Mobility of some potentially toxic trace elements in the coal of Guizhou, China

 The mobility of 10 potentially toxic trace elements (PTTE), As, Cd, Cr, Cu, Hg, Ni, Pb, Se, Tl, and Zn from 32 coals of the Longtan Group formed in Permian Period in Guizhou Province, China was investigated using sequential extraction procedures. The results demonstrate that PTTEs such as Hg, As, Se, Cd, Cu, and Pb have the highest mobility at surface conditions, and the average extractable fractions of them are 86%, 95%, 79%, 76%, 69%, and 69% of the total amount in coal, respectively. The elements in coal with the lowest leachability include Tl, Cr, and Ni, and the average extractable fractions of them are 30%, 20%, and 29% of the total amount in coal respectively. Zinc has an intermediate behavior, and the average leachable fraction of it accounts for 46% of the total amount in coal. The results demonstrate that mobility of PTTE in coal depends on the speciation of these elements. The elements associated with sulfates, carbonates, sulfides and some organic matter in coal show the highest extraction rates during the weathering process, while elements with silicate affinities are inert at surface conditions. Received: 29 December 1998 · Accepted: 10 November 1998     

Speciation of dissolved selenium in the Kaoping and Erhjen rivers and estuaries,southwestern Taiwan

Analytical methods of dissolved Se species in river water and seawater were established and applied to study dissolved Se speciation in the Kaoping and Erhjen rivers and estuaries, southwestern Taiwan. The Kaoping and Erhjen rivers and estuaries were respectively in relatively oxygenated and oxygen-deficient conditions as revealed from the distributions of dissolved oxygen, DOC, nutrients, and dissolved Mn. Concentrations of dissolved total Se increased downstream in the riverine sections, ranging from 0.6 nM to 1.2 nM for the Kaoping River and from 0.8 nM to 1.05 nM for the Erhjen River. The dissolved total Se was only slightly higher in the Erhjen middle estuary than in the Kaoping middle estuary in spite of heavier pollution in the former. The dissolved total Se behaved rather conservatively in the Kaoping estuary but nonconservatively in the Erhjen estuary resulting from anthropogenic inputs, and in this respect showed similarities with the behavior of redox-sensitive Mn. The predominant species of selenium were Se(VI) and organic Se in the Kaoping River and Se(VI) in the Kaoping estuary. The elevated concentration of Se(VI) in the Kaoping estuary may stem from the degradation of organic Se and oxidation of Se(IV). On the other hand, Se(IV) and organic Se were equally dominant in the Erhjen River, and Se(IV) was predominant through most of the Erhjen estuary. The elevated distribution of Se(IV) in the Erhjen middle estuary may result mostly from partial decomposition of organic Se, but further oxidation of Se(IV) was inhibited in reducing waters. However, Se(VI) became dominant at Erhjen outer estuary where water was oxygenated by the replacement of intruded coastal seawater. Apparently, the speciation of dissolved Se was mainly controlled by the biological and redox processes in the Kaoping and Erhjen rivers and estuaries.     

Trace elements and their behaviour during the combustion of marine oil shale from Changliang Mountain, northern Tibet, China

The Shengli River–Changshe Mountain oil shale zone represents a potentially large marine oil shale resource in China. With the aim of better understanding the geochemistry of trace elements in marine oil shale and its combustion residues, 40 raw samples, 27 oil shale combustion residues and 29 selected minerals from Changliang Mountain oil shale are studied for geochemical analyses. The contents of Se, Cd, Mo, As, Cs, Pb, Sr and U in the oil shale samples are enriched from 1.47 to 33.91 times as compared with the Clarke values, whereas the concentrations of other elements are slightly higher/lower than the respective worldwide means. The most enriched elements in oil shale combustion residues are Se, Cd, Mo, As and U with enrichment values from 4.78 to 50.92. Trace elements with high volatile behaviour such as As, Co, Ni, Sc, Sn and V occur predominantly in organic matter and/or sulphides. Other non-volatile or slightly volatile trace elements (e.g., Be, Bi, Cs, Cu, Ga, Hf, Li, Nb, Rb, Ta, Th, W, Zr and REEs) may occur mainly in original and relatively refractory minerals in raw oil shale. The potentially hazardous trace elements in Changliang Mountain oil shale include As, Cd, Mo and Se. Arsenic and Se are controlled mainly by Fe-bearing minerals (probably pyrite) in Changliang Mountain oil shale. Cadmium is present mainly in dolomite, while Mo occurs mainly in organic matter.     

