Sequestration Of Mercury Research Articles

Uptake, Efflux, and Sequestration of Mercury in the Asian Clam, Corbicula fluminea, at Environmentally Relevant Concentrations, and the Implications for Mercury Remediation

(1) Mercury (Hg) is a persistent, ubiquitous contaminant that readily biomagnifies into higher trophic level species in aquatic environments across the globe. It is crucial to understand the movement of environmentally relevant concentrations of Hg in impacted freshwater streams to minimize risks to ecological and human health. (2) The bioconcentration kinetics of aqueous Hg exposure (20, 100, and 200 ng/L) in the invasive Asian Clam, Corbicula fluminea, were measured. A toxicokinetic model, the first parameterized for Hg accumulation in freshwater clams, was developed to estimate uptake and efflux parameters and compared to previous parameter values estimated for other mollusk species. (3) Results demonstrated that even at low Hg concentrations, Corbicula record signals of contamination through bioconcentration, and both direct measurement and toxicokinetic models demonstrate large Hg bioconcentration factors (as high as 1.34 × 105 mL/g dry tissue), similar to partitioning coefficients seen in engineered Hg sorbents. (4) Our study found that Corbicula accumulated Hg at aqueous concentrations relevant to impacted streams, but well below regulatory drinking water limits, demonstrating their utility as a sensitive sentinel species and potential bioremediator.

Nano-mineral assemblages in mercury- and silver-contaminated soils: records of sequestration, transformation, and release of mercury- and silver-bearing nanoparticles.

Mercury-bearing nano-mineral assemblages (Hg-NMAs) are chemically and mineralogically heterogeneous, micrometer-sized aggregates of nanoparticles (NPs) found in contaminated soils and sediments. Although these NMAs control sequestration and release of Hg that is a global contaminant, our understanding is limited with respect to the conditions of different types of Hg-NMAs, the diversity of its minerals, the size distribution of its NPs and whether mineral replacement and alteration reactions in these NMAs result in the release of Hg-bearing NPs. For this purpose, Hg-NMAs in four sediment samples from the Guanajuato Mining District (GMD) in Mexico, a region that was polluted by Hg and silver (Ag) due to historical mining involving Hg amalgamation, are characterized at the micro- and nanoscale. Microscale examinations with SEM show that the majority of Hg-NMAs occurs in mineral surface coatings (MSC) and fillings in fractures within quartz grains and are enriched in Hg and sulfur (S) relative to Ag, and in S and selenium (Se) relative to chloride (Cl). Examinations at the nanoscale show that Hg-NMAs contain (a) residuals of the patio process such as amalgam phases and elemental Ag; (b) associations of Hg- and Ag-sulfide NPs with pyrite and marcasite; (c) associations of Hg- and Ag-sulfide NPs with goethite and clay minerals along the rims of the MSC. The latter minerals replaced the Fe-Si-rich matrix at high-water rock ratios most likely due to an increase in porosity during flooding of the Pastita River. Consequently, the rims are depleted in Hg-Ag-sulfide NPs relative to the unaltered Fe-Si-rich matrices indicating that changes in the physiochemical conditions of soils and sediments in the GMD can result in the release of Hg-Ag-bearing NPs. In this context, this study discusses whether release and dissolution of Hg-Ag-bearing NPs contribute to the recently observed elevated gaseous elemental Hg concentrations in the soil, interstitial air and ambient air, and to the fate and effects of Hg in local aquatic environments.

Dissolution Potential of Elemental Mercury in the Presence of Bisulfide and Implications for Mobilization.

