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1.
氯化物对方解石和白云石矿物溶解度的影响   总被引：12，自引：1，他引：11  
借助PHREEQC软件,文章对方解石、白云石分别在无CO2和大气PCO2条件下NaCl、KCl、CaCl2和MgCl2溶液中的溶解度进行了模拟计算,结果显示:方解石在NaCl、KCl、和MgCl2溶液中以及白云石在NaCl、KCl溶液中的溶解度比纯水中大得多,其原因主要是盐效应。由于同离子效应,在CaCl2溶液中可降低方解石溶解度,而白云石在较高浓度CaCl2或MgCl2溶液中,虽发生同离子效应,其溶解度仍较纯水中有不同程度提高。模拟还显示,方解石在MgCl2溶液中以及白云石在CaCl2溶液中溶解时将分别发生白云石化和去白云石化反应,从而促使不全等溶解继续发生。在常规离子中,按方解石、白云石溶解度提高发挥作用的重要性排序为:阴离子中都是SO24->Cl-;对于方解石溶解,阳离子中Mg2+>Na+>K+>Ca2+;对于白云石溶解,当PCO2=0或PCO2=10-3.5bar且CaCl2浓度大约在1.5mol/L以下时,Na+>K+>Ca2+>Mg2+;当PCO2=10-3.5bar且CaCl2浓度大约在1.5mol/L以上时,Ca2+>Na+>K+>Mg2+。  相似文献   

2.
利用原位低温拉曼光谱分析技术,对在设定的实验条件下合成的CaCl2-H2O体系和MgCl2-H2O体系的流体包裹体进行分析研究,结果表明低温下CaCl2水溶液和MgCl2水溶液形成的盐水合物具有各自不同的特征拉曼光谱,通过测定特征光谱,能够简易直接的鉴定这些物质,进而确定盐水体系包裹体的成分.因此,原位低温拉曼光谱技术,能够有效地测定Ca2+和Mg2+这两种盐水体系包裹体流体中常见,但显微测温过程难以观察和判别的二价阳离子.实践表明,原位低温拉曼光谱分析技术是对传统的流体包裹体显微测温技术的一个十分有效的补充,在包裹体研究领域会得到越来越广泛的应用.  相似文献   

3.
通过对pH、Eh、溶液中Fe2+浓度的定期监测以及对实验结束时生成沉淀的XRD、SEM和元素能谱扫描等手段,对比研究了不同初始浓度的As(Ⅴ)对Fe2+的化学氧化和嗜酸性氧化亚铁硫杆菌(Acidithiobacillus ferrooxidans)氧化的影响, 同时就As(Ⅴ)在实验体系中固液相之间的分配行为进行了分析.结果表明,Fe2+的化学氧化速率极低,最终氧化率低于8%,As(Ⅴ)的浓度对Fe2+的化学氧化没有影响.有A. ferrooxidans的实验体系,100 mg/L As(Ⅴ)对Fe2+的氧化具有一定的促进作用.当As(Ⅴ)浓度为500 mg～1 g/L时,Fe2+的氧化率在约60 h左右即可达到100%;但4g/L的As(Ⅴ)则会明显抑制Fe2+的氧化,Fe2+的完全氧化大约需要106 h.体系中初始的100 As/(As+S)(摩尔比)会对沉淀物的物相及结晶程度造成一定影响.As(Ⅴ)浓度为0 g/L时,微生物体系中生成的固体沉淀物黄钾铁矾的特征峰明显,随着As(Ⅴ)浓度的提高,沉淀物的结晶程度逐步下降,至4 g/L时沉淀物全部为无定形.元素能谱扫描检测到有大量的As(Ⅴ)存在于固体沉淀物中,表明在Fe2+的氧化过程中,As(Ⅴ)可能会以吸附或共沉淀的形式被固定在固相沉淀物中,这为酸性矿坑水(AMD)地区As(Ⅴ)污染的治理提供了重要的参考.  相似文献   

