Coarse Magnetite Research Articles

Study on the effect and mechanism of coarse magnetite on the flotation of fine-grained hematite

Lean hematite ore is one of the refractory iron ores in China due to its fine crystal size, deep oxidation degree and complex mineral composition. With the deep mining of mine ore, the disseminated particle size of iron minerals is finer, and the ore properties are more complex and difficult to be separated. Therefore, the research on high-efficiency beneficiation technology of fine-grained lean hematite ore is the requirement and important direction of the development of refractory iron ore beneficiation. In this paper, the carrier flotation method is used to comprehensively recover hematite, and the addition of coarse-grained magnetite can effectively improve the recovery rate of fine-grained hematite. The flotation results show that when the ratio of magnetite to hematite is 1: 1, the recovery rate of iron ore can reach more than 96.34%, and the efficient recovery is realized. Based on the results of pure mineral test, the carrier flotation test of Anshan lean hematite ore was carried out. The results show that the reverse flotation concentrate product with TFe grade of 67.88% and total iron recovery of 84.81% can be obtained, and the TFe grade of the reverse flotation tailings is 24.20%. It can be seen that compared with the traditional process, the grade of carrier flotation tailings is 2.37 percentage points lower than that of the original reverse flotation tailings; the carrier reverse flotation process can effectively improve the recovery rate of iron concentrate. In addition, the theoretical analysis of carrier flotation was carried out by contact angle, zeta potential, mineral phase microscope, SEM and XPS. It was found that the collision probability between fine mineral particles and bubbles was low, which limited the recovery of fine mineral particles in the flotation process. Fine-grained hematite can be non-selectively attached to the carrier particles, thereby affecting the adsorption of starch on it, thereby improving the recovery rate of fine particles; The carrier reverse flotation can further improve the flotation efficiency by gravity and shear force. Carrier reverse flotation provides a new idea for effective recovery of iron ore.

A dual mechanism drives the enrichment of pedogenic magnetic particles derived from red beds

Iron oxides and associated magnetic properties are considered good indicators of the pedogenic environment and regional climate. However, these indicators are under debate for soils developed from sediments. The accumulation of magnetic particles derived from sediments depends not only on the formation of iron oxides but also on the existence and transformation of detrital iron oxides. To explore the formation mechanism of magnetic particles accompanied by pedogenetic processes, a toposequence consisting of six profiles derived from red beds with contrasting drainage conditions under a subtropical monsoon climate is examined. We generally observed upward magnetic enhancement but inconsistent correlations between magnetism and iron oxide phases. The magnetic enhancement in the well drained profiles was dominated by the reverse transformation of detrital hematite to fine maghemite particles, whereas in the poorly drained profiles, coarse magnetite particles formed with soil organic matter enrichment in an anaerobic way. The lower magnetism in the transition profiles is attributed to the hydration of iron oxides into goethite before the pedogenic environment became anaerobic. The different magnetic enrichment mechanisms explain the nonlinear responses of magnetism and color to climate across temporal and spatial scales. These findings also suggest that soil magnetism is promising for tracing soil moisture and ecological evolution, especially in red soils and sediments across the surfaces of the Earth.

Effects of magnetite incorporation in a chemically bonded phosphate ceramic

In this study, coarse magnetite (>63 μm) is introduced as a reactive component in wollastonite-based chemically bonded phosphate ceramics (WPC). It is found that WPC with coarse magnetite results in the formation of new stable microstructural phases such as iron phosphate cementitious matrix. The new ceramics (M-WCP) exhibit much lower shrinkage than WPC even after heating at elevated temperatures —eight times less shrinkage at 200 °C. Stiffness increases sharply from the 11.4 GPa of WPC to 23.4 GPa by adding coarse magnetite filler (M-WPC). The stiffness of WPC is reduced by more than 50% by heating above 100 °C, while M-WPC preserves more than 70% of its stiffness when heated up to 700 °C. Compressive strength increases from the 52 MPa of WPC, up to 80 MPa (M-WPC) by introducing coarse magnetite as reactive component. The new iron phosphate cementitious material —with attractive microstructural and mechanical properties besides high dimensional and thermal stability— can be recommended for many applications in construction, waste stabilization, and storage systems for radioactive materials.