Liquid elemental mercury (Hg0L) pollution can remain in soils for decades and, over time, will undergo corrosion, a process in which the droplet surface oxidizes soil constituents to form more reactive phases, such as mercury oxide (HgO). While these reactive coatings may enhance Hg migration in the subsurface, little is known about the transformation potential of corroded Hg0L in the presence of reduced inorganic sulfur species to form sparingly soluble HgS particles, a process that enables the long-term sequestration of mercury in soils and generally reduces its mobility and bioavailability. In this study, we investigated the dissolution of corroded Hg0L in the presence of sulfide by quantifying rates of aqueous Hg release from corroded Hg0L droplets under different sulfide concentrations (expressed as the S:Hg molar ratio). For droplets corroded in ambient air, no differences in soluble Hg release were observed among all sulfide exposure levels (S:Hg mole ratios ranging from 10-4 to 10). However, for droplets oxidized in the presence of a more reactive oxidant (hydrogen peroxide, H2O2), we observed a 10- to 25-fold increase in dissolved Hg when the oxidized droplets were exposed to low sulfide concentrations (S:Hg ratios from 10-4 to 10-1) relative to droplets exposed to high sulfide concentrations. These results suggest two critical factors that dictate the release of soluble Hg from Hg0L in the presence of sulfide: the extent of surface corrosion of the Hg0L droplet and sufficient sulfide concentration for the formation of HgS solids. The mobilization of Hg0L in porous media, therefore, largely depends on aging conditions in the subsurface and chemical reactivity at the Hg0L droplet interface.

Design and fabrication of chitosan cross-linked bismuth sulfide nanoparticles for sequestration of mercury in river water samples

The existence of heavy metals in ecological systems poses great threats to living organisms due to their toxicant and bio-accumulating properties. Mercury is a known toxicant with notable malignant impacts. It has long been known to cause toxic threats to the health of living organisms since the break out of Minamata disease. The turbulent expulsion of mercury-based pollutants from the industrial sector, requires a proper solution. Many attempts have been made to design a greener and more efficient route for a satisfactory removal of mercury. In the current study, bismuth sulfide nanoparticles (BiSNPs) have been synthesized via the co-precipitation method. The BiSNPs were supported with crosslinked chitosan to enhance their sorption capacity and avoid leaching. The average size of the BiSNPs was 42 nm based on SEM micrographs. The SEM analysis of the bismuth sulfide chitosan-crosslinked beads (BiS-CB) showed that the beads possessed a spherical and smooth morphology with a size of 1.02 mm. The FTIR analysis showed that the beads possessed the characteristics bands of imine groups of chitosan, bismuth, sulfur, and glycosidic linkages present in the molecules. The XRD analysis confirmed the phase crystallinity of the BiS-CB with an average crystallite size of 11 nm. The BiS-CB was employed for the sorption of mercury from water samples. The maximum sorption capacity of 65.51 mg/g was achieved at optimized conditions of pH 5, concentration 80 ppm, in 45 min at 30 °C. The mechanism studied for mercury removal showed that sorption followed the complexation mechanism according to the SHAB concept. In conclusion, the results showed that the BiS-CB sorbent exhibited an excellent sorption capacity to remove mercury.

Rational design via surface engineering on dual 2-dimensional ZnSe/g-C3N4 heterojunction for efficient sequestration of elemental mercury

The rational structural design and regulation of heterojunction catalyst are crucial and still challenging for improving its catalytic activity and environmental friendliness. Herein, one novel dual 2-dimensional ZnSe/g-C3N4 (ZSCN) nano-heterojunction was developed by a newly designed incipient wetness impregnation method followed by in-situ selenization, which was used at the first time for future remediation of Hg0 pollution derived from coal combustion. The as-synthesized ZnSe/g-C3N4 exhibited unparalleled performance toward Hg0 immobilization under harsh experimental conditions. The coupling between g-C3N4 with ZnSe can significantly enhance its Hg0 removal performance, and the enhanced Hg0 adsorption capacity in the case of the 20ZSCN reached up to 16.59 mg·g−1, 4 times higher than 20ZSCN(mix) prepared by simple mechanical mixing. The phenomenon was attributed to the high active sites exposure rate and effective electronic transport on the heterostructure interface, which was confirmed by the density functional theory analysis. The Se2- on ZSCN surface act as the main activity center for the oxidization from Hg0 to Hg2+, and further sequestration in forms of stable HgSe. This work offers a new avenue for the rational design of a novel ZnSe/g-C3N4 2d-heterojunction catalyst with high stability and long durability in the immobilization of highly toxic Hg0 through surface engineering.

