Development of roasting plant configurations to improve economics and operability of rare earth roasting circuits

Rare earth minerals are often not leachable at atmospheric conditions without first having to crack the mineral matrix at elevated temperatures with or without the presence of strong acids. Leachability of Rare Earth minerals normally require laboratory test work to determine optimum conditions of temperature, acid type and addition rate and residence time for a particular mineral. Laboratory test work generally starts in small scale muffle furnaces and progresses to larger scale muffle furnace test work, laboratory scale rotary kilns before possibly demonstrating on small scale kilns that are available in commercial metallurgical laboratories. Feasibility studies and even commercial plant designs then copy not only the process conditions but also the piloting or demonstration plant equipment designs. Paying more attention to the configuration of commercial roasting equipment and the physical properties of the roasting chemicals and minerals by comparing alternate equipment types and configurations can significantly improve the operating and capital costs, operability and the overall financial viability of the finally selected flow sheet. The effect of different flow sheet configurations on costs have been investigated by process modeling and consideration of the physical and thermodynamic properties of the minerals, chemicals and roasting products for the case of sulphation roasting of a rare earth concentrate. Comparison of a conventional directly fired rotary kiln process with alternate flow sheets are used to demonstrate the improvements that are possible in the capital and operating costs leading to an improved and more robust flow sheet.