Coal combustion by-product quality at two stoker boilers: Coal source vs. fly ash collection system design

Fly ashes from two stoker boilers burning Pennsylvanian Eastern Kentucky high volatile A bituminous coal blends were examined for their petrology and chemistry. The source coals have similar trace element contents. One of the ash collection systems was retrofitted with a baghouse (fabric filter) system, collecting a finer fly ash at a cooler flue gas temperature than the plant that has not been reconfigured. The baghouse ash has a markedly higher trace element content than the coarser fly ash from the other plant. The enhanced trace element content is most notable in the As concentration, reaching nearly 9000 ppm (ash basis) for one of the collection units. Differences in the ash chemistry are not due to any substantial differences in the coal source, even though the coal sources were from different counties and from different coal beds, but rather to the improved pollution control system in the steam plant with the higher trace element contents.     

The formation of sinkholes in karst mining areas in China and some methods of prevention

 Mining of coal, lead and zinc, gold, and iron ore deposits in karst areas has been closely associated with sinkholes in China. Surface collapse causes an increase in mine water drainage and the possibility of major water inflow from karst aquifers, which threatens the environment in mining areas and endangers mine safety. The origin of such sinkholes is analyzed quantitatively in this paper and a combination of factors including soil weight, buoyancy, suffosion process and vacuum suction can contribute to surface subsidence. The key measures to prevent sinkholes in mining areas are to control the amount of mine drainage, reduce water-level fluctuation, seal off karst conduits and subsurface cavities in the overlying soil, prevent water inflow, and to increase gas pressure in the karst conduits. Received: 2 May 1996 · Accepted: 29 July 1996     

Mercury-tainted overbank sediment from past gold mining in north Georgia, USA

 Gold was discovered in 1829 and mined until about 1940 in north Georgia, particularly within an area known as the Dahlonega mining district. The mining operations there, which involved mercury amalgamation in stamp mills and sluices, delivered significant quantities of mercury waste to streams. This paper focuses on the downstream dispersal and storage of mercury in streambank sediments of two watersheds near Dahlonega, Georgia. Mercury concentrations for individual samples of historical sediment range from 0.02 to 12.00 ppm, with average values in streambanks near the core of the mining district ranging from 0.2 to 0.6 ppm. Mercury levels rapidly decrease in the downstream direction to concentrations that are slightly above a background level of 0.04±0.02 ppm. Mercury concentrations also appear to decrease with increasing distance from streambanks. Similar levels of mercury contamination from former gold mines probably exist in many other parts of the gold-bearing rocks of the Piedmont of the eastern United States. The bioavailability and environmental hazard posed by the contaminated sediment is not certain. Received: 8 January 1996 · Accepted: 29 May 1996     

湘西汞矿床的地质特征与成因

湘西汞矿床是湘黔汞矿带的重要组成部分.湘西汞矿受层位和构造双重控制,与岩浆活动没有直接联系,具有层带式整合矿体,矿物成分简单,汞锌矿化分带及后生成矿等地质特征.矿石硫来源于古海水硫酸盐的沉积硫;而汞的来源.则以上地幔去气作用产生的汞为主,寒武系等富汞建造的汞次之.燕山期地台活化时,以硫络合物或硫氢络合物的形式,在碱性溶液中沿深大断裂向上运转,当其与富含膏盐的客矿层相遇时,便与还原硫结合沉淀成矿.形成湘西层控后生汞矿床.     

