Preparation Of Humic Acid And Mesoporous SiO₂ From Municipal Sludge And The Study Of Their Adsorption Properties For U（Ⅵ）

With the rapid improvement of sewage treatment capacity in China,the amount of sludge has also increased substantially.It is of great significance for the development of sludge treatment and disposal technology in China to study the harmless disposal and resource treatment of sludge and to open the way for resource products.The research contents of this thesis are as follows:（1）The effects of alkali dosage,hydrothermal temperature and hydrothermal time on the dehydration effect and HA extraction rate were studied by using the moisture content of sludge and HA extraction rate as the indexes.Single factor experiment was used to determine the optimal range of the three factors,and response surface experiment was designed to further optimize the experimental parameters.The optimal process parameters of simultaneous extraction of humic acid by hot alkali dehydration were verified as follows:hydrothermal temperature 170°C,hydrothermal time 42 min and alkali sludge ratio 0.05.Under the optimal conditions,the predicted values of sludge moisture content and humic acid extraction rate were47.2%and 91.0%,which were very close to the experimental values.The properties of HA were studied by elemental analysis,infrared spectroscopy and scanning electron microscopy.The HA was characterized by ICP,FTIR and SEM.The results showed that the purity of HA was high（96.2%）,the content of heavy metals was far below the national standard limit,and the HA contained abundant functional groups,which was beneficial to its further utilization.（2）Dehydrated sludge from which HA had been extracted was used as raw material,and sodium carbonate was used as auxiliary agent.Under the conditions of 700°C,calcination time of 120 min,and mass ratio of sludge to sodium carbonate of 1:0.4,the sludge was calcined.Crystalline silica was transformed into acid soluble Na Al SiO₄and a small amount of Na Al O₂by calcination experiment.The decomposition rate of the acid-dissolved sludge is 88.7%.In addition,mesoporous SiO₂was prepared by sol-gel method,the yield was 75.5%with a high purity of 98.8%.The specific surface area was 654.9 m²/g and the average pore size was 3.36nm.（3）The adsorption properties of HA and mesoporous SiO₂for uranium were studied by static adsorption experiments.The effects of p H value,adsorbent mass,time,coexisting ions and initial concentration of U（Ⅵ）on the adsorption were investigated.The optimum adsorption conditions of HA for U（Ⅵ）were obtained as follows:p H=6,adsorbent dosage=5mg,U（Ⅵ）concentration=30 mg/L,the maximum adsorption capacity was 220.26 mg/g,and the removal rate was 93%.The adsorption kinetics of U（Ⅵ）on HA followed the pseudo-second-order kinetic model.The adsorption thermodynamics of U（Ⅵ）on HA followed the Langmuir isotherm model.The thermodynamic study indicates that the adsorption process of U（Ⅵ）on HA was spontaneous and exothermic,and low temperature was conducive to the reaction.The adsorption of U（Ⅵ）on mesoporous SiO₂ is slightly different.The optimum adsorbent dosage is 10 mg,the maximum adsorption capacity is 84.97 mg/g and the removal rate is 89.4%.The adsorption process of U（Ⅵ）on mesoporous SiO₂ was in accordance with Freundlich isothermal adsorption model,and the adsorption was spontaneous and exothermic.In this paper,the whole process of sludge dewatering,recycling and further utilization of recycling products was fully studied,and the reduction of sludge and the full recovery and utilization of energy and resources in sludge were realized.It is of great significance to improve the level of sludge treatment and disposal,protect and improve the ecological environment,and promote the sustainable development of economy,society and environment.