Potentials of Iron Oxide Bearing Wastes for Production of high quality Pellets (Balls)
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos
The steel industry produces large quantities of iron oxide bearing wastes (IROBEWAS) annually in form of dusts and sludge. These products that are captured by pollution control system (PCS) have some physical properties that make them unsuitable and uneconomical for recycling. In few companies, dusts are recycled through sintering, the sludge on the other hand, contain undesirable amount of water and micro-size grains. Very fine particles of dusts and excessive moisture in sludge prevent the gas permeability of the sinter bed thereby reducing the sintering rate and sinter yield. The gas permeability of the charge (porosity) can be greatly enhanced through balling (effective granulation) processes. A comprehensive analysis of recovery and recycling of steel wastes is carried out in this research. It identifies the sources and composition of steel wastes. The research evaluates the quantity of these materials and analyzes their balling processes. It also characterizes the physical, chemical, mechanical and thermomechanical properties of IROBEWAS. The work also examines the effects of various factors that can enhance or improve the ballability of IROBEWAS. Pellets (balls) of high mechanical properties were produced using mixture of iron ore concentrates and various volume fractions of IROBEWAS with balling disc of 40 cm diameter and 10 cm depth. An analytical equation for effective balling of IROBEWAS was also developed using dimensional analysis. X-ray Florescent Spectrophotometer Ex 310 revealed that IROBEWAS contains materials such as iron (54.3 %), carbon (2.5 %) and slagging oxides (CaO – 3.45 %, SiO2 – 6.0 %) that are similar by chemical composition to sinter charges and suitable additives to pellet and sinter burdens. Sand Compressive Strength Testing machine and Multi-purpose Materials Testing machine revealed that pellets (balls) having 60 % IROBEWAS and 14 % moisture contents possessed wet strength of 11.5 N/pellet as against industrial minimum value of 9 N/pellet, dry compressive strength of 26 N/pellet as against industrial minimum value of 15 N/pellet and induration strength of 3.84 kN/pellet when indurated at 1300oC, as against industrial minimum value of 2 kN/pellet. By standard methods of vi pellets freely from a height of 50 cm on a steel surface drop number of balls with 60 % IROBEWAS and 14 % moisture contents was found to be 7.8 times. Also Tumbler index drum revealed that pellets with 40 % IROBEWAS and 14 % moisture contents possessed tumbler and abrasive indices of 95 % and 5 % respectively The work also establishes that ballability of IROBEWAS is directly proportional to moisture and IROBEWAS contents as well as the wettability of the solid component of raw material and square of the speed of balling disc. It is, however, inversely proportional to the content of bentonite and grain sizes of the materials.