Mechanism of Hg(II) immobilization in sediments by sulfate-cement amendment

Reactive amendments such as Portland and super-sulfate cements offer a promising technology for immobilizing metalloid contaminants such as mercury (Hg) in soils and sediments through sequestration in less bioavailable solid forms. Tidal marsh sediments were reacted with dissolved Hg(II) in synthetic seawater and fresh water solutions, treated with Portland cement and FeSO₄ amendment, and aged for up to 90 days. Reacted solids were analyzed with bulk sequential extraction methods and characterized by powder X-ray diffraction (XRD), electron microscopy, and synchrotron X-ray absorption spectroscopy at the Hg L_III- and S K-edge. In amended sediments, XRD, SEM and sulfur K-edge XANES indicated formation of gypsum in seawater experiments or ettringite-type (Ca₆Al₂(SO₄)₃(OH)₁₂^.26H₂O) phases in fresh water experiments, depending on the final solution pH (seawater ∼8.5; freshwater ∼10.5). Analysis of Hg EXAFS spectra showed Cl and Hg ligands in the first- and second-coordination shells at distances characteristic of a polynuclear chloromercury(II) salt, perhaps as a nanoparticulate phase, in both seawater and fresh water experiments. In addition to the chloromercury species, a smaller fraction (∼20–25%) of Hg was bonded to O atoms in fresh water sample spectra, suggesting the presence of a minor sorbed Hg fraction. In the absence of amendment treatment, Hg sorption and resistance to extraction can be accounted for by relatively strong binding by reduced S species present in the marsh sediment detected by S XANES. Thermodynamic calculations predict stable aqueous Hg–Cl species at seawater final pH, but higher final pH in fresh water favors aqueous Hg-hydroxide species. The difference in Hg coordination between aqueous and solid phases suggests that the initial Hg–Cl coordination was stabilized in the cement hydration products and did not re-equilibrate with the bulk solution with aging. Collectively, results suggest physical encapsulation of Hg as a polynuclear chloromercury(II) salt as the primary immobilization mechanism.     

Historical variations in the stable isotope composition of mercury in a sediment core from a riverine lake: Effects of dams,pulp and paper mill wastes,and mercury from a chlor-alkali plant

The Wabigoon River (Ontario, Canada) was affected by dams starting in 1898 and was polluted with pulp and paper mill wastes starting in 1913 and mercury from a chlor-alkali plant from 1962 to 1975. A dated sediment core from a riverine lake was analysed to investigate resultant changes in the biogeochemistry of mercury as revealed by variations in mercury isotope ratios and sediment chemistry. A total mercury maximum formed by the mercury pollution coincided with minimums in the δ-values of the ¹⁹⁸Hg/²⁰²Hg, ¹⁹⁹Hg/²⁰²Hg, ²⁰⁰Hg/²⁰²Hg, and ²⁰¹Hg/²⁰²Hg ratios, and the δ-values decreased in the order δ²⁰¹Hg > δ²⁰⁰Hg > δ¹⁹⁹Hg > δ¹⁹⁸Hg. Thus, mass-dependent fractionation caused depletion in lighter isotopes, implying evaporation of Hg(0) and pollution of the atmosphere as well as the river-lake system. Concurrently, mass-independent fractionation caused ¹⁹⁹Hg enrichment, possibly reflecting an independently documented upsurge in methylmercury production, and ²⁰¹Hg depletion, suggesting removal of methylmercury with anomalously high ²⁰¹Hg/¹⁹⁹Hg ratios by aquatic organisms and accumulation of ²⁰¹Hg-depleted inorganic Hg(II) in sediments. The δ²⁰¹Hg/δ¹⁹⁹Hg ratio rose abruptly when mercury pollution began, reflecting the resultant increase in methylmercury production, and remained high but gradually declined as the pollution abated, paralleling trends shown by methylmercury in aquatic organisms. The δ²⁰¹Hg/δ¹⁹⁹Hg ratio of pre-1962 background mercury increased ca. 1898 and ca. 1913–1929, suggesting accelerated methylmercury production due to stimulation of microbial activities by the damming of the river and the input of pulp and paper mill wastes, respectively. Other variations were linked to economic and technological factors that affected pulp and paper manufacture.     

Hg,Cu,Cd,Zn 对真鲷仔鱼的急性毒性研究

本文采用静水生物试验法测定了Hg,Cu,Cd,Zn对真鲷仔鱼(2周龄)的急性毒性。结果表明:Hg,Cu,Cd,Zn对真鲷仔鱼24h的LC_(50)分别为0.025,0.31,5.00和3.70 mg/L,48h的LC_(50)分别为0.016,0.24,1.72和2.22mg/L,72h的LC_(50)分别为0.006,0.11,O.56和0.92mg/L,96h的LC_(50)分别为O.004,0.07,0.27和0.44 mg/L。Hg,Cu对真鲷仔鱼的影响极为显著,Zn,Cd的影响虽然很大,但比Hg,Cu低得多。Cd的毒性比Zn强,但毒理作用较为缓慢。4种重金属的毒性顺序为Hg>Cu>Cd>Zn。     

