| Phosphogypsum,an acidic by-products,which was produced in a large quantity from the phosphate fertilizer industry during the "wet process" of phosphoric acid.Based on the application that nonmetallic mineral materials could be used as the adsorbent for treating industrial wastewater,phosphogypsum(PG)was also investigated in this study.The modified phosphogypsum was prepared by microwave irradiation.Then it was used for treatingheavy metal wastewater from industrial plants.The relationship between the structure of the modified phosphogypsum and its adsorption behavior was extensively explored with the modern analytical techniques,such as XRD,FTIR,TG-DTA and SEM-EDS,et.al.Additionally,based on these studies which were mainly focused on the adsorption mechanism,adsorption law and factors of the modified phosphogypsum adsorbing Cu2+,Zn2+,Pb2+and Cd2+,the performance of the modified PG with microwave irradiation was explored.Furthermore,this study not only expanded the utilization of the modified PG,also provided the technological base and theory for PG in the heavy metal wastewater treatment.The main works and achievement of this thesis are as following:(1)The study on the modified phosphogypsum with microwave irradiationDue to the unmodified phosphogypsum have large pore,small specific surface area and surface charge low,we put forward the idea that the microwave can be used to modify the phosphogypsum.Results showed that the optimum preparation conditions for the modified phosphogypsum with microwave were:the microwave frequency was 2450 MHz,the microwave power was 950W,the radiation time was 12min.Under these circumstances,the specific surface area,pore size and porosity of phosphogypsum can be significantly improved through the process of microwave irradiation.BET nitrogen adsorption test showed that the specific surface area,general pore volume and the average pore diameter were 55.72 m2/g,0.2146 cm3/g and 77.036 nm,respectively.SEM image analysis showed that the modified phosphogypsum has a higher degree of particle surface roughness.In addition,it also hasmore pore,surface cracking and lattice defects than the unmodified phosphogypsum.The result of XRD was consistently with FTIR fingerprinting analysis,which showed that the main componentswere semi-hydrated gypsum(CaSO4·0.5H2O).(2)The study on the factors of Cu2+,Zn2+,Pb2+and Cd2+adsorption with the modified phosphogypsumBased on the distribution of Cu2+,Zn2+,Pb2+and Cd2+ in Non-ferrous industry wastewater,the singlemetal system which contained Cu2+,Zn2+,Pb2+ and Cd2+was prepared.The effects of mainly factorsincluding pH,adsorption time,heavy metal ion concentration,adsorbent dosage and adsorption temperature were investigated.Results showed that the optimum preparation conditions were:pH(7～8),adsorption time(60 min),heavy metal ion concentration(30mg/L-40mg/L),adsorbent dosage(0.5g/100 mL～lg/100 mL)and adsorption temperature(25～30℃).Additionally,the adsorption strength of the heavy metalon the modified phosphogypsum with microwave irradiationin the single metal wastewater system was as follows:Cu2+>Pb2+>Zn2+>Cd2+.(3)The study on the competitive mechanism of various heavy metals with the modified phosphogypsumThe competitive mechanism that the modified phosphogypsum adsorbed various heavy metals in wastewater was studied.Results showed that the adsorption of Cu2+could be promoted when Cu2+and one of other ions were used as interfering ions.When more than two ions were combined in triples or quadruples metal system,the adsorption of Zn2+、Pb2+、Cd2+by the modified phospogypsum could be prevented.The results also indicated that the adsorption order with the microwave modified phosphogypsum was as follows:Cu2+>Pb2+>Zn2+>Cd2+.(4)Research of response surface optimization with Box-Behnken modelThree main control factors of adsorption on the modified phosphogypsum,namely adsorption dose(A),concentration of metal ion(B),the pH of the reaction system(C),were optimized by Box-Behnken model response surface analysis in the mixed wastewater system.The results also predicted the relationships between three main controlling factors affects of adsorption balance.In this system,the optimum preparation conditions process conditions for the optimization Box-Behnken model response surface were as follow:pH was 7,adsorbent dose was 0.7g/100mL,heavy metal ion concentration was 50 mg/L.Under this conditions,the Cu2+,Zn2+,Pb2+and Cd2+removal rate were 95%,82%,94%and 72%,respectively.The adsorption capacity of Cu2+,Zn2+,Pb2+and Cd2+were 7.5 mg/g,6.1 mg/g,8 mg/g,5.1 mg/g,respectively.(5)Mechanism of adsorption of Cu2+,Zn2+,Pb2+and Cd2+by the modified phosphogypsumStudy on mechanism of adsorption isotherms showed that the adsorption of Cu2+,Zn2+,Pb2+ and Cd2+were accorded with Freundlich and Langmuir adsorption isothermal models,while its linear relative better comply with Freundlich isothermal adsorption equation.It also showed that the behaviour of adsorption of Cu2+,Zn2+,Pb2+ and Cd2+ was belonged to adsorbed monolayer or multilayer adsorption.Study on mechanism of adsorption kinetics showed that adsorption of Cu2+,Zn2+,Pb2+ and Cd2+ was consistenly with the Elovich equation and the intraparticle diffusion model at the initial stage.In a manner of speaking,Pseudo two order kinetic equation can be used describe the whole adsorption process.The adsorption behavious were controlled by physical adsorption,chemical adsorption and adsorption flocculation sedimentation synergistic action.Moreover,aadsorption rate was controlled by liquid film diffusion and particle diffusion.Study on mechanism of adsorption thermodynamic showed that adsorption of Cu2+,Zn2+,Pb2+ and Cd2+ was endothermic process.Temperature was beneficial to the adsorption of the spontaneous when the temperature was ranged from 10 to 30℃.However,the adsorption of Pb2+was an exothermic process.To the sum up,this paper systematically introduces the microwave irradiation modified phosphogypsum and adsorption of Cu2+,Zn2+,Pb2+and Cd2+in industrial wastewater.Modern analytical techniques were used to characterized the modified phosphogypsum.The ecperimental conditions,factor and competition mechanism were also inversitigated.What’s more,Box-Behnken model was used to analysised adsorption of Cu2+,Cd2+,Pb2+and Zn2+ removal rate and equilibrium adsorption capacity.The relationships between metal ion concentration,dosage and reaction system of pH were studied by response surface analysis.In addition,the microwave induced modification of phosphogypsum adsorption of Cu2+,Zn2+,Pb2+and Cd2+was researched from the view of static adsorption model,dynamic adsorption model and thermodynamic model and other aspects of the adsorption mechanism.Overall,this results showed that removal of Cu2+,Zn2+,Pb2+and Cd2+by the microwave induced modification of phosphogypsum is reasonable and feasible.Results of this study provided a novel insights into the utilized of phosphogypsum resources. |
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