Stepwise separation of multi-species with a single type of chemical additives (such as surfactants) is an auspicious but challenging issue in many engineering processes as one surfactant usually lacks the ability to interact with different components. One promising strategy is to develop an environment-responsive surfactant, which possesses various functional groups to anchor target constituents under different environmental conditions. In this work, we have prepared a pH-responsive surfactant (2-(benzylthio)-acetohydroxamic acid, BTHA) possessing two pH-switchable groups (i.e., thioether and hydroxamate) that can selectively interact with different target substances, thus enabling stepwise and efficient separation of a three-component mineral system. The single in-house synthesized BTHA is successfully applied to the sequential separation of pyrite, diaspore, and kaolinite from high-sulfur bauxite by simply tuning the solution pH. Specifically, under the acidic condition (pH 6.0), the hydroxamate group of BTHA is deactivated, thus only the thioether groups can directionally interact with pyrite and enable the selective flotation recovery of pyrite to 85.9%. When the solution pH is subsequently increased to 8.0, the active hydroxamate group of BTHA can tightly chelate with diaspore and result in its efficient separation from kaolinite. The bifunctional surfactant exhibits strong and selective interactions with target substrates via pH modulation, allowing the adsorption selectivity and efficient stepwise separation, which provides an innovative paradigm for the development of novel surfactants with diverse applications in the mineral, metallurgical, chemical, and renewables recycling industry.
Xiangfen Cui,Jingmei Liao,Huaying Liu,Wei Tang,Cheng Tie,Senlin Tian,Yingjie Li
The presence of organic pollutants in wastewater remains a prominent environmental concern due to the related ecological and health hazards. In response, this study employs an adsorptive methodology to address the removal of phenol and catechol, utilizing an organo-bentonite material modified with a pH-responsive switchable surfactant, dodecyldimethylamine oxide (C12DAO). The synthesized organo-bentonite (C12DAO-Bt) manifests commendable thermostability resulting from thermogravimetric analyses. The adsorption capacities of C12DAO-Bt concerning phenol and catechol intensify with the augmentation of the C12DAO/bentonite mass ratio. The utmost adsorption capacities of 150C12DAO-Bt, deduced through a pseudo-second-order kinetic model, stand at 5.72 mg·g−1for phenol and 5.55 mg·g−1for catechol, respectively. Subject to modification by a pH-responsive surfactant, conditions leaning towards weakly acidic and neutral conditions (pH = 6~7) are conducive to the adsorption of phenolic compounds. Conversely, alkaline conditions (pH = 8~9) facilitate the dissociation of adsorbates from adsorbents. The augmentation of cationic strength within the examined scope incites the adsorption procedure while impeding the desorption efficacy. In the case of cationic species with comparable ionic strengths, Na+exhibited a superior effect on the adsorption–desorption dynamics of phenol, while Ca2+exerts a more pronounced effect on those of catechol. Moreover, even following five consecutive acid–base regulation cycles, C12DAO-Bt retains a relatively high adsorption capacity and desorption efficacy, which underscores its exceptional regenerative capacity for removing phenolic compounds from wastewater.Keywords:pH-responsive surfactants;organic bentonite;reversible adsorption;phenolic pollutants;wastewater
In this study, a novel surfactant with pH-responsive properties was developed to address the challenges associated with balancing foaming and defoaming properties in traditional foam drainage gas recovery processes. The surfactant was created by employing primary amine and aldehyde monomers based on the principles of reversible dynamic covalent bonds. Optimal synthesis conditions were determined through an extensive analysis of foaming performance: a molar reaction ratio of primary amine to aldehyde at 10:0.8, a 20-minute reaction time, and a stirring speed of 300 r/min. The formation of dynamic imine bonds was confirmed through infrared spectroscopy. Surface tension measurements revealed that at pH = 8, the surfactant achieved a minimum surface tension of 31.1 mN/m, while at pH = 3, the surface tension exceeded 40 mN/m. Particle size analysis demonstrated a 26.5-fold reduction in particle size as the pH decreased from 8 to 3. Zeta potential tests indicated excellent dispersion stability within the pH range of 3–8, with Zeta potential consistently exceeding 25 mV. Furthermore, the surfactant displayed remarkable foaming and foam stabilizing effects at pH = 8, with initial and 5-minute foam heights reaching 168 mm and 132 mm, respectively. When the pH dropped below 6, the surfactant exhibited rapid defoaming. After six cycles of alternating acid-base environments, it maintained excellent foaming performance, achieving a 5-minute foam height of up to 138 mm. Importantly, it retained its foaming capabilities in formation water solutions with a mineralization degree of 200 g/L. These findings hold significant implications for the development of intelligent environmental response treatments for foam drainage and gas production, enhancing the overall efficiency of drainage and gas production operations.
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