Accumulation and speciation of selenium in evaporation basins in California,USA

The accumulation of selenium in evaporation basins (or ponds) in the San Joaquin Valley, California is of a great concern due to its potential hazards to environments. In this study, the accumulation, speciation and concentrations of Se were examined in waters as well as sediments in a system of the evaporation ponds. A significant decrease in the total dissolved Se concentration in Cell 1 in which drainage water with higher Se concentration was pumped from Inlet Channels indicated that the immobilization of Se was active in the Cell 1 and resulted in the higher Se concentration in sediments compared to the terminal cell such as Cell 9. The percentage of reduced Se species such as selenite [Se(IV)] and org-Se of total Se in drainage waters was also found increased in Cell 1 compared to Inlet Channels. The total dissolved Se concentrations in water along flow paths from Cell 1 were relatively constant except for terminal cells such as Cells 9 and 10, which showed higher total dissolved Se concentrations due to evapoconcentration. The percentage of reduced Se forms of total Se was inversely proportional to the percentage of Se(VI) depending on the redox condition of evaporation ponds along the flow paths. Sequential extractions of Se species in sediments indicated that organic associated Se and elemental Se were prevalent forms in sediments in the ponds system. The higher concentrations of elemental Se and organic associated Se in sediments in Cell 1 indicated that the immobilization of Se was active in the sediments compared to Cell 9, while the percentage of both fractions of total Se in sediments in Cells 1 and 9 was relatively constant. The organic materials from algae might provide carbon sources for Se reduction and Se sink in sediments in its elemental and organic associated forms.     

Characterization of organic matter in surface sediments of the Mackenzie River Basin, Canada

The particulate organic matter in < 63 µm surface sediments from the Mackenzie River and its main tributaries was studied using Rock-Eval pyrolysis and organic petrology. The organic matter in the sediments is dominated by refractory residual organic carbon (RC) of mainly terrigenous nature, as indicated by abundant inertinite, vitrinite, and type III kerogen. Sediments from the tributaries contained significantly more algal-derived organic matter than from the main channel of the river, highlighting the importance of low-energy system dynamics in the tributaries, which allows modest algal production, more accumulation, and better preservation of autochthonous organic matter. This is particularly true for tributaries fed by lacustrine systems, which showed the highest S1 and S2 fractions, and consequently higher total particulate organic carbon (POC) in the basin. Organic petrology of the sediment samples confirms abundant liptinitic materials (i.e., fat-rich structured algae, spores and pollen, cuticles, and resins). Forest fire and coal deposits are also confirmed to contribute to the basin. Assuming that suspended and fine surfacial sediments have a similar OC composition, the Mackenzie River is estimated to deliver a total POC flux of 1.1 Mt C/yr to its delta, of which 85% is residual carbon with liptinitic OC (S1 + S2) and S3 accounting for another 9% and 6%, respectively.     

Removal of dissolved selenium by siderite,pyrite, and sphalerite: Implications to selenium sequestration in water-saturated,anoxic coal waste rock

