Journal of Water Supply: Research and Technology—AQUA Vol 55 No 7-8 pp 471–478 © IWA Publishing 2006 doi:10.2166/aqua.2006.055

Generation of a positively charged bubble and its possible mechanism of formation

M. Y. Han, M. K. Kim and M. S. Shin

The zeta potential of bubbles was measured in various solutions containing the metal ions Na⁺, K⁺, Ca^2 + , Mg^2 +  and Al^3 + . We discovered the main factors that can affect a bubble's zeta potential, resulting in a foundation for tailoring the zeta potential of bubbles during flotation processes. Bubbles were negatively charged in solutions of metal ions such as Na⁺, K⁺ and Ca^2 +  at every concentration and pH range studied. However, the magnitude of the zeta potential decreased with an increase in concentration and a decrease in pH value. Positively charged bubbles were observed in a solution of 0.01M MgCl₂ and an alkaline pH range, and below pH 8.2 with AlCl₃ in the concentration range of 10^-5 to 10^-2 M. Metal hydroxide precipitates affected the generation of positively charged bubbles, and minor hydroxylated species also contributed to increase the zeta potential of bubbles. Generation of positively charged bubbles could be the result of a combined mechanism, with both specific adsorption of hydroxylated species and precipitation of metal hydroxides on the bubble surface.

Keywords: bubble charge; flotation; microbubbles; metal hydrolysis; metal precipitation; zeta potential

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