首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
《Applied Geochemistry》2002,17(12):1503-1513
The interaction of CO2 with municipal solid waste incinerator (MSWI) bottom ash was studied in order to investigate the resulting changes in pH and bottom ash mineralogy and the impact that these changes have on the mobility of Cu and Mo. Carefully controlled carbonation experiments were performed on bottom ash suspensions and on filtered bottom ash leachates. Changes in leachate composition were interpreted with the geochemical model MINTEQA2, and neoformed minerals were investigated by means of chemical and spectroscopic analysis. The leaching of Cu and Mo during artificial carbonation is compared to the leachability of Cu and Mo from a sample of naturally carbonated bottom ash from the same incinerator. During carbonation in the laboratory, a precipitate was formed that consisted mainly of Al-rich amorphous material, calcite, and possibly gibbsite. Carbonation to pH ≈8.3 resulted in a reduction of more than 50% in Cu leaching, and a reduction of less than 3% in Mo leaching. The reduction in Cu leaching is attributed to sorption to the neoformed amorphous Al-minerals. During natural weathering/carbonation of bottom ash, additional sorption sites are formed which further reduce the leaching of Cu and Mo on a time scale of months to years.  相似文献   

2.
A study was initiated to analyse metal flows from alum shale to the environment in an area in Öland, Sweden. The study was performed by elemental analysis and leaching experiments of alum shale together with analysis of groundwater and surface water samples.The metal concentrations in non-weathered alum shale were much higher than in weathered or burnt shale, especially for cadmium (Cd), nickel (Ni) and zinc (Zn), indicating a loss of metals during weathering or burning of the shale. The release of metals through weathering was clearly demonstrated by the leaching tests. A 36-week leaching period of non-weathered shale resulted in a drastic drop in pH and a significant increase in metal concentrations in the leachate. The metal concentrations in groundwater were inversely related to the pH. For surface waters, the concentrations of Cd, copper (Cu), Ni and Zn were generally increased compared to background values.In conclusion, metals are released through weathering or burning of alum shale, as well as from heaps of weathered or burnt shale. The release of metals is strongly related to low pH, especially for Cd, Ni and Zn.  相似文献   

3.
  相似文献   

4.
This paper investigates the mechanisms controlling Sb-leaching from fresh Municipal Solid Waste Incinerator (MSWI) bottom ash, as well as the possibilities of controlling the extent of Sb-leaching by the addition of sorbent minerals to the bottom ash. In alkaline MSWI bottom ash Sb is possibly incorporated in ettringite-like minerals. When weathering/carbonation continues the ettringite dissolves resulting in a mobilisation of Sb. At neutral pH values the leaching of Sb is likely to be controlled by sorption to amorphous Fe/Al-(hydr)oxides. It has been shown that Sb can effectively be removed from solution if salts of Fe(III) or Al(III) are added to the bottom ash. This addition of Fe(III)/Al(III)-salts leads to (1) the in-situ precipitation of Fe/Al-hydroxides and sorption/coprecipitation of contaminants such as Sb, and (2) a lower bottom ash pH and thus an increased affinity of oxyanions for sorption to Fe/Al-(hydr)oxides.  相似文献   