The onset of the right-lateral strike-slip setting recorded in magnetic fabrics of A-type granite plutons of the Ribeira belt (SE Brazil)

Strike-slip shear zones formed during continental collisions accommodate the convergence and indentation of rigid cratonic blocks. In high-temperature settings of deeply eroded orogens, such as the Neoproterozoic Ribeira belt in southeastern Brazil, the shear deformation is associated with syntectonic granitic magmatism. Anisotropy of magnetic susceptibility (AMS) and zircon U-Pb results from late A-type granites were used to investigate the timing of the strike-slip deformation. Some of these plutons show reddish colors, local rapakive textures and magnetic susceptibilities that are typically lower than older batholiths. Rock magnetic data and SEM analysis indicate that AMS of the A-type plutons is dominated by coarse magnetite and locally (titano)hematite, the latter formed by oxidizing hydrothermal fluids in the final stages of magmatic crystallization. The shape preferred orientation of mafic minerals and feldspars measured in the reddish granite facies , however, indicate that AMS reproduced the magmatic fabric defined by the silicates. Magnetic fabric orientations vary from concordant (Ouro Verde and Capão Bonito plutons) to partially concordant (Sguário pluton) with respect to the host rock shear zones, and define the transition from concentric magnetic lineations and foliations experienced by older I-type batholiths. These A-type plutons constrain the onset of the ductile transpressional deformation at ca. 595 Ma. The magmatism and shear deformation persisted up to 550 Ma in the western Ribeira belt when more brittle transtensional conditions prevailed. These results are consistent with the convergence and indentation of the Congo-São Francisco craton that partitioned the deformation across the orogen and promoted the belt lateral escape mediated by dextral shear zones.

Eruptive and depositional processes of a low-aspect-ratio ignimbrite (the Southern Kusandong Tuff, South Korea) inferred from magnetic susceptibility variability

Low-aspect-ratio ignimbrites, produced by the most lethal volcanic eruptions, are thin but laterally extensive and can serve as good stratigraphic markers in many sedimentary basins. They are commonly structureless, and require diverse analytical tools to reveal the related geological processes. This study aims to understand better the eruptive and depositional processes of the Cretaceous Kusandong Tuff, which is a several meter-thick and laterally extensive silicic ignimbrite in Korea, through rock-magnetic analyses of magnetic susceptibility (k) and isothermal remanent magnetization (IRM) together with optical and electron microscopic observations. Massive parts of the tuff show systematic vertical variation in k within each locality, and the vertical variation patterns vary from locality to locality, being classified broadly into three types: a single cycle of upward-decreasing k (type A), repetition of two or more upward-decreasing k (type B), and consistently low k (type C). A linear relationship between k and IRM indicates predominant contribution of ferri- and antiferro-magnetic minerals to k in the majority of the tuff. Integrated results of microscope images, temperature variations of k, and IRM unmixing analyses indicate that the major magnetic minerals are coarse magnetite (with occasionally partial maghemitization) of both primary and secondary origins, very fine secondary magnetite, and secondary hematite and goethite. Quantitative comparison of the unmixed magnetic mineral components reveals that those vertical k variations are related to some combination of magnetite destruction and subsequent precipitation of antiferromagnetic minerals by post-depositional alterations at different stages (types A, B, and C) and magnetite supply by deposition of additional cooling unit (type B). Despite the adverse post-depositional modifications of k, this suggests that the massive part of this tuff is a composite unit formed by accumulation of multiple cooling units from multiple pyroclastic current pulses probably associated with fluctuations in eruption rate at one or multiple source vent(s). Comparison by a k-based proxy between localities implies independence of primary magnetic mineral content on the distance from vent(s), potentially implying convection-dominated behavior in the pyroclastic current dynamics. This possible flow dynamics is inferred to be generated by sustained laterally-directed blasts from shallow-level explosion and could, in turn, lead to long-distance travel. This study exemplifies how the methodological approach using magnetic susceptibility can contribute to characterize the nature of low-aspect-ratio ignimbrite, and will help make more use of the Kusandong Tuff as a key regional stratigraphic marker as well.

