Preparation Of Mg-Al Hydrotalcites And Application In Treating The Dyeing And Printing Wastewater

China is one of the largest countries in discharging printing and dyeing wastewater all over the world. The printing and dyeing wastewater has the following features: high Chroma and COD, high organics content and large wastewater quantity. If the printing and dyeing wasterwater was not treated correctly, it would bring serious damage on the environment. The adsorption method was applied mostly to treat dyeing and printing wastewater among many methods, because its operation was convenient and efficient, and the key of the adsorption method was to find a fitting sorbent. The calcined product of hydrotalcites （HTC） could be used as the sorbent to treat printing and dyeing wastewater because of its high specific surface area and the special“memory effect”. In this paper, HTC was synthesized by an ultrasonic coprecipitation method. The present study mainly concerned itself with the preferable preparatation and operatation conditions by the static adsorption method, and the treatment effect of the industrial wastewater was also investigated. Finally, hydrotalcites was synthesized using fly ash as the source of aluminum. The main work was summarized as follows:⑴According to the results of XRD, IR, compared to the tradition coprecipitaion, the cristallinity of hydrotalcites synthesized by the method of ultrasonic was higher, the particle size and its distribution of the product was also reduced effectively using the method of ultrasonic, and the adsorption capacity of hydrotalcites and its calcined product was higher by the method of ultrasonic in the adsorption experiment.⑵The calcined product of hydrotalcites had greater adsorption capacity in absorbing Orange G when it was prepared under conditions of temperature 30℃, reaction time 40 minutes, mixed salt concentration 1.25 mol·L^-1, ultrasonic power 0.8×600 W, calcining temperature 500℃.⑶The adsorption experiment of operating conditions indicated that the adsorption capacity of Orange G on HTC could be unchanged within 6 hours, and the removal of Orange G was favored under the acid solution. When the initial pH value was 4, the maximum removal efficiency was 74.1%. With increasing dosage of HTC, the removal efficiency of Orange G increased intensively when increasing dosage of HTC. When the dosage amount was 1.4 g·L^-1, the remval efficiency of Orange G was 99.3%, which was a compete removal of Orange G. The inorganic anions could influenced the removal efficiency of Orange G on the contrary, and it was obvious that the multivalent anions had a profound interfering effect compared with monovalent anions, and the influencial order of inorganic anions: NO3- < Cl- < SO42- < CO32- < PO43-. Firstly, the removal efficiency of Orange G decreased with increasing the molar ratio of SDS and SDBS to Orange G, and then the removal efficiency increased slightly at 2.5 and 5 of the molar ratio.⑷The removal efficiency of Orange G on HTC increased with increasing temperature, and the calculative results of thermodynamic parameters, i. e.△G ,△H ,△S showed that the process of adsorption was spontaneous and endothermic, as a result increasing temperature would favor adsorption process. It was concluded that the confusion degree of the surface of the adsorbent after adsorbing was more than before adsorbing. According to correlation coefficient, Orange G adsorption on HTC was well fitted to Langmuir isothermal and the second order kinetics equation, but the mechanism of inner diffusion was not only rate-controlling step.⑸The removal treatment of industrial dyeing and printing wastewater showed that the optimum adsorption conditions included that temperature 50℃, reaction time 6 hours, dosage of HTC 14 g·L^-1, pH 4.5. The results indicated that the removal efficiency of COD, Chroma and turbidity was 91.4%, 95.2% and 91.7% respectively under above conditions, and the adsorption ability of re-use HTC was lower than the fresh.⑹The fly ash was calcined with Na2CO3, and then the sinter was solubilized by hydrochloric acid. The optimum conditions of solution of aluminum was obtained by orthogonal experiment, i. e. calcining temperature 950℃, calcining time 3 h, soakage time 4 hours, ratio of alkali to fly ash 0.7, concentration of hydrochloric acid 0.6 mol·L^-1, reaction temperature 90℃.⑺The iron in the solution was eliminated by controlling pH. The Mg-Al hydrotalcites was synthesized by the method of coprecipitation. The analytical results of XRD and IR showed that Mg-Al hydrotalcites of high level of cristallinity and purity could be synthesized using fly ash as the source of aluminum.