X-ray transmission enhances density distribution

Traditional density distribution analysis techniques have limitations in determining materials of high densities (above 4g/cc). Anglo American's iron ore business, Kumba Iron Ore, supported a research project to develop an alternative density separation technique to achieve this for the characterisation of low-grade iron ores.

Safety and innovation

Shamudulu Shamaila, who heads up this research team at Anglo American's Technical Solutions Research, elaborated on the technique that has been developed, embodying two of the group's core values: safety and innovation.

As the industry increasingly processes lower-grade haematite ore, determining the distribution of density in a sample at density values greater than 4g/cc has become necessary. Traditional "sink and float" density distribution analysis has remained pegged at this ceiling for some time and, in certain applications, it is also associated with the use of Tetrabromoethane, a chemical classified as hazardous to humans and the environment. Although the handling of such chemicals is governed by strict safety guidelines, Anglo American's commitment to safety is driven by a desire to eliminate hazardous chemicals wherever possible.

Alternative methods

Tasked with developing an alternative method to measure particle density, the Kumba Iron Ore-sponsored research project began in 2010 as a collaboration between Anglo American's Technical Solutions Research department and external instrumentation experts, JC Bachmann, a German company with leading expertise in radiometric material analysis.

The researchers were tasked with developing an alternative method to measure particle density, as well as the physical separation and classification of different particles according to their measured densities. To achieve this, optical imaging, laser and X-ray transmission (XRT) were harnessed to measure particle volumes and densities. These integrated tools are housed in an analytical unit called the XRT Washability Monitor (WAMON).

Between 2010 and 2012 modifications were made to the prototype instrument and, in 2013, analytical application commenced with haematite ore at research.

The breakthrough factor is that this technology succeeds in automated analysis of samples of size range 1mm to 25mm on a particulate level, which has previously not been readily achievable. Another benefit is that the technique has eliminated the use of the toxic chemicals traditionally used in this type of analysis. Importantly, the technology also incorporates a robotic sorter facilitating faster processing and repeatability of results.

Four sections

The XRT WAMON comprises four sections: feed, optical, XRT and sorting. The material sample is presented to the optical section via a conveyor belt, during which images are captured through line scan cameras. Next, the material is exposed to X-rays, which is similar to medical X-ray technology. At this point, the information gathered from the optical and X-ray sections is merged through a computer processing unit, making it possible to determine the density of each particle being scanned. The system retains the "address" of each particle on the belt on a continuous basis and in the robotic sorting section there is an option to sort the material into several density ranges.

The instrument's software retains detailed information of each particle and makes it possible for process engineers to draw this information into various statistical models and analyses.

The research team has effectively created an alternative technology that is configured in such a way that, in the future, it could potentially run online within a processing plant, providing real-time process analysis and allowing process engineers to respond far more timeously in making adjustments to the system. Although it is calibrated for haematite at present, it will become possible to calibrate it for other material types.

The development of this monitor reflects an international trend towards increased automation in the mining industry. It is poised to add immense future value to the industry, presenting the opportunity to automate the computation of washability curves at a reduced price, compared to the traditional sink and float method. In fact, XRT WAMON analysis is likely to come in at about half of the cost of existing manual particulate-based analysis methods. Potential savings on cost of chemicals and better process control are, therefore, estimated to be in the millions of rand.