Sequestration of mercury and cadmium by a heavy metals' tolerant Bacillus cereus strain JS-3: a microbial preparedness for terrestrial and anthropogenic hazards

A large number of heavy metals are discharged in the form of industrial effluents into the soil and natural water bodies beyond the permissible limits. Accumulation of bio-available forms of these hazardous elements in the natural sites poses both environmental and human health implications throughout the globe. In the present study, a bacterial strain JS-3 has been explored toward its tolerance for different heavy metals along with sequestration and transformation of mercury and cadmium. Strain JS-3 was characterized morphologically, physiologically, and biochemically followed by 16S rRNA homology analysis and identified as Bacillus cereus. The results highlight that isolate has a remarkable tolerance (up to 20 µg/g as an active ingredient) toward almost all heavy metals such as Pb, Cd, Ni, As, Hg and Se. After acclimatization in first 24 hours, almost comparable growth has been observed in control and mercury supplemented Tryptone Soya Broth (TSB) while a significant impact on the growth was observed in cadmium supplemented TSB. After 96 hours, almost 80% of the mercury and 70% cadmium has been sequestered in the biomass supplemented with 25 µg/g of these metal salts with a decrease in sequestration with increase in initial concentration of metals has been observed. SEM and EDX analysis further confirmed the accumulation of these metals in the biomass. XRD-analysis of the biomass revealed no characteristic peak associated with the crystalline nature of the mercuric chloride and cadmium chloride but it ensures transformation of these salts into the amorphous material within the bacterial cells.

Sequestration of Mercury in Soils under Scots Pine and Silver Fir Stands Located in the Proximity to a Roadway

Forest soils are the main source of mercury (Hg) in stream water. Stocks of Hg in forest soils are related to several factors, including forest species composition. In this study, the potential source of Hg pollution was a relatively new roadway traversing forested areas. We compared Hg accumulation in soils of two coniferous species: Scots pine (Pinus sylvestris L.) and silver fir (Abies alba Mill.). The experimental plots were located near the S7 expressway in Central Poland. The stands differed in the length of time they had been exposed to Hg, because different parts of the roadway were built and opened to traffic at different times. We analyzed 480 soil samples from organic horizons (O) and the top 10 cm of mineral soil (A) sampled from six plots. The overall average Hg concentrations (irrespective of forest stand, n = 240) was 0.225 mg kg−1 in the O horizons and 0.075 mg kg−1 in the mineral horizons. The Hg concentration in the O horizons was more than three times greater in fir stands than that in pine stands. The average Hg:C ratios in the O and A horizons were 1.0 and 2.3 mg Hg kg−1 C, respectively. Our data does not clearly show the effect of road on Hg accumulation near the road. The concentrations of Hg in investigated soils adjacent to the roadway were only slightly higher than ranges reported for unpolluted areas, and no clearly affected by the vicinity of roadway. In contrast to the other reports, our data indicate a significant impact of tree species on Hg concentrations in both the O and A horizons. Moreover, the average Hg:C ratio was strongly dependent on the tree species.

Amorphous molybdenum selenide intercalated magnetite as a recyclable trap for the effective sequestration of elemental mercury

The amorphous molybdenum intercalated magnetite [MoSe3(inter)Fe3O4] was purposefully designed and synthesized as an efficient and recyclable sorbent for immobilizing elemental mercury (Hg0) from industrial flue gases into extremely stable mercury selenide (HgSe).

Selenium Functionalized Metal-Organic Framework MIL-101 for Efficient and Permanent Sequestration of Mercury.