5.
In Flanders, recycling of bottom ash is mainly inhibited by the high leaching of Cu. Although it has been proved that dissolved organic C plays a major role in the Cu leaching, the possible role of inorganic Cu mineral speciation has never been experimentally examined. In this study the speciation of Cu is investigated using a combination of optical microscopy and electron microprobe –WDX/EDX. Several Cu species were determined. Metallic Cu (with or without an oxide shell), CuO and Cu2O were the most abundant. These particles were most likely present in wire-like structures. Copper also occurred as alloy (brass, bronze, zamak), and was found frequently together with typical elements such as Ca, Cl and S. Finally, small metallic Cu particles seemed to be trapped in or precipitated on oxides and silicates. Based on this Cu speciation study, pure Cu minerals were selected and leached as a function of time. The solubility after equilibrium of all studied Cu minerals never exceeded 20 μg/L (which equals 10% of the total Cu leaching).The effect of heating (2 h at 400 °C) on the speciation of Cu was investigated using the same combination of techniques. Results show that metallic Cu seemed to be converted to Cu oxide (mostly CuO) and that the particles were more porous after heating. These conclusions were verified by XRD analysis of the heated pure Cu minerals. After heating, the Cu minerals were also leached as a function of time, to study the impact on Cu leaching. Results indicate that their leaching had slightly increased in comparison with the non-heated Cu minerals. However, the major decrease in Cu leaching in heated bottom ash, more than neutralizes this effect and thus can be attributed to the destruction of organic matter and not to the (small) change in Cu speciation.  相似文献   

6.
在吉林东部花岗岩区地下水化学成分和化学类型研究的基础上,以Na作为参比元素,确定了花岗岩风化过程中22种主量元素和微量元素的相对活动顺序。花岗岩区地下水的地球化学类型属低矿化度(变化范围为69.51×10-6~386.49×10-6,平均值为199.48×10-6)的HCO3-Ca和HCO3-Na-Ca型。花岗岩风化过程中元素的活动性顺序(RM)从大到小依次为:B、Ca、Mo、Zn、Sr、Na、Mg、Cr、Cu、Ni、K、Co、Li、V、As、Ba、Si、Y、Fe、Ti、Al、Mn。风化产物中的粘土矿物主要为高岭土、蒙脱石,反映出本区花岗岩的风化淋滤程度较弱的特点。  相似文献   

7.
Mine tailings discharged to river systems have the potential to release significant quantities of major and trace metals to waters and soils when weathered. To provide data on the mechanisms and magnitudes of short- and long-term tailings weathering and its influence on floodplain environments, three calendar year-long column leaching experiments that incorporated tailings from Potosí, Bolivia, and soil from unaffected downstream floodplains, were carried out. These experiments were designed to model 20 cycles of wet and dry season conditions. Two duplicate columns modeled sub-aerial tailings weathering alone, a third modeled the effects of long-term floodplain tailings contamination and a fourth modeled that of a tailings dam spill on a previously contaminated floodplain. As far as was practical local climatic conditions were modeled. Chemical analysis of the leachate and column solids, optical mineralogy, XRD, SEM, EPMA, BCR and water-soluble chemical extractions and speciation modeling were carried out to determine the processes responsible for the leaching of Al, Ca, Cu, K, Na, Mg, Mn, Sn, Sr and Ti. Over the 20 cycles, the pH declined to a floor of ca. 2 in all columns. Calcium, Cu, Mg, Mn and Na showed significant cumulative losses of up to 100%, 60%, 30%, 95% and 40%, respectively, compared to those of Al, K, Sr, Sn and Ti, which were up to 3%, 1.5%, 5%, 1% and 0.05%, respectively. The high losses are attributed to the dissolution of relatively soluble minerals such as biotite, and oxidation of chalcopyrite and Cu-sulfosalts, while low losses are attributed to the presence of sparingly soluble minerals such as svanbergite, cassiterite and rutile. These results strongly suggest that the release of tailings to floodplains should be limited or prohibited, and that all tailings should be removed from floodplains following dam spills.  相似文献   

