Optimizing dissolved air flotation design and saturation

Abstract

Dissolved air flotation (DAF) of iron hydroxide precipitates at working pressures lower than 3 atm, using modified flotation units to improve the collection of fragile coagula, was studied. Conventional DAF flotation was studied as a function of saturation pressure in the absence and presence of surfactants in the saturator. Without surfactants, the minimum saturation pressure required for DAF to occur was found to be 3 atm. But, by lowering the air/water surface tension in the saturator, DAF was possible at a saturation pressure of 2 atm. This behavior was found to occur in both batch and pilot DAF operation tests and almost complete recovery of the precipitates was attained. Results are explained in terms of the minimum "energy" which has to be transferred to the liquid phase to form bubbles by a cavity phenomenon. Further, studies were conducted changing equipment design and feed bubbles size distribution (mixing micro and "mid-sized" bubbles). Thus, bubbles entrance position in the collision-adhesion zone ("capture" zone) was compared to bubble entrance position in the water flow inlet below the floating bed. A "mushroom" type diffuser was used for the "capture zone" experiment and better performance was obtained. Results are explained in terms of different mass transfer phenomena in the collection zone and in the separation zone. Finally, results obtained with the use of a column flotation cell working as normal DAF and with a wide bubble size range are presented. Results indicate good performance and some gains in process kinetics with middle size bubbles.

Replacing Synthetic with Microbial Surfactants as Collectors in the Treatment of Aqueous Effluent Produced by Acid Mine Drainage, Using the Dissolved Air Flotation Technique

“…The addition of surfactants in the pressurized water in dissolved air flotation is used to lower the air/water surface tension in the saturator, improving the separation process [15]. The unit used in this work employed a process of neutralization of the effluent with calcium oxide (CaO), conditioning with four different surfactants followed by DAF as a step in solid-liquid separation.…”

“…The development and use of fully biodegradable surfactants may ease this concern and enhance the further acceptance of this separation technology [15].…”

“…They are used for these purposes due to their ability to lower surface tensions, increase solubility, detergency power, wetting ability, and foamimg capacity [17]. Good surfactants can lower the surface tension of water from 72 to 35 mN/m [15]. The surface tension correlates with the concentration of the surface-active compound until the critical micelle concentration (CMC) is reached.…”

DAF–dissolved air flotation: Potential applications in the mining and mineral processing industry

“…reliability (Feris et al, 2001;Rubio, 1998Rubio et al, 2002a,b;Ross et al, 2003;Capponi et al, 2006). The high development in the area and the new upcoming applications outside the Scandinavian countries, where this technology is commonly employed, resulted in the organization of more specific conferences and congresses.…”

“…More, many articles (Bahr, 1985;Harbort et al, 1994;Finch, 1995;Finch and Hardie, 1999;Feris et al, 2001;Rubio et al, 2002a,b;Rosa and Rubio, 2005;Capponi et al, 2006) reviewed fundamentals, techniques and general features of flotation (usually preceded by flocculation) for environmental applications, namely, flocculation-flotation, (FF process) induced air flotation, dissolved air flotation, nozzle flotation, column flotation, centrifugal flotation and Jet flotation (Jameson type cell, Jameson, 1988).…”