Dissolution rates of metals in Fe oxides: implications for sampling ferruginous materials with significant relict Fe oxides

A study of the pattern of dissolution of synthetic and natural Fe oxides in 6 M HCl indicates that the rate of element release from synthetic Fe oxides is strongly influenced by mineralogy and the level of element incorporation. Synthetic maghemite (γ-Fe₂O₃) samples are subject to much more rapid dissolution than goethite (FeOOH) and hematite (α-Fe₂O₃). In samples dominated by hematite and maghemite, Cu, Zn and particularly Pb, in comparison to Fe, are preferentially released during the early stages of dissolution. Similar patterns are apparent from the dissolution of hematite- and maghemite-dominated samples derived from natural gossan. Comparison of XRD scans with data from the dissolution of natural gossan samples transformed by incremental heating to hematite- and maghemite-dominated assemblages suggests that the degree of crystallinity may also be a significant factor in the release of elements incorporated in the Fe oxides. Ferruginous materials made up of varying proportions of goethite, hematite, maghemite, kaolinite and quartz are important sampling materials in a range of regolith environments. These are products of complex chemical and mechanical mobilization over long periods of geological time. If the patterns of Fe oxide dissolution in 6 M HCl and the release of incorporated metals reflect stability in such weathering regimes, knowledge of the retention characteristics of incorporated metals in different Fe oxide phases, as indicated by this study, will be useful in the planning and interpretation of geochemical surveys in such regions.     

Pore water geochemistry near the sediment-water interface of a zoned, freshwater wetland in the southeastern United States

 Sediment and its associated pore water were collected from a zoned, freshwater, riparian wetland, located in the Talladega National Forest, northeastern Hale County, Alabama, to study the porewater chemistry and its spatial changes within and between the wetland ecological zones. Obvious changes in pH, Eh and element concentrations were observed between the different wetland ecological zones. Major cations (Ca, Mg, and Na) and trace elements (B, Ba, Sr, and Mn) have very good spatial correlation with Fe and Mn distributions, both in the pore water and the sediment, suggesting that adsorption on, and desorption from, iron and manganese oxyhydroxides are important processes controlling the distributions of these elements in the wetland sediment. However, an equilibrium adsorption model is not able to explain the distribution of trace elements between the pore water and sediment. A redox kinetic model gives similar vertical profiles for iron and the correlated elements as those measured in the field and thus suggests that the relative rates of ferrous iron oxidation and the reductive dissolution of ferric iron in the sediment are important variables determining the distributions of these elements in the wetland pore waters. Received: 31 October 1996 · Accepted: 27 May 1997     

The effect of distribution of iron-oxyhydroxide grain coatings on the transport of bacterial cells in porous media

 Among the demonstrated processes influencing the transport of bacteria through aquifers, the deposition of cells on mineral surfaces is one of the most important. For example, understanding the transport of introduced bacteria through aquifers is essential to designing some in situ bioremediation schemes. The impact of the presence and distribution of Fe(III)-oxyhydroxide-coated sand grains on bacterial transport through porous media was evaluated in column experiments in which bacteria (short rods; 1.2 μm length) were eluted through columns of quartz sand (0.5–0.6 mm in diameter) for several conditions of chemical heterogeneity of mineral substrate. Fe(III)-oxyhydroxide-coated sand was present as 10% of the mass, and it was arranged in three treatments: (1) homogeneously distributed, and present as a discrete layer (2) at the top and (3) at the bottom of 14-cm-long sand columns. A pulse input of 10⁸ cells ml^–1 was introduced in an artificial groundwater solution flowing at 14 cm h^–1 through the column, and eluted cells were counted. Peak breakthrough occurred at 1.0 pore volume. A large proportion of cells were retained; 14.7–15.8% of the cells were recovered after three pore volumes of solution had eluted through clean quartz sand, and only 2.1–4.0% were recovered from the Fe(III)-oxyhydroxide-coated sand mixtures. The three physical arrangements of the chemical heterogeneity resulted in essentially the same breakthrough of cells, indicating that the spatial distribution of iron coating does not affect the transport of bacteria. The results of the column transport experiments, which mimic hydrogeological conditions encountered in field problems, are consistent with our mechanistic understanding of bacterial sorption. Received: 10 April 1996 · Accepted: 17 February 1997     

