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1.
Geotechnical Properties of Low Calcium and High Calcium Fly Ash 总被引：1，自引：0，他引：1
In this paper, a comparative study has been made for physical and engineering properties of low calcium and high calcium Indian
fly ash. The grain size distribution of fly ash is independent of lime content. Fly ash particles of size >75 μm are mostly irregular in shape whereas finer fractions are spherical for low calcium fly ash. For high calcium fly ash, chemical
and mineralogical differences have been observed for different size fractions. Compared to low calcium fly ash, optimum moisture
content is low and maximum dry density is high for high calcium fly ash. Optimum moisture content is directly proportional
and maximum dry density is inversely proportional to the carbon content. The mode and duration of curing have significant
effect on strength and stress–strain behavior of compacted fly ash. The gain in strength with time for high calcium fly ash
is very high compared to that of low calcium fly ash due to presence of reactive minerals and glassy phase. 相似文献
2.
南海表层沉积物中的碳酸钙含量分布及其影响因素 总被引：1，自引：0，他引：1
通过测定南海213个表层沉积物样品中的碳酸钙含量, 综合分析整个南海海域碳酸钙含量分布特征及其控制因素.结果表明, 不同的区域海洋环境, 控制表层沉积物中碳酸钙含量变化的因素也不尽相同: 大陆架区, 碳酸钙含量主要受陆源非碳酸盐物质的稀释作用而较低; 大陆坡区, 碳酸钙因丰富的物源量、低的陆源物质输入量和弱的碳酸钙溶解作用等因素而呈较高含量; 深海盆区, 碳酸钙含量因强烈的溶解作用而较低.根据碳酸钙含量在南海整个表层沉积物中的分布趋势, 推测南海纬度14°N以北的海域碳酸钙补偿深度(CCD)为3700m左右, 纬度14°N以南的海域CCD为4000m左右.Pearson相关分析表明, 南海表层沉积物中钙质超微化石对碳酸钙的含量分布具有较高的贡献率. 相似文献
3.
黄龙嗜冷细菌两种胞外单糖对碳酸钙矿化影响 总被引：2，自引：0，他引：2
为了探究黄龙水体中嗜冷细菌的胞外代谢产物对钙华沉积速率及沉积产物的影响,本文从黄龙钙华水体中分离到优势土著嗜冷细菌,并以其标志性胞外代谢产物D-葡萄糖和D-核糖作为研究对象,研究了两种单糖组分在低温环境下对钙华沉积的影响,并通过X射线衍射(XRD)、扫描电子显微镜(SEM)、红外吸收光谱(FT-IR)等分析手段对碳酸钙晶型、形貌以及结构组成进行了表征。实验表明:D-葡萄糖在低温条件下能促进方解石型碳酸钙的沉积,并加快沉积速率。低浓度下(20 mg/L和40 mg/L)的沉积产物均为方解石型碳酸钙并对其形貌有一定的影响;高浓度下(80 mg/L和160 mg/L)能诱导少量的文石型碳酸钙的合成。D-核糖在低温条件下能促进碳酸钙的沉积,加快沉积速率。与D-葡萄糖不同,D-核糖仅能合成方解石型碳酸钙,但对方解石晶面的生长表现为抑制作用,且随浓度增大抑制作用益明显。此结果可为黄龙钙华生物成因的探究提供一定的理论研究基础。 相似文献
4.
文章在世界自然遗产地贵州荔波茂兰保护区采集土壤全钙数据,分析采用地理加权回归（GWR）方法进行空间分析的有效性,筛选识别影响土壤全钙空间分布的主要因子,建立喀斯特地区土壤全钙含量空间分布计算模型,获取研究土壤全钙空间分布基础数据。通过土壤流失方程（USLE）计算土壤侵蚀状况,对比分析土壤全钙与土壤侵蚀空间关联,揭示土壤全钙的空间迁移规律。结果表明:（1）在岩性一致条件下,相对高差和坡度是影响土壤全钙空间分布的主导因子;（2）GWR模型的预测精度优于全局回归的（OLS）,相关系数分别是0.41和0.39;（3）通过土壤全钙含量空间估算模型,计算得到研究区土壤全钙空间分布特征,土壤全钙为0 ~37.68 gkg-1。研究结论说明,在湿润气候的喀斯特地区,尽管植被覆盖度大,但土壤全钙空间分布仍然深受成土母质影响,喀斯特峰林土壤侵蚀强度大,土壤全钙含量高,物质迁移以流失为主,峰丛洼地土壤侵蚀强度小,土壤全钙含量低,物质迁移以淋溶流失为主。 相似文献
5.