An environmental magnetic record of heavy metal pollution in Vembanad lagoon, southwest coast of India

Magnetic signature of the iron-bearing minerals archived in sediments is sensitive to change in environment and therefore, studied to reconstruct the signals linked with environmental processes. In the present work, we have analyzed 11 sediment cores from Vembanad lagoon, southwest coast of India, to estimate the magnetic fluctuations associated with environmental processes. Down-core variation in magnetic susceptibility and anhysteretic, isothermal and saturation isothermal remnant magnetization and S and H-ratios have been interpreted to map the degree and spatial distribution of anthropogenic pollution in and around the lagoon. Downcore variation of magnetic susceptibility of Vembanad lagoon sediments varies from 10 to 100 × 10−8 m3/ kg. The top layers of sediment samples from river mouth regions (Periyar and Muvattupuzha rivers) show higher susceptibility values and incidentally these samples are of coarse sized. The subtle variations in SIRM/χlf ratios suggest that there are magnetic grain size differences in the samples. The SIRM and χlf relation suggests that dominant magnetic grain size in sediments. The low ARM/χlf ratios suggest a relatively higher ferrimagnetic contribution and coarser magnetite grain size. Rock magnetism data reveal that the coarse magnetic grain size is affecting the pollution of Vembanad lagoon. We also analyzed downcore variability of metal concentrations such as Fe, Mn, Cu, Zn, Ni and Cr, and all these metals exhibit higher concentrations in the top layers of the cores. Our study suggests that higher values of magnetic parameters and metal concentrations are due to various anthropogenic sources.

Topsoil Magnetic Susceptibility and Heavy Metal Contamination: A Case Study in Al-Muthanna Province, Iraq

Due to rapid urbanization and industrialization that occurred in Al- Muthanna province in southeastern Iraq during the last decade, pollutants such as heavy metals were emitted into the environment and became a serious threat to human health. Environmental pollution could be caused by different types of pollutants, which come from different sources.
 This study aims to assess the environmental magnetism efficiency for heavy metal pollution assessment using the magnetic susceptibility technique which became a more rapid and cost-effective compared to conventional methods. Increasing heavy metal contents in soils causes an increase in the magnetic mineral concentration. The study area is located in Al- Muthanna province, southeast of Iraq, and contains three cement plants, an oil refinery, bricks factories, and power plants. Fifty topsoil and subsoil samples (0-50 cm depth) were collected from five sites; Al-Jinoob cement plant (one site), Samawa oil refinery (two sites) and Al- Muthanna cement plant (two sites). In this study, magnetic properties of samples in vertical sections and levels of heavy metal elements; of selected samples from regions with different geological settings were compared. The heavy metals analysis included chromium (Cu), iron (Fe), nickel (Ni), copper (Cu), Arsenic (As) and lead (Pb), which could give indications of heavy metal pollution in soil. The highest magnetic susceptibility value (65.23 x10-8 m3kg-1) was recorded in Al-Muthanna cement plant (TSL-4) and the highest Cu concentration (602.57 ppm) was also recorded in Al-Muthanna cement plant (TSL-5-3). The results of magnetic properties show the dominance of coarse magnetite, which is supposed to have originated from pedogenic particles in natural soils, causing the positive correlation between magnetic susceptibility (χ) and anhysteretic remanent magnetisation (ARM). According to the results of frequency dependent susceptibility ratio (κfd%), the magnetic particles showed an admixture of multi-domain and pseudo-single domain behaviour. Magnetic susceptibility and heavy metal analyses results indicated emissions from nearby industrial plants. X-ray fluorescence (XRF) was carried out for heavy metal analyses which supported our results. Results of this study demonstrate the suitability of applying magnetic techniques for assessing environmental situations.

