Thermal treatment for monazite defostatization and rare earth recovery

Brazil has the second largest reserve of monazite, which is one of the three main minerals bearing of rare earth elements. In this study, a monazite concentrate, derived from the occurrence of heavy minerals in the coastal strips of the states of Bahia and Espírito Santos, was used. The best way to analyze aqueous solutions rich in rare earths by ICP-OES was also evaluated. In this work, the steps used to obtain an aqueous solution rich in rare earths from the monazite concentrate involved the following steps: addition of NaOH to the concentrate, heating at 400 ºC for 3 hours, washing with water and subsequent leaching of the remaining solid phase with HCl. Chemical and mineralogical characterizations were accomplished on the products of this process and the results indicated that the initial concentrate is rich in light rare earths, the alkaline fusion product is predominantly composed of rare earth hydroxides and free of NaOH. The acid leaching tailings showed to be rich in zirconite, indicating that the dissolution of the rare earth hydroxides formed in the previous step was complete. Spectral interferences in the lines of the predominant elements were considered in the ICP-OES analysis using individual patterns of these elements. The following lines were defined for the predominant elements: Ce 456.236 nm, Th 283.730 nm, La 384.902 nm, Nd 430.058 nm, Pr 390.844 nm, and Sm 428,079 nm. The leachate obtained after acid leaching of rare earth hydroxides was analyzed by this method and the concentrations of the predominant elements (in g/L) were: Ce 32.81, Th 14.76, La 8.58, Nd 3.35, Pr 3.02, and Sm 1.28. (author)