Separation and Determination of Aluminum in Elementary Silicon

Sample of elementary silicon was dissolved in conc.HF and the matrix silicon was expelled by volalitalization as SiF4↑.The residue was taken up with HNO3 and HCl and evaporated to near dryness by fuming with HClO4.After dissolving the residue with HCl(1+1),an aliquot of the solution was taken and extracted with Tween-20,PAR and (NH4)2SO4 in a total volume of 10 mL at pH 4.5 buffered with hexamine,to remove all of the co-existing Fe(Ⅲ),Cu(Ⅱ),Cr(Ⅲ) and Ni(Ⅱ),part of Co(Ⅱ) and Pb(Ⅱ),while Al(Ⅲ) remained quantitatively in the lower aqueous phase together with Ca(Ⅱ),Mg(Ⅱ) and Na(Ⅰ).Aluminum(Ⅲ) in the lower phase was determined spectrophotometrically with chrome azurol S at pH 4.5 in the presence of CPC.Linear relationship between the absorbance measured at 642 nm and the concentration of Al(Ⅲ) was obtained in the range of 0.02-0.50 mg·L-1,with detection limit of 0.01 mg·L-1.Recovery was tested by the standard addition method,the results obtained were in the range from 96% to 101%.Values of RSD′s (n=5) found were less than 3.5%.