RECOVERY OF VALUES FROM THE RED MUD BY METALLOTHERMIC PROCESS

Abstract

Red mud which is separated from bauxite as clayey waste material from the Bayer process of alumina production furnishes appreciably high quantitative figure of its generation as is evident from the fact that 2.5 tonnes of red mud is generated for every tonne of aluminium metal produced. With the sharply growing demand of aluminium metal, the expected world production estimate of 60 million tonnes per year of alumina upto 2000 AD, is sufficient to prove the future nuiscence regarding the disposal of extremely huge quantities of this solid waste. As a consequence, problems are that of land cost and storage, and pollution in the sense that despite using best available design and operating techniques, the mill water flowing along with it carries polluting substances. Extensive studies have been carried out but no work has been said to be successful regarding its disposal. With this view, in the present investigation, it has been considered that converting it to some useful product by taking the benefit of its mineralogy, will not only solve its disposal problem but will also enable conservation of rapidly depleting mineral resources. Red muds have been reported to consist of Fe203, Ti02 as major constituents along with several minor and trace quantities of oxides of numerous elements. Indian red muds are known for dominant presence of Fe,Q and an appreciable amount of J Ti0 , (18-22%). Extraction of titanium alone is difficult due to its highly reactive nature. However its extraction can be iii possible in the presence of solvent iron. Titanium forms solid solution with iron thus lowering its own activity. This solid solution can be defined in terms of ferrotitanium. In the present investigation, the same feature has been utilized. The idea is that, the red mud when treated aluminothermically, Fe207 and TiO2 both are reduced along with the several other trace constituents and form a ferroalloy which is basically ferrotitanium. Thermodynamic aspects and heat effects of the reduction reaction have been described to be promising for an efficient slag-metal separation. Reactors of different shapes and sizes have been reported to be used by various investigators. However, no systematic study has been reported about the effect of reactor geometry on the yield or recovery of the alloy. In the preset study, this aspect has also been included which may he considered applicable to all aluminothermic reduction processes. The present stt ;herefare, been made an the possibility of the produc ferroalloy which is basically ferrotitanium by the apes iermic reduction of red mud. The entire thesis has been divided into following seven chapters. Chapter 1 deals with the basic information about the generation of red mud in Bayer Process and its mineralogy. The problems regarding its disposal and resulting environmental hazards have been briefly taken up followed by brief introduction of the worked up topic. Chapter 2 deals with a critical review of the work carried out by various investigators and some basic principles iv and information, as given in text books relevant to the topic. Starting from the mode and chemistry of red mud generation in Bayer process, discussions have been made about red mud disposal and associated problems, physicochemical and mineralogical details, possible applications etc. To emphasize the aluminothermic application, of red mud, the related theory has been discussed with a bit'elaboration. How the selected information from literature led to the present investigation, is the matter of discussion of the chapter 3. Red mud, due to presence of appreciable amounts of FeO,. and J Ti02, may be considered equivalent to lean illmenite are and t hence it is possible to produce ferrotitanium by the aluminothermic reduction of red mud by creating favourable thermodynamic conditions and heat effects. The basic plan of the study includes the effects of following parameters to be investigated in appropriate couples on the recovery values and composition of the alloy ; (i) Amount of aluminium powder (reductant), (ii) Particle size of aluminium powder, (iii) Particle size of red mud, (iv) Scale of production, (v) Flux additions (Lime,Fluorspar and Magnesia), (vi) Booster addition (t:C103 and f(N07) , (vii) Preheating of the charge (temperature) , ti (viii) Preheating of the charge (time), (ix) Reactor geometry (Defined in terms of hid ratio) Chapter 4 deals with the methodology adopted for experimentation as well as basic calculations. In chapter 5 findings of investigation in respect of recovery and composition of the alloy produced, have been V discussed based on basic principles of aluminothermy, established facts and/or some other possible ways. Chapter F; presents the conclusions of this investigation. The present study has shown up the feasibility of production of a. metallic button consisting chiefly of Fe,Ti,Si, and Al by the aluminothermic reduction of red mud. The process, suffered inadequate in situ heat liberation which could be compensated partly by preheating and booster additions to the charge and partly by proper fluxing. Excess aluminium powder over staichiometric amount is necessary which in turn, affects the yield or recovery of the alloy in increasing fashion to a certain maximum value but carries more retained aluminium in the alloy. Good results have been found out when red mud particles are bigger than aluminium particles the difference being not beyond a maximum level. It is also concluded that for a given reactor geometry, the yield of the alloy increases to a maximum level with the increase in the scale of production. In order to go beyond this maximum level of production maintaining the yield or recovery of alloy, the geometry of the reactor must be changed. Chapter 7 includes a few suggestions about the more work, that seems could be done as an extension to this