Membrane contactor as a novel technique for separation of iron ions from ilmenite leachant

A novel system based on membrane contactor was applied for separation of iron ions during leaching of ilmenite ore in hydrochloric acid. Separation of iron would enhance leaching of ilmenite and leads to pure titanium products. The used membrane contactor cell consisted of two identical compartments separated by a porous flat sheet membrane. The ilmenite leachant was separated from the residue and placed in one compartment (marked as feed side) and an organic solution containing a selective iron extractant was placed in the other compartment (marked as receive side). Among the several tested organic extractants, trioctylamine (TOA) was found to be effective and selective for extraction of iron ions from solutions of a wide range of hydrochloric acid concentrations. TOA in kerosene and 10% 1-octanole was used as a receive phase in the membrane contactor cell. Two types of membrane materials were tested; polytetrafluoroethylene (PTFE) and polypropylene (PP) with almost similar pore sizes of about 0.5 μm. Multi separation stages by the membrane contactor were applied by replacing the receiving solution with a fresh one after 180 min of separation time. High Fe removal efficiency of about 86% after 4 separation stages using 0.2 μm PP membrane was obtained. The transport mechanism of iron was proposed mainly based on ionpair (R3NH+FeCl4−) formation in the aqueous–membrane interface and its diffusion to the organic pulp through the membrane. The separation of the aqueous and organic solutions by a membrane in this contactor technique overcame the common drawbacks of the solvent extraction such as losses of the organic reagent, emulsion formation and delay of phase separation. In other procedures, the ilmenite slurry suspension was placed as it is in the feed side of the cell to test the possibility of the continuous separation of iron during leaching. The Fe removal efficiency was found to be very low (8% after 3 h) due to fouling of the membrane. A brownish precipitate was observed on the feed side of the membrane and was growing by time leading to slowing down of the Fe transport rate. Thin Film XRD test of membrane fouling showed that Goethite α-FeO(OH), Feroxyhyte ō-FeO(OH) and iron oxy chloride (FeOCl) are the main constituents of the precipitate. In addition, SEM photomicrographs showed that the precipitated particles on the membrane surface are sphere in shape with size ranged from 1 to 2 μm.