Quantification of hafnium in selected inorganic and organometallic compounds

[摘要] English: The aim of this study was to develop a method for the dissolution and quantification ofhafnium in hafnium containing compounds (which include the metal oxide, differentinorganic compounds as well as a number of organometallic complexes). Variousdigestion techniques such as open vessel, flux fusion and microwave acid-assistedsystem were evaluated. The same time different reagents which include HNO3, HCl,H2SO4 alone and in combination with salts, e.g. (NH4)2SO4 + H2SO4 were evaluatedwhile experimental conditions such as time and temperature were varied.Different analytical techniques such as inductively coupled plasma optical emissionspectrometry (ICP-OES), infrared spectroscopy (IR), CHNS-micro analyses and X-raycrystallography were used for the quantification and characterisation of the synthesizedhafnium compounds. The criteria used to select the Hf emission wavelength for ICPOESanalysis was its sensitivity and the absence of spectral interferences from theacids used or the other elements present in solution. The experimental ICP-OES resultsobtained for the quantification of hafnium were also validated using different validationparameters which include accuracy, precision and the hypothesis test at a 95 %confidence interval to evaluate the validity of the most suitable digestion methods thatwere developed.Open vessels digestion of HfF4 using 98 % H2SO4 or 65 % HNO3 resulted in goodhafnium recoveries which ranged from 97.8 �?99.9 % with relative standard deviation(RSD) within the range of 0.4302 �?0.4327 %. The hafnium content was also quantifiedin a number of newly synthesized hexafluorohafnate complexes as well as a thiocyanatecomplex. Hafnium recoveries ranged from 79(6) to 103(3) % for the sodium,potassium, rubidium, cesium, ammonium, methyl ammonium and tetraphenylphosphine hexafluorohafnate complexes as well for the hafnyl thiocyanate complex. Allthe synthesised products were characterized with IR while the crystal structures ofK2HfF6, Rb2HfF6, Cs2HfF6 and (PPh4)2HfF6.2H2O were successfully done with X-raycrystallography.Various digestion techniques such as open vessel, flux fusion and microwave acidassistedsystem with different mineral reagents which include HCl, 65 % HNO3 andaqua regia, 98 % H2SO4, a mixture of (NH4)2SO4 in 98 % H2SO4 and a mixture of NH4Fand 98 % H2SO4 were investigated for the dissolution of hafnium oxide. Digestion bywet ashing yielded poor hafnium recoveries and ranged between 0.041(6) % and3.82(1) %. Hafnium oxide was however successfully dissolved with flux fusion usingNa2B4O7 followed by its dissolution with 98 % H2SO4. Hafnium recoveries improvedfrom 72(4) to 100.8(7) %. Relatively poor hafnium recoveries ranging between 35(2)and 58(6) % (with time variation) were obtained using NaOH as flux and hafniumrecoveries of 99(2) % were obtained using NH4HF2 as flux. Microwave acid-assisteddigestion was also employed which improved the Hf recovery from 74.9(4) to 100(3) %with time and pressure as experimental variations.The method validation of the experimental results obtained for the quantification ofhafnium using the hypothesis testing of at a 95 % confidence level was consideredsatisfactory. The experimentally obtained LOD values ranged from 0.0051 to 0.0985and LOQs ranged between 0.051 to 0.9846 ppm in the different mineral acid used inthis study. Other statistic parameters such as linearity and sensitivity were alsoinvestigated and gave satisfactory results.

[发布机构] University of the Free State