Treatment of high fluoride concentration wastewater by layered double hydroxides： Mechanism studies

An appropriate concentration of fluoride in drinking water is required to prevent dental cavities, but long-term ingestion of water that contains more than a suitable level of fluoride can cause bone disease and mottling of the teeth. Fluoride ions can be found in wastewater from the fluoride chemical industry, as well as the semiconductor, metal processing, fertilizer, and glass-manufacturing industries. The discharge standard for fluoride in industrial wastewater in China is 10 mg/L. Efficient treatment of fluoride-containing wastewater is therefore of major concern in China, following the rapid development of the fluoride chemical industry. Several methods have been used to remove fluoride from water, such as adsorption, chemical precipitation, electrodialysis, ion exchange and electrochemical processes. Layered double hydroxides （LDHs） are anionic clays with high anion exchange capacities which are effective adsorbents for removal of a variety of anionic pollutants. LDHs have been studied as potential adsorbents for removing toxic anionic species such as CrO4^2-, TcO4^-, SeO3^2-, pesticides, and anionic surfactants from aqueous systems. One of the main attractions of using LDHs for fluoride removal, is that unlike other chemical treatment methods, no chemical sludge should be produced. In the present study, an attempt was made to investigate the mechanism of fluoride removal by LDHs under different conditions using batch methods. In addition, the release of fluoride adsorbed on LDHs by treatment with an aqueous solution of Na2CO3 was studied. The residual fluoride was found to be 10 mg/L in a solution with an initial concentration of 1000 mg/L, which meets the discharge standard for fluoride in industrial wastewater in China.     

High resolution profiles of trace metals in pore waters of marine and riverine sediments assessed by DET and DGT

In polluted aquatic systems, toxic metals are often accumulated in bottom sediments. They are, however, not necessarily stored definitively because diagenetic processs can modify redox, pH and even the amount of complexing ligands, releasing the trace metals back into the pore waters and the water column. Especially the labile metal fraction in the pore waters is important since this is the bioavailable fraction determining the bio-toxicity of the sediments. The goal of our study was therefore to assess, with novel sampling techniques, this bioavailable metal fraction in the pore waters as well as the flux towards the overlying water column. High-resolution profiles of trace metals in pore waters of marine and riverine sediments were assessed by DET （diffusive equilibrium in thin films） and DGT （diffusive gradients in thin films） gel techniques. The DET technique uses a diffusive gel layer that equilibrates with the aquatic system and with this technique the concentrations of total dissolved trace metals are obtained directly. The DGT technique uses an acrylamide diffusive gel backed by a resin gel （Chelex） which binds trace metals. With the DGT technique only labile species of selected metals can be captured. According to the redox potential measurements, the marine sediments were suboxic （200 mV to -220 mV versus Ag/AgCl electrode）, while the riverine sediments were completely anoxic （-160 mV to -220 mV versus Ag/AgCl electrode）. This redox potential was apparently controlling the trace metals species in the pore waters： for example a strong correlation between Mn and Co was found in the riverine sediments （for DET and DGT sampling）, while in the marine sediments trace metals presented various behaviors.     

Improved reliability in the interpretation of geochemical measurements by the quantification of uncertainty from sampling

