Abstract
This research presents a novel precipitation method for scandium (Sc) concentrate refining from bauxite residue leachates and the effect of aqueous media on this triple-stage successive precipitation process. The precipitation pattern and the precipitation behavior of the constituent elements was investigated using different precipitation agents in three major mineral acid media, namely, H2SO4, HNO3, and HCl in a comparative manner. Experimental investigations showed behavioral similarities between HNO3 and HCl media, while H2SO4 media was different from them because of the nature of the formed complexes. NH4OH was found to be the best precipitation agent in every leaching media to remove Fe(III) with low Sc co-precipitation. To limit Sc loss from the system, Fe(III) removal was divided into two steps, leading to more than 90% of Fe(III) removal at the end of the process. Phosphate concentrates were produced in the final step of the precipitation process with dibasic phosphates which have a strong affinity towards Sc. Concentrates containing more than 50% of ScPO4 were produced in each case from the solutions after Fe(III) removal, as described. A flow diagram of the selective precipitation process is proposed for these three mineral acid media with their characteristic parameters.
Highlights
The recent agreements and climate accords in reducing carbon emission and specified deadlines for automotive industries have placed light metals and alloys under the spotlight [1]
As aluminum alloys with improved strength, thermal resistance, and weldability can be achieved with minor additions of Sc, improved oxygen-ion conductivity can be attained in solid oxide fuel cells [4,5,6]
Since Sc-containing liquors can exist in chloride or nitrate media, the effect of those aqueous media on precipitation should be investigated
Summary
The recent agreements and climate accords in reducing carbon emission and specified deadlines for automotive industries have placed light metals and alloys under the spotlight [1]. Bauxite residue (i.e., red mud) is the by-product obtained through the Bayer Process, yielding approximately four billion tons, with a previously reported annual production of 160 million tons [8,9] This alkaline waste can be considered as a valuable resource because of its metal content (Fe, Al, Ti, Sc, Rare earth elements (REEs), etc.). Complete or partial recovery of Sc from bauxite residues was reported to be achieved mainly by solvent extraction, ion exchange, or the combination of these two techniques, as a result of its low concentration in the leachates [14,15,16,17,18,19,20]. In order to cover a wider range of bauxite residues as well as other waste-generating processes, such as Ti-pigment and Ni laterite production, the design of selective Sc precipitation route for bauxite residues has to be adapted to different mineral acid media. This paper investigates the effect of different aqueous media on the recovery of Sc by a selective precipitation method
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