Separation and preconcentration of molybdenum (Vi) ions in aqueous solution using activated carbon as a collector; determination of molybdenum(vi) in tap-water, river-water and seawater.

Abstract

A method is described for the preconcentration and determination of Mo(VI) ions in aqueous solutions. A sample solution of 100 or 200 ml containing Mo(VI) was mixed with the activated carbon of 50 or 100 mg under stirring for 30 min. The solution was then centrifuged or filtere,and the concentrations of Mo(VI) in the supernatant or filtrate solution were determined by a graphite-furnace AAS. Mo(VI) was adsorbed over 90% at pH 3.3~4.0 on the activated carbon. The adsorption percentage was measured for a wide concentration range of 2 ppb~100 ppm, and the maximum adsorption amounts were determined to be 59 mg g 1 by plotting the adsorption isotherm curve and by the Langmuir plots. The maximum adsorption amount decreased to about 8 mg g 1 in the presence of EDTA. The adsorption percentage decreased with increasing amounts of the coexis-tent salts such as Na2C2O4, Na2SO4, KCl, MgCl2, CaCl2and Zn(N03)2+6H20. The presence of Zn2+ ion decreased greatly the adsorption % of Mo(VI). On the other hand, the addition of 8-quinolinol to the No-solution in the presence of Zn2+ ion increased the depressed adsorption %. After Mo(VI) in the sample solution was once adsorbed on the activated carbon of 50 mg, Mo(VI) was easily desorbed and separated from the Mo-adsorbed carbon by the addition of a few milliliters of 0.1 mol dm-3 NaOH. When the real sample of 200 ml was concentrated to 1 ml by the above procedures of adsorption and desorption, the detection limit for Mo(VI) was 0.0011 ng m-l. For the 20 duplicate samplings of each natural-water, Mo(VI)-concentrations for tap-water, river-water and seawater were determined to be 0.37 (R.S.D. = 14%), 0.23 (17%) and 7.9 (8%)ng ml-1, respectively using this method. It was also confirmed that the amounts of Mo(VI) separated from the natural water samples were proportional to the volumes of water taken. © 1989, The Japan Society for Analytical Chemistry. All rights reserved.