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1.
Magnesium concentrations in deep-sea sediment pore-fluids typically decrease down core due to net precipitation of dolomite or clay minerals in the sediments or underlying crust. To better characterize and differentiate these processes, we have measured magnesium isotopes in pore-fluids and sediment samples from Ocean Drilling Program sites (1082, 1086, 1012, 984, 1219, and 925) that span a range of oceanographic settings. At all sites, magnesium concentrations decrease with depth. At sites where diagenetic reactions are dominated by the respiration of organic carbon, pore-fluid δ26Mg values increase with depth by as much as 2‰. Because carbonates preferentially incorporate 24Mg (low δ26Mg), the increase in pore-fluid δ26Mg values at these sites is consistent with the removal of magnesium in Mg-carbonate (dolomite). In contrast, at sites where the respiration of organic carbon is not important and/or weatherable minerals are abundant, pore-fluid δ26Mg values decrease with depth by up to 2‰. The decline in pore-fluid δ26Mg at these sites is consistent with a magnesium sink that is isotopically enriched relative to the pore-fluid. The identity of this enriched magnesium sink is likely clay minerals. Using a simple 1D diffusion-advection-reaction model of pore-fluid magnesium, we estimate rates of net magnesium uptake/removal and associated net magnesium isotope fractionation factors for sources and sinks at all sites. Independent estimates of magnesium isotope fractionation during dolomite precipitation from measured δ26Mg values of dolomite samples from sites 1082 and 1012 are very similar to modeled net fractionation factors at these sites, suggesting that local exchange of magnesium between sediment and pore-fluid at these sites can be neglected. Our results indicate that the magnesium incorporated in dolomite is 2.0-2.7‰ depleted in δ26Mg relative to the precipitating fluid. Assuming local exchange of magnesium is minor at the rest of the studied sites, our results suggest that magnesium incorporated into clay minerals is enriched in δ26Mg by 0‰ to +1.25‰ relative to the precipitating fluid. This work demonstrates the utility of magnesium isotopes as a tracer for magnesium sources/sinks in low-temperature aqueous systems. 相似文献
2.
在模拟含Cu2+废水中加入Mg2+和Al3+,以NaOH为沉淀剂,研究金属盐水解即时合成层状双氢氧化物去除Cu2+的可行性,同时考察了体系终点pH值、配料中Mg/Cu摩尔比值及反应温度和时间对Cu2+去除率的影响,探讨了Cu2+去除机理及层状双氢氧化物形成过程。结果表明,实验条件下体系终点pH值显著影响Cu2+去除率,在pH值8.0~11.0范围内去除效果较好,达99%以上。通过X射线衍射分析结合即时合成法特点,废水中Cu2+主要是在晶核生成阶段以Cu/Mg/Al三元层状双氢氧化物形式被去除;三元层状双氢氧化物的形成由反应体系中Al3+、Cu2+、Mg2+分步水解导致,最适pH值约为9.0。 相似文献
3.
F. Ranjbar M. Jalali 《International Journal of Environmental Science and Technology》2016,13(8):1891-1916
This study was conducted to evaluate the efficiency of low-cost adsorbents including bentonite, kaolinite and zeolite saturated with calcium and potassium, potato and wheat residues, and three metal oxide nanoparticles functionalized with an acidic extract of potato residues in improving the quality of sodic waters. The optimization of factors such as pH, contact time, and adsorbent dosage was investigated using a solution containing sodium, calcium, magnesium, and potassium. The optimal pH and contact time were 7.0 and 24 h, respectively. The optimal dosage for using functionalized nanoparticles was 0.1 g and for using other adsorbents was 1.0 g. The sodium exchange isotherms were conducted in binary sodium–calcium and sodium–potassium and quaternary sodium–calcium–magnesium–potassium systems. Zeolite saturated with potassium was the most effective adsorbent in removing sodium from aqueous solutions with an average removal efficiency of 69.2 and 66.5 % in binary and quaternary systems, respectively. Freundlich and Langmuir equations fitted well to experimental data in both binary and quaternary systems. Cation selectivity coefficients calculated based on the Gaines–Thomas convention varied with changing pH and adsorbent dosage. Graphical and statistical evaluations confirmed that the mechanistic cation exchange model using average Gaines–Thomas selectivity coefficients in geochemical PHREEQC program was able to successfully simulate the sodium exchange on different adsorbents in both systems. The Gaines–Thomas selectivity coefficient values greater than unity and as a consequence, the negative values of the Gibbs free energy change of adsorption indicated that sodium exchange reactions in the presence of different adsorbents used is this study were exergonic and spontaneous. 相似文献
4.