Influence of Sea Level Change and Centennial East Asian Monsoon Variations on Northern South China Sea Sediments Over the Past 36 kyr

AbstractSouth China Sea (SCS) sediments can provide important paleoclimate records because of their generally high deposition rates and strong regional influence of East Asian summer monsoon (EASM) variations. However, interpretation of sedimentary records from the northwestern SCS slope is complicated because sedimentation is sensitive to sea level and provenance variations. We seek to develop a paleoclimatic record of SCS sediments by analyzing sediment magnetic properties over the past ∼36 kyr from core PC338. The dominant magnetic minerals are magnetite and hematite in most parts of the core. The hematite concentration increased profoundly over the ∼15–32 kyr B.P. period when sea level was lower than −90 m below the present level. This suggests that Red River inputs were enhanced significantly in this period. Moreover, increased coarse magnetite contents were recorded in association with an enhanced East Asian winter monsoon (EAWM) during the Last Glacial Maximum and Heinrich event 1. Low‐field and frequency‐dependent magnetic susceptibility variations were coeval with EASM‐controlled climate change recorded in South China and the SCS over the past 15 kyr, probably because regional terrestrial weathering and erosion of iron‐bearing minerals, and their transportation are dominated by climate. Rhythmic coarsening of Holocene magnetic mineral concentrations coincided with global cooling events, which indicates that core PC338 also contains signals of enhanced EAWM variations. The study demonstrates that magnetic proxies are indicative of sediment supply and deposition variations on the SCS continental slope that are useful for understanding the effects of sea level and climate change on SCS sediments.

An eolian deposit–buried soil sequence in an alpine soil on the northern Tibetan Plateau: Implications for climate change and carbon sequestration

The accumulation of eolian dust plays an important role in the development of alpine soils on the northern Tibetan Plateau. However, little is known either about the nature of soil-forming processes in the region, or about the magnitude of soil organic and inorganic carbon (SOC and SIC) storage. Here we report the results of an investigation of a typical profile, consisting of a series of buried soils developed within eolian deposits, situated at an altitude of 4951m in the Amdo zone of the northern Tibetan Plateau. Bulk density, pH, SOC and SIC content, grain-size distribution, magnetic susceptibility and mineralogical composition were measured at high resolution, and AMS 14C dating was used to provide a chronology. Based on all of the analytical data we conclude that this alpine accretionary soil profile contains three buried soils beneath the present surface soil layer. The deepest and oldest soil is the basal paleo-weathering crust (Ferralsol) which underwent active soil formation from 5540 to 7615yr. BP, or even earlier. The other soils, which are developed within the overlying eolian dust deposits, are Luvisols and they document the occurrence of two intervals of more humid conditions than the present day: from ~3455 to 5540yr.cal BP and from ~2000–2500yr.cal BP. Microscopic analysis of coarse particles from the profile reveals that high values of magnetic susceptibility at the base of the profile reflect the presence of coarse magnetite grains present as inclusions within quartz grains derived from the weathering of granitic gneiss. In addition, the magnetic susceptibility profile reflects the effects of winnowing of the eolian fraction by wind activity, and not the production of fine magnetic grains during pedogenesis. SOC is the dominant form of carbon in this alpine soil and the SOC density and average accumulation rate values within the entire interval of eolian deposits are 19.67kgCm−2 and 3.55gCm−2yr.−1, respectively. These remarkably high values indicate that this alpine accretionary soil is characterized by highly efficient SOC burial, and therefore that such soils are an important terrestrial CO2 sink. Likewise, the buried soil plays an important role in SOC storage. Finally, the characteristics of the buried soils indicate a long-term climatic trend towards aridity in the study region. This natural trend has promoted the processes of desertification and grassland degradation on the northern Tibetan Plateau, and these processes may have been exacerbated by human activity.

