Reactive transport of metal contaminants in alluvium—model comparison and column simulation

A comparative assessment of two reactive-transport models, PHREEQC and HYDROGEOCHEM (HGC), was done to determine the suitability of each for simulating the movement of acidic contamination in alluvium. For simulations that accounted for aqueous complexation, precipitation and dissolution, the breakthrough and rinseout curves generated by each model were similar. The differences in simulated equilibrium concentrations between models were minor and were related to (1) different units in model output, (2) different activity coefficients, and (3) ionic-strength calculations. When adsorption processes were added to the models, the rinseout pH simulated by PHREEQC using the diffuse double-layer adsorption model rose to a pH of 6 after pore volume 15, about 1 pore volume later than the pH simulated by HGC using the constant-capacitance model.In PHREEQC simulation of a laboratory column experiment, the inability of the model to match measured outflow concentrations of selected constituents was related to the evident lack of local geochemical equilibrium in the column. The difference in timing and size of measured and simulated breakthrough of selected constituents indicated that the redox and adsorption reactions in the column occurred slowly when compared with the modeled reactions. MINTEQA2 and PHREEQC simulations of the column experiment indicated that the number of surface sites that took part in adsorption reactions was less than that estimated from the measured concentration of Fe hydroxide in the alluvium.     

Short term validated geochemical model of CO2 sequestration

In this work we present a new approach to modeling the effects of CO2 sequestration that was tested in the Weyburn test site. The Weyburn oil-pull is recovered from Midale Beds （at 1300-1500 m depth）. This formation consists of Mississippian shallow marine evaporific carbonates that can be divided into two units： （1） the dolomific ＂Marly＂ and ii） the underlying calcitic ＂Vuggy＇, sealed by an anhydrite cap-rock. Presently, about 3 billions mc of supercrifical CO2 have been injected into the ＂Phase Al＂ injection area. The aim of our model is to reconstruct （1） the chemical composition of the reservoir; （2） the geochemical evolution of the reservoir with time as CO2 is injected and （3） the boundary conditions. The geochemical modeling was performed by using the code PRHEEQC （V2.11） software package. The ＂primitive brine＂ composition was calculated on the basis of the chemical equilibriums among the various phases, assuming reservoir equilibrium conditions for the mineral assemblage with respect to a Na-Cl （Cl/Na= 1.2） water, at T of 62℃ and P of 150 bars via thermodynamic corrections to the code database. A comparison between the chemical composition of the ＂primitive brine＂ and that analytically determined on water samples collected before the CO2 injection shows an agreement within 10%. Furthermore, we computed the kinetic evolution of the reservoir by considering the local equilibrium and the kinetically controlled reactions while taking it into account the CO2 injected during four years of monitoring. The calculated chemical composition after CO2 injection is consistent with the analytical data of samples collected in 2004, with the exception of calcium and magnesium contents.     

Finite element simulation of an embankment on soft clay – Case study

Numerical simulations and field measurements of an embankment constructed on a deposit of soft Ariake clay in Saga, Japan are compared and discussed. The simulations were made both before (Class-A) and after (Class-C) the field data became known. It is shown that the Class-A prediction resulted in poor simulations of the measured settlement–time curves, mainly due to over-estimation of the magnitude of the yield stresses of the subsoils (i.e., the sizes of the yielding loci) and under-estimation of the compressibility, hydraulic conductivity and the slope (M) of the critical state line. It is demonstrated that: (a) appropriate site investigation, soil testing and interpretation of the test results are essential for accurate prediction of the behaviour of an earth structure constructed on soft clayey deposits; (b) when using a soil model developed within the framework of Critical State Soil Mechanics to make such predictions, M value should be directly determined from tests with an appropriate effective stress path; and (c) yield stresses of soft soil layers can be calibrated by comparing the predicted undrained shear strengths (S_u) with measured values, provided the effect of strain rate and/or strain softening on the value of S_u is properly considered. The results of this analysis indicate that Bjerrum’s strain rate correction factor can be adopted as a first approximation of the correction factor applied to field or laboratory measured values of S_u.     

