Laser-based online analysis of minerals

2 Laser module for the dust analysis, ready for operation at the drilling unit

3 Singled limestone particles on a belt conveyor [RWTH-AMR]

$4 Schematic diagram of the laser sorting system. Rock particles move on a belt conveyor with speeds of up to 3 m/s from left to right. A 3D camera measures position and shape of the particles and beam of the laser analysis module (LIBS) determines the material composition. Depending on the measured results, the particles are discharged by means of compressed air jets in various fractions 1–4.$

4 Schematic diagram of the laser sorting system. Rock particles move on a belt conveyor with speeds of up to 3 m/s from left to right. A 3D camera measures position and shape of the particles and beam of the laser analysis module (LIBS) determines the material composition. Depending on the measured results, the particles are discharged by means of compressed air jets in various fractions 1–4.

5 Laser unit for single particle analysis on belt conveyors; left: Control cabinet, centre/top: Laser module, centre/bottom: Belt conveyor with sorting material and laser-induced plasmas (long-term exposition), right: Spectrometer module

6 Comparison of laser analysis with XRF, for Al (top), for Fe (bottom)

7 Deposit model for Al (top) and Si (bottom) from laser analysis

8 Calibration of the laser reading for Mg with XRF reference analyses

9 Limestone quarry in Austria

10 Distribution of the measured Mg concentrations and threshold value for the grouping

$11 Mean magnesium content of the sorted fractions for limestone and dolomite$

11 Mean magnesium content of the sorted fractions for limestone and dolomite

12 Application scenarios for laser direct analysis. The measured objects run from left to right on a belt conveyor.
Top: single-grain sorting, Middle: characterization of material streams, Bottom: characterization of material streams and grouping

1 Laser-induced plasma on a limestone

Summary: At the Fraunhofer Institute for Laser Technology, a laser method for determination of the composition of minerals was developed that can be used for the fast online analysis of a wide range of raw materials. At a limestone quarry, this method was applied to demonstrate the generation of a deposit model based on online analysis already during drilling. The non-contact multi-element analysis with which a direct sorting criterion can be determined, also facilitates automatic and economic single-particle sorting of rocks and ores. On a demonstration rig, an efficient reduction of the MgO content of limestone production samples could be realized.

1 Introduction

To ensure efficient exploitation of natural raw material deposits and their high-quality processing, many deposits, in particular those which are inhomogeneous with a complex structure require both precise mapping of the deposit as well as sorting of the extracted raw materials.The sorting processes used in the processing of minerals separate the material to be sorted based on a sorting criterion, which only indirectly correlates with the chemical composition of the material. For example, ores are separated according to their density or their surface wettability. For sorting that...