Real-time analysis of base metals in Cu and Zn solvent extraction processes

Introduction

Solvent extraction and electrowinning (SX/EW) are a twostage hydrometallurgy technique within the field of extractive metallurgy to obtain metals from their ores and convert to a pure metal cathode, ready for use in industry. SX/EW processing is best known for its use by the base metals industry (copper, zinc), but this technology is also successfully applied to a wide range of other metals including cobalt, nickel and uranium.

Solvent extraction involves the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials. These processes require a lot of energy and chemicals. Constant monitoring enables pro-active reaction of operations on changes in raw materials and lead to a more efficient use of resources. Solvents i.e. concentrated sulphuric acid (pH 0 – 2) are not easy to handle and require specific safety and environmental regulations. Real-time analysis does not require sample taking and handling by operators and ensures safer work conditions.

Instrumentation

Measurements were performed using a Malvern Panalytical Epsilon Xflow spectrometer, equipped with a 15W, 50 kV silver (Ag) anode X-ray tube, 6 software-selectable filters and a highresolution SDD30 silicon drift detector. Sample preparation Eight setup samples were prepared in the laboratory and used to calibrate the Epsilon Xflow. To prepare the standard solutions five elements Cu, Zn, Fe, Ni and Mn were solved in 5 M sulfuric acid. To dissolve all material and keep samples stable during measurements, all samples were heated and kept while measuring at 50°C to avoid recrystallization of the highly concentrated liquors.

Measurement procedure

50 ml of each solution was stabilized at 50°C using a hot water bath and was circulated through the flowcell. Only one measurement condition was used to measure the five targeted elements in the liquids (table 1). The measurement time was set at 60 seconds per sample. An example spectrum is shown in figure 1.

Table 1. Measurement conditions

Figure 1: Example Spectra of one of the samples

Calibration results

Figures 2, 3 and 4 show the calibration graphs for Cu, Zn, and Fe in sulfuric acid solution. The graphs show good correlations between certified concentrations and measure intensities. Detailed calibration results are listed in Table 2. The RMS (Root Mean Square) value is equivalent to 1 sigma standard deviation. The higher observed RMS for Cu originates due to sample inconsistencies of the higher concentrated samples.

Table 2. Calibration details (* RMS: The more accurate calibrations have the smaller RMS values)

Figure 2. Calibration graph for Cu in H

Figure 3. Calibration graph for Zn in H

Figure 4. Calibration graph for Fe in H₂SO4

High precision measurements for major, minor and trace elements

An unknown sample was circulated over 2 hours through the flowcell and kept constantly at a temperature of 50 ºC. The results for the main elements Cu and Zn are shown in Figure 5. The results for all measured elements, the absolute RMS and the Relative RMS for all the elements measured are listed in table 3.

Figure 5. Results of running a routine sample for almost 2 hours

Table 3. The results for all measured elements, the absolute RMS and the Relative RMS for all the elements measured

Conclusion

The results clearly demonstrate the capability of Epsilon Xflow to monitor concentrations of majors, minors and traces during solvent extraction processes (SX/EW). The solution is designed to handle concentrated sulfuric acid at higher operating temperatures. Besides the analytical instrument, Malvern Panalytical is ready to support the full implementation in a production environment.

The combination of state-of-the-art hardware and powerful software deconvolution algorithms in the software allow the Epsilon Xflow to provide accurate analysis every minute.