Abatement of mercury emission from coal-fired power plants remains a serious task for public health and environmental societies. Selenium functionalized metal-organic framework MIL-101 (Se/MIL-101) was prepared for mercury removal from power plants. The Se/MIL-101 exhibited a remarkable mercury adsorption capacity of 148.19 mg·g-1, which was about 154 to 705 times larger than that of commercial activated carbons exclusively applied for mercury removal from power plants. The initial mercury adsorption rate for Se/MIL-101 reached up to 44.8 μg·g-1·min-1, which was 89- to 1659-fold higher than those of mercury sorbents reported in the literature. The Se/MIL-101 maintained an excellent mercury adsorption stability under simulated flue gas atmosphere containing SO2, NO, and H2O. Gaseous elemental mercury (Hg0) converted on the Se/MIL-101 to stable and water-insoluble mercury selenide (HgSe), which guaranteed a minimum re-emission even sequestration of mercury. Moreover, the mercury-laden Se/MIL-101 could also immobilize mercury in gypsum and efficiently capture mercury ions from desulfurization effluent to an undetectable level (<0.0035 μg·L-1). With these advantages, Se/MIL-101 appears to be a promising material for efficient and permanent sequestration of mercury from power plants.

Opportunities for lignin valorization: an exploratory process

BackgroundFor decades, the pulp industry has struggled to create sustainable value-added opportunities for lignin, and the issue is now at the forefront of second-generation biorefinery research and development efforts. Our work presents a sequential process for examining potential lignin valorization. The chemical and physical properties of lignin cause issues in isolation, characterization, and standardization and, therefore, product manufacturing. First, a short list of high-opportunity lignin products was developed from the literature. Several low-hanging product opportunities were identified, from which, lignin-based powdered activated carbon (PAC) for the sequestration of mercury from power plant flue gas was selected for further examination due, in part, to lignin’s similarity to lignite coal. Next, an analysis of the web-based written content of PAC suppliers’ promotional materials was performed to assess the attributes on which PAC products are sold and purchased. Finally, potential electric generating power plant buyers/users of lignin-based PAC for mercury sequestration were surveyed to examine the importance of 16 PAC product and service attributes, identify potential entry barriers for a new PAC product, and assess the market opportunity for lignin-based PAC.MethodsThis research deployed a multi-phase market analysis based process including: a PAC vendor content analysis; and survey techniques. Phase I analyzed web-based content of PAC vendors’ promotional marketing literature tailored to power plant buyers/users for their PAC products. Phase II incorporated the Phase I results into an exploratory e-survey of select PAC buyers/users in the U.S. power generation industry. Combining these methods provides an exploratory market perspective on lignin valorization.ResultsThe top three product and service attributes for buyers/users of PAC for mercury mitigation were Product Reliability, Product Effectiveness, and Proven Product Performance; the top three barriers to entry for a new lignin-based PAC include Title V Permitting, Operational Impacts, and Compliance with Regulations. Buyers/users are undecided about trial testing a lignin-based PAC product.ConclusionsThis paper provides a logical and systematic process for exploring new product opportunities in business-to-business markets and provides insights into the market potential for lignin-based PAC for mitigating mercury emissions from US electric generating power plants.

A Synthetic Circuit for Mercury Bioremediation Using Self-Assembling Functional Amyloids.

Synthetic biology approaches to bioremediation are a key sustainable strategy to leverage the self-replicating and programmable aspects of biology for environmental stewardship. The increasing spread of anthropogenic mercury pollution into our habitats and food chains is a pressing concern. Here, we explore the use of programmed bacterial biofilms to aid in the sequestration of mercury. We demonstrate that by integrating a mercury-responsive promoter and an operon encoding a mercury-absorbing self-assembling extracellular protein nanofiber, we can engineer bacteria that can detect and sequester toxic Hg2+ ions from the environment. This work paves the way for the development of on-demand biofilm living materials that can operate autonomously as heavy-metal absorbents.