Floodplain deposits: A geochemical archive of flood history – A case study on the River Rhine,Germany

Based on the correlation between discharge and carbonate content of the suspended load of the River Rhine, Germany, a systematic geochemical, mineralogical and granulometric study was carried out to verify whether this geochemical signal is transferred to floodplain deposits and in what way these sediments and their chemostratigraphic characterization can be used as a tool for the reconstruction of the river flood history. The analysis of the time resolved changes in the composition of particulate matter during a flood event revealed that the increase of carbonate content (represented by CaO, Sr) with discharge was coupled to a simultaneous decrease in the relative amount of siliciclastics (K₂O, Rb). The association of these two groups of diametrical parameters with specific grain size fractions (carbonates with 40–200 μm; siliciclastics with >200 μm) were found to be slightly shifted relative to each other and showed different gradients during the surging and fading flood wave. This, together with the covariance of elements pertaining to minerals with different density (e.g., carbonate and heavy minerals) suggests a chemical response to the changes in discharge, which is controlled primarily by hydraulic equivalence rather than grain size. There is also a time lag between the amount of suspended load and discharge, with a maximum in suspended load shortly after the peak discharge, when the flood has already started to abate. The flood plain sediments have similar composition to the suspended load, suggesting the direct transfer of the geochemical flood signal to the floodplain sediments.     

A study on the geochemical characteristics of natural gas and gas sources in the Bozhong sag

Natural gas is composed largely of hydrocarbon gas, especially wet gas in the Bozhong sag. The carbon isotopic composition shows that the gas is of organic origin. The carbon isotopic values of ethane indicate that the natural gas is dominated by mixed gas with minor coal-generated gas and oil-type gas. A gas-source correlation study showed that the source rocks of natural gas are those of the Lower Dongying Formation, the Shahejie Formation and the pre-Tertiary. The natural gas is characterized by multi-source and continuous generation in the study area, indicating that gas exploration potential is good in the Bozhong sag.     

Solution of the MoMaS reactive transport benchmark with MIN3P—model formulation and simulation results

This paper summarizes the governing equations as implemented in the MIN3P multicomponent flow and reactive transport code (Mayer et al., Water Resour Res 38:1174, 2002) and introduces the equations in discretized form. Linearization and solution methods are presented including adaptive time stepping and update modification schemes. Code-specific details for the implementation of the GdR MoMaS benchmark simulations (Carrayrou et al., Comput Geosci, 2009) are presented. The standard version of the MIN3P code was used to solve the Easy, Medium, and Hard Test Cases, in one and two spatial dimensions, for both advection- and diffusion-dominated conditions. An analysis of the sensitivity of the solution in relation to spatial and temporal discretization parameters is provided for the Easy Test Case, selected results are presented for the Medium and Hard Test Cases, and the performance of the code as a function of discretization parameters is evaluated for all test cases.     

The effect of sorbed gas on the strength of coal – an experimental study

This paper examines the influence of sorbed gas type and pressure on the strength of coal. Particular attention is focused on the influence of gas type and pressures on drillability characteristics of coal and particle size distribution of drill cuttings. Drillability of coal has a strong bearing on the strength properties of coal. Based on fracture mechanics and mechanical rock cutting, weaker rocks are easier to drill and the drill cuttings produced are generally coarse in size. Accordingly a specially designed precision drill was used to drill coal samples under both normal atmospheric and confined gas pressure conditions. Indications of changes to coal strength as a result of increased sorbed gas pressure were examined by analysing the particle size distribution of the drill flushing. A laser controlled Malvern Mastersizer S particle size analyser with measuring range between 0.05 m and 900 m was used to study the particle size distribution. This paper demonstrates that there is a definite variation in the range of particle size distribution with particles obtained from drilling coal samples not subjected to gas pressures in comparison with those obtained from samples drilled under confined gas pressure. Gas types also have an influence. Higher proportions of coarse particles were produced when the confined gas was changed from CH₄ to CO₂. A change in the rate of drilling under varying confining pressure and gas type was also evident. The rate of drilling in air (at normal atmospheric conditions) was slower than at higher confining pressures. The highest drill rates were obtained with CO₂ confinement.     

Thermodynamic simulation of the effect of eutrophication on the behavior of heavy metals in bottom sediments by the example of the Inan’kovsky water reservoir

A thermodynamic model of the behavior of heavy metals in bottom sediments during their eutrophication is developed. The results show that liberation of heavy metals from the reduced ferrous sorbent is accompanied by sorption on clay and organic sorbents. The process is complicated by competitive correlations between heavy metals and calcium ions, while the formation of carbonate cement in the sediments yields additional sorption. As a result, the predicted concentrations of the majority of microelements, namely heavy metals, in the interstitial water of the reduced bottom sediments do not exceed the maximum permissible concentration (MPC).     