The mechanisms of abiotic sequestration of Se(VI) and Se(IV) on a sample of coal waste rock collected from the Elk Valley, Canada and on three pure mineral species (i.e., siderite, pyrite, and sphalerite) present in coal waste rock were assessed using sterile batch testing under water-saturated, anoxic conditions. Only siderite removed measurable Se(VI) from the test solutions with ~90% removal after 100 d attributed to initial adsorption to the siderite surface as Se(VI) and subsequent reduction to Se(IV) and Se(0). In contrast to Se(VI), all samples removed Se(IV) from the aqueous solutions. The rate of Se(IV) removal was pyrite > siderite > waste rock > sphalerite. The waste rock sample removed Se(IV) from solution in two stages: up to ~40% of the aqueous Se(IV) was rapidly removed (by day 1) followed by slower removal of Se(IV) with up to ~97% removal after 99 d. Se(IV) removal is attributed to the adsorption of Se(IV) and subsequent reduction to Se(0) onto the siderite and pyrite phases of the waste rock. The initial (1 d) removal of Se(IV) by waste rock was characterized using a distribution coefficient (K_d) of 15.5 L/kg. Longer-term Se(IV) removal was fitted with zero and first order removal rates. The removal of Se(IV) by sphalerite was minor and deemed to have a minimal effect on Se sequestration in the waste rock. Desorption tests on waste rock showed that the fraction of sequestered Se susceptible to desorption decreased with time as adsorbed Se(IV) was reduced to insoluble Se(0). These findings show that abiotic Se sequestration can occur in saturated, anoxic zones in coal waste rock dumps.     

贵州六枝、水城煤田晚二叠世煤的微量元素特征

通过对六枝和水城煤田 10个煤矿主要可采煤层的 45个煤样品的常量和微量元素系统研究 ,概括了这两个煤田煤中常量和微量元素的丰度和分布特征 ;阐述了煤中微量元素的亲合性。这两个煤田煤中的全硫含量在受海水影响的煤层中较高 (最高达 7.5 % ) ,而在非海水影响的煤层中较低 ( 0 .3% )。六枝煤田的全硫含量明显高于水城煤田。Ca-Mn-Ge的平均含量在六枝煤田较低 ,而在水城煤田相对较高。在这两个煤田和不同的煤层之间 ,煤中微量元素含量的变化较小。与世界烟煤中一般含量范围相比 ,这两个煤田的特征是 Mn,V,Cu,L i,Zr,Nb,Ta,Hf,T1,Th和 U的含量相对高。     

Modes of Occurrence and Cleaning Potential of Trace Elements in Coals from the Northern Ordos Basin and Shanxi Province, China

Based on the analyses of 43 elements in 16 samples of the raw coal and feed coal collected from the northern Ordos basin and Shanxi Province, the modes of occurrence of these elements were studied using the method of cluster analysis and factor analysis, and the cleaning potential of the hazardous elements relatively enriched in the coals was discussed by analyzing six samples of the cleaned coal from the coal-washing plants and coal cleaning simulation experiments. The results shows that the elements Br and Ba show a strong affinity to the organic matter, Cs, Cd, Pb, Zn and Hg partly to the organic matter, and the other trace elements are mainly associated with the mineral matter. Cs, Mo, P, Pb, Zn and S have positive correlations with the two principal factors, reflecting the complexity of their modes of occurrence. Some elements that were thought to show a faint relationship (Be with S and Sb with carbonates) in other rocks are found to have a strong interrelation in the coals. Clay minerals (mainly k     

Urbanization impact on metals mobility in riverine suspended sediment: Role of metal oxides

Spatial and temporal fractionation of trace metals and major elements in suspended particulate matter in the Seine River was investigated to study the impact of the increasing urbanization in the Greater Paris Region. Suspended sediments in the Seine River were collected between December 2008 to August 2009 upstream and downstream of Paris. They were subjected to total digestion and sequential extraction procedure certified by the Bureau Communautaire de Référence and trace metals along with major elements were analyzed with inductively coupled plasma mass spectroscopy. Metal enrichment factors increased up to eight folds after the Seine River downstream of the Greater Paris Region showing a significant contribution of urbanization. Enrichment of copper, lead and zinc downstream of Paris are followed by the increase of their reducible fraction of at least 10% implicating an increase in metals associated with iron oxides. The exchangeable fraction, which includes the carbonate-associated metals, is only significant for cadmium, nickel and zinc (more than 2 %) while the oxidisable fraction accounts for less than 20 % for the anthropogenic metals downstream except for copper. The metals can be divided to (a) “reducible” group including cadmium, lead, and zinc, associated with more than 60 % of the total Bureau Communautaire de Référence extractable metals to the reducible fraction containing mostly iron oxide phases for the downstream sites. (b) A “distributed” group including chromium, copper, and nickel that are associated to at least 3 different phase-groups: (1) oxides, (2) organic matter and sulphides and (3) mineral phases.     