A Nanoselenium Sponge for Instantaneous Mercury Removal to Undetectable Levels

Selective removal of aqueous mercury to levels below 10 ng L−1 or part per trillion remains an elusive goal for public health and environmental agencies. Here, it is shown that a low‐cost nanocomposite sponge prepared by growing selenium (Se) nanomaterials on the surface and throughout the bulk of a polyurethane sponge exhibits a record breaking‐mercury ion (Hg2+) removal rate, regardless of the pH. The exposure of aqueous solutions containing 10 mg L−1–12 ng L−1 Hg2+ to the sponge for a few seconds results in clean water with undetectable mercury levels (detection limit: 0.2 ng L−1). Such performance is far below the acceptable limits in drinking water (2 µg L−1), industrial effluents (0.2 µg L−1), and the most stringent surface water quality standards (1.3 ng L−1). The sponge shows a unique preference for Hg, does not retain water nutrients, and can significantly reduce the concentration of other heavy metal pollutants. Furthermore, the sponge shows no cytotoxic effect on human cells while exhibiting strong antimicrobial properties. The high affinity of Hg for Se results in irreversible sequestration and detoxification of mercury by the sponge, confirming the suitability for landfill disposal.

Chelating agents for the sequestration of mercury(II) and monomethyl mercury(II).

Both mercury(II) and monomethyl mercury(II) poisonings are of great concern for several reasons. As it happens for other metals, chelation therapy is the most indicated treatment for poisoned patients. The efficacy of the therapy and the reduction of side-effects can be sensibly enhanced by an accurate knowledge of all the physiological mechanisms involved in metal uptake, transport within and between various tissues, and (possibly) clearance. All these aspects, however, are strictly dependent on the chemical speciation (i.e., the distribution of the chemical species of a component in a given system) of both the metal and the chelating agent in the systems where they are present. In this light, this review analyzes the state of the art of research performed in this field for mercury(II) and methylmercury(II). After a brief summary of their main sources, the physiological patterns for the treatment of mercury poisoning have also been considered. The binding ability of various chelating agents toward mercury has been then analyzed by modeling the behavior of the main classes of ligands present in biological fluids and/or frequently used in chelation therapy. Their sequestering ability has been successively evaluated by means of a semiempirical parameter already proposed for its objective quantification, and the main characteristics of an efficient chelating agent have been evaluated on this basis.

Modeling the effect of temperature, solar radiation and salinity on Bolboschoenus maritimus sequestration of mercury

Some tidal wetland halophytes are extremely important for pollution control but due to global climate change, wetlands and their ecosystem services may suffer considerable modifications. In this context we modeled the growth and mercury (Hg) sequestration by Bolboschoenus maritimus on the most contaminated area of a temperate shallow coastal lagoon historically subjected to heavy Hg load, under gradients of climate driven variables. For calibration purposes we used field data on temperature, salinity, solar radiation, plant biomass, plant decomposition and mercury concentration in the plants. Ten different methods evaluated model performance. We then simulated B. maritimus mercury sequestration under different environmental scenarios involving increases and decreases in temperature, salinity and cloud cover. The largest effects were related to high salinity scenarios but all variables presented an inverse relation with Hg-sequestration. Our results point to a progressive decrease on Hg-sequestration until the end of the century.

Sequestration of total and methyl mercury in different subcellular pools in marine caged fish

Mercury contamination is an important issue in marine fish, and can cause toxicity to human by fish consumption. Many studies have measured the mercury concentrations in fish and estimated the threshold levels of its risk to human, but the mercury sequestration in different subcellular pools of fish is unclear. In this study, we investigated the concentration and distribution of total mercury (THg) and methylmercury (MeHg) in different subcellular fractions in the farmed red seabream, red drum, and black seabream from Fujian marine fish farms, China. We found that both THg and MeHg were dominantly bound with the cellular debris, followed by metallothionein-like protein > metal-rich granule > heat-denatured protein > organelles pools. In general, Hg bound with the metal-sensitive fraction was small, indicating that Hg may have little toxicity to the fish (muscle). For the first time we showed that MTLP fraction had the highest % of total Hg as MeHg (88–91%) among all the subcellular fractions. Furthermore, the mercury concentration and subcellular distribution in the black seabream were both dependent on the fish size. Subcellular study may shed light on the detoxification of marine fish to Hg exposure and the potential bioavailability to humans due to fish consumption.