8.
Coal mine rejects and sulfide bearing coals are prone to acid mine drainage (AMD) formation due to aqueous weathering. These acidic effluents contain dissolved trace and potentially harmful elements (PHEs) that have considerable impact on the environment. The behavior of these elements in AMD is mainly controlled by pH. The focus of the present study is to investigate aqueous leaching of mine rejects for prediction of acid producing potential, rates of weathering, and release of PHEs in mine drainage. Mine reject (MR) and coal samples from the active mine sites of Meghalaya, India typically have high S contents (1.8–5.7% in MR and 1.7–4.7% in coals) with 75–90% of the S in organic form and enrichment of most of the PHEs in rejects. Aqueous kinetic leaching experiments on mine rejects showed high acid producing potential and release of trace and potentially harmful elements. The elements (Sb, As, Cd, Cr, Co, Cu, Pb, Mn, Ni, V and Zn) in mine sample leachates are compared with those in mine waters. The concentrations of Al, Si, P, K, Ti, Mn, Fe, Co, Ni, Cu, Zn and Pb are found to increase with leaching time and are negatively correlated with pH of the solution. The processes controlling the release of these elements are acid leaching, precipitation and adsorption. The critical loads of PHEs in water affected by AMD are calculated by comparing their concentrations with those of regulatory levels. The Enrichment Factors (EFs) and soil pollution indices (SPIs) for the elements have shown that PHEs from coal and mine reject samples are mobilized into the nearby environment and are enriched in the associated soil and sediment.  相似文献   

9.
During weathering, elements enriched in black shale are dispersed in the environment by aqueous and mechanical transport. Here a unique evaluation of the differential release, transport, and fate of Fe and 15 trace elements during progressive weathering of the Devonian New Albany Shale in Kentucky is presented. Results of chemical analyses along a weathering profile (unweathered through progressively weathered shale to soil) describe the chemically distinct pathways of the trace elements and the rate that elements are transferred into the broader, local environment. Trace elements enriched in the unweathered shale are in massive or framboidal pyrite, minor sphalerite, CuS and NiS phases, organic matter and clay minerals. These phases are subject to varying degrees and rates of alteration along the profile. Cadmium, Co, Mn, Ni, and Zn are removed from weathered shale during sulfide-mineral oxidation and transported primarily in aqueous solution. The aqueous fluxes for these trace elements range from 0.1 g/ha/a (Cd) to 44 g/ha/a (Mn). When hydrologic and climatic conditions are favorable, solutions seep to surface exposures, evaporate, and form Fe-sulfate efflorescent salts rich in these elements. Elements that remain dissolved in the low pH (<4) streams and groundwater draining New Albany Shale watersheds become fixed by reactions that increase pH. Neutralization of the weathering solution in local streams results in elements being adsorbed and precipitated onto sediment surfaces, resulting in trace element anomalies.Other elements are strongly adsorbed or structurally bound to solid phases during weathering. Copper and U initially are concentrated in weathering solutions, but become fixed to modern plant litter in soil formed on New Albany Shale. Molybdenum, Pb, Sb, and Se are released from sulfide minerals and organic matter by oxidation and accumulate in Fe-oxyhydroxide clay coatings that concentrate in surface soil during illuviation. Chromium, Ti, and V are strongly correlated with clay abundance and considered to be in the structure of illitic clay. Illite undergoes minimal alteration during weathering and is concentrated during illuvial processes. Arsenic concentration increases across the weathering profile and is associated with the succession of secondary Fe(III) minerals that form with progressive weathering. Detrital fluxes of particle-bound trace elements range from 0.1 g/ha/a (Sb) to 8 g/ha/a (Mo). Although many of the elements are concentrated in the stream sediments, changes in pH and redox conditions along the sediment transport path could facilitate their release for aqueous transport.  相似文献   

10.
《Applied Geochemistry》2004,19(7):1065-1074
Potentially toxic metals exist in many reservoirs of surface water and therefore require an understanding of their occurrence, distribution, and mobility. The sediment accumulating at the bottom of the Dillon Reservoir, Colorado is contaminated with metals (Cu, Pb, Zn, Cd, Mo, etc.) that are primarily sorbed to Fe and Al hydroxides present in the sediment. The metals are derived from weathering of mineralized bedrock and mine tailings in the surrounding drainage basins. Sediment samples from the Dillon Reservoir were analyzed for major and trace elements and acidification experiments were performed to quantify the fraction of metals released from the sediment as a function of changes in pH. The highest percentages of metals are released from the sediment at low pH with the exception of Mo which has the highest percent released at near neutral pH. In addition, seasonal fluctuations in the concentrations of metals in the water of the Dillon Reservoir can be explained by changes in pH of as low as 0.2 pH units.  相似文献   

