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Flotation process using pH-sensitive surfactant; From foam structure to extraction efficiency

pH感受性界面活性剤を使用した浮選プロセス; 泡構造から抽出効率まで

Micheau, C.; 元川 竜平   ; 上田 祐生   ; Bauduin, P.*; Diat, O.*; Girard, L.*

Micheau, C.; Motokawa, Ryuhei; Ueda, Yuki; Bauduin, P.*; Diat, O.*; Girard, L.*

Flotation process takes the advantage of foam to extract and concentrate solutes (ions, molecules, colloids and particles) without using organic solvent. Among all of the potential applications, particle flotation has proven its efficiency for paper deinking, ore and mineral extraction. In addition, the interest in the flotation of clay particles has increased over the past few decades because of the environmental contamination of soil and ground water by heavy metals and radionuclides. In this study, we used Ethomeen C/25, a polyethoxylated tallow amine, for the extraction of Laponite RD, a synthetic clay. This pH-sensitive surfactant plays the role of foaming agent and collector. The objective was to determine how the foam microscopic structure depends on the molecular interaction between the clay and the surfactant and to correlate these results to the extraction efficiency. For this purpose, clay extraction experiments were performed as function of pH. High extraction yield was obtained for pH $$<$$ 10, whereas an unexpected negative recovery factor is observed for higher pHs meaning that clays are repelled from the foam interfaces. To determine the mechanisms involved in the flotation process for each pH condition, bulk and foam were investigated using electrophoretic analysis, dynamic light scattering, small-angle neutron scattering, and image analysis (see Figure 1). From these results, we described the impact of clay on foam structure and stability, and established three different flotation regimes: (i) froth flotation of gel-like clay particles at pH $$<$$ 6, (ii) foam flotation of clay aggregates at 6 $$<$$ pH $$<$$ 10, and (iii) foam fractionation with the depletion of clays at pH $$>$$ 10. A continuous process for soil remediation is designed by alternating regimes (ii) and (iii) adjusting the pH.

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