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Research of Adsorption Mechanism about Pb(Ⅱ)and Zn(Ⅱ) on the Microwave-preconditioned Phosphogypsum and Experiment of Produced Wall Materials

Author: ShuDunTao
Tutor: YangYueHong
School: Kunming University of Science and Technology
Course: Environmental Engineering
Keywords: microwave induced modified phogypsum heavy metal water building materials adsorption thermodynamics adsorption kinetics
CLC: X703
Type: Master's thesis
Year: 2012
Downloads: 64
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Abstract


Phosphogypsum (PG) is an acidic by-product produced in large quantities by the phosphate fertilizer industry during the "wet process" of phosphoric acid. PG’s chemical composition is mainly maked up of CaSO4·2H2O. As the development of phosphate fertilizer industry is growing rapidly, large amounts of phosphogypsum have been produced up to now and it is increasing at a rate of15%per year. However, large amounts of phosphogypsum not only occupy the land, pollution of surface water, but also causes more serious environmental pollution and safety problems. Therefore, how to utilizated phosphogypsum, controlled the pollution problems, used waste to control waste will become very important. Only in this way, we can improve the value of phosphogypsum and create a good social and environmental effects. This is a general concerning today about the issue of heavy metal ions which are Pb2+and Zn2+Therefore, when the pollution caused by heavy metals has become one of the world’s most serious environmental problems, how to solve the pollution caused by heavy metals has become the focus during the environmental protecters.Based on the concept of saving and environmental protection, when this concept was accepted by most people. The phosphogypsum have more surface and large adsorption capacity, it apparently that this character are accord with this concept. Insomuch as phosphogypsum have nominal price, easy availability and good adsorption capacity, it will have a place with broad prospects in application, especially in dealing with low concentrations of heavy metal wastewater which containing lead(Pb) and zinc(Zn). The disadvantages of fly ash adsorption heavy metal as follow:the poor adsorption effect and the cost of processing, for that we use the phosphogypsum to dispose heavy metal pollutants, combined with the apply of the microwave field, forming a microwave to enhanced the function of phosphogypsum. The paper are researched the mechanism about microwave enhanced the function of phosphogypsum to adsorption typical heavy metal pollutants and production the building materials in depth. Some meaningful conclusions are obtained.(1) Mechanism about Microwave enhanced the function of phosphogypsumWhen used the microwave to enhanced the phosphogypsum, power and time are studied. The optimal parameter are as follows:frequency is2450MHz), power is950w, time is12min), specific surface area is5.572m2/g(2) Behaviors about typical heavy metal pollutants on the phosphogypsumWe take the model of Box-Behnken to analysising Response surface about the phosphogypsum to remove heavy metal pollutants. The result indicated that when ph is7,adsorbent is0.7g/100mL, heavy metal concentration is50g/mL, the removal of Pb2+and Zn2+are94%,82%, independent. The capacity of Pb2+and Zn2+is8.0mg/g,6.1mg/g, independent.The adsorption data fit well both in the Langmuir and the Freundlich model, however the results show that Freundlich equation is more applicable than Langmuir equation. The Lagergren pseudo-first-order kinetics, Lagergren pseudo-second-order kinetics, Elovich equation and intraparticle diffusion model was studied in the process of adsorption.The results reveal that all the four equations are found applicable in initial stage of adsorption. The absorption of Pb2+and Zn2+on microwave-preconditioned PG is accord with pseudo-second-order reaction kinetics in the entire stage. The absorption characteristics of metal ions on microwave-preconditioned phosphogypsum was controlled by both film diffusion and particle diffusion. Thermodynamic analysis show that the process of microwave-preconditioned phosphogypsum adsorbing Zn2+are endothermic reaction, but for adsorbing Pb2+is exothermic reaction.(3) The research of building material with phogypsum.According as the research of building material with PG, explored the difference ratio of processes would have affects on the building material of compressive strength and flexural strength. Depending on the single factor and orthogonal experiment, it can be concluded that the optimum mixture ratio of each material was as follow:phosphogypsum(55%), phosphorus slag(25%), cement(20%), lime(4%), water reducer(1%), polypropylene fibe(1.2%). Through the nature conservation at room temperature, the specimen of compressive strength at the7d,28day are reach10.19MPa,28.84Mpa,respectively; flexural strength at the7d,28day are2.12MPa,3.95MPa,respectively; the finally product meets the requirements of "building gypsum "(GB9776-2008), and "chemical gypsum products"(HJ/T211-2005).To the sum up, the mechanism about microwave induced the phosphogypsum and the theory, technology of building material with phogypsum are studied in systematicness.In order to achieve the optimum parameter,we take the model of Box-Behnken to analysising response surface about the removal and adsorption capacity which was used phosphogypsum to adsorption the Pb(Ⅱ) and Zn(Ⅱ). Investigation the three factors have influence on response value whether or not significantly and interaction of three factors which are the adsobent of dosage, concentration, reaction system of pH. Moreover,it take deep-going research about microwave induced phosphorus gypsum to adsorption Pb2+, Zn2+from the static adsorption, dynamic adsorption and thermodynamic aspects. The finally results showed that microwave induced modification of phosphogypsum removal of Pb2+, Zn2+is reasonable and feasible, not only opened up the comprehensive direction of utilizatied phosphogypsum, and also for subsequent research has a certain reference value and guiding role.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Wastewater treatment and utilization
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