11.
黔中早石炭世九架炉组铝土矿含矿岩系富集Ti、Li、Sc、V、Ga、Nb、Ta、Zr、Hf、Th和稀土(REEs)等"三稀金属",具有成为独立矿床或伴生资源的潜力。这些元素大部分与九架炉组共有同一母岩,且富集程度受母岩的成分和风化作用控制。本研究选取九架炉组母岩乌当娄山关群白云岩和纳雍牛蹄塘组泥质白云岩的现代风化剖面为研究对象,研究元素在风化作用过程中的迁移特征及分布规律,进而为九架炉组微量元素的富集机制提供启示。研究获得以下认识:1)依据剖面结构、ZrHf、Nb-Ta、Y-Ho二元图特征及REE配分曲线和Eu/Eu*值的相似性表明研究区土层主要来源于基底或母岩的风化; 2)白云岩风化成土过程中Si、Fe、Cr、As、Sb、Ti、Nb、Ta、Zr、Hf、Th、REEs等元素化学性质相对稳定,富集程度较高,而Ca、Mg、Na、K、Sr、P、Mo、Cd等元素化学性质活泼,容易淋失亏损; 3)纳雍剖面REEs~(3+)和Ca~(2+)半径差与REEs富集系数相关性良好,表明碳酸盐岩风化过程中,含钙矿物磷灰石是稀土元素分配的重要控制因素; 4)九架炉组的母岩也是Ti、Li、Sc、V、Ga、Nb、Ta、Zr、Hf、Th等微量元素的主要物质来源,母岩风化过程中,这些微量元素首先在副矿物、黏土矿物、铝矿物及磷灰石等矿物相中初步富集,之后随风化碎屑物一起沉积形成微量元素超常富集地层; 5)纳雍剖面地表和地下水提供了部分P、Be、Zn、Sb、Pb、Y及REEs来源,指示水体迁入作用也是九架炉组REEs富集的重要原因。研究表明黔中九架炉组微量元素的来源较复杂,风化-沉积过程中,化学性质稳定的元素残留在风化碎屑物中并被搬运-沉积在负地形中,而化学性质活泼的元素首先被带入水体,在沉积-成岩过程中特定条件下发生二次富集作用(例如次生矿物的形成及吸附)形成微量元素富集的地层。  相似文献   

12.
This study deals with the weathering processes operating at the scale of a small catchment (Nsimi-Zoetele, Cameroon) and is focused on the role of organic colloids on mineral weathering and transport of elements in natural waters. Samples of river, spring and groundwaters from Nsimi-Zoetele were filtered through membranes of decreasing pore size (0.22 μm, 0.025 μm, or: 300,000 Da, 5000 Da) to separate colloidal fractions from the truly dissolved one. Major and trace elements and dissolved organic carbon (DOC) were analysed in each fraction. Two kinds of waters can be distinguished in the catchment: clear and coloured waters. Clear waters exhibit low concentrations of major and trace elements and DOC. Elements are carried in these solutions in a true dissolved form except Al and rare earth elements (REEs). By contrast, the higher abundances of Al, Fe and trace elements in coloured waters are controlled by the colloidal fraction. Thermodynamic equilibrium calculations show that clear waters are in equilibrium with kaolinite and iron oxi-hydroxide which are major minerals in the weathered soil. For coloured waters, the aqueous speciation of Ca, Mg, Cu, Fe, Al, La and Th was calculated taking into account the complexes with humic acids. Speciation calculations for Cu, Fe, Al, La, Th show a strong complexation with humic acids, in good agreement with the results of the filtration experiments. By contrast, although filtration experiments show a strong control of major cations by organic matter (for example 75% for Ca), speciation calculations reveal that their complexes with humic ligands do not exceed a few percent of total dissolved elements. This discrepancy is explained as an artefact induced by the organic colloids and occurring during the filtration procedure. Finally, both filtration experiments and speciation calculations show that organic matter plays an important role in natural DOC-rich waters. Organic acids increase significantly the dissolution rates of silicates and oxi-hydroxides and thus the amounts of solutes and of complexed elements leaving the catchment.  相似文献   

