Geochemical evolution of the Capim River kaolin, Northern Brazil

The Capim River kaolin, located in the eastern Brazilian Amazon, constitutes one of the most important kaolin deposits in the world. Known for its high whiteness, its noble application is in the paper industry. Studies were carried out on samples from the six facies of the deposit (sand kaolin, soft kaolin, lower transition facies, ferruginous crust, upper transition facies and flint kaolin) in order to trace its geochemical evolution. The kaolin developed at the expense of Cretaceous sandy–clayey sediments of the Ipixuna Formation. Intense lateritic processes characterized by ferruginization and deferruginization mechanisms led to the distinction of the different facies.     

Remediation and restoration of metal-contaminated sites： Concepts and appfications to mining areas

Metals, including heavy metals and metalloids, are a common group of environmental contaminants. Their sources in the environment are geogenic or anthropogenic. The growing trend in global industrialization ensures that more metals could be dispersed even in pristine ecosystems. To fuel industrialization, more metal ore mines have to be discovered and explored. These explorations often result in landscape disturbance, soil degradation and environmental contamination by unwanted mining constituents. Mine tailings brought up to the ground surface often serve as the main source of contaminants when these pyrite-rich materials oxidize. The oxidation of mine tailings results in proton generation, coupled with the dissolution of metals and other cations Unwanted anionic constituents are also produced. The so-called ＂acid mine drainage＂ may affect the productivity of farmlands and stability of receiving streams and other bodies of water-acidifying the waters and enriching the ecosystem with metals, i.e., high total dissolved solids. The acidified overburden materials become inhospitable to plant and microbial life as they are typically low in organic matter content and infertile. This exposes the landscape to runoff and erosion.     

阻燃级氢氧化镁制备过程中表面有机化改性

文章通过论述阻燃剂型氢氧化镁制备过程中的表面有机化改性,对改性剂、作用机理和改性工艺等进行了探讨,说明了对阻燃剂型氢氧化镁表面有机化改性的重要性,及在氢氧化镁制备过程中综合分析、系统研究的必要性。     

Attenuation of aqueous metal transport at two natural acid rock drainage occurrences in the Yukon Territory, Canada

Naturally acidic drainage associated with pyritic black shale has been observed in many locations in the Yukon Territory. While not necessarily linked to known mineral deposits, most of these natural acid rock drainage occurrences show elevated dissolved concentrations of trace elements, especially zinc, nickel, copper, cadmium and arsenic. Based on field observations, microbial investigation, chemical analyses and geochemical modeling, the fate and transport of potentially deleterious elements at two natural acid drainage occurrences with slightly different settings are examined. The Macintosh Creek is a small, acidic stream （pH 2.98-3.40）, 2 km long, located in the Macmillan Pass area of east-central Yukon amidst known sedimentary exhalative massive sulfide mineralization but remains undisturbed by exploration activities. Its trace metal content is apparently derived from groundwater discharges, which gave as much as 5.0, 2.5, 0.7, 0.13 and 0.03 mg/L ofZn, Ni, Cu and As, respectively. Interaction and sorption reactions with algal mats, biofilms and iron oxyhydroxides appear to be the dominant mechanisms attenuating aqueous contaminant transport along the stream. Cryogenic precipitation further consolidates the ferricrete formation and reduces the mobility of the sorbed metals. The tributaries of the Engineering Creek along the Dempster Highway in northern Yukon drain through a series of dolomite, phyllite, argillite, limestone, black shale, sandstone and conglomerate with no known concentration of mineralization. In this area, the water chemistry fully reflects the local geology with acidic streams invariably associated with black shale occurrences. Groundwater seeps in the headwaters area of the km-180 Creek completely enclosed in black shale gave pH 3.0 and as much as 148, 39, 2.9 and 9.1 mg/L of Zn, Ni, Cu and As, respectively. Sorption with iron oxyhydroxide and organic matter appear to dominate the attenuation of contaminant transport along the stream. However, once entered into carbonate-dominated terrains, secondary carbonate minerals exercise additional geochemical control on the local water chemistry as a result of neutralization.     

