Study On New Technology Of Chromite Pellet Sintering And Agglomeration Mechanism

Chromite is main raw material for smelting ferrochromium which can be used to make stainless steel products. And ore feed of smelting ferrochromium is chromite. At present resources of natural chromite lump is decreasing rapidly and its price is going higher than before. But the price of chromite fines is cheap. Agglomeration is one necessary process to utilize. So by comparing with conventional sintering, chromite pellet sintering technology (PST) and its agglomeration mechanism have been studied.The investigation on conventional sintering of chromite shows that the rate of finished sinter, the productivity, tumbler index and fuel comsuption are 73.16%, 1.17 t-m-2h-1, 61.03%, 115.80 kg-t -1 respectively under fuel content of 8.0%, moisture content of 8.0%, bentonite addition of 3%, ignition temperature of 1100 + 50 C, ignition time of 2min, ignition pressure of 5000Pa, sintering pressure of 10000Pa, cooling pressure of 5000Pa, cooling time of 3min and bed depth of 580mm.The investigation on pellet sintering of chromite shows that the rate of finished sinter reaches 77.18% and the productivity reaches 1.47 t-m. -2h-1 and tumbler index reaches 83.78% and fuel comsuption reaches 107.32 kg-t-1 under all feed size of -lmm,fuel content of 7.5%, 60% coke added into pellet inside, bentonite addition of 1%, moisturecontent of 8.0%, drying temperature of 200-250 C, drying time of 3min, drying pressure of 4000Pa, ignition temperature of 1100 + 50 C, ignition time of 2min, ignition pressure of 5000Pa, sintering pressure of lOOOOPa, cooling pressure of 5000Pa, cooling time of 3min and bed of 580mm. The quality and productivity of sinter are improved by using PST. The rate of finished sinter, tumbler index, productivity are increased by 5.50%, 37.28%, 25.64% respectively and meanwhile fuel consumption is decreased by 7.32%.The solidification mechanism of pellet sintering was studied by using microscope, SEM, EPMA. Results show that sinter of chromite consist of Fe-Cr spinel, Mg-Cr spinel, Mg-Al spinel spinel and olivine. The agglomeration of sinter mainly depends on recrystallization of spinels and liquid phase of olivine plays an assistant role as well. The micro-structure and composition of sinter was affected remarkablely by divided coke addition. There is big different between outer structure and inner, and strength of pellet is poor under 100% coke adhered at the surface of pellet. Pellets have good structure and strengthen under 60% coke added into inside pellet and 40% coke adhered at the surface of pellet. The big pore appeared and poor strengthen under 100% coke added into inside pellet. Besides, the agglomeration of pellet was affected obviously by size of balling feed. The structure of sinter is reasonable and has good connection of chromite and olivine andpowerful strength when all feed size is under lmm(including returns).The macroscopical structure of sinter is recemose.PST is important process that can strength chromite sintering and improve the quality and productivity of sinter. PST can give technical support for smelting ferrochromium by electric arc furnace.