Adsorption Behavior of Pb, Cd, Ca, Al, Zn And Co Metal Ions on Cation Exchange Resin Dowex 50 Wx 8 (Nh 4+ Form) From Aqueous Acetone-Ammonium Propionate Media.

In the field of inorganic chemistry separations, the incentive to explore the use of non-aqueous or mixed solvents has been the enhanced selectivity, discovered quite early in such media for Zeolites[1] and ion exchange resins [2]. The partial substitution of aqueous solution by organic solvent produces a number of changes in an exchange system, such as , change in the solution structure due to the interaction between water and the organic solvent, change in the hydration and salvation of the electrolyte, change in the solvent composition in the resin phase , change in the activity coefficients of the electrolyte in the solution phase as well as in the resin phase, change in the complexation of the metal ion and change in the extent of invasion by an electrolytes. All these changes are mutually dependent and affect the distribution of the metal ion. It is already known that, at equilibrium with a mixed solvent, because of the preferential up take of water by the resin, the solution composition in the resin phase often differs very much from that in the outer solution and the difference becomes greater with less polar organic solvents.


Introduction
From the investigations of ion exchange in mixed solvents, it is apparent that the adsorption equilibrium depends markedly on the properties of the organic solvent and reactions with the resin and electrolytes which determine the equilibrium.
Tthe presence of water miscible polar solvents proved to be advantageous in the metal ion exchange in complexing media. Firtz et al [3] separated many metal ions using 0.1 or 1 M hydrofluoric acid as the eluting agent, the method of separation of Al 3+ , Ti 4+ , V 4+ and Nb 5+ ions was studied by Dowex 50 WX8 resin in H + and ethylene di -ammonium forms. Yoshimo and Koiima [4] and Strelow [5] separated cadmium from zinc and other metal ions by eluting them with 0.5 M hydrochloric acid. The studies indicated that when nitric acid is used with non aqueous solvent, the larger volume of eluent is required for quantitative elution and a slower flow rate had to be employed. Strelow [6] Mann and Swanson [7] measured the equilibrium distribution coefficients which are a useful guide to possible cation exchange separations in aqueous solution. Cation exchangers permit the phenomenon of combined ion exchanger-solvent extraction (CIESE) to be exhibited 8, 9, 10 complex formation of the metal ions with organic compounds has been advantageously used to achieve difficult separations. Attempts were made to separate the metal ions in aqueous acetone propionic acid media by using Dowex 50 WX 8 in H + form. The distribution coefficients of various metal ions were found to be very high and therefore the separations.
The distribution coefficients of various metal ions were found to be very high and therefore the separations were not achieved. The distribution coefficients (K D ) were found out at various concentrations of ammonium propionate solutions. The effect of acetone percentage on the distribution coefficient is explained on the basis of variations in di-electric constants of mixed solvents.

Material and Methods
The distribution coefficient, K D was determined by batch equilibrium method. 1 g of air dried Dowex 50 W X8 (NH 4 + form) resin was taken in 250 ml glass stoppered Erlynmeyer flask. 4 ml of 0.05M metal ion solution and 50 ml of the appropriate aqueous acetone-ammonium propionate mixtures was taken. The flask was stoppered and kept for 24 hr. After 24 hrs supernatant liquid was pipetted out and acetone was evaporated. The metal ion content was determined by suitable titration method. The pyrex glass chromatographic columns of 50 ml of capacity were used The column was packed with a small glass wool at the bottom and a slurry of 10 g soaked resin was passed and was allowed to settle by occasional tapping. A care was taken to prevent the formation of air pockets.
The binary mixtures of various metal ions were prepared. It was allowed to pass down the column slowly without allowing the level of the liquid to drop below the surface of the exchanger. The proper amount of eluting agent was added. The effluent fractions were collected in test tubes by maintaining a flow rate of 1 ml/min. The presence of metal ion was tested by suitable analytical reagents in the effluent fractions. Under specified experimental conditions the first metal ion starts eluting and it is completely removed in a series of fractions collected. The second metal ion starts eluting and gets completely eluted at a particular fractions. The metal ion contents in the collected fractions were estimated by standard volumetric procedure.

Results And Discussion
The distribution coefficients of Pb, Cd, Al, Zn and Co, were found out at 0, 20, 40,60 and 70 percentages of acetone at 0.02, 0.06, 0.