EXTRACTION OF IRON VALUES FROM RED MUD

Abstract

The Bayer's process employed in the production of alumina from bauxite ore leads to generation of a byproduct rich in oxides of iron, titanium and aluminum along with the phases formed during the processing of ore. This byproduct is commonly known as "Red mud" or bauxite residue. The amount of red mud generated and the specification of red mud depends upon the quality of bauxite ore used as well as the process parameters during digestion. Furthermore, the annual production of red mud globally is around 120 million tons and most of generated red mud is stockpiled. The presence of significant iron values along with other valuable metals in the red mud which is present in large quantities makes it a potential source of several metals. The research reported in this thesis is confined to a specific Indian red mud provided by Hindustan Aluminum Corporation Ltd. (HINDALCO) with an iron content reported to 36.8% by weight. The objective of this research is to design a strategic process route to generate a concentrate enriched with iron values which is suitable for iron/steel making. It was established based on the experiments that the conventional physical beneficiation processes are ineffective for separation of iron phases. In an attempt to reduce the pH of the red mud and neutralize its toxic effect on environment, carbonation process provides significant pH reduction. Reduction roasting performed in conventional muffle furnace with charcoal as reductant yields no significant enrichment of iron values. Also with increase in temperature the iron grade in the magnetic concentrate increases however lower iron recovery indicates incomplete reduction conditions. The reaction kinetics study gives the activation energy of 43.26 KJ/mol required for enrichment of iron from 24% in feed to maximum grade of 36% in the magnetic concentrate. Microwaves are incorporated during reduction roasting in microwave furnace (800W, 2.45GHz) and domestic microwave (900W, 2.45 GHz). It was observed that the microwaves assisted reduction roasting provides significant iron enrichment as compared to muffle furnace roasting. Also, it is important to mention that on increasing the microwave power to 900W, the iron enrichment further improves and almost complete reduction takes place in just 10 minutes of exposure time. On comparison with conventional roasting technique, microwave technique enhances iron grade significantly at relatively economic conditions of exposure time and temperature. It can be conclude from the study that red mud is susceptible to microwave exposure and increases its magnetic property. A regression model developed for iron grade and iron recovery from red mud by microwave roasting infers that the exposure time is the most influencing factor for iron grade v and reduction temperature in iron recovery. It is also observed that the titanium based phases present in the red mud improves the microwave susceptibility and hence improves the iron separation. The formation of ferrite balls is significant in microwave reduction and indicates the promising potential of microwaves in production of cleaner, cheaper and environmental friendly steel.