A study on the effects of drying conditions on the stability of NaNd(CO3)2·6H2O and NaEu(CO3)2·6H2O

The effect of different drying conditions on the stability of NaNd(CO₃)·6H₂O and NaEu(CO₃)·6H₂O and the identity of the decomposition product have been investigated. The rate of decomposition and the nature of the altered phases are dependant on the drying conditions used. When the phases are oven dried at 120 °C, the decomposition is immediate and the phase completely alters to Nd₂(CO₃)₃ or Eu₂(CO₃)₃ respectively. Under less severe drying conditions, the Na rare earth carbonate phases alter to Nd₂(CO₃)₃·8H₂O and Eu₂(CO₃)₃·8H₂O over a period of 24–48 h, but they can be kept indefinitely in a water saturated environment. The implications for using Nd and Eu as actinide analogues are discussed.     

A study on the bio-hydro mechanical effects of the tree roots on the Agaclı coal reclaimed – forested land

The research area that is in the north of Istanbul (Turkey) and it is a land of open pit coal mining residuals reclaimed and turned to forest in 1988–1989. The materials that are open pit mine spoils are formed by sandy loam, sandy clay loam, heavy loam and clay (noncalcareous Pliocene I sediments). Pseudoacacia (Robinia pseudoacacia), Maritima Pine (Pinus pinaster) and Stone Pine (Pinus pinea) are planted on these materials. The aims of this research were to determine the strength of the material provided by tree roots and evaluate the performance of the forestation practices at lands especially where open pit coal mining spoil (residual) materials piled up. The research has been performed at two stages. The first one was hydro-mechanical effect concerned about material moisture depletion as a result of transpiration and the second one was bio-mechanical effects due to strength parameters of the roots and their growth pattern within the material. All results were evaluated in relation to tensile strength and displacement curves due to pre and post failure behaviors of materials and root systems. The results showed the increase of the displacement of the material was the significant indicator of the bio-mechanics tensile strength of the material provided by the tree roots. The fast growing type of tree roots have stabilized the material up to a depth for 80–100 cm by covering the coal residual materials within 12 years.     

A study on the geochemical characteristics of Upper Permian continental marginal arc volcanic rocks in the northern segment of South Lancangjiang Belt

1IntroductionThe northern segment of the South LancangjiangBelt refers to the terrain about200km east of theYunxian-Lingcang granite in the South LancangjiangBelt(Fig.1).During the seventh Five-Year Plan peri-od,Mo Xuanxue et al.(1993)undertook the resear…     

Temporal characteristics of aerosol physical properties at Visakhapatnam on the east coast of India during ICARB — Signatures of transport onto Bay of Bengal

Realizing the importance of aerosol physical properties at the adjoining continental and coastal locations in the airmass pathways onto the oceanic region, extensive measurements of aerosol physical properties were made at Visakhapatnam (17.7°N, 83.3°E), an eastern coastal location in peninsular India during the ICARB period. The temporal variations of aerosol optical depth, near surface aerosol mass size distributions and BC mass concentrations show significantly higher aerosol optical depth and near surface mass concentrations during the first and last weeks of April 2007. The mean BC mass fraction in the fine mode aerosol was around 11%. The aerosol back scatter profiles derived from Micro Pulse Lidar indicate a clear airmass subsidence on the days with higher aerosol optical depths and near surface mass fraction. A comparison of the temporal variation of the aerosol properties at Visakhapatnam with the MODIS derived aerosol optical depth along the cruise locations indicates a resemblance in the temporal variation suggesting that the aerosol transport from the eastern coastal regions of peninsular India could significantly affect the aerosol optical properties at the near coastal oceanic regions and that the affect significantly reduced at the farther regions.     

