Research On Remediation Of Cadmium And P-nitrophenol Polluted Soils By Fe/cu Modified Attapulgite Assisited With Microwave Radiation

Contaminated sites with the feature of strong toxicity, multiple pollutants and quick remediation has been gained comprehensive attention. Microwave(MW) irradiation remediation technology, as a new type of soil thermal remediation technologies, which can realize simultaneous remediation of heavy metal and organic polluted soils, has been widely used due to it's efficient,speedily and environmental friendly to target. Since soil generally absorb only small amount of MW energy, Fe, Cu or their oxides with high catalytic activity and quickly absorbing MW to elevate soil temperature, were often used as MW absorbing agents, as a result, contaminated sites reach the purpose of heavy metal stabilization and organic pollutant catalytic degradation. However,transition metals/metal oxides always have small specific surface areas,which may result in the relatively low absorbability. Attapulgite(ATP), a kind of clay minerals, has been widely used in environmental protection due to its high specific surface area, great adsorption capacity, surface reactive groups and working as catalyst support. In this paper, cupric and ferric ion modified attapulgite(Fe/ATP(Cu/ATP)), as adsorbents assisted with MW, acting as either the adsorbent of pollutants and MW or the catalytic of pollution remediation, were investigated for heavy metals stabilization and organics degradation.In this dissertation, cadmium(Cd) and P-nitrophenol(PNP) were chosen as the representative heavy metal and organic pollutant. The toxicity characteristic leaching procedure was used to evaluate the effect of polluted remediation in soil. The operations efficiency as well as remediation mechanism of Cd and PNP by Fe/ATP(Cu/ATP) assisted with MW technology were studied. The main conclusions are drawn as follows:(1) Cupric and ferric ion modified attapulgite(Cu/ATP, Fe/ATP) was prepared by deposition and ultrasonic co-precipitation separately. their structure and morphology were further characterized by scanning electron microscope(FE-SEM), energy dispersive x-ray analysis(EDAX), X-ray diffraction(XRD), fourier transform infrared spectroscopy(FTIR), Surface Area Analyzer(BET). The results show that, Cu and Fe keep on on the surface or enter into the lattice of ATP, combining with-O- and –OH. ATP modification increase the surface area, while Fe/ATP has the larger surface area than Cu/ATP. Both Cu/ATP and Fe/ATP which contain large amount of –OH and multi-valence metal ions(Cu+?Cu2+/Fe2+?Fe3+) are successfully prepared.(2) The stabilization and solidification of Cd polluted soils assisted with MW performed by Cu/ATP and Fe/ATP were studied. The results show that, modification improves the efficiency of Cd stabilization, the order is Cu/ATP > Fe/ATP > active ATP > ATP. When both Cu/ATP and Fe/ATP are added with the amount of 1%(wt%), Cd leaching concentration decrease 63.7% and 42.1% accordingly. Cu/ATP and Fe/ATP of 10% adding amount catch the 99.9%and 77.3% Cd stabilization efficiency individually. Although the Cu/ATP stabilization efficiency is higher than Fe/ATP, it shows disadvantage on long-time satbilization efficiency, which may caused by the leaching of Cu2+. The mechanism studied shows that, Cd stabilization with Fe/ATP(Cu/ATP) is resulted from the fact the active centers(—OH bonds or O–sites) on ATP can react with Cu or Fe giving Cu/Fe—O—Cd— bridges, which help Cd in surface. Using Cu/ATP as well as Fe/ATP assisted with MW show better long-time satbilization. What's more, when adding Fe/ATP, some Cd polluted soil gradually aggregate, crystallize and appear vitrification phenomenon. Cd result great long-time satbilization efficiency using Cu/ATP and Fe/ATP assisted with MW energy.(3) The remediation of PNP polluted soils assisted with MW performed by Cu/ATP and Fe/ATP was studied. The results show that, While increasing Cu/ATP and Fe/ATP amount assisted with MW from 2.5% to 20%, PNP removing efficiency accelerate nearly 1.5 times, Which up to 75% and 99% respectively. Which catch the conclution that, using Fe/ATP shows better PNP removing efficiency than Cu/ATP. the mechanism for PNP remediation using Cu/ATP and Fe/ATP assisted with MW maybe that, Cu/ATP and Fe/ATP, as catalytic, is induced and actived by MW energy, and absorbs oxygen hydrone to get the hydroxyl radicals(·OH,·O2-) for PNP oxidative degradation. Using Cu/ATP assisted with MW, PNP can desorb directly from soil by MW irradiation. PNP also can oxide by active hydroxyl radicals, moreover, when using Fe/ATP assisted with MW,with the temperature increasing, part of PNP and it'sdegradation products probably trapped and enclosed in vitrificated soils.