A. Van Lierde 《International Journal of Mineral Processing》1980,7(3):235-243
The effect of acrylate polymers on the behaviour of quartz-slime suspensions, in the presence or in the absence of calcium ions, is considered. Results of dispersion tests with polyacrylates of various molecular weights show that acrylates are capable of extending the pH range in which quartz is dispersed to weakly acid pH values: between 3.5 and 4.5, if calcium ions are not added to the system. On the other hand, in the presence of calcium ions, the dispersed state can be maintained only in a narrow pH range, between 4, 5 and 6 to 8.5, the latter value being reached only in the case of very low molecular weight polymer (5.400). At higher pH values, flocculation takes place, more intensively as the pH becomes more basic and the molecular weight of polymer higher.The mechanism by which dispersion or flocculation occurs is interpreted on the basis of experimental results of dispersion tests and zeta potential measurements. From these data, it is concluded that electrostatic effects and steric hindrance phenomena must not be ignored in explaining the behaviour of mineral suspensions, chiefly when a very low molecular weight is used. Adsorption of calcium ions on quartz surfaces appears also to play a fundamental part in the flocculation mechanism at basic pH values. 相似文献
6.
The monthly geochemical study of Bizerte lagoon principal affluent water consists in characterizing the water geochemical facies and their inorganic pollution degree by nutrients. The major elements analysis shows calcium sulfate to chloride calcium balanced facies. The geochemical analysis of water nutritive salts shows generally a good to excellent quality. Wadi Guenniche is considered more polluted as we recorded the highest nutrients contents. The principal component analysis of the connections between the physicochemical and geochemical parameters of Bizerte lagoon affluent water show that the low salinities, the turbidity, and the low contents of major sodium, chloride ions, and nutritive elements are the major factors of the environment controlling the good quality of this fresh water. 相似文献
7.
Chalk deformation and large-scale migration of calcium carbonate 总被引：2，自引：0，他引：2
Y. MIMRAN 《Sedimentology》1977,24(3):333-360
Sixty Upper Cretaceous chalk exposures were examined and sampled in Dorset, the Isle of Wight and Guildford, South England, in order to investigate the effects of tectonic deformation on the chalk fabric. Light and scanning-electron microscopes were used extensively, and chemical, mineralogical and isotopic analyses ware carried out. Two types of fabric modification were distinguished. The first type involves more than 90% volume loss by mechanical compaction at the early stages of deformation followed by dissolution and removal of calcium carbonate in the advanced stages of deformation. Chalks which have undergone this type of fabric modification are dense and consist of well rounded 0.5–3 μ calcite crystals with well developed pressure-solution contacts. These chalks contain a high proportion of calcispheres (many of which are plastically deformed) but very few well preserved planktonic foraminifera and coccoliths. They are relatively enriched in insoluble constituents and depleted in strontium. The second type of fabric modification involves introduction of calcium carbonate into the pore spaces. Chalks which have undergone this type of modification are dense and contain a high proportion of 3–5 μ polygonal interlocking calcite crystals. Fossils are virtually never deformed, and delicate foraminifera and coccoliths are well preserved. Insoluble constituents similar to those found in the unmodified chalks occur in low concentrations. Removal of calcium carbonate at crystal contacts has taken place in chalks which have been subjected to high effective tectonic stresses and at crystal peripheries in chalks which have been subjected to high pore fluid pressure. Dissolution at crystal peripheries is responsible for the extensive calcium carbonate losses, and it is termed herein ‘confining pressure solution’. Introduction of calcium carbonate occurs in rocks which were under low tectonic stresses. During deformation calcium carbonate migrates from chalks under high stresses towards those under tow stresses, while some goes into solution in sea water. Well developed joints and high pore fluid pressure might increase the rate of calcium carbonate removal by three orders of magnitude. Petrographic and isotopic data suggest-that all fabric modifications studied took place in meteoric water. 相似文献
8.
