| With the rapid development of the social economy and technology, the pollution of arsenic unknown in the past is increasingly serious in the water source. Recently, because the arsenic compounds are lethal toxicants and widely-used in the agriculture and industry, environmental scientists around the world have paid attention to the problems brought out by arsenic compounds that contaminates the environment, especially in the water sources. On the other hand, due to the abundant reserves of arsenic, the background concentration of arsenic is much higher than the maximum standards of drinking water that is 2550×10-9, in the groundwater in some areas of China, so that it does some chronic harm to local people. And according the records, there are about 110,000 tons of arsenic compounds by different means to enter the hydrosphere every year. Therefore, it makes important sense to develop a thorough, simple and economical method to remove the arsenic from the wastewater or drinking water source at present.As a low-priced nonmetallic mineral that have good selective adsorption and ion exchange characteristics, zeolites can enrich much fine particles and be regarded as ideal medium. The removal efficiency of target ions can be greatly enhanced by modifying zeolites, such as clinoptilolite and mordenit, etc, which have potential prospect in the reality. Either in China or outside, there are many studies that mostly focuses on the removal of NH4+-N and phosphate while the researches on removing arsenic from wasterwater or drinking water are rarely seen. Historically, there is an outstanding contradiction that is between the size of zeolites and removal efficiency when using zeolites for removing some pollutants from water solutions. The smaller is grains, the higher exchange and adsorption capacity and the better efficiency can be achieved, however, the more loss of zeolites with the effluent and the head loss influencing the quality of effluent. On. the contrary, to take larger grain must be at expense of sacrificing of adsorption capacity.To solve this problem, the study began to prepare of porous modified zeolite pellets. Firstly, the study selected the proper method of modification and the optimumconditions for preparing, and made the modified zeolite pellets by burning. Then, the removal efficiency of arsenic(V) by zeolite pellets and the factors influencing the efficiency, as pellet size, zeolite amout, treating time, pH and temperature, etc. were investigated thoroughly. Finally, the regeneration method and efficiency of zeolite had also been studied. Meanwhile, the modified zeolite pellets was used to treat real wastewaster for compare with the lab outcomes, and initially studied the removal performance in the NH4+-N, phosphate and fluoride, respectively.Through the research of this paper, the conclusion can be drawn. Compared with other treatments, such as treatment with sintering, hydrochloric acid (HC1) and sodium hydroxide (NaOH), the removal efficiency can be greatly enhanced by treatment with lanthanum chloride (LaCl3), the average removal efficiency increased by 30%. Thinking of the technological and economic effects, the optimum condition of modification was confirmed. The modifying concentration of LaCl3 solution is 0.5% by weight, the zeolites should be soaked for 2 to 3 hours and the total solid/liquor is 1:25 under the pH=10. After done, the sample is sintered at temperature of 500600℃ for an hour. The proper conditions of preparing modified zeolites pellets were also presented. The raw materials matching ratio as follows: the modified zeolites(-200 mesh): additive forming pores(charcoal powder):binder(soluble starch) = 89:9:2 under the 500600℃, and the diameter of pellets is 3mm, reserve time is 2 hours.It indicated by study on the factors influencing efficiency that the modified zeolite pellets are suitable to treat the simulated wastewater containing lOmg/L of arsenate with the pH being 410. The removal efficiency of arsenic(V) can be achieved above 95% by using about 8g/L pellets, as requirements of the National Drainage Standard. The modified zeolite pellets can also be used to remove NH4+-N, phosphate and fluoride from water solution to some extent. In the study, when the modified zeolite pellets was regenerated by NaOH solution with the concentration being 1.0mol/L and treating time being 34 hours, the removal efficiency of As(V) had been slightly deceased by 5% after recycling at least 10 times. Therefore, it showed that the sample also has the high strength of compressive resistance, the modified zeolitepellets can be put into practice for multiple regenerations.Gradually, as the requirements of standard of removing arsenic are strict, it must call on more and more breakthroughs and improvements further either in the fields of wastewater or drinking water. The objective of this study is to provide the new technique to remove arsenic from water solution, efficiently and economically. |