In situ time resolved synchrotron powder diffraction study of thaumasite

Structural changes during dehydration and subsequent decomposition in thaumasite Ca₃Si(SO₄)(CO₃)(OH)₆·12 H₂O were studied by in situ synchrotron powder diffraction between 303 and 1,098 K. Evolution of the crystal structure was observed through 28 structure refinements, by full profile Rietveld analysis performed in the P6₃ space group, between 300 and 417 K, whereupon the thaumasite structure was observed to breakdown. Within this temperature range, the cell parameters of thaumasite increased as a function of temperature in a nearly linear fashion up to about 393 K, at which temperature, a slight slope change was observed. Above 400 K, the thermogravimetric analysis revealed that the dehydration process proceeded very rapidly while the refined occupancy of water molecules dropped below a critical level, leading to instability in the thaumasite structure. At a same time, a remarkable change in the unit cell parameters occurring at about 417 K indicated that the crystal structure of thaumasite collapsed on losing the crystallization water and it turned amorphous. This result indicated that the dehydration/decomposition of thaumasite was induced by the departure of the crystallization water. At about 950 K, anhydrite and cristobalite crystallized from the thaumasite glass.     

A Connectivity Index for Discrete Fracture Networks

Connectivity is an important measure for assessing flow transport in rock, especially through fractures. In this paper, rock fracture systems are modelled by a discrete fracture model simulated by a marked point process. A connectivity index is then introduced to quantify the connectivity between any two points in space. Monte Carlo simulation is used to evaluate the connectivity index for stationary cases and relationships between the connectivity index and the parameters of the discrete fracture model are analysed. The average number of intersections per fracture, X_f, and the fracture intensity, P12 (P32), are calculated and the relationships between these parameters and the connectivity index are investigated, concluding that X_f is the more suitable parameter for the classification of rock mass flow properties. The relationships between the connectivity index and the percolation state of the fractured medium are also discussed. An edge correction is briefly discussed and a practical example is used to demonstrate the method of computing the connectivity index.     

模糊理论在公路边坡稳定性分析中的应用

边坡工程是一个复杂的系统工程。边坡的稳定与否直接关系到其防护工作的程度。因此,如何有效、合理地判断边坡的稳定性对整个工程的经济与社会效益极为重要。影响边坡稳定的因素众多,判断其稳定与否应考虑各因素的综合效果。论文运用模糊理论中的多因素综合评判模型对某高速公路边坡的稳定性进行研究。通过全面考虑影响因素,建立相应的评判因素集及单因素评判矩阵,运用专家评判法和判断矩阵法确定出各因素的权重。最后通过多层次模糊评判得到该边坡的稳定性评判结果。研究证明,该法在边坡稳定性分析评判中是切实可行的。     

要十分重视另一类型地质灾害的防治

文章提出另一类型地质灾害,即化学型地质灾害的定义及其分类。并认为化学型地质灾害不像物理型地质灾害那样发生瞬时灾害,而有一个延缓过程,但是一旦发生,难于挽救。化学型地质灾害体的主体是化学元素,开展地球化学调查,研究化学元素的赋存规律、土壤及沉积物承受各类元素的极限、各类元素活化的条件是揭示诱发化学型地质灾害机理的关键。因此要十分重视与加强化学型地质灾害的调查、研究、监测与治理工作。     

遥控飞艇数字航空摄影系统

提出快速获得航空影像并及时制作DOM、DLG的一种手段.介绍遥控飞艇数字摄影系统的工作原理,探讨存在的问题.     

矢量数字地图数据质量的综合评估

研究和确定了矢量数字地图数据的质量评估因子和评估标准,介绍了利用模糊综合评估方法进行质量评估的过程和做法,并给出了实例.