Study On The Adsorption Of Oily Wastewater By LDHs Preparation And Surface Modification

Hydrotalcite-like substances?LDHs?,also known as layered bimetallic hydroxides,can be formed under certain conditions in natural environment.Because of the special structure of this crystal,it has brought some unique properties.LDHs consist of two or more metal cations with different valences and hydroxyl groups,which form a positive charge layer in the crystal structure.In the middle of the layer,various anions with negative charge support the layered crystal structure and ensure the charge balance.At present,the synthesis,properties and practical application of LDHs have been carried out in a large number of ways.The layered structure and unique physical and chemical properties of LDHs can be used in wastewater treatment.Many pollutants can be removed by surface adsorption,surface complexation and ion exchange.However,most LDHs have hydrophilic surface structure,which makes it easier to adsorb polar molecules such as water molecules,and the removal efficiency of hydrophobic organic molecules is poor.The surface of LDHs crystal structure is changed from hydrophilic to hydrophobic by inserting organic anions with surfactant properties between LDHs layers.The surface modified LDHs can greatly improve the removal efficiency of hydrophobic organic pollutants,especially oils,on the basis of preserving the original adsorption properties.Finally,it was briefly analyzed and discussed the absorption mechanism of the surface modified LDHs to the oil in the oily wastewater.The object of this study is bimetallic hydroxides?LDHs?.The contents of this study include the preparation of Zn²⁺-Al³⁺-LDHs by urea method,ion exchange between the original anion and dodecyl sulfonate in the layer of LDHs plate by calcination and recombination method,the adsorption and removal effect of the improved LDHs on oil in oily wastewater is verified,and the absorption mechanism of that to the oil in the oily wastewater was simply analyzed.The main conclusions are as follows:?1?Zn²⁺,Al³⁺crystals were synthesized by urea synthesis method with different ratios of metal cations,urea dosage and total ion concentration.Vibration peaks of various anions between layers were observed and analyzed by FT-IR.It was determined that the most suitable solid for calcination of reconstituted materials was Zn²⁺,Al³⁺molar ratio,10 times of theoretical urea dosage and 0.05 mol/L total ion concentration.Test conditions.?2?The calcined products of Zn²⁺-Al³⁺-LDHs at different temperatures were observed and analyzed by thermogravimetry and FT-IR.It was determined that 300°C was the most suitable calcination temperature for the next step of dodecyl sulfonate intercalation.?3?The surface-modified organic LDHs were obtained by inserting dodecyl sulfonate into the LDHs laminates at 300°C by calcination-recombination method.The anion composition between the laminates was analyzed by FT-IR observation,and the success of dodecyl sulfonate intercalation was verified.?4?Oil absorption experiments were carried out on the prepared Zn²⁺Al³⁺CH₃?CH₂?₁₁SO₃-LDHs and the unmodified LDHs and 300°C calcined products respectively.FT-IR results showed that the oil absorption ability of the prepared Zn²⁺Al³⁺CH₃?CH₂?₁₁SO₃-LDHs and the unmodified LDHs as well as the calcined products was obviously enhanced compared with the unmodified LDHs and the calcined products.