Abstract
SYNOPSIS At a time of resource consumption, it is important to 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. In this paper we 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) as well 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. Keywords: base metal slag, portable XRF, critical elements, secondary resource.
Highlights
The consumption of critical elements for high-technology applications is increasing exponentially, and scenarios predict that future demand will exceed current annual worldwide production (European Commission 2010, 2017)
The purpose of this study is to appraise the use of combined inductively coupled plasma–mass spectrometry (ICP-MS), AAS, XRF, and portable X-ray fluorescence (pXRF) data to establish the bulk chemistry and the presence of critical elements in granulated copper slags from the Tsumeb smelter, Namibia
The granulated slag is processed in the slag milling plant and the by-product sulphuric acid is sold to industrial consumers in Namibia (Dundee Precious Metals, 2020)
Summary
The consumption of critical elements for high-technology applications is increasing exponentially, and scenarios predict that future demand will exceed current annual worldwide production (European Commission 2010, 2017). The metals are contained within the silicate glass and various slag phases, as well as within primary and weathering-induced secondary minerals, including native elements, sulphides, oxides, hydroxides, chlorides, carbonates, sulphates, arsenates, and silicates (Ettler et al, 2001; Piatak, Parsons, and Seal II, 2015). In these studies, laboratory-based methods have commonly been applied for the determination of major (>1 wt%) and trace elements (
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