Production of micro-crystalline boehmite from hydrothermal processing of Bayer plant alumina tri-hydrate

Plant alumina trihydrate (ATH, Al(OH)3) from Korea Alumina (KC) Ltdʹs Bayer alumina plant was used to synthesize boehmite, a new product used as fire retarding fillers or laminating materials. The hydrothermal treatment conditions were optimized from tests conducted with ATH-water slurries (30, 40 and 50 w/v%) at different temperatures (160–220 °C), reaction time (10–80 min) and mean feed sizes D50 (1.5–50 μm). Well crystalline boehmite was formed at a temperature > 200 °C after 60-minute treatment. The reaction pressure (1.0–2.0 MPa) has no effect on the process. The hexagonal crystal of the starting gibbsite changes to plate-like shape as boehmite is formed. After the treatment, the boehmite mean particle size (4–25 μm) is generally smaller than the original gibbsite feed (8–50 μm). For finer ATH feed (1.5–2.5 μm) there is no change in particle size after the hydrothermal treatment. The highly crystalline boehmite product containing < 0.05% Na2O and < 0.01% Fe2O3 has higher purity and whiteness than the ATH feed.