The Palar and Cheyyar River Basins in Tamil Nadu state of Southern India are characterised by different geological formations, and groundwater is the major source for domestic, agricultural and other water-related activities. Hydrogeochemical studies were carried out in this area with the objective of identifying the geochemical processes and their relation to groundwater quality. Groundwater samples were collected once a month from 43 groundwater wells in this area from January 1998 to July 1999. Sampling procedures and chemical analysis were carried out as per the standard methods. Chemical data are used for mathematical calculations and graphical plots to understand the chemical process and its relation to the groundwater quality. The chemical composition of groundwater in the central part of the study area mainly depends on the recharge from lakes and the river, which is explained by a mixing mechanism. In addition, weathering of silicate minerals controls the concentration of major ions such as sodium, calcium, magnesium and potassium in the groundwater of this area. Further, the activity ratios indicate that the groundwater is in equilibrium with kaolinite, smectite and montmorrillonite. The reverse ion exchange process controls the concentration of calcium, magnesium and sodium in hard rock formations, and dissolution of carbonate minerals and accessory minerals is the source of Ca and Mg, in addition to cation exchange in the sedimentary formations. In general, the chemical composition of the groundwater in this area is influenced by rock–water interaction, dissolution and deposition of carbonate and silicate minerals, ion exchange, and surface water interactions. 相似文献
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6.
Richard A. Jahnke Steven R. Emerson Kevin K. Roe William C. Burnett 《Geochimica et cosmochimica acta》1983,47(2):259-266
Results of pore water and sediment analyses from the western Mexican continental margin strongly suggest the present day formation of apatite. The interstitial water phosphate and fluoride profiles indicate chemical removal at a depth which corresponds to a large maximum in the phosphorus content of the sediments. Apatite is identified within this maximum via X-ray diffraction but is elsewhere undetectable in the core. Radioisotopic thorium, uranium, and radium data support the conclusion that this deposit is modern. The present day depositional environment is consistent with those reported by other workers for phosphorite formation with the exception that pore water magnesium is not depleted below its seawater value. 相似文献
7.
Removal of chromium (VI) from aqueous solutions using Lewatit FO36 nano ion exchange resin 总被引：5，自引：4，他引：1
L. Rafati A. H. Mahvi Ph.D. A. R. Asgari M.Sc S. S. Hosseini B.Sc 《International Journal of Environmental Science and Technology》2010,7(1):147-156
The removal of the chromium (VI) ion from aqueous solutions with the Lewatit FO36 ion-exchange resin is described at different conditions. The effects of adsorbent dose, initial metal concentration, contact time and pH on the removal of chromium (VI) were investigated. The batch ion exchange process was relatively fast and it reached equilibrium after about 90 min of contact. The ion exchange process, which is pH dependent showed maximum removal of chromium (VI) in the pH range 5.0–8.0 for an initial chromium (VI) concentration of 0.5 mg/dm3. The equilibrium related to Lewatit FO36 ion- exchange capacity and the amounts of the ion exchange were obtained using the plots of the Langmuir adsorption isotherm. It was observed that the maximum ion exchange capacity of 0.29 mmol of chromium (VLVg for Lewatit FO36 was achieved at optimum pH value of 6.0. The ion exchange of chromium (VI) on this cation-exchange resin followed first-order reversible kinetics. 相似文献
8.
Cation exchange capacity measurements, performed before and after removal of humic acid from Narragansett Bay sediments, indicate that low concentrations of these organic substances strongly influence the ability of the sediment to react with metal ions. Atomic absorption and spectrophotometric methods allow quantitative determination of the extent of reaction between a naturally occurring humic acid and iron in artificial seawater. Humic acid-iron complexes are formed whose solubilities depend on the humic acid-iron ratio used in the experiment. This study suggests that humic acid is a transporting agent for trace metals in a marine environment. 相似文献
9.
Serpentinized peridotites in an area south of Timmins, Ontario,have been extensively altered to tale and carbonate. In someplaces, rocks altered in this way have subsequently been decarbonatizedand converted back to a serpentine-magnetite assemblage. Chemicalanalyses of variably altered rocks indicate that the bulk chemicalchanges involved in the tale-carbonate alteration have beenthe addition of CO2, and removal of H2O and a very small amountof O2. Little or no magnesium, silicon, iron, or nickel metasomatismhas occurred. Consequently the relative partial pressures ofH2O and CO2 in solutions passing through the rocks are likelyto have been controlling factors for the alteration and subsequentdecarbonatization. 相似文献
10.