利用磁团聚简化铁矿石磁选流程

论述了含假象赤铁矿铁矿石磁选工艺流程的改进。利用磁团聚工艺省去了赤铁矿回收段单独的粗精矿再磨设备及后继的中磁场精选作业。节省了设备投资费用及生产成本,而且铁实收率较之传统工艺有所提高。对类似该矿石性质的氧化带混合铁矿石磁选流程的制定及现场流程改造有启迪意义。     

Sediment diffusive fluxes of Fe,Mn, and P in a eutrophic lake: Contribution from lateral vs bottom sediments

Water column data and porewater profiles are used to study the chemical evolution with time and with depth of a eutrophic lake. By using different approaches, diffusion fluxes for dissolved iron, manganese and phosphate are calculated and used to describe the processes occurring at the sediment-water interface as well as in the hypolimnion of the lake. These data are used in the elaboration of a qualitative model to describe the chemical behaviour of the sedimentary interface of an anoxic lake with emphasis on the Fe/P/S system. Acorona model is proposed to explain the evolution with time of the diffusion process by estimating the relative contribution of bottom and lateral sediment surfaces to the total fluxes of dissolved elements diffusing from the sediment to the overlying water. As the hypolimnion becomes more anoxic, it has been observed that lateral sediment surfaces (16 to 10 meters in depth) represents a larger supplier of diffusing dissolved components than the bottom sediment portion (bottom to 18 meters).     

铁矿浆出现的构造背景及其找矿评价意义

铁矿浆、斑岩铜矿和海相火山岩铜矿均是火山－岩浆作用的产物。铁矿浆通常形成于构造环境从引张发展至挤压过程中并以挤压条件为主时，介于斑岩铜矿和海相火岩岩铜矿的成矿条件之间，其成因及时分布与斑岩铜矿更加密切，多出现于陆相或海陆交互相环境。     

中元古界昆阳群因民组铁铜矿的成矿地球化学研究

因民组是川滇地区重要的铁铜矿赋存层位之一。系统地研究了因民组铁铜矿床的常量元素、微量元素、稀土元素、同位素和包裹体的特征，阐明成矿作用具有火山热水喷流－沉积成矿作用的地球化学特点。     

以冶山铁矿为例谈充分利用现有铁矿资源的问题

我国每年铁矿石供应缺口较大，并在逐年扩大，认真抓好现有矿山，充分利用现有铁矿资源，减少缺口，已势在必行。文章结合冶口 铁矿实际，提出有关措施，继续对矿山优惠政策，并鼓励矿山充分利用资源，加强矿山技术改造，坚持采矿与找矿并重，努力提高矿石的开采回收率，减少损失率，降低     

Self-organization of recent rhythmic iron-manganese precipitations in underground mines in the Harz mountains

A recent early diagenetic banded iron-manganese mud has been forming underground in a closed lead-zinc mine for approximately 40 years. The processes leading to the banded structure of the precipitate were studied during a period of 2 years. Therefore, 19 physical and chemical parameters were measured regularly in short intervals. The resulting time series were analysed with respect to the data sets of the monthly chemical analyses of the descendent mine water, the daily rainfall and the mineral content. The results reveal that the precipitated material undergoes internal self-organization due to interaction of redox, colloid-chemical, microbial, electrical and ripening processes, and not exclusively produced by seasonal fluctuations of material input. Thus, the primary banding of the material, caused by externally forced fluctuations of the redox conditions within the mine water, is reorganized after a short time. The finally observed bands are controlled by non-linear coupling of reaction and transport processes within the mud. A genetic model for the banded mineralization was developed and verified by numerical simulation.     

多尺度CB形态学及其在线划图像噪声清除中的应用

介绍了基于轮廓结构元的形态学（简称CB形态学）的概念及其性质,讨论了CB形态运算的快速实现。由于CB形态学处理的对象不是基于目标的形状,而是基于目标的延伸度,因此它可以用来处理线划图像。在本文中,利用CB形态学的这一特性消除线划图像上的噪声,获得了满意的结果。