Removal Of Anionic Surfactant For Oil Production From Aqueous Solution By Freshly Generated Hydroxide Precipitates

In this paper, freshly generated hydroxide precipitations (FGHP) prepared by adding the leaching solution of white mud to highly alkaline solutions, which have small particle sizes and large adsorptive surface area can be used as adsorbents to remove surfactant for oil production from aqueous solutions and a positive surface charge can be used to attract anionic surfactant. The chemical composition of the white mud was determined with X-ray fluorescence spectrometry (XRF). The morphology of the hydroxide precipitates was characterized by transmission electron microscopy (TEM). The surfactants before and after adsorption onto FGHPs were characterized by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR). The effects of dosage, contaminant concentration, pH, contact time and temperature on removal efficiencies were studied. The thermodynamics and kinetics were fitting to analyze the removal mechanism of PS onto FGHPs. The experimental results revealed that:(1) The main elements of the hydroxide precipitates, which are generated in alkaline conditions, are Ca(OH)2 and Mg(OH)2.(2) The FGHPs can remove surfactant in aqueous solutions rapidly and effectively. The removal rate reached maximum at 60 s. The appropriate leaching solution dosage was 1.5 g/L. And the optimum pH for PS adsorption onto freshly generated hydroxide precipitations was 12.0. Under the condition, the removal efficiencies for petroleum sulfonate were all over 85%.(3) The UV-visible spectrum of the desorbed surfactant solution was in accordance with the original one, indicating that during the adsorption process, the surfactant molecular structure had no change. Therefore, the adsorbed surfactant can be reused after desorption by HC1.(4) Adding leaching solution of white mud into alkaline sodium lignosulphonate (SL) solution, the appropriate contact time was 20 s, the optimum adsorbent dosage was 4.0 g/L, the optimum pH of the solution was 12.0, and the removal efficiency of SL can be up to 90% under the optimum conditions.(5) The FT-IR showed that the PS was absorbed by the FGHP.(6) Electrostatic attraction and hydrogen bonding were the main adsorption mechanisms. Moreover, adhesion and cohesion also strong affected the co-precipitation/adsorption process. Liquid bridges via hydrogen bonding, adhesive and cohesive forces linked up with MOH+/M(OH)2 particles and the surfactant molecules to form a three-dimensional network and lead to deposition.