Studies of groundwater following changes to the wastewater treatment plant and disposal field at Kinloch (Taupo area, New Zealand) showed increases in chloride (Cl) after 5 months, followed by increased calcium (Ca) and magnesium (Mg) concentrations arising as a result of cation exchange with sodium (Na) and potassium (K). Sodium (Na) and potassium (K) showed only small increases after 12 months of initial discharge, while phosphorus (P) was still being totally adsorbed by ion exchange in the aquifer. 相似文献
11.
在多级折流板反应器生物处理装置中,采用活性炭为载体人工固定化生物处理合成染料废水,出水水质稳定, 出水中的烷烃肽链变短;其对CODCr和BOD5的去除率可达96.46%、99.77% ;对SO2-4和钙镁总量的去除效率超过80.37%、78.66%;折流板反应器的容积负荷率Nv可达2.8 kg COD/(d•m3)。活性炭经生物固定化后,不仅不会影响它的处理效果,还会延长活性炭的使用寿命;当冲击性有机负荷发生时,固定化生物活性炭能够承受并能很快恢复。 相似文献
12.
The rate of silica removal from two montmorillonites (Chambers and Polkville) has been measured as a function of time, temperature, solution composition, and exchange ion on the clay. Silica removal rate increased with temperature from 200 to 350°C, decreased with time, and could be approximated initially by a parabolic rate law. Solution composition influenced silica removal rate by determining the exchange population of the clay; silica removal is most rapid when K-exchange ions are present. Thus increasing the concentration of K+ accelerated silica removal, whereas increasing the concentration of Na+, Ca2+, and Mg2+ inhibited silica removal. Activation energies for silica removal range from 5 to 10 kcal/mol. The largest values are associated with the largest concentrations of inhibitor ions in solution. Activation energies of this magnitude suggest that the rate-limiting step for silica removal is transport through a hydrated, expanded interlayer space. Application of experimental results to diagenesis in moderately to deeply buried sediments suggests that K+ uptake by montmorillonite may precede and accelerate illite formation. 相似文献
13.
J. Alcock 《Contributions to Mineralogy and Petrology》1996,124(2):209-215
Garnets that exhibit mixed growth and diffusion zoning are used to evaluate the effect of grossular content on garnet Fe–Mg exchange reactions. These garnets from the uppermost amphibolite-facies to granulite-facies gneiss of the Wissahickon Group, southeastern Pennsylvania, show variation in grossular content (0.035<X Ca<0.14) but nearly constant Mg? (X Mg/(X Mg+X Fe) and X Mn through the interior indicating re-equilibration of garnet and matrix minerals with respect to iron, magnesium, and manganese. Mg? is not correlated with calcium content, evidence that the effect of calcium on garnet Fe–Mg exchange reactions is small or is offset by other interactions in almandine-rich garnets. In either case, the data presented here indicate that correction for calcium content of garnets in the application of garnet-biotite geothermometry to high-grade metapelites is unnecessary and may lead to an overestimate of peak temperature. 相似文献
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15.
13X沸石分子筛对饮用水中NH_4~+-N吸附性能的实验研究 总被引：4，自引：1，他引：4
研究了 13X沸石分子筛对饮用水中低浓度NH+4 N的吸附性能 ,包括影响吸附的主要因素、沸石对NH+4 N的吸附效果、沸石的再生效果及沸石对NH+4 N的吸附机理。实验表明用NaOH处理的沸石比未处理的沸石对NH+4 N的吸附效果要好。在 pH值为 6 5～ 7 5、吸附时间为 2 0min、吸附温度为 2 0～ 30℃的条件下 ,沸石对NH+4 N的吸附率接近 10 0 % ,沸石对NH+4 N的吸附量可达 16 32mg/g。用直接焙烧法进行再生活化处理后的沸石对NH+4 N的吸附率仍接近 10 0 % ,沸石对NH+4 N的吸附机理是以离子交换吸附作用为主。 13X沸石吸附NH+4 N的过程符合Langmuir吸附等温模式。实验证明 ,利用 13X沸石净化含低浓度NH+4 N的饮用水具有良好的工业化应用前景。 相似文献
16.
