Scandium quantification in selected inorganic and organometallic compounds

[摘要] English: The main objective of this study was to develop an analytical method to accuratelyquantify scandium in different Sc-containing matrices including inorganiccompounds, organometallic complexes and finally low grade Sc mineral ores andresidues. The organometallic complexes (Sc(acac)3, Sc(tfac)3, Sc(btfac)3, Sc(dbm)3,Sc(hfac)3 and Sc(sacac)3) were synthesized and characterised using melting point,IR, CHNS-micro element analysis and X-ray crystallography techniques. The studyinvolved the use of different mineral acids such as HNO3, HCl and H2SO4 for thedissolution of the different samples using both open-beaker and microwave-assisteddissolution techniques. Flux fusion using NH4F·HF flux was used for the dissolutionof columbite mineral and Ta/Nb residue samples. ICP-OES was used forquantification of Sc in all samples as well as some of the other metals in the mineralsamples. The wavelengths were carefully selected to minimise any spectralinterferences and the matrix matching was also ensured throughout the study foraccurate measurements.ScCl3·H2O was dissolved in water and recoveries ranging from 99.64 - 99.79 % wereobtained. Open-beaker dissolution of Sc2O3 with HNO3, HCl or H2SO4 yielded Screcoveries ranging from 44(7) - 99.2(4) % and these recoveries were improved withthe microwave dissolution method to recoveries between 99.8(3) and 101(1) %.Excellent Sc recoveries from the most of the organometallic complexes (Sc(acac)3,Sc(tfac)3, Sc(btfac)3, Sc(dbm)3 and Sc(sacac)3) ranging from 95(3) - 99.4(6) % wereobtained while Sc(hfac)3 yielded a lower than expected recovery of 80.4(4) % due tothe possibility that the molar mass from the empirical formula known is incorrect orthat an impure product was isolated.Excellent results were obtained for the columbite ore and the Ta/Nb residue samples(Sample A and B respectively) after the NH4F·HF fusion dissolution. In the processof the beneficiation of Sc, magnetic separation was attempted for the removal of Feand Ti from the rest of the sample (both Sample A and Sample B) but was considered unsatisfactory since a large portion of the Fe in the sample did not exhibitferromagnetic properties and hence remained with the original portion (nonmagnetic)of the samples. Results also indicated the loss of a relatively significantportion of Sc in both samples. Solvent extraction with MIBK was also attempted forthe possible extraction of Ta and Nb and the results indicated that this process wasonly successful to eliminate the Ta in large quantities and that both the Ta and Nbcan be extracted with MIBK at high [H2SO4] with relatively insignificant losses of Sc,especially from Sample B.The experimental results for the scandium analysis were validated for a largenumber of validation parameters, which included accuracy, precision, sensitivity,specificity, linearity, etc. to confirm whether the newly developed analyticalprocedures were suitable for the scandium determination in terms of internationallyrequired standards (ISO 17025). The limit of detection (LOD) and limit of quantitation(LOQ) for Sc were determined to be 0.000991and 0.00991 ppm respectively, whichis sufficient to measure trace amounts of scandium. The linearity of the calibrationcurves was determined from the regression coefficient (R2) and ranged from 0.996 to1.00. Statistical tests of the experimental results were calculated using thehypothesis test of the t-statistical at 95 % confidence interval (C.I) to determinewhether the results were acceptable as recommended by ISO 17025.

[发布机构] University of the Free State