ERMS roasting (Enhanced Roasting and Magnetic Separation) is a controlled roasting process, which conditions ilmenite for selective magnetic separation from gangue minerals.
ERMS SR roasting is used for rapid leaching in hydrochloric acid to generate high grade synthetic rutile
The combination of Austpac’s roasting, leaching and acid regeneration processes is termed the ERMS SR Process.
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.
ERMS MAGNETISING ROASTING
The original ERMS roasting process was invented and patented in 1988. It features a single fluid bed roaster which is operated at ~950°C under controlled conditions so that the magnetic susceptibility of the ilmenite component in a heavy mineral concentrate is increased, while the susceptibility of other minerals such as chromite or garnet is unchanged. ERMS-roasted ilmenite is more magnetic than the other minerals and can be readily separated from them using low intensity magnetic separators. This produces an ilmenite concentrate free of chromite and garnet that can be used as a feedstock for titania slag. ERMS-roasted ilmenite is not a suitable feedstock forthe sulfate-route TiO2 pigment process because the titania fraction is rendered insoluble in mineral acid by high temperature roasting. However, this insolubility is useful if hydrochloric acid is used to selectively leach the iron and other soluble constituents in roasted ilmenite to make synthetic rutile. However in ERMS-roasted ilmenite, around 50% of the iron is in the trivalent state, so chemical reductants and long leach cycle times are required to achieve successful results. Thus two-stage oxidation-reduction roasting is now considered preferable for synthetic rutile production.
ERMS SR 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 high temperature. 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 fuel (generally coal). 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 strong rare earth drum magnetic separator. Any remaining magnetic gangue that is carried through the subsequent leaching stage is removed at the end of the process. Once leached, the ilmenite has been transformed into synthetic rutile which is non-magnetic, and it can be separated from any remaining magnetic gangue minerals such as chromite and garnet.
2. Hydrochloric Acid Leaching
Austpac has developed and patented 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, which is converted to TiO2 during the final calcination step.
Austpac developed the EARS process which is capable of economically producing strong (“super-azeotrope”) hydrochloric acid (HCl) 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. This halves the leaching time required when leaching ilmenite with the commercial 18% HCl produced by other acid regeneration processes.
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.Return to top