Application of inverse geochemical modelling for predicting surface water chemistry in Ekbatan watershed,Hamedan, western Iran

ABSTRACT

A study of surface water chemistry evolution was conducted by multivariate statistical analysis and inverse geochemical modelling using the PHREEQC computer program. Using hierarchical cluster analysis the 14 sampling sites were classified into three groups (recharge, transition and discharge areas). Water chemistry changed along a flow path so that waters with Ca–HCO₃ and Mg–Cl composition changed to Mg–Cl–HCO₃ waters. The order of abundance of the major cations was Mg > Ca > Na > K. Their average concentrations were 21, 19, 3.6 and 2.5 mg L^-1, respectively. Inverse geochemical modelling along flow paths indicated that the dissolution of sylvite and kaolinite, and precipitation of feldspars and andalusite, happened with Na entering the solution and Ca, Mg and K leaving the solution.

Editor D. Koutsoyiannis; Associate editor not assigned     

梭菌SN-1菌株参与下形成的碳酸盐矿物组合及其主要矿物成分的动态变化

在Mg/Ca比值为6的Lagoa Vermelha改良培养基中,对分离自青海湖湖底沉积物的梭菌(Clostridiumsp.)进行了为期100 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X射线衍射仪(XRD)和扫描电子显微镜(SEM)分别对矿物成分和形态进行了测定和观察。实验结果表明:细菌培养实验的沉淀物数量始终多于无菌对照实验;在梭菌SN-1菌株作用下形成的碳酸盐矿物组合的变化趋势是方解石→方解石+单水碳钙石→单水碳钙石+方解石→单水碳钙石,而无菌对照实验产物中矿物的演化方向是单水碳钙石+方解石→方解石+单水碳钙石;在综合分析SEM和XRD观测结果的基础上,推测哑铃状矿物可能是高镁方解石,而球状矿物可能是单水碳钙石。     

湘西黔东地区铅锌矿床C、O同位素地球化学特征及其对成矿过程的指示

近年来湘西黔东地区铅锌矿产勘查成果显著,已发现矿床(点)200余处,铅锌矿主要产于寒武系—奥陶系碳酸盐岩地层中。通过对该地区典型铅锌矿床碳酸盐围岩和成矿期方解石的C、O同位素组成分析,结果表明:碳酸盐围岩的δ13CPDB值(-1.16‰~1.70‰,均值0.51‰)和δ18OSMOW值(18.56‰~22.42‰,均值21.04‰)变化范围较小,组成相对均一,在δ13CPDB-δ18OSMOW图上投影点位于海相碳酸盐岩区;而成矿期方解石的δ13CPDB值(-5.80‰~0.42‰,均值-1.18‰)比围岩略低,δ18OSMOW值(12.96‰~23.05‰,均值18.36‰)有明显的下降,在δ13CPDB-δ18OSMOW图上投影点主要位于上地幔区和海相碳酸盐岩之间。根据C、O同位素组成特征并结合前人研究成果,认为成矿流体中的C主要来源于碳酸盐围岩,S来源于地层中的膏盐层,Pb、Zn主要来源于下寒武统牛蹄塘组地层,成矿流体是一种高盐度的低温热卤水,它与碳酸盐围岩的水-岩反应和降温的耦合作用是该地区成矿期方解石和矿石矿物沉淀的主要机制。     

Thermodynamic Model of Uranium and Arsenic Accumulation in Saline Lakes

正1 Introduction The attractiveness of Shaazgai-Nuur Soda Lake(pH9.2-9.4)as an alternative metal source is explained by the high concentration of dissolved uranium(~1 mg/l)due to the location of water drainage territory within the Tsagan-     

Strength Behavior of Naturally Cemented Marine Clay Due to Change in Ground Water Level