4.
根据39个丰水期地下水的水化学分析结果,对德阳市城市规划区内地下水水化学特征及空间分布进行了研究。研究表明:(1)沿地下水渗流途径,TDS以及Mg2+、Na+、SO42-浓度呈上升趋势;而Ca2+浓度却呈下降趋势。(2)地下水化学类型具有较明显的分带性,在渗流途径的上游,水化学类型以HCO3-Ca型水和HCO3-Ca+Mg型水为主;在径流途径的下游或排泄区域,水化学类型以HCO3+SO4-Ca+Mg型水和HCO3+SO4-Na+Ca型水为主。(3)区内铁锰污染比较明显,部分地区总铁和锰的含量达到Ⅳ类地下水标准,铁锰超标主要是受原生地质环境的影响;总硬度超标明显,39件水样中12件达到Ⅳ类地下水标准。  相似文献   

5.
雪玉洞岩溶地下水、地表水Ca2+、Mg2+、Sr2+变化特征研究   总被引：2，自引：1，他引：1  
通过2011年对重庆丰都雪玉洞洞内滴水和地下河河水,上覆岩层中出露的表层岩溶泉水和雪玉洞附近龙河河水等不同类型水中Ca2+、Mg2+、Sr2+浓度及Mg/Ca、Sr/Ca值的研究,发现不同水的Ca2+、Mg2+、Sr2+随外界降水条件的改变而出现明显变化。表层岩溶泉水Ca2+变化能够敏感反应外界降水条件改变,滴水对外界降雨的反应滞后接近1个月,地下河Ca2+可以反应雨季和旱季的变化,地表河水Ca2+全年比较稳定,但是对特殊干旱天气有显著响应。2011年不同类型水的Mg2+、Sr2+全年变化趋势基本一致,在降水较多的3、5、10月呈低值,在其他降水较少的月份浓度相对较高。各离子的这种变化特征主要是受到稀释效应、CO2效应以及所在地层的岩性的影响。雪玉洞不同类型水的Mg/Ca、Sr/Ca值呈现出滴水>地表河>地下河>表层岩溶泉的特点,反映出不同类型水在含水介质中滞留时间的长短,并且Mg/Ca、Sr/Ca值在降水较多的月份降低,在降水较少的月份升高;受碳酸钙的前期沉淀和运移路径差异的影响,不同类型水的Mg/Ca、Sr/Ca值变化稍有不同。因此,不同类型水的离子变化及其比值对外界降水条件变化的响应特征和时间的不同,决定了在利用元素及其比值反映外界环境变化时也要区别对待。   相似文献   

6.
重庆市南川区南部岩溶地下水水文地球化学特征   总被引：4，自引：2，他引：2  
以重庆市南川区南部地区岩溶地下水为研究对象,通过野外调查和取样测试分析,对研究区内149件地下水样品进行水化学常规分析和微量重金属元素分析,结果表明:研究区内地下水化学类型以HCO3-Ca·Mg、HCO3-Ca和HCO3-SO4-Ca型为主。地下水中主要阴阳离子HCO3-、SO42-、Ca2+和Mg2+浓度均表现出与含水岩组相对应的关系,即碳酸盐岩类岩溶水＞碳酸盐岩夹碎屑岩水＞碎屑岩水。地下水中Mg2+ /Ca2+摩尔比值表明研究区内绝大部分地下水径流过程中以方解石和白云石的共同溶解为主。地下水中微量重金属元素含量整体偏低,绝大部分水质都在Ⅲ类水标准以内,只有极个别点受到污染导致部分重金属组分偏高   相似文献   

7.
曹明达  周忠发  张强  谢雅婷  张绍云 《中国岩溶》2016,35(3):314-321,348
为揭示洞穴水地球化学特征的动态变化特征、控制因素及其环境意义,从2015年1月至2015年6月对贵州织金洞洞穴水的水化学指标进行了为期6个月的动态监测,结果表明:①织金洞洞穴水的水化学类型主要为HCO3--Ca2+-Mg2+型水,阴离子中HCO3-占84.5%以上,阳离子中Ca2+、Mg2+为优势离子;②洞穴滴水 EC、Ca2+、 Mg2+、HCO3-、SO42-浓度均大于石灰岩石裂隙水、池水相应的浓度;③洞穴水滴率、滴量、Ca2+、HCO3-以及Ca2+/HCO3-比值对气候有一定的响应,其地球化学指标具有显著的季节效应;④洞穴滴水中的EC与Ca2+离子浓度呈显著线性关系。   相似文献   

