Preparation Of Modified Sepiolite In Xiangtan And Its Performances In Adsorption Of Phosphate From Black-odor Water

At present,the urban black-odor water has become a serious issue in the construction of ecological civilization in China.Phosphorus is one of the key elements that cause the formation of black-odor water.The key to remove phosphorus from black-odor water is to select an efficient and low-cost adsorbent.As an abundant natural clay mineral in China,sepiolite is cheap and readily available,which was identified as environmentally friendly adsorbents with high specific surface area,natural nanostructures and rich active surface sites.Sepiolite was widely used in the application of environmental functional materials.The sepiolite reserves are abundant in Xiangtan,where the proven reserves account for 80%in China,which contains numerous calcium impurities.In order to develop the properties of sepiolite,it is necessary to explore the phosphate adsorption performance of sepiolite in black-odor water.In this study,HSEP₈₀₀and La/Mg-SEP were prepared by modification based on sepiolite,which applied for the phosphate treatment of black-odor water.The effects of adsorption time,phosphorus concentration,reaction temperature,initial p H of phosphorus solution,co-existing anions and humic acid on phosphorus removal efficiency of HSEP₈₀₀and La/Mg-SEP were investigated.The mechanism of phosphate adsorption of two adsorbents was discussed by means of X-ray fluorescence（XRF）,scanning electron microscope（SEM）,BET specific surface analyzer（BET）,X-ray diffraction（XRD）,Fourier transform infrared reflection（FTIR）and X-ray photoelectron spectroscopy（XPS）.The treatment of La/Mg-SEP on phosphorus in actual black-odor water samples also was obtained.This paper had acquired the following research conclusions:（1）Thermal modification can obviously improve the phosphate adsorption performance of sepiolite.The phosphorus removal efficiency of HSEP reached the peak when the calcination temperature was 800℃and the calcination time was 1.5 h.The adsorption equilibrium was quickly reached within 6 h,and the maximum phosphate adsorption capacity of HSEP₈₀₀was 34.99 mg/g with a wide p H range（4～8）,which was 16 times higher than sepiolite.The co-existing anions of Cl^–,NO₃^–and SO₄^2–rarely affected on the phosphate adsorption of HSEP₈₀₀,while HCO₃^–and humic acid had more significant effects on that.Thermal modification can significantly change the crystal structure and physical and chemical properties of sepiolite.With the increase of calcination temperature,the specific surface area of sepiolite increased constantly and the structure collapsed.When the calcination temperature was up to 800℃,the calcite in sepiolite decomposed,which transformed into active calcium（Ca O）.The results showed that the possible mechanism of the phosphate absorption by HSEP₈₀₀was mainly chemical adsorption,forming Ca₅（PO₄）₃（OH）precipitation.（2）La/Mg-SEP was prepared by co-precipitation method using sepiolite,La（NO₃）₃·6H₂O and Mg Cl₂·6H₂O,and the optimum conditions for the preparation of La/Mg-SEP were determined in the study.Under the conditions that the mass ratio of SEP:La:Mg（1.0:0.05:0.25）and the p H of the modified solution was 11,the phosphate adsorption capacity of La/Mg-SEP was up to 102.30 mg/g.The characterization results showed that the lanthanum hydroxide and magnesium hydroxide were uniformly loaded on the surface of sepoilite,and the specific surface area,pore volume and pore diameter of La/Mg-SEP increased to 81.31 m²/g,0.34 cm³/g and27.24 nm compared to sepiolite,respectively.（3）The results showed that the phosphate adsorption process was endothermic,spontaneous and entropy-increasing.The maximum phosphate adsorption capacity of La/Mg-SEP was 117.24 mg/g with a wide p H range（6～9）,which was 60 times higher than sepiolite.The La/Mg-SEP was rarely affected by co-existing anions of Cl^–,NO₃^–,SO₄^2–,HCO₃^–and humic acid with a good recycling performance after 4 times and low biotoxicity.The possible mechanism of the phosphate absorption by La/Mg-SEP included chemical precipitation,ligand exchange and electrostatic interaction,forming La–O–P compounds and Mg HPO₄,Mg₃（PO₄）₂precipitation.The phosphorus in actual light and heavy black-odor water can reach the environmental quality standard for classⅡof surface water（GB 3838-2002）after the treatment by La/Mg-SEP.