Concentration and distribution of trace elements in some coals from Northern China

The concentration, distribution and modes of occurrence of trace elements in thirty coals, four floors and two roofs from Northern China were studied. The samples were collected from the major coalfields of Shanxi Province, Shaanxi Province, Inner Mongolian Autonomous Region, and Ningxia Hui Autonomous Region. The concentrations of seventeen potential hazardous trace elements, including Hg, As, Se, Pb, Cd, Br, Ni, Cr, Co, Mo, Mn, Be, Sb, Th, V, U, Zn, and five major elements P, Na, Fe, Al, and Ca in coals were determined.Compared with average concentration of trace elements in Chinese coal, the coals from Northern China contain a higher concentration of Hg, Se, Cd, Mn, and Zn. They may be harmful to the environment in the process of combustion and utilization. Vertical variations of trace elements in three coal seams indicated the distributions of most elements in coal seam are heterogeneous. Based on statistical analyses, trace elements including Mo, Cr, Se, Th, Pb, Sb, V, Be and major elements including Al, P shows an affinity to ash content. In contrast, Br is generally associated with organic matter. Elements As, Ni, Be, Mo, and Fe appear to be associated with pyrite. The concentrations of trace elements weakly correlate either to coal rank or to maceral compositions.     

Mineral and inorganic chemical composition of the Pernik coal, Bulgaria

The mineral and inorganic chemical composition of five types of samples from the Pernik subbituminous coals and their products generated from the Pernik preparation plant were studied. They include feed coal, low-grade coal, high-grade coal, coal slime, and host rock. The mineral matter of the coals contains 44 species that belong mainly to silicates, carbonates, sulphates, sulphides, and oxides/hydroxides, and to a lesser extent, chlorides, biogenic minerals, and organic minerals. The detrital minerals are quartz, kaolinite, micas, feldspars, magnetite, cristobalite, spessartine, and amphibole. The authigenic minerals include various sulphides, silicates, oxihydroxides, sulphates, and carbonates. Several stages and substages of formation were identified during the syngenetic and epigenetic mineral precipitations of these coals. The authigenic minerals show the greatest diversity of mineral species as the epigenetic mineralization (mostly sulphides, carbonates, and sulphates) dominates qualitatively and quantitatively. The epigenetic mineralization was a result of complex processes occurring mostly during the late development of the Pernik basin. These processes indicate intensive tectonic, hydrothermal and volcanic activities accompanied by a change from fresh to marine sedimentation environment. Thermally altered organic matter due to some of the above processes was also identified in the basin. Most of the trace elements in the Pernik coals (Mo, Be, S, Zr, Y, Cl, Ba, Sc, Ga, Ag, V, P, Br, Ni, Co, Pb, Ca, and Ti) show an affinity to OM and phases intimately associated with OM. Some of the trace elements (Sr, Ti, Mn, Ba, Pb, Cu, Zn, Co, Cr, Ni, As, Ag, Yb, Sn, Ga, Ge, etc.) are impurities in authigenic and accessory minerals, while other trace elements (La, Ba, Cu, Ce, Sb, Bi, Zn, Pb, Cd, Nd, etc.) occur as discrete phases. Elements such as Sc, Be, Y, Ba, V, Zr, S, Mo, Ti, and Ga exceed Clarke concentrations in all of the coal types studied. It was also found that a number of elements in the Pernik coals (F, V, As, Pb, Mo, Li, Sr, Ti, Ga, Ni, Ge, Cr, Mn, etc.) reveal mobility in water and could have some environmental concerns.     

