A study on non-isothermal hydrogen reduction of different bauxite residue–calcium pellets for feasible recoverability of iron and alumina

Abstract

This study proposes a sustainable method for utilising bauxite residue by reducing waste and recovering iron and alumina. Bauxite residue–calcite pellets were reduced non isothermally at 1000 °C for 120 min under 4 NL/min H₂, converting iron oxide to metallic iron and alumina to leachable calcium aluminate phase. The reduced pellets were leached with 60 g/L sodium carbonate for 120 min (1:10 solid-to-liquid ratio) and subjected to 800 Gauss magnetic separation to recover iron. Analytical techniques were employed to characterise the phase composition, microstructure, and chemical properties of pellets. Microstructural analysis revealed 4–5 µm iron particles, with self-hardened pellets showing increased iron particle aggregation. Sintered pellets exhibited superior mechanical strength (tumbling index: 84.6%) and higher alumina recovery (7.2 g Al/L), while self-hardened pellets achieved greater iron recovery (43%) due to distinct texture. This benefit process demonstrates the effective recycling of bauxite residue and holds promise for industrial-scale applications.