All geochemical measurements require the taking of field samples, but the uncertainty that this process causes is often ignored when assessing the reliability of the interpretation, of the geochemistry or the health implications. Recently devised methods for the estimation, optimisation and reduction of this uncertainty have been evaluated by their application to the investigation of contaminated land. Uncertainty of measurement caused by primary sampling has been estimated for a range of six different contaminated land site investigations, using an increasingly recognized procedure. These site investigations were selected to reflect a wide range of different sizes, contaminants （organic and metals）, previous land uses （e.g. tin mining, railway sidings and gas works）, intended future use （housing to nature reserves） and routinely applied sampling methods. The results showed that the uncertainty on measurements was substantial, ranging from 25% to 186% of the concentration values at the different sites. Sampling was identified as the dominant source of the uncertainty （〉70% of measurement uncertainty） in most cases. The fitness-for-purpose of the measurements was judged using the optimized contaminated land investigation （OCLI） method. This identifies the optimal level of uncertainty that reduces to overall financial loss caused by the measurement procedures and the misclassification of the contamination, caused by the uncertainty. Generally the uncertainty of the actual measurements made in these different site investigations was found to be sub-optimal, and too large by a factor of approximately two. The uncertainty is usually limited by the sampling, but this can be reduced by increasing the sample mass by a factor of 4 （predicted by sampling theory）. It is concluded that knowing the value of the uncertainty enables the interpretation to be made more reliable, and that sampling is the main factor limiting most investigations. This new approach quantifies this problem for the first time, and allows sampling procedures to be critically evaluated, and modified, to improve the reliability of the geochemical assessment.     

Geochemistry of recent hydrothermal systems of Mendeleev Volcano （Kuril Islands） and surrounding waters

On the Kuril Islands there are 85 volcanoes, 39 of which are active. Hot springs and mud pots are wide spread in this area and have significant inputs on the chemical composition of the surrounding surface waters and environment. We present results of trace elements as well as data on H, O, S, and He isotope ratios for hydrothermal systems of the Mendeleev Volcano （Kunashir Island） and surrounding surface waters. Water and gas samples were taken from springs and holes as well as creeks and the Lesnaya River. Among the thermal water types, three main groups can be distinguished. The first group includes the waters, in which SO4^- ion predominant. The water temperature on the surface reaches 97℃, and TDS varies from a few g/L to 7 g/L. These waters are acid to superacid with pH values ranging 0.6 to 2.3. The second group is sodium-chloride waters. A maximum TDS is 14.2 g/L. The waters are neutral or alkaline; pH varies from 6.9 to 8.2. The third group is the sodium-chloride-sulfate-bicarbonate water. The Stolbovskie springs, located in the periphery of the Mendeleev Volcano are representative of this type. The pH of these waters is close to neutral. TDS is 1.9 g/L. They are rather the derivatives of sodium-chloride waters arisen from dilution of them by subsurface waters. The Kuslyi Creek and Lesnaya River are located near the Mendeleev Volcano. The most acid springs discharge into the Kislyi Creek as a result pH of this creek being 2.5, and contents of most elements rather high. For example, the contents of dissolved solids of Si, Fe, Al, Mn, Zn, in waters of the Kislaya Creek are 22.1, 8.1, 6.2, 1.29, and 0.28 mg/L, and correspondently. The water of the Lesnaya River, （Before the Kislyi Creek, pH is about 8 with TDS 102 mg/L, but after the Kuslyi Creek, pH decreases and the concentrations of chemical elements increase. Debit of the Kislayi Creek in summer season is about 370 L/sec. It means that every day only this small creek inputs in the Lesnay River about 706 kg of Si;     

Hydrogeochemical controls on surface and groundwater chemistry in naturally acidic, porphyry-related mineralized areas, southern Rocky Mountains