Process optimization for coal cleaning by enhancing the air-distribution stability of dry separator

With 0.3–0.074mm vanadium-titanium magnetite powder used as the fluidized medium, the overall fluctuation of bed pressure drop and the uniformity and stability of bed density in the secondary air-distribution fluidized bed (SAFB) were experimentally investigated. Compared with the conventional fluidized bed (CFB), SAFB demonstrated smaller fluctuations of bed pressure drop, generated more smaller-sized bubbles, and had a more even bed density, which indicated more stable separation condition. A larger value of (Umb−Umf) in SAFB indicates the larger stability region in the bed, which improves the applicability of fluidized bed. To ensure the bed stability within suitable superficial gas velocity U, the operating factors of the secondary air-distribution bed height Hd and the weight fraction of coarse magnetite powder in the mixture of separating medium α should be adjusted to vary in the ranges of 13–17mm and 80–90%, respectively. With the optimal operation parameters of the static bed height Hs, U, Hd, and α, orthogonal array testing technique was adopted to design and perform the separation experiments of 6–25mm Yiluo coking coal. Finally, the ash and sulfur contents of coal sample were reduced from 38.98% and 1.31% to 12.26% and 0.82% in SAFB, respectively. The cleaning coal with a yield of 60.74% was obtained at a separating density of 1.64g/cm3 and a probable error EP value of 0.05g/cm3. Therefore, SAFB presents better separation efficiency than that of CFB, which indicates a favorable application prospect in industry.

A systematic study to understand the effects of particle size distribution of magnetic fingerprint powders on surfaces with various porosities.

This study intends to design magnetite (Fe3 O4 )-based magnetic fingerprint powders with different particle size distributions. It also investigates the influence of particle size distribution on the visualization of latent fingermarks with as little background staining as possible on the surfaces with various porosities in a systematic way. Two strategies were used to prepare the magnetic fingerprint formulations for this study: milling of coarse magnetite particles for different durations, and mixing of sieved fine particles with different size ranges with coarse particles. Particle size analyses of the prepared magnetic powders, optical microscopy-based roughness analysis of the surfaces and SEM measurements of the visualized fingerprints and representative powders were performed. Mag2 of the formulations prepared through milling and Mag5 and Mag6 of the formulations prepared through sieving and mixing were more successful in the development of latent prints than the rest of the solutions.

Fine Coal Dry Cleaning using an Air Dense Medium Fluidized Bed with Improved Magnetite Medium

Coal beneficiation using air dense medium fluidized bed offers a number of advantages and provides an efficient solution for coal cleaning in a dry way. Recently, the development of the air dense medium fluidized bed mainly concentrate on the coarse coal (+6mm), and it is also reported that fine coal (-6mm) is hard to be separated by conventional magnetite medium. The objective of this study is to using four types of magnetite powders with different narrow size range to separate -6+3mm fine coal. The pressure-drop performance of the different magnetite medium in fluidized bed was also experimentally studied. The results show that the finer magnetite powders have a lower pressure-drop and minimum fluidization velocity than the coarse magnetite powders, and the -6+3mm fine coal can be separated effectively by -0.15+0.074mm magnetite powders, which will expand the lower separation limit of the air dense medium fluidized bed.

Magnetic responses to traffic related contamination recorded by backfills: A case study from Tongling City, China

Abstract With the development of urbanization and industrialization, traffic is creating a serious contamination problem. Conventional methods for contamination testing are generally expensive and time-consuming, while magnetic methods have been suggested to be an economic and non-destructive alternative. In this study, we measured magnetic properties and heavy metal contents in backfills along an urban road side in China, in situ on surface and on samples in vertical sections. Magnetic results and SEM images show the dominance of coarse magnetite, supposed to origin from human activities. Furthermore, there is an obvious decreasing trend of magnetic susceptibility ( χ ) and several heavy metals (Cu, Mn, Zn, Pb) with increasing distance from the road edge, symmetrically at both road sides, indicating that this is a typical traffic-related contamination signal. The detailed distribution patterns of χ and heavy metals exhibit slight variations in the surface data, probably due to the local topography and surface runoff due to rainfall. In vertical soil cores magnetic parameters show significant positive relationships ( r = 0.88–0.99) with concentrations of heavy metals (Cu, Zn, Pb, Fe). Our results suggest that backfills unaffected by the traffic contamination signal and characterized by low χ value can be chosen for contamination monitoring. Despite the complex nature of backfills and the possibility of contamination prior to their transportation to the site, they are especially important for areas where undisturbed soil is not available.

