ERMS Technology
ERMS (Enhanced Roasting and Magnetic Separation) is a controlled roasting process, which conditions ilmenite for selective magnetic separation of gangue minerals and rapid leaching in hydrochloric acid, generating a high grade synthetic rutile.

Benefits of Austpac’s ERMS SR Process:

• Capital and operating costs are competitive with other synthetic rutile processes.
• Gas-solids fluid bed units are utilised for ilmenite roasting, synthetic rutile calcining and acid regeneration.
• Ilmenite leaching is carried out at atmospheric pressure.
• The overall processing cycle time is short, therefore equipment size per unit of capacity is small.
• The process is not fuel specific, nor is it ore specific.
• ERMS SR produces the world’s highest grade synthetic rutile (+97% TiO2).
• High recoveries of ilmenite and TiO2 are achieved.
• Zero liquid discharge can be achieved.

1. Roasting
MAGNETISING ROASTING
The original ERMS roasting process featured a single fluid bed roaster, operated under controlled conditions, so that the ilmenite component of the concentrate being treated is rendered very magnetically susceptible and thus can be readily separated from gangue minerals by low intensity magnetic separators. By this means it is possible to produce an ilmenite essentially free of chromite and garnets, in a useful form for later processing into, say, titania slags. Magnetic ilmenite produced in this manner is not a suitable feedstock for the sulfate process because the titania fraction is rendered insoluble in sulfuric acid by the roasting process. However, this property can be useful if hydrochloric acid leaching is employed to selectively remove the iron and other soluble constituents to make synthetic rutile. It was noted that when magnetic ilmenite is acid leached, some 50% of the iron is in the trivalent state requiring the use of chemical reductants and long leach cycle times to achieve successful results. Thus two stage oxidation-reduction roasting is now used for synthetic rutile production.

OXIDATION-REDUCTION ROASTING
Roasting for acid leaching is carried out in two fluid bed stages, operating in tandem. In the first stage, the ilmenite concentrate is roasted in an oxidising atmosphere so that almost all of the iron is converted to the trivalent state. In the second stage, the trivalent iron is reduced to the divalent state, in which form it is very readily leached. The titania fraction is rendered virtually insoluble when the ilmenite is roasted at these temperatures. Roasting causes changes to the crystal morphology (such as the creation of micro fractures) that are also important for leaching.

Oxidation-reduction roasting is achieved at operating temperatures of 950 to 1000°C, with a total mean residence time of 2 hours, using a hydrocarbon (generally coal) as fuel. Hot reduced ilmenite is very reactive and the product is fully cooled in the absence of air when discharged from the roaster.

Even though ilmenite conditioned for leaching has a lower magnetic susceptibility, the roasted ilmenite has homogeneous properties and can be separated from the remaining gangue and fine char particles using a rare earth drum magnetic separator. Any remaining magnetic gangue is carried through the subsequent leaching stage and is removed at the end of the process. At this stage, the ilmenite has been transformed into synthetic rutile which is non-magnetic, and can be separated from any remaining magnetic gangue minerals such as chromite and residual garnets.

2. Hydrochloric Acid Leaching
Austpac has developed a continuous hydrochloric acid leach system that operates at atmospheric pressure. It is possible to make a high purity, high grade synthetic rutile of +97% TiO2 from most ilmenites.

The iron component of roasted ilmenite is highly reactive and very readily leached in hot hydrochloric acid. Any oxides of calcium, magnesium, manganese or aluminium that occur as impurities within the ilmenite are similarly dissolved. Most of the TiO2 is insoluble. A very small fraction dissolves initially, but the majority precipitates back into the grains of synthetic rutile by hydrolysis as hydrated oxychlorides, and is converted later to TiO2 by calcination.

Austpac developed the EARS process which is capable of economically producing strong (“super-azeotrope”) hydrochloric acid from waste iron chloride solutions. The use of super-azeotropic acid increases the leaching rate and decreases the amount of water that is needed to be evaporated during acid regeneration. An acid concentration of 25% by mass is normally produced.

3. Filtration & Washing
Liquid-solid separation is carried out on a four-stage vacuum belt filter. The first stage removes the iron chloride leach liquor and the remaining three stages are used for filter cake washing and air drying. The spent wash liquor is used for HCl absorption in the acid regeneration section.

4. Drying, Calcination and ERMS SR Production
The washed solids from the filter are dried and calcined in a fluid bed system. This removes residual and chemically combined hydrochloric acid and water. Calcination is achieved at ~800°C with a mean residence time of ~20 minutes, which produces a straw-coloured synthetic rutile product. Calcination requires a clean burning fuel to avoid contamination of the product.

Following calcination, high intensity magnetic separation is used to remove any residual magnetic material. This is usually a small fraction (2-3%) and comprises under-leached material and any residual gangue minerals, including chromite, which would otherwise contaminate the synrutile.

The synthetic rutile produced by the ERMS SR process is therefore very pure synrutile containing at least 97% TiO2; a premium feed stock for titanium dioxide pigment and the titanium metal manufacture.

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