Genetic expression of bacterial merC fused with plant SNARE in Saccharomyces cerevisiae increased mercury accumulation

MerC encoded by merC in the Tn 21 mer operon, is a heavy metal transporter that may be a useful molecular tool for the bioremediation of cadmium and mercury. To regulate subcellular localization, the Arabidopsis SNARE proteins SYP111 and AtVAM3 were fused to the C-terminal end of MerC. In Saccharomyces cerevisiae, green fluorescent protein (GFP)-MerC-SYP111 fusion proteins located primarily to the plasma membrane, whereas GFP-MerC-AtVAM3 was detected in the vacuolar membranes. These results suggest that SYP111 and AtVAM3 direct MerC fusion proteins to the plasma and vacuolar membranes, respectively. Yeast cells expressing MerC-SYP111 accumulated significantly more mercury than control cells or cells expressing MerC-AtVAM3. Thus, it is possible that localizing MerC to the plasma membrane of plants may represent a similarly promising strategy for improving phytoaccumulation and sequestration of mercury at polluted sites.

Towards a practical solution for removing inorganic mercury from drinking water using gold nanoparticles

We describe an innovative approach based on alloying of metals to remove metal ions from drinking water. A novel adsorbent, gold nanoparticle supported on alumina, was developed for the removal of inorganic mercury from water. The observed adsorption capacity for mercury is 4.065 gm per gm of gold nanoparticles, which is ∼10 times higher metal adsorption capacity than previously reported adsorbents. Gold nanoparticle has been supported on alumina, at a capacity of 738 mg/kg alumina, for use in practical applications. Batch and column studies were done for adsorption analysis and a practical filter has been developed. The interaction between gold and mercury was studied using UV-vis, TEM, SEM, EDAX and XRD. The chemistry of metal alloying can be utilized for sequestration of mercury from drinking water. Established separation techniques for recovery of metals from the alloy can be utilized, making this a complete solution for drinking water applications.

High‐temperature sequestration of elemental mercury by noncarbon based sorbents

AbstractThis work is concerned with sequestration of elemental Hg at high temperatures (900–1100 °C) on a sorbent that is mineral based, rather than carbon based. This sorbent consists of an intimate mixture of CaO, CaCO3, and Al2O3–2SiO2, and is manufactured in industrially relevant quantities (metric tons) from residues produced in paper recycling processes. In contrast to activated carbon (AC), this noncarbon based sorbent has special advantages in that, it can actually enhance fly ash utilization for cement manufacture, rather than diminish it, as is the case for AC.Disperse phase experiments have been conducted, using an externally heated quartz tube reactor, with sorbent feeding rates ranging from 1 to 6 g/h. Preliminary results indicate that Hg removal efficiency is sensitive to sorbent feed rates and to furnace temperature. The Hg removal percentage increased with both these variables. Two mechanisms come into play: an in‐flight Hg sorption mechanism, and an Hg sorption mechanism related to sorbent deposits on the reactor wall. A maximum total (in‐flight plus deposit‐related) Hg removal efficiency of 83–90% was obtained at temperatures of 900–1100 °C. There was negligible sorption by either mechanism at temperatures below 600 °C. Results for the in‐flight mechanism alone showed a maximum sorption efficiency at ∼900 °C, whereas that on the reactor surface increased monotonically with temperature. This suggests that sorbent deactivation can occur in‐flight at high temperatures, which is in agreement with other fixed bed results obtained in this laboratory. Deactivation was not apparent for the sorbent‐related substance formed on the reactor wall. Raw and spent sorbents were analyzed by X‐ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectrophotometer (SEM‐EDS) to identify the sorbent mineral transitions that seem to activate the process. The in‐flight mechanisms appear to involve (1) activation of the sorbent, caused most probably by an internal solid–solid reaction, followed by (2) Hg sorption, and (3) possible deactivation, if the temperatures are too high for longer period. Reactor surface mechanisms still remain to be elucidated. Copyright © 2009 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Sorption and stability of mercury on activated carbon for emission control

