On-line monitoring of aqueous base metal solutions with transmittance spectrophotometry

• Conditions on a zinc plant in Namibia were simulated with Cu, Co and Zn solutions.
• The metals could be measured online with an industrial NIR–vis spectrophotometer.
• The transmittance spectra could be visualized with linear discriminant analysis.
• PCR, PLSR and SVR models could estimate the metal concentrations accurately.

Transmittance spectrophotometry was used to monitor copper, cobalt and zinc in solution in laboratory experiments. The samples simulated plant conditions encountered on the Skorpion zinc mine in Namibia and were prepared using a simplex centroid mixture design. Principal component, partial least squares and support vector regression models were calibrated from visible and near infrared absorption spectra. All models could accurately estimate the concentrations of all the metals in solution. Although these models were affected by nickel contamination, the Cu models were less sensitive to this contamination than the Co and Zn models. Likewise, elevated temperatures led to degradation of the calibrated models, particularly the Zn models. The effects of these conditions could be visualized by a linear discriminant score plot of the spectral data.

Score plot generating by linear discriminant analysis, showing the projection of 307 spectral variables associated with different conditions in an aqueous solution of Cu, Co, Zn and Ni at different temperatures.Figure optionsDownload as PowerPoint slide