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Effects of Humic Acids on the Reduction and Release Characteristics of Mineral Bound Hg

Author: LiuLiQiong
Tutor: WeiShiQiang
School: Southwestern University
Course: Environmental Engineering
Keywords: Humic acid Mineral binding mercury Reduction Release characteristics
CLC: X53
Type: Master's thesis
Year: 2011
Downloads: 107
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Abstract

Trace amounts of toxic heavy metals, mercury is recognized as the most dangerous environmental pollutants. Natural release of mercury and man-made pollution is an important source of mercury in soil. Mercury into the soil, the minerals in the soil has a strong adsorption of mercury, more than 95% can quickly soil suction held or fixed to the fixed mineral state exists, its activity is very low, and thus become a potential source of mercury. Soil mercury reduction and volatilization into the atmosphere, thus the long-distance transport, making it a global pollutants. Mercury and its compounds in the soil can also Runoff into the water, pose a potential threat to human health through the enrichment of the aquatic food chain. Migration and transformation of mercury in the environment by the constraints of the composition and nature of the environmental media, humus is a kind of natural organic matter, widely found in soil, lakes, rivers, oceans and sediments medium. Humic acid, humic acid as the major component, containing a phenolic hydroxyl group, a carboxyl group, a carbonyl group, quinone group, a methoxy group, and a variety of reactive groups, and having a strong complexation and adsorption capacity and the redox ability, and environment of heavy metal ions interact, change its existence morphology and biological activity. Existing research focuses on humic acid on metal ion complexation characteristics, but very little for the redox properties of humic acid and its the variable tariff metal ions environmental behavior research. To this end, this paper uses the diffusion absorption method to study the humic acid mineral bound mercury reduction, the mineral-bound mercury reduction and light conditions, analysis of differences in the ability of different humic acid redox and their causes; Research humic acid mineral combined with the impact of the release of mercury process to reveal its mechanism of humic acid on mercury interface migration process, to provide a scientific basis for the understanding of the biogeochemical cycling of mercury and environmental mercury pollution control. The main results are as follows: humic acid on the mineral-bound mercury reduction results show that: Both humic acid (produced from Tianjin Guangfu Fine Chemical Research Institute (TJ) and Shanghai Ju Feng Chemical Technology Co., Ltd. (SH) two humic acid reagent separation and purification) 5 mineral bound Hg have a significant reduction, and the reduction rate carried out with the reaction time is incremented. Double constant equation, Elovich equation and exponential equations can better fit the dynamic process of SH and TJ the CaCO3-Hg, Fe2O3-Hg and MnO2-Hg reduction (r gt; 0.8). Double constant equation, Elovich equation and the parabolic equation can better fit the kaolin-Hg and bentonite-Hg reduction (r gt; 0.86). Among them, the goodness-of-fit of the exponential equations and parabolic equations optimal, indicating that the proliferation of humic acid on the mineral-bound mercury reduction may be very important in the process. Humic acid mineral bound mercury reduction and retention of mineral types and their spatial structure. Shading and lighting conditions, the five kinds of mineral bound mercury in two humic acid (SH and TJ) under the action of the average reduction rate difference was significant (P lt; 0.05), in the order of: CaCO3-Hg (0.67%) gt; The kaolin-Hg, Fe2O3-Hg (0.42%) (0.35%) gt; the MnO2-Hg (0.19%) GT; bentonite-Hg (0.14%). Light on the humic acid reduction mineral bound mercury has a strengthening effect the Fe2O3-Hg and bentonite-Hg, the average reduction rate Dark 1.34 and 1.35 times respectively, light strengthening effect is more obvious. Light has an impact on the amount of mineral-bound mercury reduction and reduction rate, photochemical catalytic reduction of humic acid Hg2 may Fe3-and Cr6 the photosensitive reduction mechanism with humic acid. Both humic acid binding mercury reduction on the five types of minerals showed a significant difference (P lt; 0.1) and SH