In southern Rocky Mountains, catchments characterized by acidic, metalliferous waters that are relatively unaffected by human activity usually occur within areas that have active or historical mining activity. The US Geological Survey has utilized these mineralized but unmined catchments to constrain geochemical processes that control the surface- and ground-water chemistry associated with near surface acid weathering as well as to estimate premining conditions. Study areas include the upper Animas River watershed, Lake City, Mt. Emmons, and Montezuma in Colorado and Questa in New Mexico. Although host-rock lithologies range from Precambrian gneisses to Cretaceous sedimentary units to Tertiary volcanic complexes, mineralization is Tertiary in age and associated with intermediate to felsic composition, porphyritic plutons. Pyrite is ubiquitous. Variability of metal concentrations in water is caused by two main factors： mineralogy and hydrology. Parameters that potentially affect water chemistry include： host-rock lithology, intensity of hydrothermal alteration, sulfide mineralogy and chemistry, gangue mineralogy, length of flow path, precipitation, evaporation, and redox conditions. Springs and headwater streams have pH values as low as 2.5, sulfate up to 3700 mg/L and high dissolved metal concentrations （for example： Al up to 170 mg/L; Fe up to 250 mg/L; Cu up to 3.5 mg/L and Zn up to 14 mg/L）. With the exception of evaporative waters, the lowest pH values and highest Fe and Al concentrations occur in water draining the most intense hydrothermally altered areas consisting of the mineral assemblage quartz-sericite-pyrite. Stream beds tend to be coated with iron floc, and some reaches are underlain by ferricrete. When iron-rich ground water interacts with oxygenated waters in the stream or hyporheic zone, ferrous iron is oxidized to ferric iron, which is less soluble, leading to the precipitation of iron oxyhydroxides.     

Water chemical behavior at Yangtze （Changjiang） River estuary

Geochemical cycling has received wide attention due to the need to understand the pathways of pollutants through our present environment. In this regard the Yangtze River plays a significant role in putting those pollutants into the East China SeafWorld Oceans. The Yangtze River is of high sedimentation rate and water discharge. The watershed covers variable climate regions from temperate to subtropical and from semiarid to humid. Twenty three （23） sampling locations at the estuary have been selected for understanding the dynamic relationships. The elements （Cl^-, SO4^2-, Na^＋, K^＋, and Ca^2＋） show conservative behavior during mixing of fresh water with saline water whereas Mg^2＋, Mn^2＋ show a non-conservative pattern . The relationships between Na^＋/SO4^2- and Cl^-/SO4^2- molar ratios show a mixing of more than two water sources.     

Structural Evolvement of Heating Treatment of Mg/AI-LDH and Preparation of Mineral Mesoporous Materials

Although hydrotalcite, or layered double hydroxides （LDHs）, is not a common mineral, it is an important material that can be easily synthesized in laboratory. In this study, structural evolvement and BET surface area changes of heat treated Mg/AI-LDH is evaluated by XRD, TEM and N2-BET analyses. The results indicate that the magnesium-aluminum LDH with carbonate as interlayer anion, periclase-like oxides was formed at temperatures of 400-800℃. Meanwhile, 2-3 nanometer mesoporous were formed during decomposition of LDH. However, the heat treated samples still preserve the morphology of the original LDH plates. Periclase-like formed from LDH heat treatment may re-hydrolyze and recover the structure of LDH. However, crystallinity of the recovered LDH is lower than that of the original LDH. This heat treatment will result in formation of （Mg, Al）-oxide nano-crystals and nanopores among the nano-crystals. When heating temperature exceeds 1000, the periclase-like （Mg, Al）-oxide is transformed into a composite with periclase （MgO） and spinel phases. The periclase can be re-hydrolyzed and dissolved in HCl solution. After acid treatment, the sample with a high surface area is composed of spinel nano-crystals and nanopores among them. Our results will provide a new and economic way to synthesize mesoporous materials through pathways of phase transformation of precursor materials with different composition.     

采矿引起的边坡倾倒滑移变形机理与变形安全性分析研究—以抚顺西露天矿边坡为例

在矿山开发、水电建设过程中倾倒变形问题日渐突出。倾倒变形边坡一般具有反倾边坡结构,变形的过程和机理比较复杂、涉及的变形岩体范围较大、危害严重。论文以抚顺西露天矿边坡为例,通过岩体位移监测资料的跟踪分析、底面摩擦模拟试验,以岩体力学、松散介质力学原理为理论基础,探讨了采矿影响下边坡倾倒滑移体的变形机理,分析认为采矿引起的倾倒滑移变形问题是在特定的地质构造和采矿工程条件下产生的,并提出了岩体变形安全性分析方法。通过工程实例,验证了方法的实用性,并针对实际问题提出了变形整治对策。