Response of Soil Water Chemistry to Simulated Changes in Acid Deposition in the Great Smoky Mountains

Watershed recovery from acidic deposition, such as the Noland Divide Watershed in the Great Smoky Mountains National Park, is difficult to predict because of complex biogeochemical processes exhibited in soils. Laboratory soil columns and in?situ pan lysimeters were used to investigate soil solution response to simulated reductions in acid deposition. Controlling for influent SO42-, NO3-, and NH4+ concentrations in the column experiments, effluent pH declined similarly to 4.4 among five experimental scenarios from an initial pH of approximately 4.7 and 6.1. Influent-effluent chemical comparisons suggest nitrification and/or SO42- desorption controls effluent pH. Sulfate adsorption occurred when SO42- influent was greater than 25??μmol?L-1 and desorption occurred below 15??μmol?L-1, which would equate to approximately a 61% reduction in current SO42- deposition levels. Base cation depletion occurred in column experiments, in which 64–60??μmol?L-1 Ca2+ and 24–27??μmol?L-1 Mg2+ reductions were measured. Cation depletion rates were pH dependent, primarily caused by soil cation exchange and not weathering. In these soils with base saturation below 7%, complete Ca2+ and Mg2+ depletion was estimated as 90 to 140?years. Protons released by SO42- desorption via ligand exchange are expected to cause further base cation depletion, thereby delaying watershed recovery. Field experiments found SO42- sorption dynamics to be limited by kinetics and hydrologic interflow rates, illustrating how precipitation intensity can influence ion transport from soil to stream. Results from this study provide important information for predicting watershed recovery in the future and suggest needs for further research.     

A thousandfold creep strengthening by Ca addition in die-cast AM50 magnesium alloy

The effect of calcium addition on the microstructure and creep strength of the die-cast AM50 magnesium alloy was investigated. The α-Mg grains with the diameter of 4.9 μm are surrounded by the eutectic phases for the AM50-1.72 mass pct Ca alloy, while the β(Mg₁₇Al₁₂) particles are located mainly on the grain boundaries of the α grains for the AM50 alloy. The minimum creep rates of the AM50-1.72 mass pct Ca alloy are three orders of magnitude lower than those of the AM50 alloy at 423 K typically below 120 MPa. The thousandfold creep strengthening by the Ca addition is ascribed to the thermally stable eutectic phases appearing in the AM50-1.72 mass pct Ca alloy, which is expected to yield effective grain boundary strengthening or to resist the plastic flow of the α-Mg grains.     

P204萃取硫酸铜溶液中的钙

针对某铜盐厂硫酸铜产品杂质钙含量较高的现状,选用P204从硫酸铜溶液中萃取钙。考察P204质量浓度、相比O/A、萃取时间、水相平衡pH等对铜钙萃取分离的影响。结果表明,P204萃取钙的适宜条件为:P204质量浓度1.2mol/L,O/A=5∶1,振荡时间3min,pH=1.5。四级逆流萃取后,水相中钙质量浓度低于0.05g/L。     

地浸采铀过程中含矿层堵塞特征研究

酸法与碱法浸铀是当前我国铀矿采冶主要地浸工艺,浸铀过程中均会产生含矿层堵塞。含矿层堵塞是地浸采铀中的一种普遍现象,也是制约铀浸出效益的重大瓶颈。根据巴彦乌拉铀矿矿石酸法柱浸试验和十红滩铀矿矿石碱法浸铀试验结果,分别对酸法和碱法浸铀过程中含矿层堵塞的原因进行了系统研究。结果表明,矿物黏土化蚀变是造成酸法地浸中含矿层堵塞的重要原因;碳酸钙沉淀是造成碱性地浸中含矿层堵塞的主要原因;溶浸液的pH、HCO^-₃浓度及Ca²⁺浓度过高都会引起碱性浸铀含矿层碳酸钙沉淀,碳酸钙溶解沉淀特征受pH、Ca²⁺、HCO^-₃的边界值控制。     