reduction ability in TJ, with humic acid containing a redox-active group content and E4 / E6 (polycondensation and aromatic degree). These results indicate humic acid mineral bound Hg reduction conceptual model can be expressed as three processes: First, the mineral-bound Hg surface rupture, and humic acid under the action of mineral combined with the release of mercury, humic acid, mercury and minerals coordination among adsorption, humic acid active groups mercury reduction, most of the H expansion spread to the overlying air. However, the detailed mechanism of this process remains to be further studied. Humic acid release characteristic of mineral bound Hg results show that: the role of humic acid, mercury from the mineral in various forms (Hg0, Hgionic, and HgHA) combined with the state to release and are subject to a variety of factors. As the reaction time progresses, the two types of humic acid (commercially available humic acid SH and natural humic acid JY) under the action of five mineral binding mercury emission increments stabilized, release the total amount of the order: bentonite-Hg gt; CaCO3-Hg gt; Fe2O3-Hg gt; kaolin-Hg gt; MnO2-Hg, show that the combination of kaolin and MnO2 Hg more solid, easy to release, and humic acid mineral bound mercury release impact and holding mineral type. Mineral combined total mercury emission increases as humic acid (SH and JY) increasing concentration increased, and the difference was significant (P lt; 0.01). Of CaCO3-Hg the kaolin-Hg and MnO2-Hg in various forms of mercury emission increases as the pH increases increase: Fe2O3-Hg decrease with increasing pH value; the SH role of bentonite-Hg emission was first decreased and then increased, JY under the action of the first increased and then decreased. Promote the role of humic acid mineral combined with the release of mercury light. SH role, the the Mn02-Hg no significant difference between the total release of the rest of the minerals showed a significant difference (P lt; 0.05), higher than the shading and the light conditions of release. The most obvious of which the bentonite-Hg, the lighting conditions of release 7% more than the shading. SH role under the CaCO3-Hg, the bentonite-Hg and JY role CaCO3-Hg-Hg kaolin and bentonite-Hg total releases under different temperature conditions showed a significant difference (P lt; 0.05), and its significance different seasons of the temperature change is that you can use to govern different mineral types of mercury-contaminated soil. Under the action of two humic acid the CaCO3-Hg in the presence of SO42-largest total releases, MnO2-Hg greater in the absence of coexisting ions, Fe2O3-Hg Cl-coexistence showed a larger release, and kaolin - The release of Hg and bentonite-Hg, with humic acid types. Thus, for different mineral types of mercury-contaminated soil by adding different interfering ions to promote the release of soil mercury to repair the contaminated soil. 5 mineral bound Hg, Cl-and SO42-release process almost all greater than Al3 can be speculated that the anions than cations can be enhanced mineral combined with the release of mercury. Different humic acid release of mineral-bound Hg difference. Two humic acid (SH and JY) under the action of kaolin-Hg and Fe2O3-Hg of total releases significant difference (P lt; 0.05), the remaining three mineral binding mercury was not significantly different. SH on the total release of the CaCO3-Hg and bentonite-Hg, compared to JY high, indicating that SH and CaCO3 and soap strong ten surface adsorption, thus replacing the mercury with mineral binding sites, the release of mercury will more; JY and kaolin, Fe2O3 and MnO2 surface adsorption capacity, and replace mercury releases more. Humic acid combined with the release of mercury impact on fossil and mineral type. JY role of the mineral mercury releases Hg0 more high the JY reduction than SH. Consistent performance by its basic nature. Scanning electron microscopy results show that: humic acid combined with the reduction of mercury and release characteristics of the mineral may be mineral surface structure changes and humic acid is added. Addition of humic acid, mineral and mineral-Hg surface becomes fluffy, dense structure there is a clear traces of \These structural changes affect the intensity of the absorption of minerals bound mercury held, thus affecting the reduction and release of humic acid on the mineral-bound mercury.

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