The Influence of CO on the Carbon Isotopic Composition of CH4 in Closed Pyrolysis Experiment With Coal

A low-mature coal (R_o=0.4%, from the Manjia'er depression, Tarim Basin, China) was subjected to closed system pyrolysis, in sealed gold tubes, under isothermal temperature conditions. The carbon isotopic compositions of the pyrolyst fractions (hydrocarbon, CO₂, CO, etc.) at two temperature points (350°C and 550°C) were measured. The results showed that {ie359-1} value is generally heavier at 350°C than that at 550°C, because the high abundance of CO generated at low temperature would greatly influence {ie359-2} value, and the retention time of CO in gas chromatograph is close to that of CH₄. But CO is formed through chemical reaction of the oxygen-containing functional group −C=O, e.g. lactones, ketones, ether, etc. at low temperature, while CO₂ comes mainly from decarboxylization. The carbon isotopic composition of coal gas from Lanzhou Coal Gas Works was definitely different from that of thermally pyrolysed products from coal. The {ie359-3} value of coal gas was abnormally heavier than {ie359-4}. At the same time, the reversed sequence ({ie359-5}) of {ie359-6} and {ie359-7} happened. The bond energy of free ions generally decides the sequence of generation of hydrocarbon fractions according to the chemical structure, whereas the stability of pyrolysate fractions and their carbon isotope fractionation are affected by the C−C bond energy. This study was supported by the National Basic Research (973) Program of China (No. 2001CB209102).     

The Influence of CO on the Carbon Isotopic Composition of CH_4 in Closed Pyrolysis Experiment With Coal

1IntroductionThecarbonisotopiccompositionofnaturalgasesisregardedasacontanttracerusedinthegeochemicalresearchofnaturalgases .Basedonthecarbonisotopiccomposition ,thegenetictypesofnaturalgasesarebasicallydividedtodeterminethematurationofnaturalgasesandmakegas sourcecorrelations (Stahl,1 973;StahlandCarey ,1 975;Stahletal.,1 977;James ,1 983;Schoell,1 983,1 988;DaiJinxingetal.,1 992 ;FuJiamoetal.,1 992 ;XuYongchang ,1 994 ) .Theformationofnaturalgasescouldbededucedintermsofcarbonisotopicvar…     

Comparative study on the geochemical characteristics of rare earth elements in deep-sea sediments from different regions of the Pacific OceanSCIEI北大核心CSCD

太平洋深海沉积物中富集稀土元素(REY,包括钇),被认为是富有潜力的新型稀土资源。(含)沸石粘土、深海粘土和多金属软泥是主要的富含REY的沉积物类型,其中(含)沸石粘土和深海粘土在中、西北太平洋海盆大面积分布,而多金属软泥则多分布于靠近东太平洋洋脊热液活动的深海盆地中。目前关于中、西北太平洋海盆的深海粘土和(含)沸石粘土已有较多的研究,但关于多金属软泥中REY的研究较少。不同区域、不同类型深海沉积物中的稀土元素赋存状态有何差异?影响稀土富集的机制又是什么目前尚不清楚,也就进一步影响了对深海沉积物稀土资源的勘查和开发工作。本文分析对比了太平洋不同区域不同类型深海沉积物的地球化学特征及矿物学特征。结果表明,总体上,中、西北太平洋海盆深海沉积物中,尤其是(含)沸石粘土中的REY含量明显高于东太平洋海盆多金属软泥REY含量,其REY的富集主要与磷酸盐有关。超常富集REY(∑REY>2000×10^(-6))的沉积物中的CaO/P_(2)O_(5)比值趋向于一致(~1.4),几乎接近于磷灰石CaO/P2O5比值(~1.3),因此REY主要赋存载体为磷灰石,该区沉积物中REY的富集可能受到磷酸盐化的影响;东太平洋海盆多金属软泥明显受到热液影响,铁和锰的含量明显增加,但其∑REY含量集中于500×10^(-6)~800×10^(-6),不随铁和锰的增加而变化,REY的富集仍与磷酸盐关系密切,而与铁锰物质和铝硅酸盐关系不大。中、西北太平洋海盆富稀土的深海沉积物形成时处于较强的氧化环境,同时又有充足的含磷物质补给,才造成REY在该区沉积物中的超常富集;而东太平洋海盆多金属软泥虽然处于氧化环境,但缺少足够的磷补给,所以其∑REY含量通常低于中、西北太平洋海盆沸石粘土中∑REY含量。     

Teaching GIS in the Gulf Co-operation Council Universities – With a case study of the geography department, University of the United Arab Emirates