Combination of magnetic parameters and heavy metals to discriminate soil-contamination sources in Yinchuan — A typical oasis city of Northwestern China

Various industrial processes and vehicular traffic result in harmful emissions containing both magnetic minerals and heavy metals. In this study, we investigated the levels of magnetic and heavy metal contamination of topsoils from Yinchuan city in northwestern China. The results demonstrate that magnetic mineral assemblages in the topsoil are dominated by pseudo-single domain (PSD) and multi-domain (MD) magnetite. The concentrations of anthropogenic heavy metals (Cr, Cu, Pb and Zn) and the magnetic properties of χlf, SIRM, χARM, and ‘SOFT’ and ‘HARD’ remanence are significantly correlated, suggesting that the magnetic minerals and heavy metals have common sources. Combined use of principal components and fuzzy cluster analysis of the magnetic and chemical data set indicates that the magnetic and geochemical properties of the particulates emitted from different sources vary significantly. Samples from university campus and residential areas are mainly affected by crustal material, with low concentrations of magnetic minerals and heavy metals, while industrial pollution sources are characterized by high concentrations of coarse magnetite and Cr, Cu, Pb and Zn. Traffic pollution is characterized by Pb and Zn, and magnetite. Magnetic measurements of soils are capable of differentiating sources of magnetic minerals and heavy metals from industrial processes, vehicle fleets and soil parent material.

An investigation of the magnetic carriers and demagnetization characteristics of the Gulang loess section, northwestern Chinese Loess Plateau

We report the results of a rock magnetic and paleomagnetic investigation of unit L9 of the Gulang (GL) loess section, in the northwestern Chinese Loess Plateau (CLP). We demonstrate that the dominant magnetic remanence carriers are coarse-grained pseudo single-domain/multidomain magnetite particles, and hematite. The application of either thermal (THD) or alternating-field demagnetization (AFD) yielded several normal polarity intervals interbedded with intervals of reversed polarity, but which cannot be correlated with standard geomagnetic polarity time scales. A greater number of normal polarity intervals, however, were evident after THD than after AFD. We propose that the normal polarities are either the result of overprinting of a viscous remanent magnetization (VRM) carried by coarse magnetite particles on the original depositional remanent magnetization (DRM); or that they represent genuine geomagnetic excursions (such as the Kamikatsura and Santa Rosa excursions) which are difficult to identify. In addition, we propose that in the case of the GL loess section, the effect of thermal demagnetization tails of a VRM is a possible reason why THD treatment yielded a greater number of normal polarity intervals than does AFD. However, reversed polarities obtained by either THD or AFD may be credible for sedimentary intervals with a relatively high content of hematite particles which preserve the primary DRM. Although numerous studies have proposed that THD provides more reliable paleomagnetic directions for loess sediments from the CLP, our results suggest that careful attention needs to be paid to the type of demagnetization method chosen, especially in the case of coarse-grained loess deposits.

