CO2-driven cation leaching after tropical forest clearing

The objective of this study was to investigate the role of dissolved CO₂ (H₂CO₃*) as a mechanism of cation removal from surface soils under secondary land uses in the tropics. Soil leachate columns were prepared with 0–10 cm soils from mature and secondary forest, and managed pastures, and extracted with H₂CO₃* from deionized water equilibrated with 0%, 0.5%, 1%, and 10% CO₂ (g). Extraction of soil cations slowed over time following an exponential form for the cumulative data. The rate of cation concentration decline varied as a function of CO₂ concentration with the 10% solution resulting in a greater percent decline with extraction volume. Potassium removal from the exchange sites of all soils and for all solutions was nearly complete ranging from 85% to 97% while removals of Mg (31% to 71%) and Ca (12% to 42%) were lower. The asymptotic patterns of cation loss observed in this study suggest that H₂CO₃* acid-driven losses of cations may become self-limiting over time. Other stronger acids from atmospheric deposition or organic sources may serve to perpetuate cation removal, and re-forestation on these cleared lands would certainly re-distribute cations from soils to vegetation.     

Abundance, Sources and Speciation of Trace Elements in Humus-Rich Streams Affected by Acid Sulphate Soils

The behaviour of trace elements (Al, As, Cd, Co, Cr,Cu, Fe, Mn, Ni, V, Zn) was studied in five humus-richstreams (dissolved organic carbon = 14–40 mg/L)impacted by acid sulphate soils developed in marinesulphide-bearing fine-grained sediments. During heavyrainfalls in autumn, on which the study focusses, themetals Al, Cd, Co, Cu, Mn, Ni and Zn are extensivelyleached from these acidic soils (pH = 2.5–4.5), whileAs, Cr, Fe and V are not leached more strongly fromthis soil type than from areas of till and peat. Aspeciation experiment, based on anion and cationexchange of the stream waters in the field, showedthat (1) the metals Al, Cd, Co, Mn, Ni and Zn aretransported in the streams mainly as inorganiccations, (2) Cu exists mainly in cationic form but isalso to a significant extent associated with dissolvedhumic substances, (3) Fe occurs mainly in the anionicfraction explained by organic coating on colloidal Feoxyhydoxides and (4) the hydrochemistry of As, Cr andV is complex as these elements may exist in severalunquantified anionic fractions and to a minor extentin cationic species/forms. Whereas the proportion ofacid sulphate soils in the catchments had a largeimpact on concentrations levels of several elements inthe stream waters, these soils did not have a largeaffect on the speciation of elements in water.     

硅酸盐中金属离子对Si—O键影响的量子化学研究

本文用CNDO/2法,研究了不同金属离子对硅桥氧键(Si—O~(br))及硅端氧键(Si-O~(ter))的影响。得到了硅酸盐骨架中硅氧键的性质与氧的成键状态、配位数以及金属离子影响之间的规律性。用得到的这些规律,可望较好地研究矿物学、地球化学、硅酸盐材料及冶金炉渣结构等同题。     

阳离子浓度对泥沙沉速影响实验研究

应用了静态沉降实验方法中的移液管法,初步研究了水中常见阳离子对河流中细颗粒泥沙沉速的影响,这些阳离子包括Na+、Ca2+、Mg2+和Al3+等。实验结果表明,阳离子浓度对泥沙沉速的影响可以分为两个阶段:①随着阳离子浓度的增加泥沙沉速也增大;②当离子浓度大于某值时,离子浓度对泥沙沉速的影响不大。在同样离子浓度条件下,离子价态高者影响较大。同时分析了长江和黄河干流中下游河段的水化学特性;分析结果表明,在一般的河水水质的情况下,有必要考虑水中阳离子(主要是Ca2+、Mg2+)对细颗粒泥沙沉速的影响。     

高岭石对重金属离子的吸附机理及其溶液的pH条件

高岭石对Cu^2+,Pb^2+离子的吸附实验及高岭石的溶解实验表明,高岭石对重金属离子的吸附有别于石英单一表面配位模式,离子交换和表面配位模式并存,并随溶液pH由酸性往碱性的变化发生规律性的演替：pH<6.5时主要表现为外圈层配位的离子交换吸附,且在pH<4时由于受到高岭石表层中铝的高溶出及溶液中较高离子强度的影响,高岭石对Cu^2+,Pb^2+离子的吸附率较低,pH为5～6时由于高岭石端面的荷电性为近中性,吸附率则有明显的提升并且表现为一个吸附平台;pH>6.5时离子交换和表面配位均为重要吸附机制,pH再升高时沉淀机制则起着重要作用。研究表明,pH调控高岭石-水界面溶解与质子化-去质子化反应过程,并影响着Cu^2+,Pb^2+离子的吸附行为。最后采用Sverjensky(1993)表面配位的物理模型对吸附结果作了描述。     

Estimates of current and historical fluxes of N, Ca, and K in the forest ecosystem Möhlin

Data on element fluxes (Ca, K, N) are presented which were obtained in the course of an extended project on element-cycling in a forested ecosystem near Möhlin, northwestern Switzerland. Current fluxes of Ca, K, and N could be compared with historical fluxes (1969–1993) with the help of soil chemistry inventories since 1969, data on the forest management, and atmospheric deposition. Since 1969, soil chemistry has significantly changed due to a distinct disintegration of humus. The decomposition of organic matter influenced strongly the element cycling. Due to this mineralization high amounts of N were released. It is, however, not fully clear in which chemical form N has been transferred out of the system. Two possible hypotheses on the N losses are defined. According to the calculated proton budget and measured element changes in the soil, it is hypothized that a large part of the mineralized organic N presumably was transformed into N₂ or more likely into N₂O. A complete nitrification of organically bound N to NO₃ ^– is also discussed but is, however, considered as less probable. In contrast to K, Ca proved to be a very sensitive element: the exchangeable Ca stock has been decreased sharply. The analysis of the current fluxes of Ca, K, and N reveals that nitrogen is abundantly present in the forest system with the consequence that the ecological balance is shifted in favour of N. Accordingly, the supply of base cations is rather scarce for the plants. Furthermore, the influence of forest management on element fluxes seems to be substantial, especially on the fluxes of base cations, but can be reduced with simple measures (e.g. removal of the bark of coniferous trees).     

