| With the development of national economy and the acceleration of urbanization process,the scale and quantity of water supply plants are expanding,and the traditional coagulation sedimentation process is still the mainstream way of water treatment,which also leads to the increase of by-product drinking water treatment residuals.Drinking water treatment residuals are a kind of resource containing a lot of aluminum and iron.At present,the vast majority of sludge is directly landfilled without any treatment,which is not only the damage to the environment,but also a waste of resources.Due to the unique physical and chemical properties of drinking water treatment residuals,it is a feasible scheme to reuse it for the adsorption of pollutants.However,there is the problem for recover and regenerate.The main component of drinking water treatment residuals is aluminum or iron.Therefore,it is assumed that it is possible to synthesize hydrotalcite like compounds from the residue of drinking water treatment to recover phosphorus.Therefore,in this study,Mg/Al/Fe hydrotalcite-like compounds were successfully prepared by coprecipitation method with drinking water treatment residuals as raw material after determining the most appropriate hydrochloric acid leaching conditions.The structure and adsorption performance of the materials synthesized under different conditions were analyzed,and the phosphorus adsorption efficiency of the materials was evaluated.It was proved that the materials could effectively recover phosphorus from water,and the structure was characterized by physical and chemical methods,the adsorption mechanism was revealed.Finally,based on the adsorption study of other anions such as Cr,F,Br and the binary adsorption system constructed with P,the adsorption commonness of Mg/Al/Fe hydrotalcite-like compounds for anions and the selective adsorption principle of P were supplemented.The study includes the following three aspects:(1)Mg/Al/Fe hydrotalcite-like compounds were prepared by coprecipitation method with drinking water treatment residuals from a waterworks in Beijing as raw material under the conditions of solid-liquid ratio of 0.1 g/ml,reaction time of 2 h,reaction temperature of 40 ℃ and hydrochloric acid concentration of 2 mol/L.According to the results of phosphorus adsorption experiment and X-ray diffraction characterization,the best preparation conditions are as follows: the proportion of trivalent metal ions is 0.45,the preparation p H is 9.0,the Al: Fe ratio is 1:1 and the preparation temperature is 60 ℃.The material has typical layered structure and large specific surface area.(2)The adsorption behavior and process of phosphorus on Mg/Al/Fe hydrotalcite-like compounds were studied.The results show that the dosage,initial concentration,p H and coexisting ions all have effects.The results show that the Langmuir and Freundlich equations can well describe the isothermal adsorption curve of Mg/Al/Fe hydrotalcitelike compounds for phosphorus,and the Langmuir saturated adsorption capacity is 51.1mg/g;The material reached equilibrium adsorption in 4 h.The adsorption of phosphorus is a spontaneous reaction of exothermic entropy reduction.Combined with the physicochemical characterization results of the materials before and after adsorption,the adsorption forms of phosphorus on the materials can be summarized as physical adsorption,surface complexation,ion exchange and surface chemical precipitation.(3)The adsorption behavior and process of Cr,F and Br on Mg/Al/Fe hydrotalcite-like compounds were studied.The results of influencing factors were similar,but p H did not change the adsorption form.On the adsorption kinetics,the pseudo second order kinetic model fitted better;on the adsorption isotherm,the Freundlich model fitted better,and the Langmuir saturated adsorption capacities of chromium,fluorine and bromine on the materials were 34.9 mg / g,15.42 mg / g and 13.7 mg / g,respectively.Ion exchange is a common form of anion adsorption on materials.In the experiments of P-Cr,P-Br and PF binary adsorption systems,the materials have strong selective adsorption for P in the former two systems.When F exists,the adsorption of P will be inhibited,but a certain amount of P can still be adsorbed.The selective adsorption of P depends on strong ion exchange and unique adsorption form.This study provides a new idea and theoretical support for the resource utilization of drinking water treatment residuals for the selective adsorption removal and resource recovery of phosphate in water. |
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