Calciothermic reduction of titanium oxide in molten CaCl<Subscript>2</Subscript>

Titanium oxides were reduced to metallic titanium using the liquid calcium floating on the molten CaCl₂. A part of Ca dissolved into CaCl₂ and reacted with TiO₂ settled below CaCl₂. The by-product CaO also dissolved by about 20 mol pct into CaCl₂, which was effective in reducing the oxygen concentration in the obtained Ti particles. The compositional region in the Ca-CaCl₂-CaO system was examined for the less oxygen contamination in Ti and the better handling in leaching. A large amount of the residual calcium oxidized the titanium powder in leaching. The metallic Ti powder less than 1000 mass ppm oxygen could be obtained only for 3.6 ks using 5 to 7 mol pct Ca-CaCl₂ at 1173 K. The powder was slightly sintered like sponge, and contained approximately 1500 ppm Ca. The anatase phae, the intermediate product in the refining process of TiO₂, could be also supplied as raw material as well as rutile.     

无机盐改性麦糟在低浓度含砷水中的吸附性能研究

含砷废水的排放已成为国内外饮用水源最大的安全隐患之一.采用无机盐改性麦糟作为吸附剂,对低浓度含砷水进行吸附试验研究.确定最佳改性条件为1.5 mol/L NaCl 与麦糟按1 L∶100 g 混合均匀,室温下改性12 h.在不调节pH 值（溶液pH 值为7）,改性麦糟投加量5 g/L 条件下,初始浓度为0.1 mg/L 的含砷水可在60 min 达到吸附平衡,且最终使出水满足《生活饮用水卫生标准》（GB5749-2006）中砷含量（0.01 mg/L）要求.考察了溶液共存阴离子对改性麦糟吸附含砷水的影响,并验证了NaCl 改性麦糟处理含砷水源地水的效果.      

Effect of pH and calcium concentration on calcium diffusion in streptococcal model-plaque biofilms

Demineralization during a cariogenic episode is affected by storage and transport in dental plaque of ions released from enamel, and by the effect on both of plaque fluid pH and ion concentrations. To investigate this, 45Ca effusion from a condensed film of streptococci was measured at pH 7, 6 and 5, and 0-20 mmol/l calcium. Cells were loaded into effusion chambers and the appearance of 45Ca and [3H]-inulin in carrier-containing but initially tracer-free buffer was measured. Ratios of 45Ca and [3H]-inulin activity in the initial suspending solution and at equilibrium in the clearance solution, permitted calculation of extracellular volume and bound calcium. The rate of Ca appearance was proportional to the retarded diffusion coefficient (rDe), which was related to the effective diffusion coefficient (De) by: rDe = De/(1 + R) in which R is the ratio of bound to free Ca2+. The rate of Ca2+ effusion increased with calcium concentration, converging on a value of 2.8 x 10(-10) m2/sec. At low pH it reached convergence at a lower [Ca]. This demonstrates that calcium effusion is dependent on binding, so a high proportion of binding sites in plaque will reduce mineral loss in vivo. Loss of binding sites at low pH will increase mineral loss.     

废覆铜板分选残渣生物脱毒工艺优化及机理

废覆铜板分选残渣量大,残留铜质量分数约为1%,潜在利用价值高.为了获得废覆铜板分选残渣生物浸出脱毒工艺最优条件及探明其生物浸出相关机理,首先采用Box-Behnken响应曲面法设计三因素(参数因子包括初始pH值、固形物含量和Fe²⁺浓度;响应值为铜浸出率)三水平共计17个实验的优化实验方案.响应面多项回归拟合分析指出:铜浸出率回归模型与实际试验拟合性较好,实验误差较小,对废覆铜板分选残渣中铜生物浸出过程优化具有一定参考性.在最优化条件下(初始pH值为1.65、废覆铜板分选残渣投加量300 g·L^-1和Fe²⁺质量浓度为6.13 g·L^-1)经过4 h生物浸出获得(92.2±0.27)%的铜浸出率.其次,废覆铜板残渣生物浸出脱毒放大改进实验中(100 L搅拌槽):增加曝气和搅拌,同时外加酸调控体系pH值<2.5,延长浸出至6 h,铜最大浸出率>98%,浸出渣中铜残留质量分数≤0.02%.未反应缩核动力学模型显示残渣中铜生物浸出过程受界面传质和固体膜层内扩散混合控制.综上所述,废覆铜板分选残...     