8.
梭菌对含镁方解石形态的控制及其可能机理   总被引：1，自引：0，他引：1  
在 Mg/Ca 摩尔比为 4∶1 的 Lagoa Vermelha 培养基中对一株分离自青海湖底沉积物的梭菌 SN-1（Clostridium sp.）进行了为期 55 d 的碳酸盐矿物培养实验,同时还完成了一组无菌对照实验。利用扫描电子显微镜对沉淀物进行了系统的观察,用 X- 射线衍射仪对沉淀物的矿物成分进行了测定。结果表明：（1）SN-1 可以促进特殊形态含镁方解石的形成,而无菌对照实验产物中仅见不规则状的碳酸盐矿物;（2）特殊形态的含镁方解石可能是在细菌表面成核和生长的结果,它们的演化趋势是（杆状）→哑铃形→花菜状→球形。作者认为这是因为梭菌两端的带负电基团比菌体中间丰富,易聚集更多的 Ca2+和 Mg2+,Ca2+和 Mg2+离子作为“阳离子桥”吸引 CO32-,其结果是两端的晶体生长相对较快、中间生长相对较慢,进而形成哑铃形含镁方解石;“哑铃”继续生长,其两端会长成两个“花菜”或半球;若两个半球相接并闭合则发展为球状矿物。  相似文献   

9.
本文通过两组不同水镁石-苯酚投料比的实验,研究固体沉淀物与水质变化的关系。实验显示,水镁石解离出的Mg2+与苯酚降解的中间产物能形成难溶盐,并发生沉淀分离,促进含苯酚废水臭氧化降解的效率。当苯酚的初始浓度为47 g/L,初始碳镁原子比(C/Mg)为30时,经3小时充分臭氧化曝气后,投加的水镁石全部耗尽。XRD、TG/DSC结果显示新形成的沉淀物为草酸镁。反应终点的pH值在4以下,TOC去除率为40%。当体系的初始C/Mg(原子比)为1,苯酚的初始浓度为1.5 g/L时,同样的臭氧化曝气过程体系残留的沉淀物仍是水镁石。反应终点的pH值在10左右,TOC去除率为92.8%。研究证明,苯酚臭氧化过程也是体系酸化的过程,至少在高C/Mg比条件下新生的质子能与水镁石解离出的羟基中和,水镁石解离出的Mg2+可与草酸根结合沉淀出草酸镁。  相似文献   

10.
塔里木盆地哈得逊油田石炭系地层水化学特征及成因   总被引：3，自引：0，他引：3  
塔里木盆地哈得逊油田石炭系地层水化学分析结果表明,地层水是以阴阳离子分别为Cl-和(Na++K+)为主的CaCl2型水,具有高矿化度特征(112～291 g/L)。地层水的钠氯系数均值为0.78,脱硫酸系数均值为0.23,Schoeller碱交换指数(IBE)均值为128。地层水化学参数在平面上相对变化不大,在剖面上随深度的增加,HCO3-、SO42-含量具有减小的趋势,而其他离子变化相对较小,表明研究区内的地层水形成于深部封闭环境条件下。地层水化学分析表明,该区地层水经历了强烈的阳离子交替吸附和水岩相互作用。(铁)白云石化作用导致了Ca2+的富集和Mg2+的亏损,形成了现今的地层水离子分布特征。石炭系地层水在构造反转油气藏调整时期一直处于相对封闭的流体动力环境中,这种环境有利于油气的聚集与保存。  相似文献   

