to be more competitive.
Understand the true value of what you have — partner with CSIRO
Essentially, when it comes to ore, it’s not simply a matter of ‘good’ and ‘bad’. The most significant thing you can do to combat the perception of ‘low performance’ is find out your value-in-use.
At CSIRO, our deep understanding and comprehensive range of evaluation techniques and analytical equipment — from laboratory to pilot-scale — puts our group in a unique position to understand the optimal value-in-use of an ore product.
Want to know more about how we can help you understand the properties of your ore? Give me a call on +61 7 3327 4761 or email me directly on Keith.Vining@csiro.au.
Lu, L and Ishiyama, O, 2015. Iron ore sintering. Ch 14 in L Lu (Ed.), Iron Ore. Mineralogy, Processing and Environmental Sustainability, Woodhead Publishing Series in Metals and Surface Engineering: Number 66, 395-433.
Lu, L, Holmes, R J and Manuel, J R, 2007. Effects of alumina on sintering performance of hematite iron ores. ISIJ International, 47(3), 349-358.
Webster, N A S, O’Dea, D P, Ellis, B G and Pownceby, M I, 2017. Effects of gibbsite, kaolinite and Al-rich goethite as alumina sources on silico-ferrite of calcium and aluminium (SFCA) and SFCA-I iron ore sinter bonding phase formation. ISIJ International, 57(1), 41-47.