13.
Factor analysis was applied to the hydrochemical data set of Manukan Island in order to extract the principal factors corresponding to the different sources of variation in the hydrochemistry. The application of varimax rotation was to ensure the clear definition of the main sources of variation in the hydrochemistry. The geochemical data of dissolved major, minor and trace constituents in the groundwater samples indicates the main processes responsible for the geochemistry evolution. By using Kaiser normalization, principal factors were extracted from the data for each location. The analysis reveals that there are four sources of solutes: (1) seawater intrusion; (2) leaching process of underlying rock mediated by pH; (3) minerals weathering process and (4) dissolution of carbonate minerals characterized by high loadings of Ca, Zn and Mg. Such processes are dominated by the significant role of anthropogenic impact from the over abstraction of fresh water from the aquifer. Those factors contributed to the changes of the groundwater geochemistry behavior explain the effect of rising extraction of freshwater from the aquifer.  相似文献   

14.
Serpentinite rocks, high in Mg and trace elements including Ni, Cr, Cd, Co, Cu, and Mn and low in nutrients such as Ca, K, and P, form serpentine soils with similar chemical properties resulting in chemically extreme environments for the biota that grow upon them. The impact of parent material on soil characteristics is most important in young soils, and therefore the incipient weathering of serpentinite rock likely has a strong effect on the development of serpentine soils and ecosystems. Additionally, porosity generation is a crucial process in converting rock into a soil that can support vegetation. Here, the important factors affecting the incipient weathering of serpentinite rock are examined at two sites in the Klamath Mountains, California. Serpentinite-derived soils and serpentinite rock cores were collected in depth profiles from each sampling location. Mineral dissolution in weathered serpentinite samples, determined by scanning electron microscopy, energy dispersive spectrometry, electron microprobe analyses, and synchrotron microXRD, is consistent with the order, from most weathered to least weathered: Fe-rich pyroxene > antigorite > Mg-rich lizardite > Al-rich lizardite. These results suggest that the initial porosity formation within serpentinite rock, impacting the formation of serpentine soil on which vegetation can exist, is strongly affected both by the presence of non-serpentine primary minerals as well as the composition of the serpentine minerals. In particular, the presence of ferrous Fe appears to contribute to greater dissolution, whereas the presence of Al within the parent rock appears to contribute to greater stability. Iron-oxidizing bacteria present at the soil–rock interface have been shown in previous studies to contribute to the transition from rock to soil, and soils and rock cores in this study were therefore tested for iron-oxidizing bacteria. The detection of biological iron oxidation in this study indicates that the early alteration of these Fe-rich minerals may be mediated by iron-oxidizing bacteria. These findings help provide insight into the incipient processes affecting serpentinite rock weathering, important to the development of extreme serpentine soils and the biota that grow on them.  相似文献   