Reprint of “Seasonal and daily variation of mercury evasion at coastal and off shore sites from the Mediterranean Sea”

Dissolved gaseous mercury (DGM) was measured continuously using two newly developed techniques and a manual technique. The continuous techniques were based on the equilibrium between the aqueous and gaseous phase (DGM = Hg_extr / H', Hg_extr is the measured mercury concentration in the gas phase, H' is the Henry's Law coefficient at the desired temperature). In order to calculate the annual mercury evasion from the Mediterranean Sea, diurnal and seasonal measurements of DGM, total gaseous mercury in air (TGM), water temperature and wind speed were performed. During August 2003, March–April 2004 and October–November 2004 measurements of these parameters were conducted on board the RV Urania. The continuous measurements of DGM showed a diurnal variation in concentration, at both coastal and off shore sites, with higher concentrations during daytime than nighttime. The concentration difference could be as large as 130 fM between day and night. The degree of saturation was calculated directly from the measurements, S = Hg_extr / TGM and was found to vary between the different seasons. The highest average degree of saturation (850%) and the largest variation in saturation (600–1150%) was observed during the summer. The spring showed the lowest variation (260–360%) and the lowest average degree of saturation (320%). The autumn also showed a large variation in saturation (500–1070%) but a lower average (740%) compared to the summer cruise. This might be explained by the temperature difference between the different seasons, since that parameter varied the most. The flux from the sea surface was calculated using the gas exchange model developed by Nightingale et al. [Nightingale, P.D., Malin, G., Law, C.S., Watson, A.J., Liss, P.S., Liddicoat, M.I., Boutin, J., Upstill-Goddard, R. C., 2000. In situ evaluation of air–sea gas exchange parameterization using novel conservative and volatile tracers. Global Biogeochemical Cycles, 14(1):373–387]. The evasion varied between the different seasons with the highest evasion during the autumn, 24.6 pmol m^− 2 h^− 1. The summer value was estimated to 22.3 pmol m^− 2 h^− 1 and the spring to 7.6 pmol m^− 2 h^− 1. Using this data the yearly evasion from the Mediterranean Sea surface was estimated to 77 tons.     

Temporal trends of mercury in marine biota of west and northwest Greenland

Temporal trends in mercury concentrations ([Hg]) during the last two to three decades were determined in liver of shorthorn sculpin, ringed seal and Atlantic walrus from northwest Greenland (NWG, 77 degrees N) and in liver of shorthorn sculpin and ringed seal from central west Greenland (CWG, 69 degrees N) during the last decade. Stable-nitrogen (delta(15)N) and carbon (delta(13)C) isotope values were determined in muscle of ringed seals to provide insight into potential trophic level changes through time. Log-linear regressions on annual median [Hg] did not reveal any temporal trend in shorthorn sculpin from CWG and NWG and walrus from NWG. In ringed seals from NWG, an increase in [Hg] of 7.8% per year was observed. When based on delta(15)N-adjusted [Hg] this rate increased to 8.5% but was still non-significant. In ringed seal from CWG no trend was found in [Hg] during the period 1994-2004. However, during the last part of the period (1999-2004) the [Hg] increased significantly. Including tissue delta(15)N values as a covariate had a marked effect on these results. The annual changes in delta(15)N-adjusted [Hg] was estimated to -5.0% for the whole period and 2.2% during the last 5 years compared to -1.3% and 12.4%, respectively, for the non-adjusted [Hg].     

Transport and dispersion of particulate Hg associated with a river plume in coastal Northern Adriatic environments

The role of suspended particulate matter (SPM) as an important carrier of mercury (Hg) dispersed into the Gulf of Trieste and in the adjacent Grado lagoon (Northern Adriatic Sea) was studied during a high Isonzo River inflow and the resulting river plume formation. Despite the fact that extreme flood events are rare during the year, they account for most of the PHg influx (37-112 ngL(-1)) into the Gulf of Trieste. When the river plume is diverted to the SW under the influence of an E-NE wind, the tidal flux acts as a "transport belt" carrying the PHg, mostly inorganic, into the Grado lagoon. A preliminary estimation indicates that the amount of PHg entrapped in the lagoon basin following a tidal semi-cycle accounts for 1.4 kg/12h, which corresponds to about 49% of the total Hg carried by the tidal flow. These findings should be considered in future remediation strategies in the lagoon environment.