Quantitative analysis of flotation feed using Laser Induced Breakdown Spectroscopy (LIBS) in On-Line, Real Time mode

1. Technical task

• Evaluating the possibility of on-line, real-time LIBS analysis of slurry (60-65% Solid Content) directly in an unpressurized pipe after the hydrocyclone.

• Quantitative analysis SiO₂ and other impurities (Fe₂O₃, Al₂O₃) in low concentrations as well as matrix elements (CaCO₃, MgCO₃). Online LIBS analysis accuracy estimation.

2. Installation site

For measurement, the industrial hydrocyclone was used to increase the solid content from 30% up to 60-65%. The LIOS OnLine system was installed after the hydrocyclone directly over an unpressurized half-pipe, allowing receiving the chemical analysis of slurry in real-time.

3. Samples

The samples taking during the calibration process have the following chemical composition as per laboratory XRF results:

Analyzed Parameter	Minimum, %	Maximum, %
SiO2	0.3	1.0
Fe2O3	0.1	0.3
Al2O3	0.009	0.25
CaCO3	94	97
MgCO3	2	5

4. Experimental section

The experiments were conducted using the LIOS OnLine analysis system based on LIBS and equipped with two lasers of 100 mJ energy each. Spectral data was received using spectrometers with the following ranges: λ = 244-360 nm. These ranges were chosen as most suitable for elements of interest.
Comparing XRF and LIBS analysis, errors derived from sampling, splitting and lab analytical error should be taken into the consideration.

5. Qualitative spectral analysis

As can be seen from the spectra received, elements of interest can be clearly detected and identified. Range: λ = 244 – 360 nm.


Thus, calibration curves for quantitative analysis could be calculated for all of the identified analytes.

 6. Quantitative analysis

According to chemical data of the samples "Lab vs LIBS" calibration curves were calculated. "Lab" refers to the chemical data, while "LIBS" to the laser analysis.

Lab vs LIBS calibration curves

Following table summarizes potential errors that were calculated according to calibration curves:

Analyzed Parameter	R2	Average error	RMSE
Fe2O3	0.9	0.008	0.010
Al2O3	0.87	0.01	0.013
SiO2	0.88	0.037	0.049
CaCO3	0.92	0.149	0.177
MgCO3	0.89	0.104	0.143

  In addition to LIBS analysis, the errors summarize the errors derived from sampling, splitting and lab analytical.

6. Conclusions

• Good correlation between laboratory data and LIBS results and low analytical errors provide good possibilities for implementation of the LIOS OnLine system to perform on-line, real-time measurement of Flotation Feed, fulfilling the Customer’s analytical requirements.

• In addition to LIBS analysis, the accuracy calculation also includes an error, derived from sampling, splitting and lab analytical error.

• Implementation of online LIBS analysis will allow controlling the product quality in real-time, every several minutes and not once in several hours.