Global recycling experience of red mud - a review. Part i: pyrometallurgical methods

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This review considers the papers aimed to find an effective solution to the red mud utilization problem. Red mud or bauxite residue is a hazardous materials that are generating during production of alumina by the Bayer process. Depending on the composition of bauxite and the technology, production of 1 ton alumina forms from 0.9 to 1.5 tons of this waste. The global inventory of red mud is estimated at about 4 billion ton in 2015. The main quantity of bauxite residue is not processed, but pumped into land-based ponds and it leads to environmental pollution. In 2010 in Hungary a pond containing red mud were collapsed, freeing about 700 thousand m3 of liquid waste, as a result 10 people were died, about 350 houses were destroyed and significant regions were polluted. Red mud obtained by different plants has various chemical and phase compositions. Despite this fact the main components of red mud is iron-containing minerals, so bauxite residue can be considered primarily as a raw material for the metallurgical industry. This part of the review considers pyrometallurgical methods for of red mud treatment, including both methods of low-temperature reduction at temperatures of 1050 - 1200 °C and high-temperature reduction melting, as well as utilization methods of the resulting slags. These slag utilization methods can be used for extraction of alumina, titanium and rare-earth metals, obtaining building materials such as various cements, mineral wool and flux materials for metallurgy. Methods of alkali removing, drying and agglomeration of red mud also considered. It has been shown that the best ways of bauxite residue recycling are the pyrometallurgical methods with obtaining of iron-containing product and slag for the production of building materials or metallurgical fluxes. These techniques make possible to utilize a large amount of red mud with exception of additional waste formation. This is the first part in a series of three related reviews examining the world experience of red mud recycling by various ways.