湖南膨润土矿床成因类型及矿床实例

根据成矿地质条件及矿床特征,笔者将湖南省膨润土矿床归纳为四种成因类型:即滨海火山碎屑沉积矿床、内陆湖泊沉积矿床、浅海沉积矿床及风化残余矿床。文中对不同成因的矿床特征进行了简要介绍,并对湖南膨润土矿找矿标志进行了初步归纳。最后在全省范围内划分出六个找矿远景区,以期引起同行们的注意。     

Shrinkage and desiccation cracking in bentonite–sand landfill liners

Data are reported on the shrinkage and desiccation cracking exhibited by bentonite-enhanced sand mixtures (BES) upon air-drying. Mixtures containing 10 and 20% bentonite by dry weight, compacted at moisture contents ranging from 8 to 32%, were investigated. Hydraulic conductivity data for BES specimens saturated and tested immediately after compaction, and for similar specimens that had no visible damage after air-drying, are also presented.

All the mixtures exhibited volumetric shrinkage upon air-drying with the amount of shrinkage increasing with increasing moisture content during compaction. At any initial moisture content mixtures containing 20% bentonite shrink more than those containing 10% bentonite, but the shrinkage is insensitive to the compactive effort. Compacted beds of BES containing 10 and 20% bentonite exhibit no visible desiccation cracking as the top surface is dried when compacted at 15 and 14% moisture content, respectively, and only minor cracking when compacted at initial moisture contents of 20 and 15%, respectively. For the range of mixtures tested, it appears that cracking only occurs when BES undergoes more than about 4% volumetric shrinkage when air-dried. The saturated hydraulic conductivity of intact BES specimens is unaffected by a drying episode prior to testing.     

A new laboratory set-up for measurements of electrical, hydraulic, and osmotic fluxes in clays

If clays are subjected to flows of fluid, electrical charge, chemicals, or heat, in most cases, flows of different types occur simultaneously, even if only one driving force is acting. These are so-called coupled flows. Examples of coupling phenomena are streaming potential and electroosmosis, induced by the flows of fluid and electrical charge, respectively.

Since the 1960s, laboratory devices have been constructed to measure streaming potentials and/or electroosmosis in clays or clayey soils. Due to their mechanical and hydraulic properties, clays are not easy to work with. Consequently, laboratory devices have to deal with various complications. A new design for an experimental set-up is proposed. Contrary to earlier devices, the clay sample is mounted in a flexible wall permeameter, which avoids sidewall leakage caused by the possible swell or shrink of the clay. Gold-coated gauze electrodes completely cover the surfaces of the sample, which are in contact with the solution reservoirs that ensure one-dimensional flow. In addition, the thickness of the sample is monitored during the experiment. The chemical composition of the reservoir fluids is controlled during the experiment. The device is flexible with respect to changing the solutions of both reservoirs independently, applying different hydraulic gradients, and measuring or applying electrical potentials. Finally, it is possible to mount undisturbed clay samples in the set-up, keeping them in situ during the whole experiment.

With this set-up, an extensive program of measurements of coupling phenomena like streaming potentials, electroosmosis, and membrane potentials in a sodium montmorillonite is started. Preliminary results of streaming potential measurements are presented and demonstrate that the build-up of a streaming potential due to a hydraulic gradient is a reproducible process that influences the water flow through the clay, and that the extent of the streaming potential depends on the salt concentration of the permeating solution.     

