The X-ray fluorescence technique meets the requirements of qualitative and quantitative analysis of widely variable major, minor and trace elements including rare earth elements (REE) in geological samples. Although the REE are generally enriched in phosphate rock, yet there are only few elements e.g. La, Ce and Nd can be directly analyzed by XRF method. The analysis of the other REE required additional chemical treatment of the samples (known and unknown) to insure similarity in matrix material, and to obtained lowest spectrum overlap with analytical line of the REE. In addition, the chemical treatment is intended to increase the REE concentration to a level that makes L-lines intensity measurement by XRF is possible. The whole subject represents the core of the present study.
The chemical treatment includes three main stages: (1) digestion of the sample using nitric, hydrochloric, hydrofluoric and perchloric acids. (2) Oxalate precipitation to separate elements with oxidation state of +2 or more (including REE) according to the solubility of their oxalate precipitate. After proper filtration, the precipitate on the filter paper is transferred and dissolved in diluted nitric acid. (3) Precipitation of the separated element as hydroxide on aluminum hydroxide carrier. The hydroxide precipitate were pressed into pellet which is subjected to intensity measurement of the L line of the REE. The study display the results of evaluation of the present analytical method which indicate to (in average) analytical accuracy and precision better than 10% and 3% respectively.
Key words: phosphorites, phosphatic ore, REE, Akashat Fm., XRF.