Abstract: According to the coal-based reduction technology,the effect of reduction temperature,curing time and C/O molar ratio on the microstructure of the reduced marine placer-graphite briquettes were analyzed by using scanning electron microscope (SEM) and X-ray diffraction (XRD).Meanwhile,the separation and agglomeration behavior of iron slag as well as the reduction results of metallic mineral were also discussed,and the micro-mechanism of reduction was clear.The results show that the metallization rate and briquette strength could reach 94.23% and 243.3 N/P at reduction temperature 1 300 ℃ for 30 minutes and w(C)/w(O) 1.1；Metallization rate and compress strength increased with reduction temperature and time,forming more iron joined crystal and slag bonding,which can increase the strength of the sample；Appropriate C/O ratio can provide sufficient reductant during the deep reduction without residual graphite to threaten the compress strength.The phase-transition in solid reduction of marine placer was summarized as Fe_3-xTi_xO₄→Fe+FeTiO₃→Fe+Fe₂TiO₅.

Key words: Marine placer, Deep reduction, Microstructure, Metallization