The change in strength and deformation behavior of a typical marine clay deposit formed under shallow water is presented and discussed for the conditions of changing water table. This is a costal marine clay deposit with moderate carbonates along the east coast of India. The soil samples were taken from tidal flats where the sea had receded some time back, and the behavior of this deposit had been studied for the conditions of 1976, with high water table, and for the conditions of 2001, with depleted water table. Undisturbed soil samples were taken from sheeted open test pits. Standard consolidation and triaxial shear tests were conducted. Consolidation tests conducted on the samples taken for 1976 conditions with high water contents indicate that cementation effect are erased out under moderate stresses. Beyond this stress range, it behaves like soft, normally consolidated clay. In contrast, the results obtained from samples taken during 2001, with depleted water table, clearly indicate that the soil behaves like an over-consolidated one, and the improvement in the system is due to the chemical bonding and desiccation.     

Bacteria-Induced Cementation Process in Loose Sand Medium

Several conventional methods for treatment of soil are available for engineers. The most widely used method includes solution/grout, but they alter the ground pH level and could be toxic. In order to avoid the potential environmental harms and make use of naturally occurring microorganisms, biological methods to improve the engineering properties of soils have been intensely studied. This article presents the results of a research project in which Sporosarcina pasteurii (formerly known as Bacillus pasteurii) was used to induce biological cementation in loose sand medium. The bacteria was injected into sand, which led to the development of cementation (calcium carbonate crystal) between sand grains. The calcification was observed using a scanning electron microscope (SEM).     

Study of magnesium precipitation based on biocementation

Abstract

Magnesium carbonate has a cementing character like calcium carbonate, and the addition of magnesium ion enables the microbe cementitious material to have the denser microstructure with the lower porosity. The effects of various factors, such as the concentration of Ca²⁺ and Mg²⁺, on the urease activity were studied. Comparison of the productive rates for calcium carbonate and magnesium carbonate were carried out, as well as productive rates for magnesium carbonate with adding different amount of urea to medium. Calcium acetate and magnesium acetate were, respectively, used for sands solidification. Results showed that the increase in urea concentration and magnesium ion enhanced urease activity, while calcium ion significantly impaired urease activity. Sodium chloride and acetate ion had little influence on it. Productive rates for magnesium carbonate were dramatically smaller than its calcium counterpart. However, adding urea to medium allowed for more magnesium precipitation, and the higher the urea concentration, the more the magnesium precipitation. The sand columns with adding urea to medium can have a high strength despite using magnesium acetate. Therefore, the method could solve the problem of insufficient magnesium precipitation. The results will act as a guide for the application of biocementation technology with magnesium carbonate.     

南海珊瑚砂砾屑灰岩磷质胶结物的数字影像分析及其环境意义

应用计算机数字影像学原理,建立了对磷质胶结微细纹层研究的数值化方法,研究了西沙东岛珊瑚砂砾屑灰岩磷质胶结物的胶结结构和微纹层特征,定量地刻画了微条纹的宽度和颜色变化信息。东岛珊瑚砂砾屑灰岩磷质胶结物的形成以沉淀胶结为主,不同时期形成的胶结物微条纹系列,由于受到气候、生态因素的影响,具有不同的宽度、明暗度组合;对3个层次磷质胶结物的分析表明,在2900~5700 aBP西沙群岛东岛存在至少3次鸟类和植物的繁盛期;不同时期微纹层的气候、生态记录对比发现,相对稳定的气候条件有利于岛屿海鸟数量的扩大;提供了一种新的方法来探索岛屿鸟粪磷质胶结物的结构和生态环境意义。     

近平衡状态海水中方解石和文石沉淀速率及动力学研究

利用"freedrift"开放反应系统,研究人工海水中近沉淀平衡状态时二氧化碳分压(p(CO2))的变化对方解石、文石沉淀速率及其动力学方程的影响.反应在恒定的温度(25.0℃±0.2℃)、p(CO2)环境下进行,通过实验得到了不同p(CO2)环境下,方解石和丈石的沉淀速率及动力学方程.研究发现:(1)晶体类型和碳酸盐...