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

The paper presents a novel method for the flotation separation of Pb2+ with ternary association complex system prior to the determination by spectrophotometry. The effects of different parameters, such as the dosages of KI and hexa decyl trim ethyl ammonium bromide (CTMAB), various salts and acidity etc. on the flotation yield of Pb²⁺ have been investigated to select the experimental conditions. The possible flotation mechanism of Pb²⁺ was discussed. The results showed that by controlling pH1.0, in the presence of 1.0 g NaNO₃, when the dosage of 0.1 mol·L^-1 KI solution was 1.00 mL and 0.01 mol·L^-1 CTMAB solution was 0.50 mL respectively, the water-insoluble ternary association complex of (CTMAB)₂(PbI₄) which produced by Pb²⁺ and I^-, CTMAB cation (CTMAB⁺) floated above water phase and liquid-solid phases were formed with clear interface, while Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺, Mn²⁺ and Al³⁺ could not be floated, so Pb²⁺ was floated quantitatively at pH1.0. Thereby, the quantitative separation of Pb²⁺ from the above metal ions could be achieved. A new method of determination of trace lead by flotation separation was established. The proposed method has been successfully applied to the determination of Pb²⁺ in the sample of synthetic water and the flotation yield was 96.3%~106.6%.