Kalahari Manganese Ores - Phase Analysis Using Quantitative XRD

Quantitative mineralogy using XRD and TOPAS Rietveld refinement helps in enhancing manganese smelter operation in South Africa. Precise knowledge of the phase composition of the ore helps in establishing the empirical relationships between the quantitative mineralogical data and the amounts of energy and reductant required during the smelting process.

South Africa is a major producer of manganese globally. Most of the material is obtained by smelting ores having complex mineralogy. Quality control of the smelter feeds is traditionally carried out using bulk chemical methods. However, the energy and reductant (e.g. coal) required to process the material in the smelter is determined by the ore’s phase composition, since the minerals have different melting points and valence states of manganese. Therefore, the quantitative mineralogy of the manganese ore from the Kalahari deposit (Northern Cape province) was recently studied applying XRD and DIFFRACplus TOPAS.

Experimental “pro XRD” Aspects

XRD and TOPAS Rietveld analysis are preferred to scanning electron microscope (SEM) techniques for the mineral system for the following reasons:

  • XRD sample preparation is cost-effective for a smelter
  • Mineral identification using XRD is considered better than EDS
  • Sub-micron level texture of particles hinders determination of hematite and other minerals using EDS, while this is not applicable for XRD
  • The acceptable accuracy limits for the key phases (1 – 2 wt-%) is good enough for determining the smelting behaviour of the ore

Two Mn-ore reference materials, SARM 16 and 17, and drill core samples were measured with the help of a D500 diffractometer, a secondary graphite monochromator, Cu radiation, and a scintillation counter. Step scanned powder patterns were studied using TOPAS and applying the fundamental parameters approach.

TOPAS quantitative analysis does not have tube ageing problems, does not need calibration, takes into account the whole powder pattern and thus is not affected by peak overlap. Moreover, physically intact crystallite size and strain parameters can be obtained apart from the phase concentrations.

Results

Quantification of nine minerals were done in low-grade ore and up to 12 were quantified in high-grade ore. The 3 sigma absolute standard deviation of the phase content is below 1 wt-%. The accuracy of the XRD and TOPAS Rietveld method, which is rapid, was validated by independent but slower and more challenging methods such as quantitative SEM and ICPOES. Element and oxide concentrations were determined from the XRD phase composition as per phase stoichiometry. They were in good agreement with the results from micro-analysis (see Figure 2).

Conclusions

XRD and TOPAS analysis offer quantitative mineralogy results ideal for quality control in Mn smelters. This is significant as different ore compositions may satisfy the ore’s grade requirements but at the same time display different process parameters. The TOPAS results are reliable and permit the prediction of smelter operation parameters such as the amount of the reducing agent and energy consumption of the furnace. This shows that XRD and TOPAS have a large potential for optimizing smelter operation and ore quality control applications. In addition, the application of fast one-dimensional detectors which can discriminate fluorescence radiation (LynxEye) enhances data collection speed and helps in routine quality control.

This information has been sourced, reviewed and adapted from materials provided by Bruker AXS Inc.

For more information on this source, please visit Bruker AXS Inc.

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