Rapid Measurement Of Rare Elements In Bayan Obo Ore By EDXRF

This study, as a part of XRF (X-ray fluorescence) sorting of low-grade minerals inBayan Obo multi-metal deposit, was aimed to provide physical basis and to determineconditions for XRF sorting in the field. XRF sorting uses the XRF spectra of elements toseparate different minerals, in which blocks of ores pass a detection chamber so swiftlythat the XRF instrument of the sorting machine must accomplish the measurement in lessthan0.1second, making the conventional XRF method incompetent. The Russia madesorting machine LPPC4-150adopts a so-called peak-to-background ratio (PTBR, the ratioof the height of a characteristic peak of the targeted element in its XRF spectra overundisturbed background) to determine the concentration of the interested element. Thisstudy delimitated the valid range of PTBR and applied parameters determined in thelaboratory to the field operation for picking REE rich minerals in the Bayan Obo deposit.Towards the above goals, a XRF instrument was set up in the laboratory with an X-raytube, a detector, and a data collector; PTBR was introduced into XRF measurement bymodifying the commonly used algorithm in order to realize fast measurement. As a test forPTBR,50samples made from milled Bayan Obo ore blocks were rapidly passing the lab-made instrument to measure the PTBR; meanwhile the same samples each were subject tochemical analysis of REE. The measured PTBR was correlated to chemical content of REEwith a coefficient R=0.897, indicating that the PTBR method can be used for rapidmeasurement of REE in Bayan Obo ores. The relative error was less than50%for thesamples having higher than4%REE and was increasing drastically when the grade of thesamples less than4%, delimitating a low side border for PTBR application.To test the validity of PTBR for un-modified Bayan Obo ores, large number of oreblocks was subject to PTBR, then to chemical analysis. The results indicated that thesmaller the size was, the higher the correlation was between PTBR and chemical content ofREE. On the other side, LPPC machine was unable to recognize the ore blocks well when the size was less than4cm. Taken together, the optimal ore block size for REE sorting wasdetermined to be4-5cm. With this size, the LPPC machine sorting of REE mineralsgenerated result as following: picking16%REE rich ores can successfully recover about30%of REE minerals, and the grade increased11%from average6%.