Precipitation of boehmite in sodium aluminate liquor

Gibbsite is generally precipitated from sodium aluminate liquor in the presence of huge quantity of gibbsite seed at a temperature between 60 and 70 °C. This gibbsite is then calcined to produce alumina. Boehmite is a stable phase at higher temperature (> 100 °C) and formation of boehmite below 100 °C in supersaturated sodium aluminate liquor is unusual. In the present study an attempt has been made to produce boehmite under atmospheric pressure conditions. Effect of various parameters such as temperature, alumina/caustic (Al2O3/Na2O) ratio, seed size, amount of seed, organic additives, precipitation time, etc., on boehmite formation has been investigated. At higher temperature and low alumina/caustic ratio, boehmite is found to be precipitated under atmospheric pressure by adding boehmite seed. The optimum quantity of seed required for precipitation has been found to be 300 g L− 1. Reduction in precipitation temperature could be achieved by using different organic additives. Tartaric acid has been found to be highly effective in reducing the temperature of boehmite precipitation to 50 °C. Increase in precipitation time increased boehmite production.