Treatment of iron ore slime for value addition

Typical Indian iron ore slime in a steel plant contains 56% iron, 6.78% Al2O3 and 5.8% SiO2. Value addition to this reject / waste material has been investigated using chemical treatment and electrowinning. Two alternate chemical treatment routes have been explored: (i) acid extraction of iron followed by alkali treatment and (ii) alkali extraction of aluminum oxide and silica from iron ore slime. Alkali extraction improved iron content up to 65% w/w. Acid extraction could improve the same up to 63% w/w. Electrowinning of iron from oxalic acid solution using steel cathode and a lead anode, surrounded by a synthetic cloth diaphragm, produces high purity iron deposits on the cathode surface. Chemically treated iron ore slime is suitable for iron production using blast furnace whereas the elemental iron produced by electrowinning can be used directly for steelmaking. Along with the process details, a preliminary calculation of the economics of the two processes has been presented.

Research Highlights
► Iron ore slime which is a waste material contains 56% of iron.
► Two different chemical treatment methods and electrowinning method were separately studied to upgrade iron content up to 60% or above.
► Acid extraction and alkali extraction can upgrade iron content maximum 63% (w/w) and 65 % (w/w) respectively.
► Electrowinning directly produces high purity iron without involvement of blast furnace.
► Electrowinning is an attractive option as it is the least expensive and it does not require further processing of ore slime in blast furnace.