11.
周根陶  郑永飞 《地质科学》2000,35(3):325-335
通过缓慢分解Ca2+-Mg2+-HCO3--Cl--H2O溶液和以菱锶矿(或碳钡矿、白铅矿)为晶种的附晶生长法,在0-90℃温度范围内定向合成了碳酸钙同质多象变体.矿物合成实验结果表明,随着温度升高,有利于亚稳态文石和不稳定六方方解石的生成;随着溶液中Mg2+离子浓度增大和Ca(HCO3)3溶液浓度减小,均有利于亚稳态文石的形成.以XRD和SEM技术为实验手段,详细研究了碳酸钙同质多象转变过程.结果显示:在流体参与的情况下,文石→方解石和六方方解石→方解石的同质多象转变速率很快,并且其转变的矿物学机理为溶解/再沉淀.  相似文献   

12.
Cobalt, like Mg, may cause the precipitation of aragonite rather than calcite in aqueous solutions due to the adsorption and crystal poisoning of calcite by a hydrated ion. Solutions containing NaCl and CaCl2, having the ionic strength and Ca content of seawater (35‰ salinity), were spiked with known amounts of CoCl2. Calcium carbonate was precipitated by the addition of 0.7 ml of 1 M Na2CO3. All experimental runs were made at 25°C, and all products were examined by X-ray diffraction. At low concentrations of Co (< 5·?4M) calcite and vaterite formed. At concentrations from 5·10?4 M to 2·10?3M, the products consisted of combinations of calcite and vaterite; aragonite and calcite; aragonite and vaterite; calcite, vaterite and aragonite. In solutions of 3·10?3M CoCl2, most precipitates were aragonite with only one sample containing a small amount of calcite. All precipitates from 5·10?3M CoCl2 solutions either contained aragonite or were amorphous. Solutions with concentrations of 1 · 10?2M CoCl2 produced only amorphous precipitates. All precipitates contained an amorphous violet phase, assumed to be basic cobaltous carbonate (2CoCO3·Co(OH)2·H2O).  相似文献   

13.
Highly supersaturated solutions of Ca2+ and CO2−3 ions rapidly precipitate amorphous calcium carbonate, ACC, the logarithmic thermodynamic solubility product of which is about −6.0 at 25°C. The ACC initially formed is transformed to a mixture of several crystalline calcium carbonate polymorphs within several minutes. The transformed polymorphs are vaterite and calcite at low temperature (14 to 30°C), and aragonite and calcite at high temperature (60 to 80°C). At intermediate temperatures (40 to 50°C) the formation of all three polymorphs was observed. Metastable polymorphs are gradually transformed to the stable form, calcite. It takes about 200 min at 25°C and 370 min at 30°C for the complete transformation of vaterite to calcite, and 1000–1300 min for that of aragonite to calcite at 60–80°C. At 50°C, vaterite is predominantly transformed at first to aragonite within 60 min, and then the aragonite is transformed to calcite in about 900 min. The results of the change in the ion activity product of the solution and the abundances of the polymorphs strongly suggest that the polymorphic transformation of vaterite and aragonite to calcite takes place through dissolution of the metastable phase and growth of the stable phase, calcite. The rate-determining step of the transformation is the growth of calcite. The relative abundance of vaterite becomes higher at 25°C with increasing concentrations of calcium and carbonate ions in the supersaturated solution. When the ion activity product of the initial supersaturated solution is lower than the solubility product of ACC at 25°C, only vaterite directly precipitates after some induction period. The vaterite crystals formed are free of calcite seeds and the vaterite saturated solutions are stable for several days.  相似文献   

14.
Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition (δ13C) values of the carbonate sediment (?1‰ to ?2‰) have no relation to the oxygen isotope composition of the carbonate (δ18O) values (?7‰ to ?8‰), with both isotopes showing a low variability. The carbonate content is low (<20%). Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with δ13C values between approximately +0.5‰ and +3‰, and δ18O values between ?1‰ and ?5‰. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg–calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg–calcite. Evaporation and biological processes are the main reasons for the salinity and carbonate mineralogy influence of the surface-sediment carbonate in Bosten Lake. The lake water residence time and the CO2 exchange between the atmosphere and the water body control the carbon and oxygen isotope composition of the carbonate sediment. In addition, organic matter pollution and decomposition result in the abnormally low carbon isotope values of the lake surface-sediment carbonate.  相似文献   

