Lohmeier, and 3 co-authors, reported in 2020 that at a time of resource consumption, it is important to again study the chemical composition of mining and
metallurgical wastes to prevent the dissipative loss of metals and metalloids from the mining value chain. In particular, the recovery of critical elements from wastes is an option to increase the resources of such materials that are economically significant and have an overall supply risk. The authors report on the chemical composition, in particular the critical element content, of granulated slag originating from historical smelting activities in the Tsumeb area, Namibia. Laboratory-based inductively coupled plasma–mass spectrometry (ICP-MS) and X-ray fluorescence (XRF) analyses as well as portable X-ray
fluorescence (pXRF) demonstrate that the slags are on average enriched in base metals (Cu 0.7 wt%, Pb 2.7 wt%, Zn 4.7 wt%), trace metals and metalloids (Cd approx. 50 mg/kg, Mo approx. 910 mg/kg) aswell as critical elements (As approx. 6300 mg/kg, Bi approx. 3 mg/kg, Co approx. 200 mg/kg, Ga approx. 100 mg/kg, In approx. 9 mg/kg, Sb approx. 470 mg/kg). While metals and metalloids such as As, Mo and Pb can be determined reliably using pXRF instruments, the technique has inherent limitations in evaluating the contents of certain critical elements (Ga, Sb). However, there are positive correlations between the As, Mo, and Pb contents determined by pXRF and the Ga and Sb contents obtained through ICP-MS and XRF. Thus, quantitative pXRF analysis for As, Mo, and Pb allows calculation of Ga and Sb abundances in the slags. This work demonstrates that pXRF analysers are a valuable tool to screen smelting slags for their chemical composition and to predict the likely contents of critical elements.
This study aimed to chemically characterize the granulated copper slag at the Tsumeb smelter site and to demonstrate its potential as source of critical raw materials. In addition, it was shown that pXRF is a useful addition to the techniques for chemical characterization of pyrometallurgical wastes.
The results of this study demonstrate that:
- Tsumeb slags are enriched in base metals (Cu, Pb, Zn), trace metals and metalloids (Ba, Cd, Mo, S, Se), and critical elements (As, Bi, Ga, In, Sb, Sn, Te, U),
- The critical element As can be determined in smelting slags by pXRF at excellent precision and accuracy,
- Other critical elements like Ga and Sb may be determined using element proxies (As, Mo, Pb) and simple linear regression functions, and
- pXRF can be used as an additional low-cost tool for screening the chemical composition of smelting slags.
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