Date of Award

2021

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering (PhD)

Administrative Home Department

Department of Chemical Engineering

Advisor 1

Komar Kawatra

Advisor 2

Timothy Eisele

Committee Member 1

Tony Rogers

Committee Member 2

Gowtham

Abstract

Red mud is an industrial slurry waste that is produced as a byproduct of the Bayer process for alumina. The waste is generated in large quantities, up to a ratio of 2:1 against the valued product alumina. Red mud exhibits many chemical and physical properties that categorize it as a hazardous material. Due to the addition of sodium hydroxide in processing, the pH is typically at values close to 13. Small particle size discourages separation from water for disposal, so drying red mud happens over many years.

The pH of red mud can be reduced with inexpensive reagents. Carbon dioxide is a greenhouse gas that is finding a great deal of research into potential sinks to reduce the footprint on the atmosphere. Combining carbon dioxide with red mud can effectively reduce the pH while also providing a sink for the greenhouse gas. Carbon dioxide is able to reduce the pH of red mud from 13 to 10 over long periods of time.

Red mud can be utilized to produce a variety of value-added products. Most red muds around the world contain a large quantity of iron, titanium, aluminum, and rare earth elements. One method of removing the iron is through the iron nugget process which reduces iron and removes impurities in a single step. The iron nugget process is able to produce blast furnace quality pig iron (over 90% iron purity) with the addition of a carbonate flux material. Rare earth elements are concentrated in the slags from the iron nugget process and can be removed with acid leaches.

The current view of red mud as a waste material is misleading. The proposed work will investigate methods to reduce the hazardous nature of red mud by reducing the pH and also remove valuable minerals. This will effectively give value to the waste product while simultaneously reducing the overall amount of red mud waste that needs to be disposed.

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