Solving Clay Problems in Mining Using Combined NIR and XRD

Rapid, semi-automated measurement of quantitative mineralogy can be achieved with the combination of Bruker Fourier-Transform Near-Infrared (FT-NIR) spectroscopy and X-ray powder diffraction (XRD), thus facilitating improved ore recovery and cost savings in the mining industry.

This FT-NIR and XRD combination provides the total mineralogy, including swelling clays. The individual requirements of the mine decide the extent to which each technique is used.

Quantitative Mineralogy

Valuable metals can be efficiently recovered from the ore if the quantitative mineralogy of the source rock is known. For instance, determining the hardness of the rock will be helpful in deciding:

  • the amount of explosives required
  • the drilling time of blast holes
  • the grinding time
  • the type of crusher and mill utilized for comminution
  • the energy used by the mill

Minerals exhibit different separation behavior and reactivity during metal recovery in leaching or flotation.

Advantages of XRD and NIR Combination

Metal recovery will be affected by the presence of gangue minerals, which may consume leach acid or cause the collapse of froth flotation bubbles. The combination of XRD and quantitative TOPAS Rietveld analysis provides quantitative minerals analysis in the mining industry.

XRD is rapid and simple to perform, yielding accurate quantitative results without the need for standards. It is also possible to automate the preparation, to ascertain a reproducible quality of samples. Hence, XRD is an ideal instrument to analyze hard minerals like plagioclase, feldspar and quartz. In addition, XRD can differentiate minerals of very similar chemistry, for instance, the different metal sulfides. Nevertheless, XRD is limited to the analysis of crystalline matter.

Clays are soft minerals, which do not have well defined crystal structure. Their structure may change via swelling, depending on cation exchange or humidity. This causes difficulties in quantification by XRD. Large concentrations of swelling clay are an important concern in mining operation, as they may avoid the acid flow in the leach pad or affect the concentrator process by impacting the stability of froth bubbles. This in turn leads to less recovery of metals. However, the volitional properties of swelling clays make them useful for impermeable liners below stock piles. Soft minerals typically facilitate blasting, drilling and comminution.

NIR spectroscopy quantifies the change of absorption or transmission by molecular vibrations of molecules such as carbonate, hydroxyl and water groups. These molecules are present in most soft minerals, making NIR spectroscopy an ideal technique for exploring those soft minerals.

NIR is a rapid technique requiring minimal sample preparation. This quantitative method uses calibrations that are specific to the mining sites and those matrix effects are detected by XRD.

Cation exchange capacity tests are conducted for calibration of clays. In this manner, NIR can be used to compliment or even substitute for XRD for quantifying clay minerals.

Figure 1 is the schematic representation of using XRD and NIR based on the requirements of the mine. XRD enables monitoring hard minerals, metal sulfides concentration, and other phases that are not determined by NIR.

The schematic representation of using XRD and NIR depending on the requirements of the mine

Figure 1. The schematic representation of using XRD and NIR depending on the requirements of the mine

It is possible to calibrate the NIR for many different minerals (typically soft minerals). The use of a FT-NIR tool enables the mine to monitor selected minerals and apply the data for process improvement.

However, XRD analysis is still required for the NIR data calibration, an essential process for mines. This can be either performed internally or by a third party.

Conclusion

The combination of NIR and XRD is required for the analysis of complete bulk and clay mineralogy. In this case, the NIR may be used for swelling clay only, while the XRD for other phases.

About Bruker X-Ray Analysis

X-Ray Diffraction (XRD) is a high-tech, non-destructive technique for analyzing a wide range of materials, including fluids, metals, minerals, polymers, catalysts, plastics, pharmaceuticals, thin-film coatings, ceramics, solar cells and semiconductors.

Throughout industry and research institutions, XRD has become an indispensable method for materials investigation, characterization and quality control. Example areas of application include qualitative and quantitative phase analysis, crystallography, structure and relaxation determination, texture and residual stress investigations, controlled sample environment, micro-diffraction, nano-materials, lab- and process automation, and high- throughput polymorph screening.

This information has been sourced, reviewed and adapted from materials provided by Bruker X-Ray Analysis.

For more information on this source, please visit Bruker X-Ray Analysis.

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