夏坡——辉曲膨润土矿地质特征及开发利用

夏坡－辉曲膨润土矿是以蒙脱石粘土矿物为主，矿石分砂质膨润土和膨润土两种类型的沉积成因矿床。矿石已用于油田钻井泥浆原料、炼铁团球粘结剂、陶瓷原料和综合利用石英砂原料。     

膨润土颗粒混合物的堆积性质与水-力特性研究进展

膨润土颗粒混合物是高放废物深地质处置库中的一种缓冲/回填材料,掌握其堆积性质与水-力特性是开展处置库安全性能评估的关键基础。本文全面回顾和总结了近年来国内外学者对膨润土颗粒混合物的堆积性质、持水特性、结构特征、渗透特性、胀缩特性及本构模型等方面的研究进展与取得的成果,展望了几个值得进一步研究的问题。结果表明,颗粒混合物的堆积性质与粒径级配密切相关;湿化过程中,颗粒混合物由初始松散结构逐渐转变为胶结融合结构,孔隙结构逐渐趋于均一化,并伴随着颗粒破碎和错动,进而影响其水-力特性。考虑到处置库实际运营环境的复杂性,颗粒混合物的原位填充技术以及多场(热-水-力-化)耦合条件下颗粒混合物的水-力特性是今后值得深入研究的方向。     

Model suggested for an important part of the hydro-mechanical behaviour of a water unsaturated bentonite

The hydro-mechanical behaviour of a clay-based buffer material for nuclear waste disposal has been investigated in a laboratory program. In this program, the main focus was on the influence of confinement on water uptake and swelling pressure during suction decrease. The laboratory program and some of the results are presented by Dueck [Dueck, A., 2006. Laboratory results from hydro-mechanical tests on a water unsaturated bentonite. submitted for publication.].

The results from the laboratory tests were used to find a relationship between water content, void ratio, swelling pressure and suction. Two equations for swelling pressure represent the outline of the model.

In the first equation, the swelling pressure developed during water uptake is normalised by a pressure corresponding to the swelling pressure at saturation. This is done in order to be independent of void ratio. A relationship between the normalised swelling pressure and the degree of saturation is suggested.

The second equation describes a relationship between the swelling pressure, the water content and the actual suction (or relative humidity). The equation is based on a thermodynamic relationship and includes the retention curve (i.e. water content vs. suction under free swelling conditions).

The model can be used for a state where two of the four variables; water content, void ratio, swelling pressure and suction are known and can thus be useful to evaluate field measurements and model late stages of the wetting process. An example of an application is given. The equations are mainly based on results from tests with increasing degrees of saturation under constant void ratio but are also suggested for use with increasing void ratio.     

Additives for Slurry Shields in Highly Permeable Ground

Summary. For tunneling projects in saturated soils tunnel boring machines (TBMs) with slurry shields are widely used. However, in coarse, highly permeable soils the suspension penetrates the ground and the required support pressure cannot be built up. For the Zimmerberg Base Tunnel near Zurich permeabilities much greater than 10⁻³ m/s were expected. This value is usually considered as the critical limit for the applicability of slurry shields. Therefore it was aimed to find additives for the bentonite suspension which would allow it to attain a higher suspension pressure. For these investigations an apparatus has been developed. It allows the maximum attainable support pressure for a given suspension and a ground to be determined. It reflects the real situation, produces reproducible results and is insensitive to the inevitable variation of individual parameters. In the tests the additives polymer, sand and vermiculite were studied and their effects on the attainable maximum suspension pressure investigated. For the best combination, i.e. with a well defined proportion of the individual components, suspension pressures could be attained which were about 10 to 20 times higher than those with an ordinary bentonite suspension. Successful excavation of the Zimmerberg Base Tunnel proved the validity of the laboratory tests containing 200 kg bentonite per m³ water.     

The tectonic evolution of Cenozoic extensional basins,northeast Brazil: Geochronological constraints from continental basalt 40Ar/39Ar ages

