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.

address: 18 mark.healy@nuigalway.ie 19 20Highlights 21  Separate size fractions of bauxite residue were treated with gypsum and seawater. 22  Alkalinity was reduced following treatment with the gypsum and seawater. 23  The effect on composition and P adsorption of the treated samples were examined. 24  Gypsum was found to be the most successful in enhancing the P adsorption capacity. 25 26 2 Abstract 27Bauxite residue (red mud), the by-product produced in the alumina industry, is being 28 produced at an estimated global rate of approximately 150Mt per annum. Due to its highly 29 alkaline nature, many refineries use neutralisation techniques such as mud farming 30 (atmospheric carbonation), direct carbonation using carbon dioxide or reactions with 31 seawater, to treat the bauxite residue and reduce its alkalinity prior to disposal in the BRDA 32 (bauxite residue disposal area). Applying a treatment can render the bauxite residue non-33 hazardous and may also prepare the bauxite residue for reuse, particularly as an adsorbent. In 34 this study, gypsum and seawater treatments were applied to the various bauxite residue 35 samples obtained and the effects on its mineral, elemental and physiochemical properties 36 were examined, as well as the effect on its phosphorus (P) adsorption capacity. It was found 37 that in addition to reducing the alkalinity of all bauxite residue samples used, the P adsorption 38 capacity was also enhanced following amendment with seawater or gypsum, particularly with 39 gypsum. A positive correlation was detected between P adsorption and both Ca and CaO. A 40 negative correlation was detected between the P adsorption and pH of the media. Fitting the 41 data obtained from a batch adsorption experiment to the Langmuir adsorption isotherm, the 42 maximum adsorption capacity was estimated to range from 0.345 to 2.73 mg P per g bauxite 43 residue, highlighting the re-use potential for bauxite residue as an adsorbent for P. 44 45 Keywords: bauxite residue; adsorption; bauxite residue filter; aqueous solution; phosphate 46 removal 47 48 49 50 51 421 18

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The use of rapid small-scale column tests to determine the efficiency of bauxite residue as a low-cost adsorbent in the removal of dissolved reactive phosphorus.