单生卵囊藻对DIC的利用及其对CaCO3沉积影响的研究 总被引：4，自引：0，他引：4
以生长在钙华池中的单生卵囊藻（Oocystis solitaria Wittr）为研究对象,利用pH漂移方法,探讨了封闭系统中单生卵囊藻在岩溶水和非岩溶水环境下对溶解无机碳（DIC）利用及其对水体Ca^2＋沉积影响的差异。结果表明,单生卵囊藻在低CO2浓度时,通过胞外碳酸酐酶的催化,以HCO3^-作为无机碳源进行光合作用。在岩溶水环境下单生卵囊藻DIC利用能力要高于非岩溶水环境（4．78倍）,而在此过程中对水体中Ca^2＋沉积的影响也更高（2．13倍）。在岩溶水（非岩溶水）环境下,有42．6％（8．9％）的Ca^2＋通过物理化学效应以CaCO3形式沉积,其余Ca^2＋可能被藻体生长而吸收利用．． 相似文献
9.
通过对卡斯卡迪亚水合物脊和墨西哥湾布什山冷泉渗漏流体的原位测定总S和总Ca浓度分析,发现渗漏流体的总S和总Ca浓度约为海水浓度的50%~70%,讨论了冷泉流体活动特征以及流体的总S和总Ca浓度的控制因素。在这两个冷泉渗漏区海底渗漏流体的总S和总Ca浓度随时间变化的趋势比较一致,均是发生在流体渗漏流量速率高频变化周期。流体的总S和总Ca浓度的降低,可能主要受冷泉区海底广泛存在的甲烷缺氧氧化作用控制,同时也可能受到水合物分解、粘土矿物的去水反应和油气藏破坏产生的纯水的稀释作用的影响。 相似文献
10.
Wu Y Ajo-Franklin JB Spycher N Hubbard SS Zhang G Williams KH Taylor J Fujita Y Smith R 《Geochemical transactions》2011,12(1):7-20
Ureolytically-driven calcium carbonate precipitation is the basis for a promising in-situ remediation method for sequestration of divalent radionuclide and trace metal ions. It has also been proposed for use in geotechnical engineering for soil strengthening applications. Monitoring the occurrence, spatial distribution, and temporal evolution of calcium carbonate precipitation in the subsurface is critical for evaluating the performance of this technology and for developing the predictive models needed for engineering application. In this study, we conducted laboratory column experiments using natural sediment and groundwater to evaluate the utility of geophysical (complex resistivity and seismic) sensing methods, dynamic synchrotron x-ray computed tomography (micro-CT), and reactive transport modeling for tracking ureolytically-driven calcium carbonate precipitation processes under site relevant conditions. Reactive transport modeling with TOUGHREACT successfully simulated the changes of the major chemical components during urea hydrolysis. Even at the relatively low level of urea hydrolysis observed in the experiments, the simulations predicted an enhanced calcium carbonate precipitation rate that was 3-4 times greater than the baseline level. Reactive transport modeling results, geophysical monitoring data and micro-CT imaging correlated well with reaction processes validated by geochemical data. In particular, increases in ionic strength of the pore fluid during urea hydrolysis predicted by geochemical modeling were successfully captured by electrical conductivity measurements and confirmed by geochemical data. The low level of urea hydrolysis and calcium carbonate precipitation suggested by the model and geochemical data was corroborated by minor changes in seismic P-wave velocity measurements and micro-CT imaging; the latter provided direct evidence of sparsely distributed calcium carbonate precipitation. Ion exchange processes promoted through NH4+ production during urea hydrolysis were incorporated in the model and captured critical changes in the major metal species. The electrical phase increases were potentially due to ion exchange processes that modified charge structure at mineral/water interfaces. Our study revealed the potential of geophysical monitoring for geochemical changes during urea hydrolysis and the advantages of combining multiple approaches to understand complex biogeochemical processes in the subsurface. 相似文献
11.
JOBST HÜLSEMANN 《Sedimentology》1967,8(2):121-145
A joint survey by the Woods Hole Oceanographic Institution and the U. S. Geological Survey, begun in 1962, aims at the geologic exploration of the Atlantic continental margin. This report describes the distribution of carbonate in the surface sediments between Nova Scotia and Hudson Canyon. Samples of surface sediment on a 10-mile grid reveal that over more than 90% of its area the shelf sediment contains less than 5% calcium carbonate. These low values are due to low production by aquatic organisms, a consequence of low average water temperatures. A few locales on the shelf have high carbonate concentration owing to a prolific sessile or nearly sessile fauna. Seaward of the shelf concentrations of calcium carbonate increase regularly with depth to about 30% on the upper continental rise; this increase reflects a greater relative abundance of planktonic Foraminifera due to a decrease in the rate of deposition of land derived detritus. Limestone outcrops are very rare in the area. 相似文献
12.