15.
Large volumes of coal fly ash are continually being produced and stockpiled around the world and can be a source of environmentally sensitive trace elements. Whilst leaching tests are used for regulatory purposes, these provide little information about the true geochemical behaviour and ‘reactivity’ of trace elements in coal ash because they are poorly selective. Isotope dilution (ID) assays are frequently used in soil geochemistry as a means of measuring the reactive pools of trace metals that are in equilibrium with soil pore waters. This paper examines the applicability of multi-element ID assays in measuring the labile or reactive pool of Cd, Pb and Zn in a range of fresh and weathered fly ash, where pH is generally much more alkaline than in soils. The method generally worked well using 0.0005 M EDTA as a background electrolyte as it provided robust analytical ICP-MS measurements as well as fulfilling the important principle of ID that non-labile metal should not be solubilised. Reactive pools were equivalent to 0.5–3% of the total Pb pool and 4–13% of the total Cd pool. For Zn, where samples had pH < 11.5, the reactive Zn pool varied between 0.3% and 2%; when fresh ash samples with pH > 11.5 were tested, the method failed as the spiked isotope appeared to be sorbed or precipitated. Ash weathering was found to exert little impact on the lability of Cd, Pb and Zn. Isotope dilution results were compared with 0.43 M HNO3 and 0.05 M EDTA extractions, these commonly being used as analogues of the ID assay, and concluded that these can be used as fast, cost-effective and simple proxies for the ID assays. Results suggest that ID methods can be used to enhance knowledge of trace element behaviour in fresh and weathered fly ash.  相似文献   

16.
贵州威宁地区宣威组底部稀土含矿岩系的成因类型一直有较大争议.在野外实地调查的基础上,运用矿物学、岩相古地理与地球化学等手段进行了系统性研究.结果显示,区内二叠系宣威组底部稀土含矿岩系广泛分布,连续性好,含矿段厚度为2~16 m,并伴生有铌、锆、镓等元素;稀土氧化物平均品位0.15%,最高可达1.60%.主量、微量和稀土元素分析表明威宁地区稀土含矿岩系中含有来自玄武岩及火山灰的典型矿物,稀土配分模式与玄武岩相比具有继承性,研究区化学风化作用较强、成分成熟度较高代表其经过长距离搬运,遭受了改造;峨眉山玄武岩为该稀土层提供了主要物质来源,稀土层受源岩成分的控制,经历了沉积分选及再循环作用,还遭受了来自上地壳的中酸性岩浆物质源区的混染.其成因机制可能为在晚二叠世炎热、潮湿、强风化的环境中,玄武岩经过风化剥蚀后,搬运至沉积基底低洼处的三角洲平原亚相中的洪泛平原微相环境,与火山灰一同沉积沉淀,在风化和淋滤作用下稀土等元素以离子形式被解析出来,从而被吸附性强的高岭石等黏土矿物吸附于表面,或进入矿物晶格,形成富稀土层.   相似文献   

17.
Quaternary alkaline basalts of Middle Atlas, are weathered into spheroidal volumes organized into weathering cover. In the profile studied, the study of transformations from a fresh core basalt to the most weathered rinds, has been analysed using BESI images (backscattred electron image analysis). A part from the microscopic analysis of each weatherted basalt, proportions of primary minerals, clays and pore space has been quantified in different stages of weathering. Indeed, in fresh core basalt, weathering is characterized by a first dissolution of the glass, followed by feldspar transformations in twinning plans, cleavages and in micropores inherited from the magmatic and cristallographic history of the rock.

In most basaltic weathered rinds, pore spaces given by the dissolution of the glass, were filled by a mixture of clays and iron products. In these samples, feldspars are completely dissolved giving important porosity occupied by small quantity of halloysite and kaolinite. The olivine and pyroxene transformations are accompanied by weak pore space formation. At the bottom of the soil, this porosity decreases in response to filling by later secondary products which come from the upper part of the soil by weathering solutions.  相似文献   


18.
An overview is presented on possible mechanisms that control the leaching behaviour of the oxyanion forming elements As, Cr, Mo, Sb, Se, V and W in cementituous systems and alkaline solid wastes, such as municipal solid waste incinerator bottom ash, fly ash and air pollution control residues, coal fly ash and metallurgical slags. Although the leachability of these elements generally depends on their redox state, speciation measurements are not common. Therefore, experimental observations available in the literature are combined with a summary of the thermal behaviour of these elements to assess possible redox states in freshly produced alkaline wastes, given their origin at high temperature. Possible redox reactions occurring at room temperature, on the other hand, are reviewed because these may alter the initial redox state in alkaline wastes and their leachates. In many cases, precipitation of oxyanions as a pure metalate cannot provide a satisfactory explanation for their leaching behaviour. It is therefore highly likely that adsorption and solid solution formation with common minerals in alkaline waste and cement reduce the leachate concentration of oxyanions below pure-phase solubility.  相似文献   