Hydrochimie et faciès géochimiques des eaux souterraines,Plaine de Bekaa

Résumé

L'étude géochimique des eaux souterraines dans la Plaine de la Bekaa montre un faciès calco-magnésien, bicarbonaté, à saturation vis-à-vis de la calcite et de la dolomite, à faible minéralisation et de faible conductivité. Les formations carbonatées (calcite et dolomite) constituent les roches encaissantes des eaux souterraines dans la Plaine de la Bekaa. La recharge des nappes souterraines est à haute altitude et a comme origine les eaux des précipitations qui tombent sur les hautes montagnes qui encadrent la Bekaa à l'est et à l'ouest. Une dissolution des formations gypseuses existe. La minéralisation se fait en système ouvert. Par conséquent le CO₂ d'origine biogénique joue un rôle important dans la minéralisation.

Citation Awad, S. (2011) Hydrochimie et faciès géochimiques des eaux souterraines, Plaine de Bekaa. Hydrol. Sci. J. 56(2), 334–348.     

Rate of strontium sorption and the effects of variable aqueous concentrations of sodium and potassium on strontium distribution coefficients of a surficial sediment at the Idaho National Engineering Laboratory, Idaho

 The rate of strontium sorption and the effects of variable aqueous concentrations of sodium and potassium on strontium sorption were measured as part of an investigation to determine strontium chemical transport properties of a surficial sediment at the Idaho National Engineering Laboratory (INEL), Idaho. Batch experimental techniques were used to determine the rate of strontium sorption and strontium distribution coefficients (K_ds) between aqueous and solid phases. Rate experiments indicate that strontium in solution reached an apparent equilibrium with the sediment in 26 h. K_ds were derived using the linear isotherm model at initial sodium concentrations from 100 to 5,000 mg/l and initial potassium concentrations from 2 to 150 mg/l. K_ds ranged from 56±2 to 62±3 ml/g at initial aqueous concentrations of sodium and potassium equal to or less than 300 and 150 mg/l, respectively. K_ds ranged from 4.7±0.2 to 19±1 ml/g with initial aqueous concentrations of sodium between 1,000 and 5,000 mg/l. These data indicate that sodium concentrations greater than 300 mg/l in wastewater increase the availability of strontium for transport beneath waste disposal ponds at the INEL by decreasing strontium sorption on the surficial sediment. Wastewater concentrations of sodium and potassium less than 300 and 150 mg/l, respectively, have little effect on the availability of strontium for transport. Received: 6 February 1997 · Accepted: 31 March 1997     

Sorptive flotation for metal ions recovery

In this study, the abstraction of nickel, copper and zinc ions from aqueous solutions has been investigated in a laboratory batch scale mode. A combined two-stage process is proposed as an alternative of the heavy metals removal from aqueous solutions. The first stage is the sorption of heavy metals onto non-living microorganisms followed by dispersed-air flotation of the loaded biomass. Three types of strains were used: Penicillium chrysogenum, Saccharomyces carlsbergensis and Streptomyces rimosus. The main parameters studied were solution pH, biomass concentration, surfactant concentration and flocculant concentration. The biomass reuse after elution was also examined. Remediation is a possible application of flotation being cost-effective and with readily available equipment and know-how. The application of this process looks promising.     

Reactive transport modelling of groundwater-bentonite interaction: Effects on exchangeable cations in an alternative buffer material in-situ test

Bentonite clays are regarded a promising material for engineered barrier systems for the encapsulation of hazardous wastes because of their low hydraulic permeability, swelling potential, ability to self-seal cracks in contact with water and their high sorption potential. SKB (Svensk Kärnbränslehantering) has been conducting long term field scale experiments on potential buffer materials at the Äspö Hard Rock Laboratory for radioactive waste disposal in Sweden.The Alternative Buffer Material (ABM) test examined buffer properties of eleven different clay materials under the influence of groundwater and at temperatures reaching up to 135 °C, replicating the heat pulse after waste emplacement. Clay materials were emplaced into holes drilled in fractured granite as compacted rings around a central heater element and subsequently brought into contact with groundwater for 880 days. After test termination, and against expectations, all clay materials were found to have undergone large scale alterations in the cation exchange population. A reactive-diffusive transport model was developed to aid the interpretation of the observed large-scale porewater chemistry changes. It was found, that the interaction between Äspö groundwater and the clay blocks, together with the geochemical nature of the clays (Na vs Ca-dominated clays) exerted the strongest control on the porewater chemistry. A pronounced exchange of Na by Ca was observed and simulated, driven by large Ca concentrations in the contacting groundwater. The model was able to link the porewater alterations to the fracture network in the deposition hole. The speed of alterations was in turn linked to high diffusion coefficients under the applied temperatures, which facilitated the propagation of hydrochemical changes into the clays. With diffusion coefficients increased by up to one order of magnitude at the maximum temperatures, the study was able to demonstrate the importance of considering temperature-dependant diffusion in understanding and predicting geochemical alterations of engineered barriers systems after relatively short exposure times following waste emplacement.