Coalbed methane producibility from the Mannville coals in Alberta, Canada: A comparison of two areas

Selenium concentrations were measured in five rock cores from a mine in Boone County, West Virginia to determine their relationship to sulfur, rock type and stratigraphic location. The samples spanned the Winifrede and Coalburg coal beds of the Middle Pennsylvania upper Kanawha Formation and included coals and clastic lithologies. The coals generally contained the highest concentrations of Se and the sandstones the lowest. No correlation was observed between total Se and sulfur concentrations for either the entire data set or for individual lithologies. Better correlations were identified for log concentrations between total Se and total organic carbon. Principal component analysis identified a strong sulfur–acid component, interpreted to be due to sulfide mineral presence, which correlates well with S but not with Se. Coal sample chemistry is more likely to load onto this component while clastic rock chemistry is more likely to load onto the second, non-sulfur component. Se concentrations load onto both components indicating they are not controlled by a single overriding chemistry. Selective extractions indicate that Se is distributed between both sulfide and organically-bound fractions, as defined by the test. Overall, the lack of correlation between Se and S, the distribution of Se among extracted fractions, and the loading of Se onto both sulfur and non-sulfur components support that the Se in these rock layers is distributed in more than one chemically-bound form. Non-coal rock units with the highest concentrations of Se were found adjacent to coal beds, suggesting that redistribution of Se may have occurred post-deposition. The acidic domed swamps that formed these coals were low in sulfur and a reasonable chemical setting to accumulate Se if it were introduced. The preservation of Se in the domed swamp peat coupled with post-depositional redistribution may partly explain the data presented.     

Geochemistry of coals from the Elk Valley coalfield, British Columbia, Canada

The Elk Valley coalfield of British Columbia is one of the major coal producing areas in Canada. The coals are of Cretaceous and Jurassic–Cretaceous age and range in rank from high-volatile to low-volatile bituminous (%Ro_max: 0.8–1.6). Coal seams from outcrops and active mines in this coalfield were analysed for rank and maceral composition using reflected light microscopy, for geochemistry using AAS, INAA, and ICPES, and also by proximate and ultimate analyses. The Elk Valley coal seams contain low average concentrations of hazardous elements such as As, Mo, Pb, and Se. However, there are seams that contain relatively high concentrations of some of these elements, such as 8 mg/kg and 108 mg/kg of arsenic. When the geochemistry of coal seams is compared within the different parts of the coalfield, the elemental composition amongst the seams from various sections located in the central area of the coalfield is similar. Coal seams in the northern area of the coalfield have different geochemistry than coal seams in other areas of the coalfield; seams in the northern area have much higher As, Br, Cr, Cu, Fe, K, and Na content, but contain less Ca.     

Mineral matter in coals: cleat minerals and their origin in some coals from the english midlands

In four coal seam profiles from the Cannock Coalfield, West Midlands, the cleat (joint) frequency is a function of lithotype (greatest in vitarin) and is inversely related to bed thickness. The cleat minerals were studied: (1) under the microscope (optical and electron); (2) by X-ray diffraction; and (3) chemically. The minerals present are pyrite, marcasite, sphalerite, galena (sulphides), quartz, kaolinite (silicates), ankerite, calcite (carbonates) and apatite. This sequence has features in common with diagenetic sequences recorded in other rock types and it is concluded that the cleat minerals in coal form in response to pore fluid evolution and movement during burial diagenesis. The elements are thought to originate from both the coal and the associated sediments, mainly mudrocks. Similarities in diagenetic sequences are in part a reflection of the importance of organic maturation reactions in all the rock types in the sequence, whereas differences are attributed to the dominance of these reactions in the coal itself.     

Selenium source identification and biogeochemical processes controlling selenium in surface water and biota,Kendrick Reclamation Project,Wyoming, U.S.A.

