Spectrophotometric Determination Of Trace Amount Of Molybdenum And Silver In Ore Samples After Separation And Enrichment By Ion Exchange Resins

In this paper, 732 type cation exchange resin and 717 type anion exchange resin were used as sorbents for the separation and preconcentration of trace molybdenum and silver in aqueous media, respectively. Performances of these two kinds of ion exchange resins adsorbing and desorbing molybdenum and silver were investigated in detail. Optimal experimental conditions including resin amount, pH, flow rates of sample and eluent solutions, sample volumes, etc. were analyzed. The interference effect of some cations and anions was also studied. A simple, rapid and sensitive spectrophotometric method for the determination of trace molybdenum（or silver） in ore samples after preconcentration and separation onto ion exchange resin colum was established. The main research contents and experimental results as follows:1. The optimal analytical conditions for the determination of molybdenum by the thiocyanate spectrophotometric method as follows: 5 mL 1:1 HCl, 0.4 mL 2% CuSO4 , 2.0mL 10%ascorbic acid and 50% potassium thiocyanate mixture solution were added a 25 mL flask, respectively. The color development reaction was completed after 10 min, and steadied in 3 h; the wavelength of maximum absorbance was 460 nm, the apparent molar absorptivity was 1.66×10⁴ L mol^-1 cm^-1, and the equation of calibration curve was A=0.0572 C_μg/25mL+0.0124 with a correlation coefficient r = 0.9994.The optimal analytical conditions for the determination of siver by the michaelis copper thiosulfate spectrophotometric method as follows: 2 mL pH 4.5 HAc-NaAc buffer solution, 1.0 mL 0.2g L^-1 TMK, 1mL 50g·L^-1DBS, The color of the complex development reaction completeded after 30 min, and steadied in 3 h; the wavelength of maximum absorbance was 545 nm, and the apparent molar absorptivity was 8.91×10⁴ L mol^-1 cm^-1, and the equation of calibration curve was A=0.033C_μg/25mL+0.0025 with correlation coefficient r = 0.999.2. The experimental conditions for the ion exchange resins adsorbing and desorbing molybdenum was studied. The optimal experimental conditions as follows: the static adsorption experiment was carried out for 15 min with a sorbent dosage of 1.0 g at room temperature. The optimum pH for maximum adsorption of Mo was found to be 7.5. In the dynamic adsorption process, Mo solutions at pH=7.5 was passed through the resin column at a flow rate of 2.5 mL·min^-1. 10mL of 0.5 mol·L^-1 NH₄NO₃ and 2.0 mol·L^-1 HNO₃ mixture solution was used as eluent to desorb Mo from the resin column. An enrichment factor of 30 was obtained for 300 mL of sample solution. The dynamic saturated adsorption capacity was 63.08 mg?g^-1.The experimental conditions for the ion exchange resins adsorbing and desorbing molybdenum was studied. The optimal experimental conditions as follows: the static adsorption experiment was carried out for 30 min with a sorbent dose of 0.5 g at room temperature.The Adsorption percentage of siver is reach biggest at the pH range of 1⁴. In the dynamic adsorption process, Ag solutions at pH=1⁴ was passed through the resin column at flow rate of 3.0 mL·min^-1. 10 mL pH=9.0 of 0.5 mol·L^-1 Na2S2O3 was used as eluent to desorb Ag from the resin column, and the sorption efficiency was reached 97%. An enrichment factor value of Florisil was 10 of sample solution. The dynamic saturated adsorption capacity was 48.11 mg·g^-1.3. The detection limits （3σ） of determining Mo（VI） ions with ion exchange resin as sorbents was 0.056μg·mL^-1 （n=11）, and the relative standard deviations was 2.2%（n=7）,it was show that this method has good reproducibility and precision. In the conditions of pH 7.5, except for WO₃^- interferring to the adsorption and Fe³⁺ interferring to the determination ,the other coexisting ions almost didn’t have effects and the allowable volume for these species were large. So It were not interfered for adsorption and desorption molybdenum onto anion exchange resin . The WO₃^- ions was masked by citric acid when tested in solution, and the when determining, Fe³⁺ ion was formed a red complex with thiocyanate, however, It was reduced Fe²⁺ to no effect the determination by using ascorbic acid , and the Fe²⁺ has certain catalysis for action.The detection limits （3σ） of determining Ag（I） ions with cation exchange resin as sorbents was 5μg·L^-1, and the relative standard deviations was 1.1%. Except for Pb²⁺、Au³⁺, other coexisting ions almost didn’t have effects and the allowable volume for these species were large. Moreover, the experimental results indicated that there exist some interference for some Al、Cu、Co、Ni ions and they can also be eliminated by proper masking methods ions, and no interference for the other ions in the adsorption When the determination of Ag in the ore samples, due to higher levels of coexisting elements, may be appropriate to reduce the sample volume.The estiblished method was applied to determine some reference samples, and the results were quite satisfactory.