Red mud as secondary source for critical raw materials – extraction study

Abstract

BACKGROUND Red mud is a by‐product of alumina extraction from bauxite by the Bayer process produced in the billion tons scale worldwide. Red muds, or more generally bauxite residues, are regarded as waste, but may potentially be valuable sources of critical raw materials (CRM). In the present study both conventional extracting agents (mineral acids) and small molecular weight complexing agents (organic acids) were evaluated regarding their efficiency to extract CRM such as rare earth elements (REEs) from red mud. On a molar base, highest extraction efficiencies for REEs were achieved using HCl compared with the other acids investigated. Consequently, an experimental design approach was used to determine optimal conditions for CRM extraction using HCl. Instead of maximizing the extraction of a number of selected metals, the maximum economic potential as the sum of all metals (total metal extracted × economic value of the respective metal) was chosen as the application relevant response variable. Four explanatory variables (i.e. HCl concentration, contact time, temperature and slurry concentration) were used. RESULTS Optimal conditions maximizing the economic potential were predicted for 5.98 mol L−1 HCl, 21 h contact time, 50°C, and 56.7 g L−1 slurry concentration. Indeed, experimentally determined economic potential corresponded well (71% of predicted) with the predictions, allowing a maximum recovery of 297.6 US $ t−1. CONCLUSION Though the studied red muds were relatively low in CRM concentrations, the systematic approach developed here allows straightforward transfer to other red muds, harnessing the potential of the latter as important secondary source for CRM. © 2017 Society of Chemical Industry

Re‐using bauxite residues: benefits beyond (critical raw) material recovery

“…The combined presence of ferric, aluminium and tectosilicate‐like compounds in bauxite residue makes it capable of immobilizing toxic metals from polluted soils . CRM extraction from bauxite residue will result in acidic solid residues (refractory mineral fractions with acid remains) . Mixing acidic residues from CRM extraction with original bauxite residues (in an appropriate ratio) for soil improvement may be the ‘golden way’ of unifying remediation (mitigating risks and decreasing costs) with resource recovery (e.g.…”

“…One thus‐far little tapped CRM secondary source may be bauxite residues . Depending on the origin of the residues, they may contain considerable amounts of CRMs, in particular REE and Sc …”

“…To understand the impacts and benefits of CRM recovery from bauxite residues, a brief overview of bauxite residue generation / deposition, associated impacts and strategies for bauxite re‐use is given as well. For technical details, the reader is referred to several extensive reviews on bauxite residue management and element recovery …”

Determination of Trace Elements in Bauxite Using Laser Ablation‐Inductively Coupled Plasma‐Mass Spectrometry on Lithium Borate Glass Beads

“…, Ujaczki et al . ). Analysis of the major and trace element composition of bauxite not only serves to constraining ore grade but also provides information on parent rocks and the nature and conditions of genetic processes.…”

“…The natural weathering processes that cause Al accumulation also promote enrichment of other relatively immobile constituents of original parent rocks. This happens to such an extent that waste products of industrial processing receive increasing attention as potential economic sources of trace elements, such as gallium, scandium and rare earth elements (Ochsenk€ uhn-Petropoulou et al 1994, Paramguru et al 2004, Zhang et al 2005, Borra et al 2015, Ujaczki et al 2017). Analysis of the major and trace element composition of bauxite not only serves to constraining ore grade but also provides information on parent rocks and the nature and conditions of genetic processes.…”