The major tributaries draining the Kendrick Reclamation Project (KRP) account for an average of 52% of the total Se load measured in the North Platte River downstream from Casper, Wyoming. The Casper Creek drainage basin contributed the largest Se load of the five tributary sites to the North Platte River. The 4-d average Se concentration in water samples from one site in the part of the North Platte River that receives irrigation return flows exceeded the 5 μg/l U.S. Environmental Protection Agency's aquatic life criterion five time during a 50-d monitoring period in 1989. In agreement with the water-quality data, muscle and liver tissue rom rainbow trout collected from the same part of the North Platte River had Se concentrations exceeding levels known to cause reproductive failure and chronic Se poisoning. On the basis of Se: Cl, ¹⁸O/¹⁶O and D/H ratios in water from Goose and Rasmus Lee Lakes (closed-basin systems), the large Se concentrations in those lakes were derived by natural evaporation of irrigation water without leaching of soluble forms of Se from soil or rocks. Water samples from Thirtythree Mile Reservoir and Illco Pond (flow-through systems) showed considerable enrichment in Se over evaporative concentration, presumably due to leaching and desorption of Se from soil and rock. The Se: Cl ratios of irrigation drain water collected from the KRP indicate that leaching and desorption of soluble forms of Se from soils and rocks are the dominant processes in drain water. Results of a Wilcoxon matched-pairs test for 43 paired drain-water samples collected during June and August 1988, indicated there is a statistically larger concentration of Se (0.01 significance level) during the June sampling period. The larger concentrations of Se and other chemical constitutents during the early part of the irrigation season probably were due to dissolution of seleniferous salts that have accumulated in soils within the KRP since the last irrigation season. The large Se concentrations in water samples from wetland sites in the KRP were reflected in the aquatic-bird food chain. Most waterfowl and shorebirds nesting at the KRP showed Se concentrations in livers and eggs greater than levels suspected of causing adverse reproductive effects.     

Determination of elemental affinities by density fractionation of bulk coal samples from the Chongqing coal district, Southwestern China

The occurrence and distribution of major and trace elements have been investigated in two coal-bearing units in the Chonqing mining district (South China): the Late Permian and Late Triassic coals.The Late Permian coals have higher S contents than the Late Triassic coals due to the fixation of pyrite in marine-influenced coal-forming environments. The occurrence of pyrite accounts for the association of a large number of elements (Fe, S, As, Cd, Co, Cu, Mn, Mo, Ni, Pb, Sb, Se, and Zn) with sulphides, as deduced from the analysis of the density fractions. The marine influence is probably also responsible for the organic association of B. The REEs, Zr, Nb, and Hf, are enriched by a factor of 2–3 with respect to the highest levels fixed for the usual worldwide concentration ranges in coal for these elements. The content of these elements in the Late Permian coal is higher by a factor of 5–10 with respect to the Late Triassic coal. Furthermore, other elements, such as Cu, P, Th, U, V, and Y, are relatively enriched with respect to the common range values, with maximum values higher than the usual range or close to the maximum levels in coal. The content of these elements in the Late Permian coal is higher than the Late Triassic coal. These geochemical enrichments are the consequence of the occurrence, in relatively high levels, of phosphate minerals, such as apatite, xenotime, and monazite, as deduced from the study of the density fractions obtained from the bulk coal.The Late Triassic coal has a low sulphur content with a major organic affinity. The trace element contents are low when compared with worldwide ranges for coal. In this coal, the trace element distribution is governed by clay minerals, carbonate minerals, and to a lesser extent, by organic matter and sulphide minerals.Major differences found between late Permian and Triassic coals are probably related to the source rocks, given that the main source rock of the late Permian epicontinental marine basin is the Emeishan basalt formation, characterised by a high phosphate content.     

