Improving the physical properties of hydrotalcite in seawater neutralised red mud slurries

Overview

Topic status: In progress

Project Description

The digestion of bauxite in the production of alumina results in a highly caustic waste product commonly known as red mud. It is recent practice, in the alumina industry, to react red mud with seawater in order to reduce the causticity of the waste via the formation of hydrotalcite (Mg6Al2(OH)16CO3•xH2O).

A better understanding of hydrotalcite formation in the seawater neutralisation process is required in order to improve the material handling side of the process. Previous studies have shown that the settling rates of hydrotalcite are particularly slow, and require the addition of red mud to aid the process. However, there is an upper limit to the quantity of red mud that can be added before the rheology of the slurry becomes unsuitable for current pumping and storage systems. Therefore, conditions of the neutralisation process need to be explored to determine the parameters required to increase the physical properties of hydrotalcite, which will reduce the amount of red mud required to settle the hydrotalcite out. The empirical formula of Bayer derived hydrotalcite also needs to be determined to allow for the accurate prediction of the quantity of hydrotalcite that forms during neutralisation, and thus allows for better predictions of the physical properties of the resultant slurry.

Knowledge of the actual Mg:Al ratio of Bayer derived hydrotalcite will also improve the correlation between the prediction model and actual results. It is hoped that a method for a mud-free system (mud not required for settling purposes due to increased physical properties of hydrotalcite) can be developed.

Research Activities

This research will focus on identifying conditions that cause an increase in the physical properties of Bayer derived hydrotalcite. A range of conditions are to be investigated to establish a method that produces the optimum physical properties of hydrotalcite for settling purposes. An investigation on the effects of reactor type, supersaturation and seeding on hydrotalcite particle size and agglomeration will be undertaken, followed by investigations on other variables such as flow rate, contact time, agitation, and seawater ratio. The full characterisation of each of the synthesised Bayer hydrotalcites will be required, including settling rates and the determination of the empirical formula of each Bayer hydrotalcite formed. Students working on this project will coordinate tests with Rio Tinto Alcan.

Objectives

The project objectives are to:

  • identify conditions that cause an increase in physical properties of Bayer derived hydrotalcite and the resultant effects on settling rates
  • characterise the different Bayer hydrotalcites and their respective settling rates
  • determine the empirical formula of Bayer derived hydrotalcite.

Project Duration

The project duration is for up to 8 weeks and specific times can be tailored to the individual needs of the student (generally between the hours of 9am and 5pm) within the general time period mid-November to mid-February. A top up scholarship may be available for this project and will be confirmed closer before the project commences.

Study level
Vacation research experience scholarship
Supervisors
QUT
Organisational unit

Science and Engineering Faculty

Research area

Chemistry

Contact
Please contact a supervisor for enquiries.