Combining laser-induced breakdown spectroscopy (LIBS) and time-gated Raman spectroscopy for underwater ores...

As the land-based mineral deposits are depleting fast, deep-sea metal mineral resources have been proven to have a great mining value. Traditional deep-sea mineral detection techniques require ore samples to be brought back to the laboratory by geological sampling methods for chemical analysis. This approach suffers from substantial time delays and cannot provide real-time, large-scale and rapid feedback during the mining process. Therefore, there is a critical demand for the rapid and in-situ technique of underwater ores identification without requiring the ore samples to be brought back to the laboratory.

We combined LIBS and time-gated Raman spectroscopy for the rapid identification of underwater ores. An integrated LIBS-Raman setup was built based on a same laser and a same spectrometer, to acquire both the elemental and molecular information of ore samples immersed in deionized water. PLS-DA was used to establish the classification model based on the LIBS and Raman spectra. Two data fusion strategies including data-level fusion and feature-level fusion were used for the combination of LIBS and Raman data. The data fusion strategies offer a significant improvement in ores classification compared to using the individual LIBS or Raman data. The data-level fusion model provides the best classification accuracy of 99.11%, while the feature-level fusion model has a slightly lower accuracy of 98.44% but with a much reduced computation time. The feature selection by successive projections algorithm (SPA) involved in the feature-level fusion improves the computing efficiency and the interpretability of the model.

The present results demonstrated the capability of LIBS and Raman techniques for the rapid identification of underwater ores. The integrated setup that combining LIBS with time-gated Raman spectroscopy based on a same laser source and a same spectrometer could be beneficial for developing down-sizing and low-power consumed underwater devices for the future deep-sea mining applications.