| With the rapid development of national economy and the vigorously promote of industrialization, Heavy metal pollution incidents occur frequently,endangering the ecological environment and human health seriously.Pb and its compounds is a kind of non-biodegradable environmental pollutants and itsnature is stable, which can be through into the environment by the waste water, waste gas and waste residue. It can cause produce pollution and do harm to human health. Even as poison of the central nervous system, it is much harmful to the human body, especially the children’s health and mental damage is very serious. As a result, the repair technology of Pb environmental pollution has received the widespread attention.Since the late 1980 s, some people reported zero-valent iron can be used to restore the removal of chlorinated organic compounds in aqueous solution. In recent years, the use of zero-valent iron processing water pollution has become a very popular research field, especially in the aspect of heavy metal removal has been widely used. Nanoscale zero-valent iron(NZVI) not only has the characteristics of zero-valent iron, and has stronger adsorption,a larger specific surface area and higher reaction activity than ordinary zero-valent iron. But NZVI also has problem, such as chemical properties is not stable, easy to oxidation, easy to reunite. Research has shown that fixing the NZVI on the carrier can make it into a certain type of NZVI, which can effectively prevent particles from getting together and increase the reactivity.Considering the corn starch has non-toxic, cheap, biodegradable, no secondary pollution etc. This study choose corn starch as the carrier make into a new type of composite material which can becalled corn starch supported nano zero-valent iron(NZVI/CS). Respectively using NZVI/CS and NZVI remove the Pb(Ⅱ) in the solution. According to the orthogonal test to determine the best conditions for removal of Pb(Ⅱ). The mechanism of the removal of Pb(Ⅱ) in the solution are discussed in this paper, by using macroscopic analysis methods of isothermal adsorption, thermodynamics and dynamics model and microscopic technique,such as scanning electron microscope(SEM), energy spectrum(EDS), specific surface area(BET) and X-ray diffraction(XRD). The main research contents and results in this paper are:1.The best condition of the liquid phase reduction NZVI/CS: the ratio value of BH4-and Fe3+ is 4:1, corn starch and NZVI is 1.5:1. According to orthogonal experiment intuitive analysis, we determine the order of the test effect: p H of solution> dosage of NZVI/CS> reaction temperature> reaction time, and the best removal conditions were determined. Through the contrast the best conditions of experiment, we found NZVI/CS has a better removal performance. Within 60 min, the removal rate can reach to 100%, which NZVI and corn starch is only 83% and 51%, therefore, the introduction of corn starch can effectively improve the stability and reactivity of NZVI.2.For two kinds of materials for the isothermal adsorption, thermodynamics and kinetics, the study found that two materials of Pb(Ⅱ) were more in line with the Langmuir adsorption isothermal adsorption equation, which belong to the monolayer chemical adsorption; Adsorption of Pb(Ⅱ) was spontaneous endothermic reaction, and with the increase of initial concentration of Pb(Ⅱ), spontaneous degree became more and more low, with the increase of temperature, the better adsorption effect. When the Gibbs free energy ΔG0 in-20~0kj/mol, was belong to the physical adsorption; Pseudo Second-order dynamic model would describe the process of adsorption Pb(Ⅱ) in a better way. The apparent activation energy Ea calculated using Arrhenius equation in 0~40kj/mol, was belongs to the physical adsorption. Therefore, two kinds of materials for adsorption of Pb(Ⅱ) are both of physical adsorption and chemical adsorption.3.Known from the analysis of SEM: compared with NZVI/CS and NZVI, particle size uniform and smooth surface, particle size decreased significantly, the average particle size was around 50 nm. The main presenting was chain sphere, and the reunion phenomenon significantly was reduced; By the analysis of EDS: the surface element Fe content of NZVI/CS was significantly increased and the O element content was reduced than NZVI. The introduction of corn starch reduced the degree of oxidation and increased the specific surface area of NZVI. Known from the analysis of BET: the specific surface area of NZVI was 28.44 m2·g-1 and NZVI/CS was 46.82 m2·g-1, it was showed that after using the corn starch load of NZVI, the size of particle became more smaller, and the specific surface area was increased; By XRD analysis showed that before the NZVI/CS reaction, the characteristic peak was around 2θ= 44.7°, which was corresponds with the 110 crystal face(2θ= 44.6732°) of the strongest diffraction peak of iron. With no diffraction peak of iron oxide, showed that the sample was mainly of elemental iron, almost no iron oxides, and the product purity was highly. The width of the diffraction peak showed that NZVI/CS was more fine grain size. After reaction of NZVI/CS,the diffraction peak was appeared at 2θ=35°,which was corresponding to strong diffraction peak of Fe3O4(2θ=35.46°). |
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