SEPARATION AND PRECONCENTRATION OF VANADIUM(V) ION IN AQUEOUS-SOLUTION USING ACTIVATED CARBONS AS A COLLECTOR - DETERMINATION OF VANADIUM(V) IN TAP WATER AND RIVER WATER

A method is described for the preconcentration and determination of vanadium(V) ion in aqueous solutions. A 100 ml of sample solution containing vanadium(V) was mixed with 50 mg of activated carbon (to be hereafter abbreviated as AC) under stirring for 30 min. The solution was then filtered or centrifuged and the concentrations of vanadium(V) in the filtrate or supernatant solution were determined by a graphite furnace AAS. The optimum pH values for the adsorption were 4.0 approximately 5.0. It was found that the adsorption amounts increased greatly by the addition of 8-quinolinol (oxine) to the sample solutions. The adsorption percentage was measured for a concentration range of 0.5 approximately 80 ppm of the vanadium(V) by 50 mg of AC in 100 ml of solution. The maximum adsorption amounts were determined to be 16 and 34 mg g-1 without and with the oxine of 2.5 mg, respectively. It was also found that the oxine of 8.7 mg (i. e., 87% of oxine added) was adsorbed on the AC surface when the solution containing 10 mg of oxine with 50 mg of AC was stirred for 30 min; such an AC is abbreviated as AC(Ox). When the sample solution was filtered through a small filter paper coated with the AC(Ox) of 58.7 mg, the maximum adsorption amounts of vanadium(V) increased to 55 mg g-1, in which the molar ratio of Ox to vanadium was 1:1. The adsorption percentage of V on the AC(Ox) was little affected by the coexisting salts such as NaCl, CaCl2, Zn(NO3)2.6 H2O, and CH3COONa, where each salt was added up to 10 g per 100 ml of the sample solution, while decreased with increasing amounts of Cu(NO3)2.3 H2O, Na2C2O4, and Na2[H2edta].2 H2O. After vanadium(V) in the sample solution was once adsorbed on the AC(Ox), vanadium(V) was easily desorbed from the AC(Ox) by the addition of HCl of 1 mol dm-3. When a 200 ml of real sample was concentrated finally to 1 ml by the above adsorption- desorption procedures, the detection limit for vanadium(V) was 0.045 ng ml-1. For 15 samples of each natural water, vanadium(V) concentrations for tap water and river water were determined to be 1.2 (R. S. D. = 24%) and 2.9 (R. S. D. = 10%) ng ml-1, respectively.