Investigation On The Removal Of Emulsified Oil From Alkali/surfactant/polymer Flooding Produced Water By Surfactant-modified Sepiolite

Adsorption technology as a simple,low-cost,and efficient method has been extensively used in the field of water purification,such as desalination,and oil/water separation process.Sepiolite(Sep)is a natural clay mineral with a large specific surface area,which is a promising adsorbent material However,the surface of sepiolite is hydrophilic.As a result,natural sepiolite is ineffective adsorbent for emulsified droplets(EOs)of low-polarity or non-polar organic pollutants.In this study,tetradecyl trimethylammonium bromide(TTAB),cetyl trimethylammonium bromide(CTAB),and octadecyl trimethylammonium bromide(OTAB)were used to modify natural sepiolite via an ion exchange reaction to form organic sepiolite(organo-Sep)hybrids.This modification is particularly critical in order to obtain good affinity between organo-Sep hybrids and emulsified oil droplets(EOs).The loading cationic surfactants varied the surface wettability of Sep from highly hydrophilic to increasingly hydrophobic,and a charge inversion from negative to positive occurred.Therefore,the as-prepared organo-Sep hybrids were successfully employed as adsorbents for removing EOs from simulated oily wastewater.The morphology,texture,and surface properties of Sep and organo-Sep hybrids were characterized by various characteristic techniques,including SEM,XRD,FT-IR,water contact angle analyzer,surface area analyzer,and Zeta potential analyzer.The influence of alkyl chain length of surfactant,initial pH,temperature and contact time on oil removal efficiency was investigated.The thermodynamics was used to explain the removal mechanism of EOs on organo-Sep hybrids.The experimental results revealed that:(1)SEM images,XRD,and FT-IR analysis confirmed that the EOs adsorbed on organo-Sep hybrids.After modification,the BET surface area of Sep increased from 297.8 m2/g to 698.6 m2/g while the total pore volume from 0.840 cm3/g increased to 3.080 cm3/g.Water contact angle measurements also showed that the surface wettability of the natural Sep varied from highly hydrophilic to progressively hydrophobic with an increase in the alkyl chain length of surfactants.The results of Zeta potentials suggested electrostatic attraction between positive hybrids and negative EOs,thus allowed more EOs to be attracted to the particle surfaces.(2)The removal efficiency of EOs depends on the variation of the alkyl chain length of the surfactant,initial pH,temperature and contact time.Kinetic studies indicated that the removal of EOs from simulated oily wastewater is rapid,and reached equilibrium within 4 h.It was found that 98-99%of EOs was successfully removed by organo-Sep hybrids at 60?.Regeneration of the saturated organo-Sep hybrids was achieved by using petroleum ether rinse with high removal efficiency of EOs after five cycles.(3)The equilibrium data were well described by the Langmuir isotherm.The maximum adsorption capacities of TTAB-Sep,CTAB-Sep,and OTAB-Sep for EOs were 434.7,448.3,and 454.9 mg/g,respectively,at pH 6 and 60 ?.(4)Thermodynamic parameters revealed that the adsorption process is spontaneous,feasible and endothermic in nature,and is controlled by physisorption.Specifically,it involves some interactions,including electrostatic attraction,capillary action,hydrogen bonding,partition,and hydrophobic interactions between the EOs and the active sites on the organo-Sep surfaces.