A leading strategy for control of mercury emissions from combustion processes involves removal of elemental mercury from the flue gas by injection of activated carbon sorbent. After particulate capture and disposal in a landfill, it is critical that the captured mercury remains permanently sequestered in the sorbent. The environmental stability of sorbed mercury was determined on two commercial, activated carbons, one impregnated using gaseous sulfur, and on two activated carbons that were impregnated with sulfur by reaction with SO 2. After loading with mercury vapor using a static technique, the stability of the sorbed mercury was characterized by two leaching methods. The standard toxicity characteristic leaching procedure showed leachate concentrations well below the limit of 0.2 mg/L for all activated carbons. The nature of the sorbed mercury was further characterized by a sequential extraction scheme that was specifically optimized to distinguish clearly among the highly stable phases of mercury. This analysis revealed that there are two forms in which mercury is sequestered. In the sorbent that was impregnated by gaseous sulfur at a relatively low temperature, the mercury is present predominantly as HgS. In the other three sorbents, including two impregnated using SO 2, the mercury is predominantly present in the elemental form, physisorbed and chemisorbed to thiophene groups on the carbon surface. Both forms of binding are sufficiently stable to provide permanent sequestration of mercury in activated carbon sorbents after disposal.

High-temperature sorbents for Hg, Cd, Pb, and other trace metals: Mechanisms and applications

This paper is concerned with the sequestration of mercury, cadmium, lead, sodium and potentially other volatile and semi-volatile metals by high-temperature mineral, non-carbon based dispersed sorbents. The focus here is on kaolinite and lime powders (for Pb, Cd, and Na), and on intimate kaolinite/calcite/lime mixtures (for Hg), both of which undergo morphological and chemical changes when exposed to high temperatures. These changes play critical roles in the metal capture mechanisms, initially enhancing metal capture, either through a eutectic melt on the surface, or through some other transformation, but ultimately causing sorbent de-activation through a catastrophic melt that causes pore closure. Results and interpretation from two types of experiments are presented. The first employed a 20 kW downflow combustor, a low-pressure impactor and application of the aerosol fractionation method to quantitatively determine the fraction of metal sequestered by the sorbent at the sampling point. The second employed an externally heated quartz reactor and simulated flue gases containing mercury and injected sorbent. Quantitative, rate models have been extracted from the data to describe the global reactions of dispersed kaolinite with lead, sodium, and cadmium metal vapors. They have also been derived for the global reaction of cadmium with dispersed hydrated lime, which was ineffective for Na and Pb but very effective for Cd. Qualitative results showing the effective scavenging of Pb and Cd by the intimate kaolinite/calcite/lime mixture are also presented. The intimate kaolinite/calcite/lime mixture was also shown to capture metallic mercury through two mechanisms, namely, an in-flight mechanism and one involving interactions between Hg, the sorbent and the quartz reactor walls. The in-flight mechanism had similarities to those observed previously between kaolinite, lead, cadmium and sodium, in that mineral transformations played a key role in both sorbent activation and sorbent de-activation. At a constant residence time, the in-flight mechanism exhibited a maximum effectiveness at 900 °C, followed by apparent de-activation. Spent in-flight sorbent showed the presence of calcium silicates and calcium aluminosilicates. The wall deposit mechanism increased in efficacy with temperature and did not show a maximum, and showed the presence of substantial amounts of captured mercury. Adding to the complexity of this process is that Hg capture by this mixture required the presence of O 2 in the flue gas, albeit at low levels of 4000 ppm.