15.
Adsorption and Desorption of Phosphate on Calcite and Aragonite in Seawater   总被引：3，自引：0，他引：3  
The adsorption and desorption of phosphate on calcite and aragonite were investigated as a function of temperature (5–45 °C)and salinity (0–40) in seawater pre-equilibrated with CaCO3. An increase in temperature increased the equilibrium adsorption; whereas an increase in salinity decreased the adsorption. Adsorption measurements made in NaCl were lower than the results in seawater. The higher values in seawater were due to the presence of Mg2+ and Ca2+ ions. The increase was 5 times greater for Ca2+ than Mg2+. The effects ofCa2+ and Mg2+ are diminished with the addition of SO4 2- apparently due to the formation of MgSO4 and CaSO4 complexes in solution and/or SO4 2- adsorption on the surface of CaCO3. The adsorbed Ca2+ and Mg2+ on CaCO3 (at carbonate sites) may act as bridges to PO4 3- ions. The bridging effect of Ca2+is greater than Mg2+ apparently due to the stronger interactions of Ca2+ with PO4 3-.The apparent effect of salinity on the adsorption of PO4 was largely due to changes in the concentration of HCO3 - in the solutions. An increase in the concentration of HCO3 - caused the adsorption of phosphate to decrease, especially at low salinities. The adsorption at the same level of HCO3 - (2 mM) was nearly independent of salinity. All of the adsorption measurements were modeled empirically using a Langmuir-type adsorption isotherm[ [PO4]ad = KmCm[PO4]T/(1 +Km [PO4]T) , ]where [PO4]ad and [PO4]T are the adsorbed and total dissolved phosphate concentrations, respectively. The values of Cm (the maximum monolayer adsorption capacity, (mol/g) and Km (the adsorption equilibrium constant, g/(mol) over the entire temperature (t, °C) and salinity (S) range were fitted to[ Cm = 17.067 + 0.1707t - 0.4693S + 0.0082S2 ( = 0.7) ][ ln Km = - 2.412 + 0.0165t - 0.0004St - 0.0008S2 ( = 0.1) ]These empirical equations reproduce all of our measurements of[PO4]ad up to 14 mol/g and within ±0.7 mol/g.The kinetic data showed that the phosphate uptake on carbonate minerals appears to be a multi-step process. Both the adsorption and desorption were quite fast in the first stage (less than 30 min) followed by a much slower process (lasting more than 1 week). Our results indicate that within 24 hours aragonite has a higher sorption capacity than calcite. The differences between calcite and aragonite become smaller with time. Consequently, the mineral composition of the sediments may affect the short-term phosphate adsorption and desorption on calcium carbonate. Up to 80 % of the adsorbed phosphate is released from calcium carbonate over one day. The amount of PO4 left on the CaCO3 is close to the equilibrium adsorption. The release of PO4 from calcite is faster than from aragonite. Measurements with Florida Bay sediments produced results between those for calcite and aragonite. Our results indicate that the calcium carbonate can be both a sink and source of phosphate in natural waters.  相似文献   

16.
There are 59 springs at the Gevas–Gurp?nar–Güzelsu basins, 38 of these springs emerge from the fractured karst aquifers (recrystallized limestone and travertine) and 21 emerge from the Yuksekova ophiolites, K?rkgeçit formation and alluvium. The groundwater samples collected from 38 out of the total of 59 springs, two streams, one lake and 12 wells were analyzed physico-chemically in the year 2002. EC and TDS values of groundwater increased from the marble (high altitude) to the ophiolites and alluvium (toward Lake Van) as a result of carbonate dissolution and connate seawater. Five chemical types of groundwater are identified: Ca–Mg–HCO3, Mg–Ca–HCO3, Mg–Na–HCO3, Na–Ca–HCO3 and Mg–Ca–Na–HCO3. The calculations and hydrochemical interpretations show that the high concentrations of Ca2+, Mg2+ and HCO3 ? as predominant ions in the waters are mainly attributed to carbonate rocks and high pCO2 in soil. Most of the karst springs are oversaturated in calcite, aragonite and dolomite and undersaturated in gypsum, halite and anhydrite. The water–rock interaction processes that singly or in combination influence the chemical composition of each water type include dissolution of carbonate (calcite and dolomite), calcite precipitation, cation exchange and freshening of connate seawater. These processes contribute considerably to the concentration of major ions in the groundwater. Stable isotope contents of the groundwater suggest mainly direct integrative recharge.  相似文献   