19.
In this work we have studied the geochemistry of stream waters arising from waste dumps at the Peña de Hierro mine (Iberian Pyrite Belt, SW Spain), and we have correlated them with the mineralogical and geochemical characteristics of the wastes to asses the source and factors affecting the release of trace elements. The mineralogical composition and geochemistry of 58 borehole samples of waste dumps were studied in the <2 mm fraction. Twenty-eight water samples collected in winter and summer from streams emerging from the waste dumps were analysed for pH, Eh, conductivity, temperature, sulphates and major and trace elements. The leachates from pyrite-rich volcanic tuffs produced very acidic waters, usually with pHs below 2 and reaching values as low as 0.7. The partial dissolution of gossan, which is mainly composed of Fe oxy-hydroxides and is rich in trace elements, released high concentrations of Fetot (up to 33 g/L), As (up to 72), Mo (up to 11 mg/L). On the other hand Cd, Zn and Pb reached up to 0.85, 142 and 0.42 mg/L, respectively, in the stream arising from roasted pyrite ashes and other pyritic wastes. Several elements such as Al, Fe, As, Co, Cu and Mo were strongly correlated with the pH, but Cd and Zn were not correlated under such acidic conditions. The precipitation of jarosite seems to be an important factor in the retention of Pb. The mobility sequence of trace elements shows that Co, Zn and Cd were among the most mobile elements; Cu, As and Mo had intermediate mobility, and Pb was the most immobile. This work shows that uncontrolled waste dumping increases the pollution potential, and a selective management could reduce the release of trace elements into stream waters and mitigate the contamination.  相似文献   

20.
Recent work on the weathering of high standing islands (HSI’s) of New Zealand (Goldsmith et al., 2008), Dominica (Goldsmith et al., 2010) Martinique and Guadeloupe (Rad et al., 2006) and portions of the Philippines (Schopka et al., 2011) shows weathering rates based on stream water chemistry for areas draining andesitic terrains are comparable to weathering rates determined for basaltic terrains, indicating that andesite weathering might be much more important in drawing down atmospheric CO2 than previously recognized. While an easily erodible parent material has been largely attributed to sustaining rates at these locations, little is known to known regarding its associated reaction kinetics. We conducted a series of batch dissolution experiments on andesitic material collected from ∼10,000 year old tephra deposits from Dominica to determine the dissolution rate of major and trace mineral phases to better understand geochemical processes controlling weathering flux from these areas. Dissolution experiments were conducted over a range of pH (4 and 7) on bulk samples and mineral separates.The dissolution rates based on Si release from the Dominica tephra bulk samples were similar, and ranged from 0.04 to 0.13 μmole Si/g-day in water, and ∼0.14 to 0.27 μmole Si/g-day in dilute acid (initial pH ∼4). Although the bulk of the ash is predominately composed of vesicular felsic (Na–Al–Si) volcanic glass, reaction rates and stoichiometry indicate ash dissolution is dominated by the reactivity of trace Mg or Ca-bearing silicate phases (olivine, pyroxene or amphiboles) and Ca–phosphate phases (apatite), especially under slightly acidic conditions. Analysis of reacted phases by SEM shows little evidence of alteration of glassy material, whereas surfaces of Ca–Mg inosilicates, olivine and apatite show etched features indicative of dissolution. Results of the dissolution experiments suggest that, although these phases are relatively minor components of the ash, they contribute disproportionately to the overall weathering flux, and their reactivity may be particularly important in areas where physical weathering and erosion are constantly exposing new fresh surfaces available for chemical reaction.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号