Within universities there has developed a clear theoretical convergence between Geographical Information Systems (GIS) and geography (Antenuccl, 1991). Studies have revealed that one of the qualified departments to teach GIS within universities is the geography department. This study focuses on: the importance of establishing GIS as a major curriculum element within universities. In geography departments, economic geography students require a strong statistical/mathematical background to allow them to work with major databases. They should know how to design a specific database for economic activities, such as agriculture and manufacturing, and tertiary industry and how to relate this database to a map, so that changes can be monitored more accurately. In any aspect of geography spatial location is a key factor and GIS allows spatial patterns to be interpreted with great facility. Therefore it is important that students have a good knowledge not only of computers and related software on economic geography, but also on GIS systems (Burrough, 1993). The work of geography students from the United Arab Emirates (UAE) and other Gulf Co-operation Council (GCC) geography departments is examined to evaluate the importance of training in GIS technology. This paper evaluates the effects of implementing GIS as a tool in teaching economic geography. At present there are 15 geography departments in the GCC which offer economic geography. Of those 15 departments, only 3 provide GIS courses within their curriculum, and 4 have basic equipment, although 6 additional departments are to introduce GIS in the near future. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of pre-existing discontinuities on the residual strength of rock mass – Insight from a discrete element method simulation

When rock failure is unavoidable, the designer of engineering structures must know and account for the residual strength of the rock mass. This is particularly relevant in underground coal mine openings. Pre-existing discontinuities play an important role in the mechanical behavior of rock masses and thus it is important to understand the effects of such pre-existing discontinuities on the residual strength. For this purpose, the present study demonstrates a numerical analysis using a discrete element method simulation. The numerical results indicate that fracture intensity has no significant influence on the residual strength of jointed rock masses, independent of confining conditions. As confining pressures increase, both peak and residual strengths increase, with residual strength increasing at a faster rate. The finding was further demonstrated by analyzing documented laboratory compressive test data from a variety of rocks along with field data from coal pillars. A comprehensive interpretation of the finding was conducted using a cohesion-weakening-friction-strengthening (CWFS) model. The effect of rock bolts on rock mass strength was also evaluated by using a discrete element method model which suggested that rock bolts can significantly increases residual strength but have limited effect on increasing the peak strength of rock masses.     

Leaching experiments on a Mn-rich slag from the recycling of alkaline batteries – Solid phase characterization and geochemical modeling

Square sections of a Mn-rich slag from an alkaline battery recycling plant were submitted to 6-month batch leaching procedures. High-Purity Water (HPW), acidic (pH 4) and alkaline (pH 12) conditions were used in order to observe the behavior of primary solid phases as well as the constituent elements (Mn, Mg, Al, Si, Ca). The experiments were coupled with both KINDIS(P) modeling and mineralogical study (SEM-EDS). Experimental results showed that the Mn-rich slag was sensitive to acidic conditions which induced the dissolution of primary phases. Moreover, pH 4 conditions did not result in the formation of newly formed solid products, leading to the greatest mobilization of metallic elements (especially Mn). Alkaline conditions favored the precipitation of secondary phases, especially rhodochrosite, calcite and Mg-saponite, inducing low mobilization of the contained elements. The KINDIS(P) modeling allowed the stability of primary phases and newly formed products to be predicted. Although the modeled results have to be considered with caution, they allow the assessment and understanding of future environmental behavior of the solid material in given conditions. In this case, the reuse of Mn-rich slag in acidic conditions has to be avoided because of the acidic dissolution of the primary phases.     

Effect of the Si/Al ordering on structural parameters and the energetic stabilization of vermiculites – a theoretical study

The effect of the Si/Al distribution in the tetrahedral sheets of the vermiculite mineral has been investigated employing density functional theory. The structures of six models for vermiculite with the structural formula (Mg₄)(Mg₁₂)(Si₈Al₈)O₄₀(OH)₈·24(H₂O) per unit cell were fully optimized. The models differ by the T···Mg²⁺···T coordination of the interlayer Mg²⁺ cations by two central cations from the adjacent tetrahedral sheets of the 2:1 vermiculite layers (T,T=Si,Al). We observed the formation of very strong hydrogen bonds between water molecules solvating the interlayer Mg²⁺ cations and the surface basal oxygen atoms of the 2:1 layers. The directionality of hydrogen bonds is the major factor determining the layer stacking in the vermiculite structure. Results showed that the most stable model is that where only silicon atoms in the tetrahedral sheets coordinate all interlayer Mg²⁺ cations.