Removal Of Anionic Surfactants From Aqueous Solution By Using In-Situ Formed Magnesium Hydroxide Particles

As surfactants have been widely used in industry,the amount of wastewater containing anionic surfactants has been increasing,and the existence of surfactants has made this type of wastewater complex in nature and difficult to treat.Therefore,it is important to study the efficient treatment technology of anionic surfactant wastewater.In this study,alkali and soluble magnesium salts were innovatively added into the wastewater to generate in-situ formed magnesium hydroxide precipitation（IFMH）with high surface free energy and green economy for efficient and rapid treatment of common anionic surfactants sodium dodecyl benzene sulfonate（SDBS）and lauryl ether sulfate sodium（SLES）by adsorption co-precipitation method.The main study contents and results are as follows:（1）The basic properties of the IFMH were investigated and the results showed that:The precipitate produced by the alkali and magnesium salts added to the SDBS wastewater was Mg（OH）₂ loaded with SDBS（IFMH-SDBS）;The isoelectric point of IFMH was about 12.3,and the adsorption co-precipitation process would change its crystallization mode and crystal agglomeration mode.（2）The effects of different agent dosing methods on the removal of SDBS were investigated and the advantages of IFMH were analyzed,and the results showed that:The removal effect of two IFMHs(the drop Mg²⁺System and the drop OH-system)was far better than Mg（OH）₂;When the concentration ratio of Mg²⁺to OH^-was at a larger value,the IFMH generated under the drop Mg²⁺system had a better and more stable treatment effect on SDBS than the drop OH^- system;In the process of SDBS treatment by IFMH,the adsorption of SDBS and the crystallization of Mg（OH）₂ were carried out simultaneously.In addition to the in-situ formed Mg（OH）₂ crystals,SDBS could be combined with particles such as Mg²⁺,Mg（OH）64 growth radicals and MgOH⁺ under weak interactions such as electrostatic gravity and hydrogen bonding and be adsorbed onto IFMH to form precipitate particles,thus achieving the removal of SDBS.This adsorption co-precipitation process makes IFMH have a higher surface charge compared with ordinary Mg（OH）₂ and can treat SDBS more efficiently.（3）The effect of IFMH on the treatment of SDBS wastewater was investigated and the process conditions were optimized,and the results showed that:The optimal reaction conditions were MgCl₂ dosing of 2.0 g/L,initial pH of 12.3（equilibrium pH was about 10.5）and stirring time of 20 s.Under these conditions,the removal rate of SDBS could reach 84.34%;The removal of SDBS by IFMH increased from 78.42%（100 mg/L）to 88.67%（500 mg/L）with the increase of the initial concentration of SDBS;During the adsorption process,the presence of anions Cl^-and NO₃^- in the solution had a small effect on the removal of SDBS,but the high concentration of SO₄^2- reduced the removal efficiency of SDBS.（4）A thermodynamic study of the adsorption process was carried out and the results showed that:The adsorption process of IFMH on SDBS could be spontaneous and exothermic,and high temperature was not beneficial to the reaction;The reaction proceeded in the ordered direction and the degree of freedom was reduced;The saturation capacity of IFMH on SDBS could reach 4073 mg/g at 303 K.（5）It was confirmed that IFMH has high efficiency not only for SDBS,but also for SLES removal,indicating that the technology has some universality.When SLES in solution was treated with IFMH,the initial pH of 12.0,MgCl₂ dosing of 4.0 g/L and stirring time of 60 s were the optimal reaction conditions for efficient and economical treatment,and the removal rate of SLES（200 mg/L）could reach 88.33%under these conditions.In this study,the in-situ formed magnesium hydroxide was used to treat anionic surfactants through the adsorption co-precipitation process to address the problem of difficult treatment of surfactant-containing wastewater.The influencing factors and adsorption characteristics of in situ generation of magnesium hydroxide for adsorption of anionic surfactants were analyzed,the process conditions were optimized,and the mechanism of action was discussed,which can provide an important theoretical and technical basis for the treatment of anionic surfactant wastewater and composite industrial wastewater containing anionic surfactants.