The Boa Vista and Cubati Basins, Paraíba, Brazil, are NW–SE extension-related intracratonic basins that resulted from tectonic stresses after the opening of the South Atlantic. These basins contain lacustrine fossiliferous sediments, bentonite beds, and basalt flows that preserve Cenozoic continental records. ⁴⁰Ar/³⁹Ar ages for six whole-rocks from two distinct basaltic flows underlying the sediments in the Boa Vista basin are 27.3 ± 0.8 and 25.4 ± 1.3 Ma, while three grains from a basaltic flow overlying the sediments yield 22.0 ± 0.2 Ma. The sediments at the nearby Cubati Basin are overlain by a basalt flow with ages of ∼25.4 Ma. Three whole-rocks from an NE–SW-trending trachytic dyke cross cutting the sediments at the Boa Vista Basin yield ⁴⁰Ar/³⁹Ar ages of ∼12.45 ± 0.06, 12.59 ± 0.07, and 12.58 ± 0.07 Ma. Three whole-rocks from a nearby volcanic plug (Chupador) yield an age of 23.4 ± 0.1 Ma. The geochronological results combined with stratigraphic correlations between the two basins allow bracketing the age of the main sedimentary and bentonic units within the Boa Vista and Cubati Basins between 25.5 ± 1.3 and 24.9 ± 0.1 Ma. The ages, combined with field observations reveal that the formation of the Boa Vista and Cubati basins is associated with mantle-derived magmas channelled through reactivated Precambrian shear zones. Our geochronological results suggest that a temporal link with the Fernando de Noronha and Saint Helena hot spots can be excluded as possible sources of the Boa Vista and Cubati magmas. Rather, the extensional tectonics in the 30–20 Ma interval, long after Gondwana break-up, may be associated with the re-activation of continental-scale shear zones that channelled small batches of mantle-derived magmas.     

Investigating the influence of total electrolyte concentration and sodium–calcium ion competition on controlled dispersion of swelling clays

The influence of clay dispersion method on dewatering behaviour of a run-of-mine bentonite was examined to better understand the roles of calcium–sodium ion exchange and overall electrolyte concentration on the suppression of swelling and subsequent stabilisation of the clay. As with previous work, controlled dispersion of the clay directly into a swelling suppressing environment was observed to yield order of magnitude improvements in dewatering behaviour [de Kretser, R.G., Scales, P.J. and Boger, D.V., 1997. Improving clay-based tailings disposal: a case study on coal tailings. AIChE Journal. 43 (7), 1894–1903.]. The calcium ion, even after normalisation for its valence, yielded significantly better clay stabilisation performance than the sodium ion indicating the greater benefit afforded via divalent ion-exchange driven controlled dispersion. However the results also highlighted a synergistic effect of the double layer suppression effect on the efficacy of ion-exchange mediated controlled dispersion through simultaneous swelling suppression and structure preservation during the transient process of ion exchange on hydration. Studies of controlled dispersion in dual ion, Na⁺ and Ca²⁺, systems illustrated that although the efficacy of controlled dispersion deteriorated with an increase in the Na⁺ to Ca²⁺ ratio, even small amounts of calcium character could generate significant improvements in dewaterability over the pure sodium case. This result was relevant in terms of defining an operational window for the commonly used, but sparingly soluble calcium source, gypsum where the low deliverable calcium level could be more than offset by the controlled dispersion benefits of maintaining a higher overall salinity level. Based on the results presented, the potential impact of practical implementation of a controlled dispersion framework within a mineral processing operation was illustrated via numerical modelling of the operation of a steady state thickener.     

辽宁省阜新北窝棚膨润土矿岩石矿物学特征

北窝棚膨润土矿是近几年在阜新地区紫于盆地中发现的几处膨润土矿之一,为了全面评价北窝棚膨润土矿物理化学特性,利用X射线荧光仪、X射线粉晶衍射仪、红外光谱仪、差热分析仪等测试技术,对北窝棚膨润土矿进行了系统分析研究。测试结果显示:北窝棚膨润土矿主要化学成分为Si O2和A12O3,次要成分中Ca O和Mg O含量较高,K2O和Na2O的含量相对较低,属于钙基膨润土;膨润土矿中主要矿物组分为蒙脱石,杂质矿物为长石、石英和方石英;红外光谱分析和差热分析也验证了北窝棚膨润土矿为钙基膨润土,并具有良好的耐热性能。对合理开发北窝棚膨润土矿具有十分重要的指导意义。