Hallimond tube flotation experiments have been carried out on the two calcium minerals scheelite and calcite using dodecylammonium chloride as collector. The main variables studied were the calcium ion concentration and the pH.In the case of scheelite, addition of calcium chloride markedly lowered the flotation recovery. Recovery was also lowered when the pH was reduced below about 10. Since it is known that the zeta potential of scheelite is almost independent of pH this confirms that co-adsorption of un-ionized amine is necessary for good flotation. Other un-ionized long-chain molecules can replace the amine; thus it was shown that excellent flotation can be obtained event at about pH 7 by adding dodecanol together with dodecylammonium chloride. With the completely ionic trimethyldodecylammonium chloride recoveries were poor and were independent of pH.In the case of calcite, calcium chloride had no immediate effect on flotation recovery, but at low collector concentrations marked depression occurred after many hours standing in the presence of calcium ions. The effect of pH on flotation of calcite was anomalous and there appear to be two pH regions in which recoveries are high.The results are discussed and attention is drawn to the need for more thorough studies of the calcium carbonate/water interface. 相似文献
13.
福建沿海地区芦柑的地质环境适宜性评价 总被引：2，自引：0，他引：2
通过福建省沿海地区不同地质环境区芦柑果实、叶片、果园土壤营养元素含量的对比，在芦柑品质评判、土壤和叶片营养诊断的基础上，分析了影响芦柑品质和产量的地貌、地质、地球化学因素。认为农作物营养平衡是制约农产品品质、产量的主要因素，而地质地球化学环境是影响农作物营养平衡的主要因素，其中土壤pH值偏低和ca等元素缺乏对芦柑品质影响最大。提出了优质高产芦柑果园土壤营养元素全量的诊断标准。土壤pH值偏低和ca等元素缺乏问题对柑橘生产的影响可以通过土壤改良、合理施肥加以解决。 相似文献
14.
Paul Thorn 《Hydrogeology Journal》2011,19(2):445-461
Elevated salinity in groundwater (over 250?mg/l chloride) in a fractured chalk aquifer in the municipality of Greve, Denmark, has been attributed to seawater intrusion from the Baltic Sea, resulting in the closure of a number of wells nearest to the coastline. However, a recent study in eastern Denmark shows that the salinity could also be from ancient connate pore waters. Historical chemistry data from bulk-water samples collected from wells have been used to determine the source. The sample data were studied with respect to their historical changes and temporal trends in chloride, carbonate, sulfate, sodium, potassium, magnesium, and calcium. Wells in the southern third of the municipality are relatively low in sodium and carbonate and high in chloride and calcium/magnesium, indicating waters undergoing saline intrusion. Wells in the northern two-thirds of the municipality are high in carbonate and sodium, but low in chloride and calcium/magnesium, indicating a freshening of the aquifer. This is confirmed by the temporal trends in chloride, where chloride levels in the northern wells remain constant, whereas in the south, chloride increases as abstraction continues. Therefore close monitoring for seawater intrusion should be conducted in the southern third of the municipality. 相似文献
15.
从地方病和环境污染性疾病看微量元素与钙的关系 总被引：1，自引：0，他引：1
从地方病和环境污染性疾病看微量元素与钙的关系李广生井玲（白求恩医科大学,长春１３００２１）关键词微量元素钙地方病环境污染性疾病我国几种主要地方病都与一定的微量元素有关,这已为大家所熟知。而值得重视的是,除了微量元素之外,它们又都在某些环节上与宏量元素... 相似文献
16.
微生物沉积碳酸钙固化砂质黏性紫色土试验研究 总被引：1，自引：0，他引：1
重庆紫色土是一种砂质黏性土,地区降雨集中,水力冲蚀作用剧烈,极易产生水土流失,微生物诱导方解石沉积(MICP)技术因能耗低、污染小而广泛应用于土体加固中。通过正交试验优化了巨大芽孢杆菌(BNCC 336739)的培养基和培养条件,活菌数增长126%,活性良好。采用巨大芽孢杆菌,进行低水压(9.8kPa)灌注固化砂质黏性紫色土试验,探究了固化效果的变化规律。结果表明:随固化次数增加,碳酸钙生成量和干密度逐级增加,无侧限抗压强度与碳酸钙生成量正相关;碳酸钙有效沉积越来越少,强度提高趋于稳定,固化9次后强度提高77%;随孔隙被碳酸钙填充和上下碳酸钙硬壳的形成,渗透性不断降低,最终下降两个数量级;通过试样上、中、下三部分碳酸钙生成量C的样本标准差s来反映碳酸钙分布离散程度,发现割线弹性模量在s的影响下随C增加而波动上升,波动表现为在C相近或s相差很大时,s越小割线弹性模量越大。研究成果可以为MICP技术在紫色土地区的地基、边坡加固和水土流失防护等工程应用提供科学依据和参考。 相似文献
17.
