An investigation of air/water interface in mixed aqueous solutions of KCl, NaCl, and DAH

Flotation of soluble salts such as borax, potash, and trona is carried out in their saturated solutions. The high ion concentration of the flotation suspension can affect the floatability of the minerals as well as the coalescence behaviors of the bubbles. The bubble coalescence can be inhibited in the presence of dissolved ions at high ion concentrations as well as with the use of surfactants. In this study, the effect of the mixtures of KCl, NaCl, and dodecyl amine hydrochloride (DAH) on air/water interface was investigated with surface tension and bubble coalescence time measurements for potash flotation. The surface tension measurements indicated that lower surface tension values obtained with mixed KCl and NaCl solutions than their single solutions. In addition, the surface tension of the mixed KCl and NaCl solutions increased with the NaCl and the ionic strength of the solution. The dynamic surface tension measurements indicated that while ion adsorption on air/water interface was so fast, DAH molecules required more time for adsorption probably related to the viscosity of the solution. In addition, the bubble coalescence time measurements showed that the bubble coalescence could be inhibited with the use of DAH in the absence and presence of KCl and NaCl. In the absence of DAH, the bubble coalescence time was determined as 100 ms, 270 ms, and 650 ms, respectively for 100% KCl, 100% NaCl, and 50%KCl+50% NaCl salt solutions. Therefore, the trend in the success of the salt solutions for the inhibition of bubble coalescence can be written as 100%KCl<50%KCl+50%NaCl<100% NaCl according to the bubble coalescence time. The results of this study indicated that there was no clear relationship between the surface tension and the inhibition of the bubble coalescence. However, the bubble coalescence time measurements showed that while the bubble coalescence time was 650 ms in the presence of Na⁺ ions, it was 100 ms in the presence of K⁺ ions 100 ms. It can be concluded from the results obtained from this study that the bubble coalescence phenomena may be managed by the specific ion pairing types in solutions which significantly affect the flotation recovery of minerals.