The objective of this study is to locate as closely as possible the sites of strontium, magnesium, sodium, and potassium in modern aragonitic corals, specifically whether these cations are adsorbed, or are substituted in the carbonate lattice or are incorporated in organic components. In addition to locating the sites of each of these four elements we wanted to find out quantitatively how much of each element occurs at each site. The experiments in this study are based on the dissolution rate of aragonite in distilled water and on the substitution of strontium and magnesium by calcium and sodium. Special attention has been given to the occurrence of strontium, magnesium, sodium, and potassium in the organic components of the corals. The main site for strontium in the corals is in the aragonite lattice. Twenty-five per cent of the total magnesium occurs in adsorbed sites and in organic compounds. The rest of the magnesium may be located in the aragonite lattice, but it is easily removed by repeated leaching or by replacement with calcium ions. Another possibility is that magnesium may occur in a dispersed mineral phase more soluble than aragonite because magnesium was released at a higher Mg to Ca ratio than is found in the solid coral; also because no local concentration of magnesium could be detected with an electron microprobe. About 12% of the total sodium is in adsorbed sites and is included in the organic compounds. The rest of the sodium might be in the lattice replacing calcium, but the low total exchange capacity is not enough to provide the needed charge balance. Another possibility is that sodium is located in a proposed mineral phase. Potassium is in adsorbed sites and incorporated in the organic compounds to an extent greater than all the other elements studied (30% of the total potassium), but again the evidence suggests that the remaining potassium is in a proposed mineral phase. Calcite is detected on the surfaces of aragonite corals after 5 months in the substitution experiment. The change of argonite to calcite took place after the inhibitor magnesium was exchanged from the surface sites and replaced by calcium. The organic compounds in corals contain small amounts of strontium, magnesium, sodium and potassium. Strontium is preferentially enriched in the organic compounds over magnesium. 相似文献
17.
氮迁移转化对地下水硬度升高的影响 总被引：15，自引：0，他引：15
城市地下水硬度升高是一个普遍的环境问题,研究表明地下水硬度高值区与硝酸盐污染在空间上的分布具有一致性。通过室内土柱试验和化学热力学模拟,讨论了污水入渗过程中氮迁移转化对水土系统钙镁迁移的影响。结果表明：在连续入渗条件下,阳离子交换作用是控制地下水硬度升高的主要过程;在间歇入渗条件下,硝化作用改变了土水系统的酸碱条件,使钙镁难溶盐溶解,导致地下水硬度升高。 相似文献
18.
Christopher J. Hatton 《Contributions to Mineralogy and Petrology》1984,86(1):45-53
The coefficient for iron and magnesium exchange between olivine and liquid is modelled as a function of temperature in the simple system MgO-FeO-SiO2, and is found to be temperature insensitive in the range 1,200–1,400° C, but temperature sensitive at higher temperatures. In natural systems silica and the alkalis have a strong effect on the exchange coefficient. This effect is approximated by a simple mixture model for the silicate liquid.The influence of pressure is theoretically estimated by the Clapeyron equation, and accord between predicted and observed values is found in experimental melts formed at 20 to 30 kbar. The equation for the exchange coefficient as a function of temperature, pressure and composition is used to test models for the reversal in the normal fractionation trend in the eastern and western Bushveld Complex. Multiple magma intrusion is the only satisfactory hypothesis for this feature. 相似文献
19.
Laboratory and pilot testing of electrocoagulation for removing scale-forming species from industrial process waters 总被引：1，自引：1，他引：0
M. C. Schulz J. C. Baygents Ph.D. J. Farrell Ph.D. 《International Journal of Environmental Science and Technology》2009,6(4):521-526
This study investigated the performance of electrocoagulation using iron and aluminum electrodes for removing silica, calcium and magnesium from cooling tower blowdown and reverse osmosis reject waters. Experiments were conducted at both the bench and pilot scales to determine the levels of target species removal as a function of the coagulant dose. At the bench scale, aluminum removed the target compounds from both cooling tower blowdown and reverse osmosis reject more efficiently than iron. A 2 mM aluminum dose removed 80 % of the silica and 20 to 40 % of the calcium and magnesium. The same iron dose removed only 60 % of the silica and 10 to 20 % of the calcium and magnesium. When operated with iron electrodes, pilot unit performance was comparable to that of the bench unit, which suggests that such systems can be scaled-up on the basis of coagulant dose. However, when operated with aluminum electrodes the pilot unit underperformed the bench unit due to fouling of the electrode surfaces after a few hours of operation. This result was completely unexpected based on the short-term experiments performed using the bench unit. 相似文献
20.
V.N. Viswanathan D.V. Ramana Rao K. Kumar S.J. Raina 《International Journal of Mineral Processing》1979,6(2):73-83
By use of a recarbonation process, it is possible to separate magnesium carbonate and calcium carbonate from dolomites/dolomitic limestones. Magnesium carbonate can be used for manufacturing basic refractories and magnesium chemicals; the portion rich in calcium carbonate can be used for cement manufacture if the MgO content is below 3%. In this paper the process developed for the purpose and the results of bench scale tests are reported. The results indicate that, under optimum conditions, both objectives can be fulfilled by the recarbonation process. 相似文献