Process Mineralogy of a Sedimentary Iron Ore in Eastern Chongqing

Objective To investigate the process mineralogical properties of sedimentary iron ore from eastern Chongqing, clarify the iron occurrence state, mineral intercalation characteristics and thermal weight loss performance of the ore, evaluate the feasibility of conventional beneficiation, and explore the potential of roasting for iron grade upgrading. Methods Multiple testing and analytical methods including MLA, optical microscopy, X-ray diffraction, chemical analysis, and simultaneous differential thermal-thermogravimetric analysis (DTA-TG) were adopted to systematically analyze the material composition, mineral embedding features, ore textures and structures, as well as thermal weight loss behaviors of the target iron ore. Results The total iron (TFe) grade of the ore is 35.68%. Iron elements mainly reside in siderite and hematite (limonite), with distribution ratios of 71.16% and 25.27% respectively, which are the primary recoverable iron-bearing phases. The ore develops massive, disseminated and layered structures, along with allomorphic granular, porphyritic, clastic, reaction rim and oolitic textures. Most siderite occurs as lumpy or irregular vein aggregates ranging from 0.1 mm to 2.0 mm in size; partial siderite lumps are wrapped by iron oxide reaction rims with variable thickness of 0.01~0.20 mm, and intergranular spaces are filled with calcite. Hematite exists as granular aggregates with uneven particle sizes cemented by calcite aggregates, and also distributes as irregular fine reticular veins in the ore. The average FeO content of siderite reaches 58.093%, accompanied by minor impurities such as magnesium and manganese. In addition, the granularity of major mineral aggregates varies greatly. The ore achieves a weight loss rate over 20% after roasting, which can significantly raise the theoretical iron grade. Conclusions Due to uneven granularity of valuable minerals and carbonate impurities, qualified iron concentrate cannot be produced via conventional mineral separation. Roasting treatment can modify the ore’s beneficiability and has promising prospects for producing qualified iron concentrate.