Emplacement of magma in Eastern Iceland dikes: Insights from magnetic fabric and rock magnetic analyses

The anisotropy of magnetic susceptibility (AMS), coupled with mineral magnetic identification, has been investigated in about 640 samples from 27 basaltic dikes of Tertiary age in Eastern Iceland. The dikes are a few meters thick and they have been sampled all across. Three types of magnetic fabrics with well-defined mean principal axes of anisotropy are recognized. In the first one the maximum axis is vertical and the minimum axis coincides with the pole of the dike plan (“geometrically normal” fabric). The second fabric shows opposite orientation (“geometrically inverse” fabric). The third type is when these two fabrics coexist with the “normal” one at the margins and the “inverse” one in the center of the dike (“mixed” fabric). No relationship is observed between the type of fabric and the width of the dikes. Each fabric is carried by clear magnetic assemblages made of low ( x ∼ 0.15) Ti-content fine-grained magnetites for the “normal” one and high Ti-content (around TM60) coarse magnetite grains for the “inverse” fabric. Upon heating, the magnetic properties and the orientation of the anisotropy ellipsoid characterizing the “inverse” fabric in the mixed dikes change and evolve toward the “normal” type. These two geometrically “normal” and “inverse” fabrics are interpreted as primary ones, representing different physico-chemical conditions during the emplacement of the magma. The AMS results indicate that, during the volcanic events occurring about 10 Myr ago, the extrusion of the magma was vertical at the depth of the studied sites in eastern Iceland.

Environmental magnetic responses of urbanization processes: evidence from lake sediments in East Lake, Wuhan, China

SUMMARY We present a study on the environmental magnetic response to urbanization processes from nine sediment cores from East Lake in Wuhan, China. The concentration of magnetic particles, heavy metals and organic matter in the upper 2–18 cm of the sediment cores have been significantly elevated due to the input of coarse magnetite grains from industrial (e.g. power generation and steelmaking) and other anthropogenic activities (e.g. vehicle emissions). Concentration-related magnetic parameters, such as magnetic susceptibility (χ), saturation isothermal remanent magnetization and anhysteretic remanent magnetization, are significantly correlated with concentration of heavy metals and organic matter, for example, Pearson's correlation coefficients are 0.921 for χ-Cu, 0.660 for χ-Pb and 0.848 for χ-loss-on-ignition, respectively. The magnetic properties of the lake sediments document the pollution history caused by human impact on the lake catchment during urbanization. The environmental quality of the lake was fairly good before the 1960s. Magnetic, heavy metal and organic matter contents of the sediments were low and relatively constant, which indicates relatively stable natural inputs from the lake catchment. Pollution trends since the 1960s are reflected in downcore magnetic property variations of the lake sediment. The concentration of magnetic particles in the lake sediments started to increase since 1957, when the Wuhan Iron and Steel Company and the Qingshan Thermal Power Plant, which are located upwind of the lake, were built and put into production. Lake pollution was further aggravated since the acceleration of industrialization and urbanization in East Lake area in the 1980s, which is verified by the elevated concentration of heavy metals and organic matter in the sediments. The magnetic mineral concentration in the lake sediment increased continuously until it peaked in the 1990s and has remained a high level since then. These results suggest that magnetic properties respond sensitively to environmental status, and that the magnetic properties of sediments can provide an excellent record of the industrial and anthropogenic history in an urban lake catchment.

Alternative Materials for Dense Medium Separations

In response to concerns regarding cost and future supply of magnetite, a study has been performed to evaluate the potential of alternative materials that can be used to generate a dense medium for coal-cleaning applications. Alternative materials included waste steel slag, fine sand, and high-density material existing in run-of-mine feed. Under certain conditions, each of the materials tested provided separation efficiencies that meet industrial standards including probable error values of around 0.03. Dense medium derived from the non-magnetite sources achieved organic efficiency values exceeding the 95% level over a medium density range from 1.3 RD to 1.6 RD with lower than normal density offsets. Lower cost, coarse magnetite provided excellent separation efficiencies when medium density values above 1.6 RD are sufficient to meet product grade requirements.

