Improving alumina grade from Malaysian bauxite via roasting and magnetic separation prior to the Bayer process

Costantine Joannes; Roshaida Arbain; Tinesha Selvaraj; Anuar Othman; Ismail Ibrahim; Coswald Stephen Sipaut.

Bauxite ore is a sedimentary rock which is known to be the primary ore for alumina (Al2O3) production and can be further refined as Aluminum (Al). This element is vital and widely used in transportation, packaging, electrical appliances and household products. The Bayer process is the most common process used for alumina extraction. However, producing a high grade of alumina is challenging due to the presence of impurities. This study investigates the effect of without (Method 1) and with pre-treatments (Method 2) prior to the Bayer process, to produce precipitated alumina trihydrate (ATH) from Malaysian bauxite. In Method 2, the raw bauxite (-45 μm) underwent pre-treatments including roasting at 500°C and a wet magnetic separation at 3.0 A. Whereas, the Bayer process in both methods was performed using 3.0 M NaOH with a liquid to solid ratio of 1:5, stirred at 400 rpm and heated at 90°C for 1 hour. The pregnant solution underwent precipitation by adding 6 g of Al2O3 seeds, stirred at 200 rpm at 70°C for 24 hours and left for 5 days. The raw bauxite of Felda Bukit Goh, Kuantan, Pahang, mainly consists of 48.02 wt. % Fe2O3, 31.85 wt. % Al2O3, 14.10 wt. % TiO2 and 4.92 wt. % SiO2. Gibbsite was the predominant mineral. Via AAS analysis, the Al2O3 grade detected was 35.2%. After the Bayer process, it was observed that the Al2O3 grades of the bauxite residues in methods 1 and 2 were 32.15 % and 28.20 %, respectively. This indicates that there was more dissolution of Al2O3 over pre-treatments. The Al2O3 grades measured from the precipitated ATH can be achieved up to 77.14% with 7.64% recovery, whereas without pre-treatments, 70.44% Al2O3 with 5.72% recovery.

KEYWORDS: Alumina Trihydrate; Bauxite; Bayer process; Magnetic separation; Roasting.



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