电解锰渣的理化特性分析研究

电解锰渣是电解金属锰生产过程中产生的固体滤渣,含有锰化合物、铵盐等物质。随着电解锰行业的快速发展,电解锰渣引发了严重的环境问题。实验采用XRD、TGA-DTA和SEM等手段对电解锰渣中化学成分、物相组成和矿物形貌进行分析。结果表明:电解锰渣含有大量Si、Ca、S、Al、Fe组成的化合物,主要物相包括SiO2、FeS2、CaSO4及CaSO4·nH2O。矿物颗粒之间交错堆积,发现柱状晶体颗粒。锰渣中可溶性锰离子主要以(NH4)2Mn2(SO4)3化合物存在。     

The Effect of Sulfur Concentration in Liquid Iron on Mineral Layer Formation During Coke Dissolution

The effects of sulfur concentration in liquid iron on mineral layer development between coke and iron as coke dissolves in a 2 mass pct carbon-iron liquid have been investigated at 1773 K (1500 °C). The initial sulfur in iron concentrations used ranged from 0.006 to 0.049 mass pct. Key findings include that the two-stage dissolution behavior exhibited in the carbon transfer from coke to iron, as reported in a previous study by the authors, at low initial sulfur in iron contents, was also apparent at the higher values used in this study. This two-stage behavior was attributed to a change in the mineral layer density as a result of changes in mineral morphology at the interface. In addition to confirming the two-stage behavior of the carbon-transfer kinetics at the higher sulfur concentration in iron levels, after a period of time, a solid calcium sulfide layer formed on the mineral layer. The sulfide layer formed after approximately 40 minutes, and the proportion of sulfide in the mineral layer increased with increased experimental time and initial sulfur concentration in iron. It was usually found at the iron side of the mineral layer and was associated with calcium-enriched calcium aluminates. Thermodynamic analysis of this layer confirmed that the sulfide is stabilized as the mineral layer is enriched by calcium.     

General Chemical Equilibrium Model for Stabilized/Solidified Wastes

Chemical equilibrium models have an important role in predicting the behavior of stabilized/solidified (s/s) wastes for risk assessment. Such a model has been developed for wastes treated by conventional solidification/stabilization and it is named SOLTEQ-B. This model is an improvement over a previous version (SOLTEQ) in terms of speed and reliability of convergence. The improvement is due primarily to use of a different method of describing the equilibrium characteristics of calcium silicate hydrate, which is the primary product of cement hydration. SOLTEQ-B was evaluated using experimental data from a series of batch equilibrium tests of pure s/s binder and s/s binder/waste mixtures.?SOLTEQ-B accurately predicted pH during neutralization by CO2 or nitric acid and also accurately predicted concentrations of the primary components of cement (Ca, Si, Al, and SO4).     

Heavy Metals Removal from Acidic and Saline Soil Leachate Using Either Electrochemical Coagulation or Chemical Precipitation

This study compares electrocoagulation and chemical precipitation for heavy metals removal from acidic soil saline leachate (SSL) at the laboratory pilot scale. The electrocoagulation process was evaluated via an electrolytic cell [12 cm (width)×12 cm (length)×19 cm (depth)] using mild steel electrodes (10 cm width×11 cm high), whereas chemical precipitation was evaluated using either calcium hydroxide [Ca(OH)2] or sodium hydroxide (NaOH). By comparison with chemical precipitation at a pH varying between 7 and 8, electrocoagulation was more effective in removing metals from SSL having a relatively low contamination level (124?mg?Pb/L and 38?mg?Zn/L). For SSL enriched with different heavy metals (each concentration of metals was initially adjusted to 100 mg/L) and treated at a pH lower than 8.5, with the exception of Cd, the residual metal concentrations at the end of the experiments were below the acceptable level recommended for effluent discharge in urban sewage works (less than 4 mg/L of each residual metal concentration was recorded) using electrocoagulation, contrary to chemical precipitation using NaOH (more than 15 mg/L of each residual metal concentration was recorded). By comparison, chemical precipitation using Ca(OH)2 was effective in reducing Cr, Cu, Ni, and Zn under the permissive level, but not for Cd and Pb. However, both chemical precipitation processes needed to be operated at higher pH values (around 10.0) to be more effective in reducing metals from SSL and, therefore, required a pH adjustment of the effluent before discharge, whereas electrochemical treatment had a practical advantage of producing an effluent having a pH close to the neutral value and suitable for stream discharge in the receiving water. On the other hand, electrocoagulation was also found to be very efficient for removing Pb from very contaminated solutions (250–2,000 mg?Pb/L). At least 94% of Pb was removed regardless of the initial Pb concentration in the SSL. Electrochemical coagulation involves a total cost varying from 8.67 to 13.00 $/tds, whereas 0.84 to 16.73 $/tds is recorded using chemical precipitation. The cost included only energy consumption, chemicals consumption, and metallic sludge disposal.     