17.
Shoreline carbonate deposits of Pleistocene Lake Bonneville record the conditions and processes within the lake, including the evaporative balance as well as vertical and lateral chemical and isotopic gradients. Tufas (swash‐zone) and tufaglomerates (cemented, subaqueous colluvium or beachrock) on multiple, well‐developed shorelines near the Silver Island Range, Utah, also present an opportunity to examine physicochemical lake processes through time. Three shorelines are represented by carbonate deposits, including the 23–20 ka Stansbury stage, 15–14.5 ka Bonneville stage, and 14.5–14 ka Provo stage. Mean δ18OVSMOW values of all three shorelines are statistically indistinguishable ( ～ 27 ± 1‰), when a few Bonneville samples of unusual composition are neglected. However, differences in primary carbonate mineralogy indicate that the correspondence is an artefact of the different fractionation factors between calcite or aragonite and water. Second, in order to sustain a much smaller, shallower lake during the colder Stansbury stage, the climate must have also been relatively dry. Third, δ18O values in tufa are higher than tufaglomerate by ～ 0.5‰, consistent with greater evaporative enrichment of lake water in the swash zone. Fourth, mean δ13C values for the Provo, Stansbury and Bonneville shorelines (4.4, 5.0 and 5.2‰, respectively) show that carbon species were dominated by atmospheric exchange, with the variations produced by differences in the oxidation of organic matter. Comparisons of shoreline carbonates with deep‐lake marls of the same approximate age indicate that shoreline carbonate was much higher in δ13C and δ18O values (both ～ 2.5‰) during Bonneville time, whereas isotopic differences were minor (both ～ 1‰) in Stansbury time. In particular, the Bonneville stage may have sustained large vertical or lateral isotopic gradients due to evaporative enrichment effects on δ18O values. In contrast, the lake during the much shallower Stansbury stage may have been well mixed. Differences in the primary mineralogy (Stansbury and Bonneville, aragonite > calcite; Provo, calcite > aragonite) reflect profound differences in lake chemistry in terms of open versus closed‐basin lakes. The establishment of a continuous outlet during Provo time probably reduced the Mg2+/Ca2+ ratio of lake water. Curiously, regardless of primary mineralogy, tufaglomerate cements are enriched in Na+ and Cl? and depleted in Mg2+ relative to capping tufa of the same age. This probably reflects vital or kinetic effects in the swash zone (tufa). We suspect that ‘abiotic’ effects may have been important in the dark pore space of developing tufaglomerate, where the absence of light suppressed photosynthesis. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

18.
Holocene stromatolites are described from Lake Walyungup, a coastal hyposaline lake in south-western Australia. At summer low water, this groundwater-fed depression comprises two permanent shallow water bodies and an ephemeral southern pool, set within an areally extensive littoral zone of variably cemented carbonate crust. Up to 5 m of organic-rich carbonate mud has been deposited within each of these basins in less than 7000 years. Stromatolites rim the water bodies with individual columns up to 2 m tall. Stromatolite-capped tepee structures in subparallel alignment are widespread in the littoral crust, suggesting a linkage between stromatolite growth and zones of groundwater discharge. Lake Walyungup stromatolites, regardless of external morphology and setting, are coarsely laminated and have aragonitic mesoclot microfabrics. These microfabrics are similar to those from lithified portions of active thrombolitic microbialites from nearby Lake Clifton. Hydromagnesite is a minor to subdominant phase (up to 47 wt%) of the carbonate mineral assemblage in Lake Walyungup. It occurs mainly in the littoral zone as a diagenetic replacement of precursor aragonite, particularly within the mesoclot fabric of stromatolites, but also in sediments (strandline and dune sand, crusts) derived mainly from erosion of stromatolites. In contrast with nonreplaced and impermeable inorganic aragonitic cements, stromatolite mesoclots are microper- meable. Micropermeability is inferred to facilitate hydromagnesite diagenesis. Dolomite is also present in minor amounts as a pore fill in stromatolites, and as a subdominant to dominant (up to 100 wt%) phase in thin, mudcracked micrite layers within the crust package. The layered dolomite may be precipitated directly from the lake water. Major element abundance of the lake water is: Na+ > Mg2+ » K+ > Ca2+ for cations, and Cl? » SO42? ≈ HCO3? > CO32? for anions. Compared to other nearby coastal lakes, Lake Walyungup has a high pH (> 9·0), and an extremely high molar Mg/Ca ratio of > 90. Groundwater in the area has a Mg/Ca ratio generally less than 1. The unusual Mg/Ca ratio in Lake Walyungup is partially a result of in-lake processes with additional minor contribution of Mg2+ sourced from basal marine sand because no Mg-rich bedrock source has been found in the region.  相似文献   

