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

Abstract

Since the world economy has been confronted with an increasing risk of supply shortages of critical raw materials (CRMs), there has been a major interest in identifying alternative secondary sources of CRMs. Bauxite residues from alumina production are available at a multi‐million tonnes scale worldwide. So far, attempts have been made to find alternative re‐use applications for bauxite residues, for instance in cement / pig iron production. However, bauxite residues also constitute an untapped secondary source of CRMs. Depending on their geological origin and processing protocol, bauxite residues can contain considerable amounts of valuable elements. The obvious primary consideration for CRM recovery from such residues is the economic value of the materials contained. However, there are further benefits from re‐use of bauxite residues in general, and from CRM recovery in particular. These go beyond monetary values (e.g. reduced investment / operational costs resulting from savings in disposal). For instance, benefits for the environment and health can be achieved by abatement of tailing storage as well as by reduction of emissions from conventional primary mining. Whereas certain tools (e.g. life‐cycle analysis) can be used to quantify the latter, other benefits (in particular sustained social and technological development) are harder to quantify. This review evaluates strategies of bauxite residue re‐use / recycling and identifies associated benefits beyond elemental recovery. Furthermore, methodologies to translate risks and benefits into quantifiable data are discussed. Ultimately, such quantitative data are a prerequisite for facilitating decision‐making regarding bauxite residue re‐use / recycling and a stepping stone towards developing a zero‐waste alumina production process. © 2018 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Characteristics of Calcium-Aluminate Slags and Pig Iron Produced from Smelting-Reduction of Low-Grade Bauxites

“…It is emphasized here that the reduction of Fe 2 O 3 and Fe 3 O 4 by CO (g) through reactions [3] and [5] is more feasible than reactions [2] and [4]. FeO and even Fe can be also formed in solid state; however, we here assume that Fe is mainly produced from FeO in the slag.…”

“…[1] A large number of efforts have been made to valorize this most-abundant industrial byproduct in the world in building materials, [2] using it as the rare earth element's source, [3] producing green direct-reduced iron (DRI), [4] consuming inorganic polymers and pozzolanic material, [5] and so on. However, none of these fields has moved to a large-scale commercial production due to economic reasons and particular challenges in processing the red mud.…”

Calcium and sodium recovery from microwave‐pretreated red mud with added solid ammonium chloride

“…Red mud is an industrial by‐product of the Bayer process, which produces alumina from bauxite ore. A total of 1–1.5 Mg of red mud is generated as a by‐product to obtain 1 Mg of alumina . As the inventory of red mud increases, effective storage and processing solutions are required . The disposal and storage of red mud are difficult because it has high alkalinity (pH 10–13) and contains various types of heavy and radioactive elements .…”

“…Al, Co, Cu, Pb, Ni, Mg and Zn) and rare earth elements (e.g. Ti, Mo, W and Re) . The experimental results using industrial by‐products showed that leaching methods using microwaves were more efficient than conventional methods …”

“…1 As the inventory of red mud increases, effective storage and processing solutions are required. 2,3 The disposal and storage of red mud are difficult because it has high alkalinity (pH 10-13) and contains various types of heavy and radioactive elements. 4 A suitable treatment method for red mud has not been well established because of its harmful impacts on a disposal site.…”