On-stream Xrf Analysis of Heavy Metals at Ppm Concentrations

An XRF analyser suitable for measuring up to 15 liters of slurry has been tested in the laboratory. A range of slurries consisting of approximately 40 wt% solids and low concentrations of tantalum were obtained and measured. The accuracy of the analyser has been determined to be ±2 ppm (1 sigma). Improvements are planned that will significantly increase the speed and accuracy of the analyser and facilitate its adaptation to online / byline monitoring of mineral process streams. INTRODUCTION CSIRO Minerals is developing methods for the on-stream measurement of parts-permillion (ppm) concentrations of heavy metals in process slurries using K-shell X-ray fluorescence (XRF). As part of this ongoing development, an investigation was carried out on mineral slurries containing approximately 100 ppm of tantalum (Tantalum concentrations are reported as tantalum oxide (Ta2O5) as a proportion of the dry solids mass). MEASUREMENT OF SLURRIES WITH THE CSIRO ANALYSER Sample provision and third-party analysis CSIRO Minerals was supplied with eight samples from a tantalum production facility. Each sample consisted of at least 10 liters of slurry, containing 31-42 wt% solids. The solids content was determined by drying the samples in an oven at 110°C for at least 2 days and weighing the residue. After each slurry had been dried and sub-sampled for analytical XRF analysis, the remaining dry ore was weighed and reconstituted with water for measurement in the CSIRO analyser. The original set of only eight slurries was considered too small for multivariate analysis. Therefore, additional samples were prepared based on this set. Firstly, the tantalum concentrations of two of the samples were increased in 5 ppm intervals by the addition of Ta2O5 powder. Secondly, iron oxide (Fe2O3) was added to one sample to increase its iron content to 2, 4 and finally 8 wt%. These additions were made to investigate the effects of changing matrix composition on the Ta measurement. In this way, the core set of 8 samples was expanded to 22 samples suitable for measurement. Copyright ©JCPDS International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume 47. 130