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) Ltd's 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.

A hydrothermal leaching process was developed to produce fire retarding micro-boehmite (4–25 mm) using plant aluminium hydroxide (alumina trihydate, ATH) (< 50 mm in mean size). Well crystalline product of high purity (< 0.05% Na2O and < 0.01% Fe2O3) and whiteness (rating 97.8) could be produced at > 200 °C, 1–2 MPa after 1 hour.Figure optionsDownload as PowerPoint slideHighlights
► We use hydrothermal leaching to make fire-retarding boehmite.
► Alumina trihydrate was feed material.
► Well-crystalline product of high purity and whiteness is produced.
► ATH coarser than 50 μm cannot be used for synthesis.
► Hydrothermal leaching removes soda and other impurities.