| At the turn of the 21 century, through an increase of the world population and rapid economic development, China is facing considerable crisis in water sources and quality. Especially critical is the increased crisis of water quality.China has serious water pollution problems in both groundwater and surface water. Cr(VI) is largely used in tanneries, printing, dyeing, production of colorants, electroplating etc. It is a common pollutant which exists in nature. Organochlorine compounds in manufacturing industries, cleaning industries; organic solvents, pesticides, herbicides producing industries and some chemical productions are used in great quantities leading to a large discharge of products containing chlorine. Many surface waters and groundwaters face the problem of organochlorine compound pollutions. Therefore, treatments of water containing organochlorine compounds and heavy metals are of great interest.Since Scholars proposed the possibility of using metallic iron filings to remediate underground water, the use of Fe0 for underground water pollutants remediation became a very active domain of research. Since zero valent iron is characterized by cheap price, a high reductive and rapid speed reaction; it became one of the most effective materials in remediating underground water sources. So far, zero valent iron is largely used in the treatments and purification of chlorine containing organic matters, nitrogenous organic compounds, heavy metals and other pollutants. But due to the existence of different materials in underground water such as humic acid, hard ions etc, the removal and elimination of chlorine would be affected. Therefore, in this research nano-scale iron and nano-scale Ni-Fe and Pd-Fe bimetallic particles were the main tools for remediation of polluted water containing hexavalent chromium and 2,4 DCP. Besides, investigations were emphatically done on the inhibition due to the existence of humic acid (HA) against the reductive removal of zero valent iron (ZVI). Initially, we dealt with the mechanism of ZVI remediation inhibition by HA. Through our experiments, we investigated methods of overcoming the ZVI remediation inhibition by HA and those opposing to the inhibition mechanism. Results showed the following:(1) The effect of humic acid on the catalytic reductive dechlorination by nanoscale Pd-Fe and nanoscale Ni-Fe bimetallics inhibition was obvious and that inhibition was shown when one reached the low concentration 5 mg L"1 of Humic acid. The inhibition of the catalytic reductive dechlorination of 2,4-DCP follows the addition of HA. As quantities of HA were increasing, the results were getting better. The reason why humic acid can inhibite catalytic reductive dechlorination by nanoscale Pd-Fe and nanoscale Ni-Fe bimetallics is that it can be adsorbed on the surface area of particles of bimetallic Pd-Fe and Ni-Fe and then reduces the reactivities of particles preventing the evolution of the reaction. When HA exists, factors influencing the results of the catalytic reductive dechlorination by nanoscale Pd-Fe and nanoscale Ni-Fe bimetallics are:doses of HA, pH, nickel ration, nanoscale Ni-Fe dosage and the reaction temperature. The experimental results showed that larger nickel ratio, a lower pH, higher nanoscale Ni-Fe dosage and higher reaction temperature are favorable to dechlorination reaction. The dechlorination efficiency has only little to do with the initial concentration of 2,4-DCP. When HA exists, the nanoscale Pd-Fe and nanoscale Ni-Fe bimetallic catalystic reductive dechlorination kinetics model can be described as a first order reaction kinetics. When computing the catalystic dechloriantion of 2,4-DCP by nanoscale Pd-Fe in our experiments, we found that HA dosages have linear relationship with reaction rates. When HA dosages increased, the reaction rates also increased, and with the HA dosages increasing, the reaction rate constants decreased linearly.(2) HA's inhibiting effect on the nano-scale zero-valent iron to remove Cr(VI) reaction is obvious, and this trend became remarkable with the concentration of HA increasing. However when the concentration of HA reaches a certain extent, this trend is no longer obvious. The mechanism of HA on the nano-scale zero-valent iron to remove Cr(VI) is double:on one hand, humic acid would be adsorbed on the nano-scale zero-valent iron surfaces, occupying their active surfaces leading to the inhibition of the reaction. On the other hand, the humic acid in solution also can be used as electron transport bodies (Media of electrons transfer) to promote the reaction.(3) Adding stabilizer CMC in the preparation of nanoscale Fe0 could prevent from the agglomeration of nanoscale particles, and maintain them at a high degree of dispersion, and then maintain their high reactivity. CMC stabilized nanoscale Fe0 at a certain extent, can promote the remediation reaction, and eliminate the inhibitory effect brought by HA. When the HA is 40 mg L-1, add 0.5 g L-1 of CMC, the removal efficiency of Cr(VI) increased from 49.1% to 78.6%, the value is very close to 82.65% when there is no HA. This indicated that in the preparation of nanoscale Fe0, add stabilizer CMC can eliminate the inhibition due to the presence of HA to some extent. The anti-inhibition mechanism of CMC to HA's inhibition is that the existence of CMC overcomes the effects of magnetism. Under the effect of electrostatic repulsion and steric hindrance, nanoscale Fe0 particles cannot agglomerate easily, but maintain a highly decentralized state which can maintain biggest surface areas. Besides weakening the physical interaction, CMC can wrap the surface of nanoscale Fe0 particles, and that can inhibit the reaction between high active sites of ZVI's surface and surrounding media (dissolved oxygen and water). Although the surface passivation may prevent particles'reactions with the target pollutants, however, the particle sizes are very small and specific surface areas are huge, so the treatment efficiencies are several times better than unstabilized ZVI particles.(4) In the preparation process of nanoscale Fe0, adding some magnetite can provoke the adhesion of nano-scale zero-valent iron to the magnetite surfaces. Therefore, they would prevent iron particles from agglomerating, so it can hold them at a high degree of dispersed state in order to maintain their high reactivity. In our experimental conditions, results showed that the most appropriate efficiency of Fe3O4 and Fe0 was 10:1.Stabilized nanoscale Fe0 by Fe3O4 can also promote the reaction to some extent, and eliminate the inhibitory effect brought by HA. However, anti-inhibition mechanisms of Stabilized nanoscale Fe0 by Fe3O4 and Stabilized nanoscale Fe0 by CMC are different. The anti-inhibition mechanism of Fe3O4 to HA is, on the one hand, nanoscale Fe0 attached to magnetite surfaces make it difficult to agglomerate for Fe0 particles showing a high dispersion state. On the other hand, the addition of Fe3O4 solved problems of electron transfers due to the surface passivation of Fe0 promoting the electron transfer on the surface of Fe0, and allowing the increase of Fe0 reduction capacity.
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