Improving decomposition efficiency of aluminate liquor through preparation and introduction of active seed during the decomposition process

Abstract

The aim is to determine the optimal parameters for the preparation and dosing of active seeding (finely dispersed aluminium hydroxide) to control the decomposition of aluminate liquor in the Bayer process. Laboratory tests were carried out on a temperature-controlled rotating water bath (Intronics, Australia). The granulometric analysis of the obtained aluminium hydroxide was carried out using the VideoTest image analysis system and a Carl Zeiss Axioskop-40 microscope (Germany) supplemented with Image Analysis software. Finely dispersed aluminium hydroxide (active seed) was obtained by mixing an alkaline aluminate solution and recycled water in various ratios. The filling order of solutions was determined – first, recycled water, followed by cooled alkaline aluminate solution. Optimal conditions for the preparation of active seeding were established: the solution was held for 48–72 hours at 50°C at an aluminate solution to recycle water ratio of 60% and 40%, respectively. The dosing of the obtained active seeding into the head decomposers was examined. It was demonstrated that using active seeding in continuous decomposition mode stabilises the particle-size distribution of the production-grade aluminium hydroxide. The presence of active seeding allowed the initial decomposition temperature to be reduced from 62°C to 58°C without altering the particle-size distribution of aluminium hydroxide. In addition, the study confirmed the positive effect of active seeding on increasing the degree of decomposition of the aluminate liquor up to 1.5%. Therefore, based on the research results, it was established that the use of the new method for preparing and dosing active seeding into the main decomposers leads to the intensification of the decomposition process in alumina production.