19.
Conventional hydrochemical techniques and statistical analyses were applied to better understand the solute geochemistry and the hydrochemical process of shallow groundwater in the Qinghai Lake catchment. Shallow groundwater in the Qinghai Lake catchment is slightly alkaline, and is characterized by a high ion concentrations and low water temperature. The total dissolved solids (TDS) in most of the samples are <1,000?mg/L, i.e. fresh water and depend mainly on the concentration of SO4 2?, Cl? and Na+. Groundwater table is influenced directly by the residents?? groundwater consumption. Most of the groundwaters in the Qinghai Lake catchment belong to the Ca2+(Na+) ?CHCO3 ? type, while the Qinghai Lake, part of the Buha (BHR) and the Lake Side (LS) samples belong to the Na+?CCl? type. The groundwater is oversaturated with respect to aragonite, calcite and dolomite, but not to magnesite and gypsum. Solutes are mainly derived from strong evaporite dissolution in Daotang, BHR and LS samples and from strong carbonate weathering in Hargai and Shaliu samples. Carbonate weathering is stronger than evaporite dissolution with weak silicate weathering in the Qinghai Lake catchment. Carbonate weathering, ion exchange reaction and precipitation are the major hydrogeochemical processes responsible for the solutes in the groundwater in the Qinghai Lake catchment. Most of the shallow groundwaters are suitable for drinking. More attention should be paid to the potential pollution of nitrate, chloride and sulfide in shallow groundwater in the future.  相似文献   

20.
Calcite crystals were grown in a closed system by recrystallization of synthetic and natural aragonite crystals, in the presence of various CaCl2-MgCl2 solutions with and without NaCl.The distribution of Mg2+ between calcite and solution at the entire temperature range is heterogeneous, closely following the Doerner-Hoskins (Doerner and Hoskins, 1925) distribution law. λMg2+C is strongly dependent on temperature, being: 0·0573 ± 0·0017 at 25°C, 0·0681 ± 0·0019 at 35°C, 0·0778 ± 0.0022 at 50°C, 0·0973 ± 0·0021 at 70°C, and 0·1163 ±0 ·0034 at 90°C. λMg2+C is independent of the absolute concentration of Ca2+ in solution as well as of the presence of NaCl.Relatively high λMg2+C values are obtained during the initial reaction stages when too-highly reactive synthetic aragonites are recrystallized. SEM micrographs show that calcite crystals grown from such aragonites are imperfect and that their earlier formed Mg-rich cores redissolve later, resulting in apparently inconsistent λMg2+C values.Calculations applying the new λMg2+C value for 25°C and the solubility data for magnesian calcites (Chaveet al., 1962) demonstrate that although no calcite should be expected to precipate directly from open sea water, its direct precipitation (or recrystallization from aragonite) is possible in closed diagenetic systems which still contain marine solutions, provided a temporary increase in the dissolved calcium concentration takes place.The λMg2+C values obtained allow for a new insight into processes of calcite cementation of reefs and a variety of other carbonate sediments, and for a more precise definition of dedolomitization chemistry.  相似文献   

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