Modes of Occurrence and Geological Origin of Beryllium in Coals from the Pu''''an Coalfield, Guizhou, Southwest China

The concentration, modes of occurrence and geological origin of beryllium in five workable coal beds from the Pu'an Coalfield of Guizhou were studied using the inductively coupled-plasma mass spectrometry (ICP-MS), floating and sinking experiments (FSE) and sequential chemical extraction procedures (SCEP). The results show that the average concentration of beryllium in coals from the Pu'an Coalfield is 1.54μg/g, much lower than that in most Chinese and worldwide coals. Beryllium in the Pu'an coals was not significantly enriched. However, it should be noted that the No. 8 coal bed from the study area has a high concentration of beryllium, 6.89μg/g, three times higher than the background value of beryllium in coal. Beryllium in coal mainly occurs as organic association and has predominantly originated from coal-forming plants when its concentration is relatively low. The concentration of beryllium occurring as organic association is close to that distributed in inorganic matter when beryllium concentration of coal is similar to its background value, and in addition to coal-forming plants, beryllium is mainly derived from detrital materials of terrigenous origin. When beryllium is anomalously enriched in coal, it mainly occurs as organic association and is derived from volcanic tonsteins leached for a long geological time and then adsorbed by organic matter in peat mire.     

恩施渔塘坝富硒碳质岩石中硒的形态分析

湖北恩施渔塘坝是中国人群硒中毒爆发性流行的地区,也是恩施较为典型的高硒地区之一。其北部出露的富硒碳质岩石,通常认为是渔塘坝硒的主要来源。采用7步连续化学浸提技术,将富硒碳质岩石中硒分为水溶态、可交换态、有机态、元素态、酸性提取态、硫化物／硒化物态和残渣态硒,使用氢化物-原子荧光法测定了岩石总硒和硒形态。结果表明,碳质页岩和碳质硅质岩中硒主要以有机态、硫化物／硒化物态和可交换态硒为主,碳质泥岩中硒以有机态、元素态和硫化物／硒化物态硒为主。碳质泥岩中的水溶态硒显著低于碳质页岩和碳质硅质岩中的水溶态硒,但元素态硒的比例显著高于后两者,说明碳质泥岩是富硒碳质岩层中硒易于富集的场所。富硒碳质岩中的可利用态硒主要以Se^4＋为主,而非是Se^6＋和有机硒。可交换态和有机结合态硒中Se^4＋与岩石总硒的显著正相关关系表明,Se^4＋离子的分布影响着岩石总硒,有机质与粘土在硒富集的地球化学过程中承担了重要作用。     

长江水质地球化学

文章在对1958—1990年期间长江水系191个站点水质监测资料进行统计分析的基础上,研究了长江主要离子的地球化学。结果表明,长江水系各地河水总溶解性固体(TDS)含量的差别达一个数量级(49·7~518·1mg/L),TDS的平均值为205·9mg/L,是全球河流均值的3倍。相比之下,河水TDS含量的季节性变化并不大,尽管河水流量的季节变化很大。长江的主要离子化学主要受岩石风化作用,尤其是碳酸盐矿物的溶解作用所控制。长江中上游的川贵地区酸雨严重。酸雨作用于当地广泛分布的石灰岩和富含碳酸盐的三叠纪砂页岩,导致近半个世纪来长江水质的酸化趋势,使大部分河段SO24-和Ca2+含量增高,总硬度与总碱度的比值增高。     

Selenium distribution in the local environment of selected villages of the Keshan Disease belt,Zhangjiakou District,Hebei Province,People's Republic of China

The distribution of Se in cultivated topsoils, grains, human hair and drinking water has been studied in 15 villages from a Keshan disease area of the People's Republic of China, villages being classified into 3 groups according to the Keshan disease incidence in the local population. In grain, hair and water the total Se follows expected trends; i.e. the highest concentrations are found in the villages where there is no incidence of Keshan disease. However, the soils from the high-incidence Keshan disease villages have the highest total Se content, an apparent contradiction, as Keshan disease is a response to a Se deficient environment. Soil analyses suggest that the organic content of the soils is a major factor in controlling the availability of Se and it is the high-incidence Keshan disease villages that have the most organic-rich soils. Although higher in total Se, the organic-rich soils have little bioavailable Se resulting in a Se deficient food chain. Soil pH is also seen to be a related factor in restricting the availability of Se and all the grain samples collected on soils with a pH <7.6 had a total Se content of less than 10% of the total soil Se. In an environment that can be classified as Se deficient small changes in the soil organic content and pH can have a critical affect on the Keshan disease status of a village.