Study on Determination of Trace Copper by Spectrophotometry after Flotation Separation Using Microcrystalline Adsorption System

The paper presents a novel method for the flotation separation of Cu²⁺ using microcrystalline adsorption system prior to the determination by spectrophotometry. The effects of different parameters, such as the dosages of NH₄SCN and octadecyl trimethyl ammonium bromide (OTMAB), various salts on the flotation yield of Cu2+ have been investigated to select the optimum experimental conditions. The possible flotation separation mechanism of Cu²⁺ was discussed. The results showed that under the optimum conditions, octadecyl trimethyl ammonium bromide cation (OTMAB⁺) reacted with SCN^‐ to produce the microcrystalline matter (Ms‐M) of (OTMAB⁺·SCN^‐), the water‐insoluble ternary association complex of [Cu(SCN)₄] (OTMAB)₂ which produced by Cu²⁺ and SCN^‐, OTMAB⁺ was quantificationally adsorbed on the surface of Ms‐M of (OTMAB²⁺·SCN^‐) and was floated above water phase, the liquid‐solid phases were formed with clear interface. In this condition, K⁺, Na⁺, Ca²⁺, Mg²⁺, Al³⁺, Fe²⁺, Mn²⁺, Ni²⁺, Cd²⁺ and Co²⁺ could not be floated. Therefore, Cu²⁺ was separated completely from the above metal ions. A new method of determination of trace copper by flotation separation was established. The proposed method has been successfully applied to the determination of Cu²⁺ in plating waster water, and the results agreed well with AAS method. The recoveries were 93.3%～107.8%, and the RSD was 1.9%～2.1%.