Attenuation of Roadway-Derived Heavy Metals by Wood Chips

Wood chips were evaluated for their ability to attenuate heavy metals in roadway runoff. Column experiments with controlled synthetic runoff composition and flow rate were used to assess effects of flow rate (intercepted sheetflow from a 3-m wide roadway section), runoff salt concentration, wood exposure to alternating wetting and drying cycles, wood aging, competition among dissolved heavy metals, and removal of particle-associated heavy metals. Overall, wood chips damped the “pulse” of copper in the synthetic runoff such that the effluent was characterized by lower concentrations (3–25% of input) over longer periods of time, but with little retention of the total copper mass. The most effective treatment was wood chips aged up to 9 months. Increased aging and chip water content reduced effluent concentrations, relative to no treatment. Flow rate had no effect on effluent concentrations. The presence of salt (>2?mS/cm) or dissolved lead (500?μg/L) in the runoff caused greater copper effluent concentrations than the no treatment case. Removal of suspended particles (and associated contaminants) was greater than 85% with an estimated capacity of 0.16?g/gwood. Field evaluation with concentrated flow to a gutter containing a wood chip treatment showed little effect on total or dissolved copper and zinc runoff concentrations and indicated that wood chips may be a source of contaminants in subsequent storm events. Applications of wood chips to treat roadway runoff would not provide a significant decrease in total maximum daily load contributions (e.g., kg/d); however, there may be some scenarios for which wood chip treatments to decrease peak storm water concentrations of dissolved heavy metals in sheetflow runoff is desirable.     

Grain boundary segregation of antimony in iron base alloys and its effect on toughness

The equilibrium grain boundary segregation of antimony was investigated in iron base alloys (Fe-Sb, Fe-C-Sb, Fe-Ni-Sb) after annealing at temperatures between 550 and 750°C. Utilizing Auger electron spectroscopy (AES) the concentration of antimony at intergranular fracture faces was determined as a function of bulk concentration and equilibration temperature. The segregation of antimony in Fe-Sb alloys with mass contents of between 0.012 and 0.094 % Sb was described by the Langmuir-McLean equation. The evaluation leads to the free enthalpy of segregation ΔG_segr = ?19 kJ/mol - T 28 J/mol K. The relatively low value for the segregation enthalpy ΔH = ?19 kJ/mol indicates a rather small tendency for grain boundary segregation of Sb. However, its embrittling effect is strong, scanning electron micrographs (SEM) of fractured samples show that the percentage of intergranular fracture strongly increases with an increasing coverage of antimony at the grain boundaries. The data for Fe-0.93% Sb and Fe.1.91% Sb (mass contents) do not fit in the thermodynamic evaluation obviously due to formation of antimonide precipitates in the grain boundaries. The addition of carbon to Fe-Sb alloys results in a higher grain boundary cohesion which is caused by two effects of carbon, displacement of antimony from the grain boundaries by carbon and enhanced grain boundary cohesion. In the Fe-Ni-Sb alloys additional segregation of nickel was found at the grain boundaries but no enhanced antimony segregation, as expected from previous models of other authors, assuming Ni-Sb cosegregation.     

Si含量对316H钢耐铅铋腐蚀性能的影响

316H钢具有较好的高温力学性能和耐腐蚀性能,是铅铋快堆主要候选结构材料.Si元素的加入会提升材料在铅铋中的耐蚀性,同时也会对组织产生影响.通过向316H钢中加入不同含量的Si元素,采用OM、SEM、XRD进行组织分析,对不同Si含量试验钢在550℃氧控的铅铋环境下进行动态腐蚀性能研究.结果表明,Si元素可有效提升31...     

