The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.

Reflectance Spectrum Analysis of Mineral Flotation Froths and Slurries

Olli Haavisto

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Electronics, Communications and Automation for public examination and debate in Auditorium AS1 at Helsinki University of Technology (Espoo, Finland) on the 11th of December, 2009, at 12 noon.

Overview in PDF format (ISBN 978-952-248-237-2)   [3020 KB]
Dissertation is also available in print (ISBN 978-952-248-236-5)


The global demand of mining products has increased during recent years, and there is pressure to improve the efficiency of mines and concentration processes. This thesis focuses on froth flotation, which is one of the most common concentration methods in mineral engineering. Froth flotation is used to separate valuable minerals from mined ore that has been crushed, mixed with water and ground to a small particle size. The separation is based on differences in the surface chemical properties of the minerals. Monitoring and control of flotation processes mainly relies on the on-line analysis of the process slurry streams. Traditionally, the analysis is performed using X-ray fluorescence (XRF) analyzers that measure the elemental contents of the solids in the slurries.

The thesis investigates the application of visual and near-infrared (VNIR) reflectance spectroscopy to improve the on-line analysis of mineral flotation froths and slurries. In reflectance spectroscopy the sample is illuminated and the spectrum of the reflected light is captured by a spectrograph. The main benefits of VNIR reflectance spectroscopy with respect to XRF-based analysis are the relatively low cost of the equipment required and the easy and fast measurement process. As a consequence, the sampling rate of the reflectance spectrum measurement is radically faster than in the XRF analysis. Data-based modeling is applied to the measured VNIR spectra to calculate the corresponding elemental contents. The research is conducted at a real copper and zinc flotation process.

The main results of the thesis show that VNIR reflectance spectroscopy can be used to measure temporal changes in the elemental contents of mineral flotation froths and slurries in the analyzed process. Especially the slurry measurements from the final concentrates provide accurate information on the slurry contents. A multi-channel slurry VNIR analyzer prototype is developed in this thesis. When combined with an XRF analyzer, it is able to measure the slurry lines with a very fast sampling rate. This considerably improves the monitoring and control possibilities of the flotation process. The proposed VNIR analyzer is adaptively calibrated with the sparse XRF measurements to compensate for the effect of changes in other slurry properties. The high-frequency slurry analysis is shown to reveal fast grade changes and grade oscillations that the XRF analyzer is unable to detect alone. Based on the new measurement, a plant-wide study of the harmful grade oscillations is conducted in order to improve the performance of the flotation process.

This thesis consists of an overview and of the following 7 publications:

  1. Olli Haavisto, Jani Kaartinen, and Heikki Hyötyniemi. 2006. Optical spectrum based estimation of grades in mineral flotation. In: Proceedings of the 2006 IEEE International Conference on Industrial Technology (ICIT 2006). Mumbai, India. 15-17 December 2006, pages 2529-2534. © 2006 IEEE. By permission.
  2. Olli Haavisto, Jani Kaartinen, and Heikki Hyötyniemi. 2008. Optical spectrum based measurement of flotation slurry contents. International Journal of Mineral Processing, volume 88, numbers 3-4, pages 80-88. © 2008 Elsevier Science. By permission.
  3. O. Haavisto and H. Hyötyniemi. 2008. Partial least squares estimation of mineral flotation slurry contents using optical reflectance spectra. In: Proceedings of the 11th Conference on Chemometrics in Analytical Chemistry (CAC 2008). Montpellier, France. 30 June - 4 July 2008, volume 2 (Process Analysis), pages 81-85. © 2008 Cemagref. By permission.
  4. Olli Haavisto and Heikki Hyötyniemi. 2009. Recursive multimodel partial least squares estimation of mineral flotation slurry contents using optical reflectance spectra. Analytica Chimica Acta, volume 642, numbers 1-2, pages 102-109. © 2008 Elsevier Science. By permission.
  5. Olli Haavisto and Jani Kaartinen. 2009. Multichannel reflectance spectral assaying of zinc and copper flotation slurries. International Journal of Mineral Processing, volume 93, number 2, pages 187-193. © 2009 Elsevier Science. By permission.
  6. Olli Haavisto. 2010. Detection and analysis of oscillations in a mineral flotation circuit. Control Engineering Practice, volume 18, number 1, pages 23-30. © 2009 Elsevier Science. By permission.
  7. Olli Haavisto and Heikki Hyötyniemi. 2009. Reflectance spectroscopy in the analysis of mineral flotation slurries. In: Luis Bergh (editor). Pre-prints of the Workshop on Automation in Mining, Mineral and Metal Industry (IFACMMM 2009). Viña del Mar, Chile. 14-16 October 2009, 6 pages. © 2009 International Federation of Automatic Control (IFAC). By permission.

Errata of publications 2, 3 and 6

Keywords: froth flotation, mineral concentration, reflectance spectroscopy, data-based modeling, X-ray fluorescence

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© 2009 Helsinki University of Technology

Last update 2011-05-26