Iron is the fourth most abundant element in the Earth's crust, but economic concentrations are dominated by comparatively rare iron oxide forms; magnetite (Fe3O4), hematite (Fe2O3), goethite (FeOH), limonite (FeO(OH)nH2O) and siderite (FeCO3). The mineralogy of iron ore impacts its commercial value and how it is processed. Identifying iron mineralogy along with gangue minerals which impact the beneficiation are an essential part of iron ore analysis.
Most iron ore is used to manufacture steel which is impacted by the concentration of other elements present in the ore as they affect steel quality. For this reason, standard iron ore analysis is a multi-element analysis which reports the major rock forming elements and a suite of trace elements. .
Iron ore samples are fused with a lithium borate fusion containing an oxidising agent followed by XRF instrument analysis for major rock forming elements and selected trace element concentrations. Results can be reported as either un-normalised or normalised to 100% (excluding the LOI). Loss on Ignition (LOI) is always carried out as part of the multi-element analysis.
|Code||Analytes & Ranges (%)||Description|
|Al2O3||0.01-100||K2O||0.001-6.3||Sn||0.001-1.5|| Fused disc XRF.
LOI included as part
of this procedure.
|Loss on Ignition.
Thermo-gravimetric Analyser (TGA).
ALS offers a range of LOI methods by either furnace or Thermogravimetric Analyser (TGA). A variety of temperatures are available, either at a single temperature or range of temperatures run consecutively to fully characterise the volatile component of samples. To identify only the unbound water in a sample heating is limited to 105ᵒC whereas if water bound in crystals and other volatile components are required, heating is typically increased to 1000ᵒC.
Thermogravimetric analysis is when the mass of a sample is measured with time and temperature changes. Measurements can be customised as required to fully characterise volatile components, especially for samples with variable amount of water bound in minerals.
|OA-GRA10||H2O (moisture)||Gravimetric procedure after drying at 105ᵒC for 2 hours|
|OA-GRA11||H2O (moisture)||Gravimetric procedure after drying at 105ᵒC for 24 hours|
|OA-IR05||H2O (moisture)||Infrared detection system measurement of water with heating to 110ᵒC|
|OA-IR06||H2O and crystalline bound water||Infrared detection system measurement of water with heating to 110ᵒC|
|OA-GRA05xf||Loss on Ignition at 500ᵒC||A sample is pre-dried at 105ᵒC before heating to 500ᵒC to determine loss on ignition|
|OA-GRA05||Loss on Ignition at 1000ᵒC||A sample is heated to 1000ᵒC as received to determine unbound water plus bound volatile component in total.|
Davis tube recovery (DTR) is a lab-scale version of the ore beneficiation process that separates magnetic from non-magnetic fractions. After crushing and pulverising, samples are placed in an angled tube on the DTR instrument and agitated while passing water through the tube. The tube is positioned between the poles of a strong electromagnet which prevents magnetic particles from washing through the tube with the non-magnetic particles.
The separation of magnetic from non-magnetic particles is affected by the pulverisation size specifications – the finer the grinding, the more magnetic fraction will be recovered as it will be freed from non magnetic gangue minerals which would increase the weight to magnetic strength. Initial test work may be required to identify the optimum protocol for a new ore deposit to ensure the method approximates the mine scale beneficiation.
|DTR_PREP||Multi-stage sieving and pulverising.|
|DTR_FeRec||DTR iron recovery.|
|ME_XRF21h/c/t||XRF analysis on various DTR fractions (head, concentrate, tailing). 0.7g sample each|
|OA-GRA05xh/xc/xt||Loss on Ignition reported as part of this method.|
|Fe-VOL05||Ferrous iron by titration (FeO; 0.01-100%). 1g sample|
|MAG-DTR||Recovery of magnetic fraction by DTR|
Magnetic susceptibility (Mag-Sus) is a dimensionless measurement of how magnetised a material will become in a magnetic field. The measurement is functionally the proportion of sample that is magnetic. This is often an estimation of magnetite content but other ferromagnetic minerals, like maghemite and ilmenite (FeTiO3), are also magnetic and will be included in the total.
Yes. ALS routinely monitors fineness after both the crushing and pulverising steps. A subsample of the material is passed through the screen size specified by the method to ensure the required percentage of material passes. This information is recorded and can be accessed via Webtrieve™ and/or reported as QC data.
Characterising bulk density/specific gravity of ore and waste is an essential part of any deposit estimation process.MORE INFORMATION