Effect of inorganic carbonate and organic matter in thermal treatment of mercury-contaminated soil

Wildfire effects on mercury fate in soils of North-Western Siberia

Arctic soils store 49 Gg mercury (Hg) - an extremely toxic heavy metal, whereas soil Hg can be released to the atmosphere by wildfires. For the first time we investigated the effects of wildfires on the fate of soil Hg in North-Western (NW) Siberia based on GIS maps of areas burned during the last 38 years and a field paired comparison of unburned and burned areas in tundra (mosses, lichens, some grasses, and shrubs) and forest-tundra (multi-layered canopy of larch trees, shrubs, mosses, and lichens). These field surveys were deepened by soil controlled burning to assess the Hg losses from organic horizon and mineral soil. The soil Hg stocks in the organic horizon and in the top 10 cm of the mineral soil were 3.3 ± 0.6 and 16 ± 3 mg Hg m-2 for unburned tundra and forest-tundra, respectively. After the burning by wildfires, the soil Hg stocks decreased to 2.4 ± 0.1 and 6.6 ± 0.2 mg Hg m-2 for tundra and forest-tundra, respectively. By the averages annual burned areas in NW Siberia 527 km2, wildfires in tundra and forest-tundra released 0.19 and 2.9 Mg soil Hg per year, respectively, corresponding to 28 % and 59 % of the initial soil Hg stocks. These direct effects of wildfires on Hg volatilization are raised by indirect post-pyrogenic consequences on Hg fate triggered by the vegetation succession and adsorption of atmospheric Hg on the surface of charred biomass. Charred lichens and trees accumulated 4-16 times more Hg compared to the living biomass. Blackened burned vegetation and soil reduced surface albedo and slowly increased soil temperatures in Arctic after wildfires. This created favorable conditions for seeding grasses and shrubs after wildfire and transformed burned high-latitude ecosystems into greener areas, increasing their capacity to trap atmospheric Hg by vegetation, which partly compensate the burning losses of soil Hg.

Morphological analysis of mercury in solid wastes from natural gas processing plants: optimization of a temperature-programmed decomposition and desorption method

Determination of mercury species over solid waste from natural gas processing plants is a prerequisite for solid waste decontamination and mercury recycling. The temperature-programmed decomposition and desorption method (TPDD) is a promising technique to determine the mercury species over solid waste. Mercury species over solid wastes with complex components and similar desorption temperature, however, cannot always be determined using only the TPDD method. In the present study, the EPA 3200 method was applied to optimize the TPDD process for speciation of the mercury compound over solid wastes collected from a natural gas processing plant, including four spent adsorbents and three sludges. The mercury species with similar desorption temperatures over solid wastes were completely separated by the EPA 3200 method optimized TPDD process. The mercury species over spent adsorbents and sludges could be determined based on the fingerprints of the mercury compounds. The mercury compounds over spent adsorbents were specified to be Hg0 and/or M-Hg amalgam, HgS(black) and HgO(red), of which HgS(black) was the primary mercury compound. However, the mercury species over sludge were analyzed to be Hg0 and/or M-Hg amalgam, HgCl2(minor), HgS(black), HgO(yellow) and HgS(red). The mercury recovery rates of solid wastes ranged from 73% to 120%. With the above results, it was considered that the EPA 3200 method optimized TPDD process was a promising method to specify and semi-quantify the mercury compounds in solid waste.

The Effects of Different Soil Component Couplings on the Methylation and Bioavailability of Mercury in Soil

Soil composition can influence the chemical forms and bioavailability of soil mercury (Hg). However, previous studies have predominantly focused on the influence of individual components on the biogeochemical behavior of soil Hg, while the influence of various component interactions among several individual factors remain unclear. In this study, artificial soil was prepared by precisely regulating its components, and a controlled potted experiment was conducted to investigate the influence of various organic and inorganic constituents, as well as different soil textures resulting from their coupling, on soil Hg methylation and its bioavailability. Our findings show that inorganic components in the soils primarily exhibit adsorption and fixation effects on Hg, thereby reducing the accumulation of total mercury (THg) and methylmercury (MeHg) in plants. It is noteworthy that iron sulfide simultaneously resulted in an increase in soil MeHg concentration (277%). Concentrations of THg and MeHg in soil with peat were lower in rice but greater in spinach. A correlation analysis indicated that the size of soil particles was a crucial factor affecting the accumulation of Hg in plants. Consequently, even though fulvic acid activated soil Hg, it significantly increased the proportion of soil particles smaller than 100.8 μm, thus inhibiting the accumulation of Hg in plants, particularly reducing the concentration of THg (93%) and MeHg (85%) in water spinach. These results demonstrate that the interaction of organic and inorganic components can influence the biogeochemical behavior of soil Hg not only through their chemical properties, but also by altering the soil texture.

Recent advances in soil remediation technology for heavy metal contaminated sites: A critical review

With the increasing development of industry and urbanization, heavy metal contaminated sites have become progressively conspicuous, particularly by unreasonable emissions from electroplating, nonferrous metals smelting, mine tailing, etc. In recent years, soil remediation technologies for heavy metal contaminated sites have developed rapidly. New and effective remediation technologies have emerged successively, and more successful practical applications have appeared. Therefore, systematical summarization of the current progress is essential. As a result, in this paper, some mainstream soil remediation technologies for heavy metal contaminated sites, including physical remediation (soil thermal desorption and soil replacement), bioremediation (phytoremediation and microbial remediation), chemical remediation (chemical leaching, chemical stabilization, electrokinetic remediation-permeable reactive barrier, and chemical oxidation/reduction), as well as various combined remediation are comprehensively reviewed. The influencing factors, advantages, disadvantages, remediation mechanism, and practical applications are also deeply discussed. Besides, the corresponding remediation strategies are put forward for the remediation of heavily polluted sites such as the chemical industry, smelting, and tailing areas. Overall, this review will be beneficial for the in-depth understanding and provide references for the reasonable selection and development of soil remediation technology for heavy metal contaminated sites.