A method of using the X‐ray fluorescence spectrometer has been adopted for the analyses of lead phosphates, and eight samples of phosphates from Broken Hill and three from the Flinders Ranges, South Australia, were analysed by this means. Of these, five were found to be mimetite and six pyromorphite, several being rich in calcium. Dividing the sources into geochemical areas we find that the specimens from Broken Hill have no vanadium and a low alkaline metal earth content while those from the Flinders Ranges have a small, but noticeable vanadium content and high alkaline metal earth content. A poorer X‐ray diffraction fit of a calcium‐rich mimetite to the hexagonal structure indicates that the monoclinic structure could be of more importance in the members of this composition. 相似文献
18.
和村-孙庄盆地富锶矿泉水赋存地质条件 总被引：2，自引：0，他引：2
和村-孙庄盆地锶矿泉水属低钠低矿化度含锶重碳酸钙镁型中性低温矿泉水。通过对盆地构造、岩溶发育、地下水动态等特征的分析与研究认为,奥陶系中统峰峰组二、三段岩溶裂隙含水层为盆地内的主要富锶矿泉水地层,锶元素来源于碳酸盐和岩浆岩,矿泉水中氚浓度（33．86±3．44TU）含量表明,该矿泉水形成年龄为10～20a,具有远源补给、深层循环特征。 相似文献
19.
Enzyme induced carbonate precipitation (EICP) is an emerging soil improvement method using free urease enzyme for urea hydrolysis. This method has advantages over the commonly used microbially induced carbonate precipitation (MICP) process as it does not involve issues related to bio-safety. However, in terms of efficiency of calcium carbonate production, EICP is considered lower than that of MICP. In this paper, a high efficiency EICP method is proposed. The key of this new method is to adopt a one-phase injection of low pH solution strategy. In this so-called one-phase-low-pH method, EICP solution consisting of a mixture of urease solution of pH?=?6.5, urea and calcium chloride is injected into soil. The test results have shown that the one-phase-low-pH method can improve significantly the calcium conversion efficiency and the uniformity of calcium carbonate distribution in the sand samples as compared with the conventional two-phase EICP method. Furthermore, the unconfined compressive strength of sand treated using the one-phase-low-pH method is much higher than that using the two-phase method and the one-phase-low-pH method is also simpler and more efficient as it involves less number of injections.
相似文献20.
First principles calculations have been used to investigate the condensation reactions of hydrated calcium bicarbonate monomers in a simulated aqueous environment. The reaction pathway for the calcium bicarbonate dimerization process has been computed at the density functional theory-PBE level with the COSMO dielectric continuum model to simulate the hydrated environment. The results indicate that calcium bicarbonate dimers form via an associative mechanism: the first step involves a sevenfold calcium bicarbonate intermediate followed by the loss of one water molecule from the first coordination shell of calcium. Both steps are characterised by a low energy barrier of approximately 2 kcal mol−1, suggesting that the dimerization process is not kinetically hindered in aqueous solution. However, the Gibbs free energies for the condensation reactions to form the calcium bicarbonate dimers and the species Ca(HCO3)2(H2O)4, Ca(HCO3)3(H2O)3− and Ca2(HCO3)(H2O)103+, computed using the PBE and mPW1B95 density functional theory levels for the gas-phase component and the UAHF-CPCM solvation model for the hydration contribution, are all positive, which indicates that the formation of these early calcium bicarbonate clusters is thermodynamically unfavourable in aqueous solutions. Our calculations therefore suggest that the oligomerization of calcium carbonate is not spontaneous in water, at the conditions considered in our simulations, i.e. T = 298 K and neutral pH, which indicates that the nucleation of calcium carbonate cannot occur through a homogeneous process when calcium-bicarbonate ion pairs are the major source of CaCO3 in the aqueous environment. 相似文献