Adsorption Of Cu,Zn And Tetrecycline In Wastewater By Amphoteric Surfactant Modified Sepiolite

The agriculture,livestock,poultry and aquaculture industry is developing rapidly and turned to be scale and intensive.Heavy metal and antibiotics in the agricultural wastewater may harm to the environment and human health.Adsorption is an easy,economical and environmental-friendly method,which becomes the current research hotspot.Natural minerals have advantages of huge specific surface area,complex pore structure,and are easy to get,which has been used as the adsorption material.Nevertheless,natural minerals have much impurity,small channel and other ores,which were hardly to reach the theoretic specific surface area and leading to a low adsorptive capacity.By the means of the proper modification,the natural minerals become the high efficient adsorbent for heavy metals and antibiotics.It provides a new research direction for the treatment of livestock,poultry and aquaculture wastewater.Sepiolite is a magnesium-rich silicate layered natural clay mineral and has huge specific surface area,which has been used to adsorb contaminant in wastewater.This research use amphoteric surfactant to modify sepiolite to study the adsorptive mechanism.The structural properties of sepiolite was obtained by electron microscope?SEM?,X-ray diffraction?XRD?,surface area analysis?BET?,Fourier transform infrared spectroscopy?FT-IR?and Zeta potential analysis.The effects of adsorption temperature,time,adsorbent dosage,initial pH and initial concentration of solution on the adsorption of Cu²⁺,Zn²⁺and tetracycline were investigated.The main results were obtained as follows:1.The amphoteric surfactant,dodecyl dimethyl betaine?BS-12?,was loaded on natural sepiolite?SEP?.The structure and physicochemical characteristics of modified sepiolite?BSSEP?were obtained by electron microscope?SEM?,X-ray diffraction?XRD?,surface area analysis?BET?,Fourier transform infrared spectroscopy?FT-IR?and Zeta potential analysis.After the modification treatment,the surface of BSSEP became more smooth than SEP and the structure became more compact than SEP,and the specific surface area increased from 4.83 to 5.42 m²/g.The modification treatment did not alter the basic structure of sepiolite,and the layer spacing increased from 0.929nm to 0.930 nm.When the pH in 2⁷,BSSEP and SEP surface were both negatively charged.The basic skeleton of BSSEP remains unchanged,and there was a strong absorption peak near 2985 cm^-11 and 1427 cm^-1,which was the absorption peak of telescopic vibration bond-CH₂ and C-N.These results showed that BS-12 was loaded on the sepiolite.2.The effects of adsorption temperature,time,adsorbent dosage,initial pH and initial concentration of solution on the adsorption of Cu²⁺,Zn²⁺and tetracycline were studied by single factor experiment.It was found that the adsorption capacity of BSSEP was higher than that of SEP.Orthogonal experiments were designed to investigate the effect of adsorption conditions on the adsorption capacity.The optimum adsorption conditions were obtained,the initial concentration of Cu²⁺was 20 mg/L,the initial pH was 5,the dosage of BSSEP was 6 g/L,and the temperature was 30°C,and the removal rate of Cu²⁺was 93.46%.The initial concentration of Zn²⁺was 20 mg/L,the initial pH was 7,the dosage of BSSEP was 5 g/L,and the temperature was 35°C,and the removal rate of Zn²⁺was 96.48%.The initial concentration of tetracycline was 5 mg/L,the initial pH was 7,the dosage of BSSEP was 7 g/L,and the temperature was 20°C,and the removal rate of tetracycline reached 99.32%.The initia pH was 4,the dosage of BSSEP was 5 g/L,and the temperature was 30°C,and the removal rate of Cu²⁺,Zn²⁺and tetracycline in mixed wastewater were 59.58%,22.45%and 52.90%,respectively.3.The adsorption kinetic results of SEP and BSSEP to Cu²⁺and Zn²⁺met pseudo-first-order kinetic equation,while tetracycline met pseudo-second-order kinetic equation.The adsorption equilibrium times shortened 60,20 and 10 min,respectively.Modification treatment improved the adsorption rates.The adsorption thermodynamic characteristics of Cu²⁺,Zn²⁺and tetracycline met Langmuir isothermal adsorption model,and the maximum adsorption capacity increased 0.56,2.28 and 6.13 mg/g,respectively.Modification treatment improved the adsorption ability.4.Gibbs free energy changes??35?G?of the adsorption were less than zero,enthalpy changes??35?H?were greater than zero.As the temperature increased,the adsorption distribution cofficient increase,which indicated that the adsorption were spontaneous endothermic process and the process included physical adsorption.The adsorption can be described by Langmuir isotherm adsorption model,which indicated that the adsorption process was single molecule layer adsorption.The modification loaded BS-12,leading into hydrophobic carbon chain and carboxyl group.The process included chemical adsorption.Therefore,the adsorption were the effects of physical and chemical adsorption.5.HCl solution can be used to desorb the adsorbed Cu²⁺,Zn²⁺and tetracycline,and the desorption percents were 68.30%,78.34%and 88.12%,respectively.As the increase of HCl concentration,the desorption percents increased.The desorption process facilitates the regeneration of adsorbents and the recycling of heavy metals and tetracycline.