Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe Separation and enrichment of micro and nano sized particles from aqueous solutions by fotation using colloidal gas aphrons Priyabrata Pal a, ⁎ , Chen Liu a , Mohammed Abu Haija b , Emad Alhseinat a , Fawzi Banat a, ⁎ a Department of Chemical Engineering, Khalifa University, Abu Dhabi, United Arab Emirates b Department of Chemistry, Khalifa University, Abu Dhabi, United Arab Emirates ARTICLE INFO Keywords: Surfactants Colloidal gas aphrons Bubble size Fine particles Froth fotation ABSTRACT The aim of this work was to investigate the separation and enrichment of micro and nano sized particles by batch and column fotation using colloidal gas aphrons (CGAs). The CGAs were produced using anionic sodium do- decylbenzenesulfonate (SDBS) and cationic hexadecyltrimethylammonium bromide (HTAB) surfactants. The physical properties of the surfactant solutions, formation of CGAs, liquid drainage from the foam as well as liquid rise and bubble size of CGAs were measured. In the batch process, carbon particles showed that the CGAs produced with HTAB enhanced the performance of separation ratio 1.45 and enrichment ratio 1.14. The % removal of carbon was found to be 77% for 100 μm particles while it was 82% using 45 μm particles. By using SDBS, 91% removal was achieved for 400 mg/L concentrated iron particles having size 500 nm. In the column fotation, the % removal of carbon particles was 54% while it was 42% for iron particles. Thus, CGAs generated from anionic SDBS and cationic HTAB surfactants were proved to be efective in separating micro and nano sized particles based on electrostatic interactions. 1. Introduction Separation of micro and nano sized particles from aqueous solutions via fotation is gaining attention in recent years [1]. Flotation is suitable for treating solutions having particles as it provides several advantages such as rapid operation, low space requirement, higher removal ef- ciency, fexibility at various scales for diferent pollutants and low cost of operation [2,3]. About four decades ago, surfactants were used in ore processing units and found to be a promising process as it helped in higher separation of particles [4,5]. In froth fotation, air bubbles are introduced into a mixture of fnely divided particles in water with surfactant that aids attachment of the bubbles to the particles. The bubble particle collision is an important phenomenon to carry out the fotation. The bubbles having ionic charge opposite to those of the particles are attracted towards each other and taken up by the buoyancy. The separation of particle increases with the increase in particle size [6,7]. Further, in the froth phase entrainment plays an important role. The tendency of less dense fne particles to be entrained into the froth is high due to their lower mass and momentum [8]. The stable bubble particle aggregates are essential to obtain high removal efciency [9]. The bubble size is another important parameter in fotation. As the CGAs bubble size becomes smaller, the available interfacial area becomes high providing more contact with the particles, and thus more separation of particles is achieved [10,11]. This work aimed at using small bubbles known as colloidal gas aphrons (CGAs) for the separation of fne particles. The colloidal gas aphrons (CGAs) are micro bubbles mostly below 100 μm diameter in size and classifed as kugelschaums as explained by Sebba [12]. It can be prepared by stirring the surfactant solution at high speed to entrap the air and produce microbubbles. CGAs have high interfacial area, are extremely stable and easy to transport for enhan- cing the particle separation [13–16]. Some of the earlier reported fne and light particles which tend to foat and do not settle under gravity are yeast [17,18], pulp and cellulose fber [19,20], magnesium hydro- xide and polystyrene [21,22], copper and silicon oxides [23], and various suspensions [24]. Two diferent mechanisms can explain the suspended particles removal from aqueous solutions using CGAs. The frst is known as ‘bubble entrained particulate fotation’, where parti- cles are rising up due to buoyant action of smaller bubbles [25–27]. The second one is ‘ion fotation’, where charged species form an ion com- plex with oppositely charged CGAs to be foated up at the top of the surface [1,28,29]. However, the removal of particles ranging from micron to nano size using CGAs has not been reported earlier [17,22]. The main aim of this research work was to prepare the CGAs using anionic and cationic surfactants and check their separation ratio, en- richment ratio, and percentage removal of particles having micron size https://doi.org/10.1016/j.jwpe.2019.01.012 Received 27 August 2018; Received in revised form 7 January 2019; Accepted 15 January 2019 ⁎ Corresponding authors. E-mail addresses: pal.priyabrata@ku.ac.ae (P. Pal), fawzi.banat@ku.ac.ae (F. Banat). Journal of Water Process Engineering 28 (2019) 123–128 2214-7144/ © 2019 Elsevier Ltd. All rights reserved. T