Palaeoenvironmental and palaeoseismic implications of a 3700-year sedimentary record from proglacial Lake Barrancs (Maladeta Massif, Central Pyrenees, Spain)

A multidisciplinary study including sedimentological, mineral magnetic, and palaeobotanical techniques applied to a sediment core recovered from proglacial Lake Barrancs in the seismically active Maladeta Massif has provided the basis for documenting environmental changes and palaeoseismic activity in the Central Pyrenees for the last ca. 3700 yr. Lake Barrancs is located downstream of the Tempestats and Barrancs cirque glaciers and sedimentation is dominated by clastic input corresponding to seasonal changes in sediment supply. Slow fine particle settling during the winter and sediment-loaded homopycnal flows during the warm season, triggered by snow-melting and glacier outwash, have resulted in deposition of rhythmites composed of clays, silts, and sands. The predominance of finer-grained sediments and the low concentration of relatively finer magnetite grains suggest that glacier activity was very small, if not absent, before ca. A.D. 350. Their replacement by coarser-grained sediments and the overall increased (but highly oscillating) concentrations of relatively coarser magnetite grains in the uppermost 4.3 m of the record suggest the onset of glacial activity and enhanced snow-melting in the catchment of Lake Barrancs after A.D. 350. We suggest that this onset of glacial and enhanced snow-melt activity was driven by a complex balance between winter precipitation and annual mean temperatures, among other climatic variables. Peat layers suggest two dramatic lake-level drops at A.D. 300 and A.D. 450, when Lake Barrancs was drained. The mechanisms for such extreme hydrological events are not clear. Changes in the precipitation/evaporation ratio cannot account for such desiccation events. Dam failure is unlikely since there are no geomorphological evidence of breaching processes. Geomorphological and structural evidence demonstrates active faulting since formation of Lake Barrancs and reactivation during earthquake shaking. Based on this, we propose an alternative explanation for the desiccation events that involves the draining of the lake through pre-existing fractures opened by earthquakes. Further studies in Lake Barrancs and other lakes from the Maladeta massif are necessary to validate the hypotheses presented here concerning the response of glacial and snow-melt activity to climate variability and the palaeoseismic record of the Central Pyrenees.

Magnetic properties of sediments from Lake Chaohu and its response to sedimentary dynamics

对巢湖西部柱样以及杭埠河流域土壤的环境磁学研究表明,磁铁矿是决定磁性特征的主要磁性矿物,杭埠河流域是巢湖西部沉积物的主要来源．靠近巢湖西岸的柱样AC1砂含量较高,χ、SIRM值较大而χ_ARM/SIRM较低,说明磁铁矿含量较高、颗粒较粗．距岸稍远的柱样AC2砂含量较低,χ、SIRM值也较低,其变化与χ_ARM较相似,与粘土含量变化也有一定程度的相似,AC2沉积物χ、SIRM值较ACI小,但χ_ARM/SIRM较高,说明磁铁矿含量较低且颗粒较细．杭埠河流域土壤的磁性测量结果表明,砂、砾含量高的粗骨土磁性最强,富含粗颗粒磁铁矿．巢湖柱样沉积物砂的含量随踞岸远近而不同, 反映了沉积环境的水动力不同,由此产生明显的磁性特征差异,实质是对沉积动力的响应．研究表明磁性参数χ_ARM/SIRM 可以间接反映沉积物中粘土含量的高低变化．;Magnetic study on core sediments from western Lake Chaohu and soils from Hangbu River Catchment suggests that magnetite is the dominant magnetic mineral, and soils from Hangbu River Catchment are the main source of lake sediments. Core ACI near the bank shows higher proportion of sands and higher χ、SIRM values but lower χ_ARM values, indicating higher concentration of magnetite with coarse size. Core AC2 more far away from the bank shows lower proportion of sands and lower χ、SIRM values. The similar variations of χ、SIRM with χ_ARM, and to a lesser degree with clay fraction, in combination with higher χ_ARM/SIRM values, indicating lower concentration of magnetite with fine size. Magnetic properties of soils in the catchments indicate that skeletal soils with abundant sand and gravel fraction are magnetic strong which are contributed by coarse magnetite. Content of sand fraction in core is a reflection of water energy which is dependent on the distance to the bank. Therefore, the distinct magnetic properties of different cores are due to sedimentary dynamics. It is found that χ_ARM/SIRM can be used to indicate the variation of clay contents in sediments