Advanced interpretation of the luminescence decay-time of minerals for sorting purposes
Navid Khajehzadeh *
Department of Electrical Engineering and Automation, Aalto University School of Electrical engineering,
Helsinki, Finland, Doctoral Student, Mobile: +358 50 409 0486,
Email: navid.khajehzadeh@aalto.fi
The grade of material entering into comminution, classification and concentration steps of mining is directly affecting the sustainability. Among different sensor based techniques, the determination of materials using photo-physical parameters has led to the development of multitude of apparatuses such as time-resolved laser-induced fluorescence spectroscopy (TR-LIFS). TR-LIFS technique measures the minerals re-emitted light when excited by a flash light. This re-emission time (named luminescence life-time) can be modelled by exponential decay-time curves. The decay time parameter of the model is a characteristic and unique property of the mineral and it is highly improbable that two different luminescence emissions will have exactly the same decay time. There have been various methods proposed to extract decay-time parameters of luminescence life-time. However, the challenge of data processing appears when luminescence cannot be modeled as a mono-exponential decay due to the simultaneous presence of several fluorescent species and different non-radiative relaxation paths. For instance, method of moments can be suggested as a capable method for mono-exponent decay-time analysis while is discouraged for the higher number of decay parameters. In this research a mathematical modelling algorithm rapidly learning the correct number of decay time parameters will be proposed. The method is based on finite Legendre Transformation (fLT) on the data.
Legendre Transformation decomposes the data down to Legendre domain components. The advantages of
Legendre domain fitting over time domain fitting are the speed and precision. After improving the speed using fLT, the right number of decay-time parameters are learned with a new designed cost function. A penalty term correlated with the number of exponent parameters of the model is executed in the regularization part of the cost function. The proposed approach will significantly enhance the interpretation of the minerals and it improves the efficiency of the ore sorting accordingly.
KEYWORDS
Luminescence, Decay-time, finite Legendre Transformation, Sorting