FILTRATION BEHAVIOR OF FINELY GROUND HEMATITE SLURRIES.

摘要

The future of the iron ore industry is in the direction of exploiting low grade, fine grained nonmagnetic ores which require fine grinding and complex beneficiation schemes. The concentrates from the beneficiation circuits must be filtered and pelletized before shipping them to the blast furnace. Filtration of concentrate slurries to the desired moisture level for pelletization has been recognized as one of the most visible problems in the iron ore processing industry. This thesis is aimed at understanding the vacuum filtration behavior of fine iron ore slurries with and without the addition of flocculants and surfactants.; A laboratory-scale filtration apparatus with automated features was designed and used in the research. Experiments were carried out on wet ground hematite in the fineness range of 1460 to 3100 cm('2)/g.; Specific cake resistance of untreated cakes varied linearly with solids specific surface area, and such cakes were incompressible. Slurry pH was found to be significant with increasing fineness; higher cake formation rates were obtained around the isoelectric point of the material at which the particle aggregation is the highest. Residual moisture of untreated filter cakes increased with increasing material fineness and reached an asymptotic value of 14.5 percent which corresponded to fully saturated cakes.; The flocculants reduced the cake and filter medium resistances appreciably and led to faster formation rates; however, they had minimal effect on the rate of cake dewatering and the residual cake moisture. The nonionic flocculants were more effective than the cationic ones in improving the cake formation rate. The use of surfactants with unflocculated slurries caused severe dispersion of particulates which increased the form time. However, surfactants when used along with the flocculated slurries could cause considerable reductions in the cake moisture. Based on the various experimental results, the fundamental significance of the role of flocculants and surfactants was discussed.; Suitable nondimensional groups were formulated by combining the driving inertial forces and the opposing capillary forces, and were correlated with the cake dewatering kinetics and residual cake saturation. The results suggested that the cake dewatering process is controlled by the equilibrium conditions but not by the rate of dewatering.