Surface Chemistry Studies on Surfactant Properties Relevant to Flotation De-inkin

Abstract: The objective of this work was to investigate thephysico-chemical properties of common de-inking chemicals. Thishas been done by means of equilibrium and dynamic surfacetension measurements as well as foaming experiments. Thesurface tension is especially important in the flotationprocess since the bubble size and stability is stronglyinfluenced by the surface tension of the solution and this inturn affects the flotation process. The surface tension and cmchave been determined at different pH for the oleic acid, and itcould be noticed that the pH influences both the cmc and theequilibrium surface tension value to some extent. Also thedynamic surface tension of oleic acid solutions at differentconcentrations and temperatures has been studied. Thesemeasurements were carried out high above the cmc, and anincrease in temperature influences the surface tensionreduction more than an increase in concentration. The largetemperature dependence is due to a decreased stability of themicelles at elevated temperatures. Equilibrium surface tensionmeasurements were also performed with mixtures of oleic acidand nonionic surfactants. Here a strong positive synergisticeffect was obtained, which means that a given surface tensionreduction can be obtained at lower surfactant concentrations.Also, foaming experiments have been carried out with both pureand mixed surfactant systems. The total foam volume wasapproximately the same for both the pure surfactant systems atall tested concentrations and for the mixtures. However, theamount of liquid entrapped in the foam differed considerablydepending on concentration for the pure systems and the foamwas slightly more stable for the mixtures than for the purecomponents. Also, more liquid was entrapped in the foam forsome compositions, indicating that the bubbles were smaller andthe aqueous films between the bubbles were thicker.