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Study on the Determination of Trace Zinc by Spectrophotometry after Flotation Separation with Ternary Association Complex System

The paper presents a novel method for the flotation separation of Zn 2+ with ternary association complex system prior to the determination by spectrophotometry. The effects of different parameters, such as the dosages of N H 4SCN and dodecyl trimethyl ammonium chloride (DTAC), various salts and acidity etc. on the flotation yield of Zn 2+ have been investigated to select the experimental conditions. The possible flotation mechanism of Zn 2+ was discussed. The results showed that by controlling pH 4.0, in the presence of 1.0 g NaBr, when the dosage of 0.1 mol·L -1 NH 4 SCN solution was 2.50 mL and 5.0 x 10- 3 mol·L -1 DTAC solution was 2.00 mL respectively, the water-insoluble ternary association complex of [Zn(SCN) 4 ] (DTAC) 2 which produced by Zn 2+ and SCN - , DTAC cation (DTAC + ) floated above water phase and liquid-solid phases were formed with clear interface, while K + , Na + , Ca 2+ , Mg 2+ , Al 3+ , Fe 2+ , Mn 2+ , Cd 2+ , Co 2+ and Ni 2+ could not be floated, so Zn 2+ was floated quantitatively at pH 4.0. Thereby, the quantitative separation of Zn 2+ from the above metal ions could be achieved. A new method of determination of trace zinc by flotation separation was established. The proposed method has been successfully applied to the determination of Zn 2+ in plating waster water, and the results agreed well with AAS method. The recoveries were 93.6%∼106.4%, and the RSD was 1.8%∼2.3%.