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 degrees C. This gibbsite is then calcined to produce alumina. Boehmite is a stable phase at higher temperature (>100 degrees C) and formation of boehmite below 100 degrees 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 degrees C. increase in precipitation time increased boehmite production. (C) 2008 Elsevier B.V. All rights reserved.