Effect of vanadium on grain boundary segregation of phosphorus in low alloy steels

The phosphorus grain boundary segregation at 853 K was investigated in three low alloy steels with different vanadium content. Kinetic dependence of the phosphorus grain boundary concentration was determined experimentally by means of AES and described theoretically, as well. To assess the influence of the individual alloying elements on the phosphorus segregation, the metal composition of carbide phases at 853 K was predicted by means of thermodynamic calculations and confirmed by experimental measurements (TEM + EDX). The vanadium was found to enhance the phosphorus grain boundary segregation by reducing the amount of dissolved and segregated carbon. Thereby, the equilibrium of mutual displacement C (segregated) ? P (segregated) was shifted to more phosphorus segregation. The results achieved indicate that vanadium indirectly increases sensitivity of low alloy steels to intergranular embrittlement.     

Distribution of Metals for Particulate Matter Transported in Source Area Rainfall-Runoff

In urban drainage, metals partition between dissolved (fd) and particulate (fp) phases. Metals also distribute across particulate matter (PM) gradations. In this study, granulometric metal distributions were examined for similar urban paved source areas in Baton Rouge, La.; Cincinnati; New Orleans; Little Rock, Ark.; and N. Little Rock, Ark. Metal distributions were examined for PM fractions from <25?μm to >4,750?μm, as suspended (< ～ 25?μm), settleable ( ～ 25–75?μm), and sediment (>75?μm bed load) fractions. For all areas, analysis of PM indicated that metal mass and concentration (mole/m2) were distributed across the gradation. A cumulative gamma distribution constitutive model related metal mass and PM size. The study focused on Baton Rouge, La. where event-based and composited PM metal distributions were statistically similar. For influent and settled runoff, fp dominated Cr, Cu, Zn, As, Cd, and Pb partitioning. Influent Cu, Zn, Cd, and Pb exceeded discharge criteria for receiving water beneficial uses on a total metal basis. A constitutive model for Pb and Zn mass distributions at Baton Rouge, La. was combined with Newtonian settling and ideal overflow rate to examine two limiting cases of storm events loading a screened hydrodynamic separator. For low and high flow events, modeling reproduced metal mass of eluted PM (2 to ～ 250?μm) from an HS within 4% of measurement, but when influent Pb and Zn exceeded discharge criteria so did HS effluent. As a separate unit operation, 1 h of quiescent settling did reduce Pb, but not Cu, Zn, and Cd to discharge criteria levels.     

Bedload Layer Thickness and Disturbance Depth in Gravel Bed Streams

A field investigation in ten gravel bed stream reaches determined that substrate disturbance depth associated with a moving bedload layer was a small multiple of the bed surface D90. Disturbance depth during plane bed transport of coarse, heterogeneous mixtures appeared similar in magnitude to particle exchange depth and moving layer thickness. Maximum disturbance depth was distributed approximately uniformly over the most active areas of the streambed when local scour and fill were negligible. The distribution upper bound was the smaller of approximately 1.5 times the competent grain size or twice the surface D90, and was invariant with flow strength once the largest grains present were mobilized. Disturbance depth did not scale with grain sizes smaller than D50 when larger grains were mobilized. Thicker traction carpets were not predicted to occur because much larger shear stresses then observed naturally were needed to mobilize two or more layers of the bed simultaneously. Bedload transport rate in coarse streambeds is suggested to increase primarily with mobile fraction of bed surface area and grain velocity, than with layer thickness.     

Effect of metabolic acidosis on the potassium content of bone

Metabolic acidosis induces resorption of cultured bone, resulting in a net efflux of calcium (Ca) from the bone and an apparent loss of mineral potassium (K). However, in these organ cultures, there is diffusion of K between the medium and the crystal lattice, causing difficulty in interpretation of the acid-induced changes in mineral ion composition. To determine the effects of acidosis on bone mineral K, we injected 4-day-old neonatal mice with pure stable isotope 41K, equal to approximately 5% of their total body K. Calvariae were dissected 24 h later and then cultured for 24 h in medium without added 41K, either at pH approximately 7.4 (Ctl) or at pH approximately 7.1 (Ac), with or without the osteoclastic inhibitor calcitonin (3 x 10(-9) M, CT). The bone isotopic ion content was determined with a high-resolution scanning ion microprobe utilizing secondary ion mass spectrometry. 41K is present in nature at 6.7% of total K. The injected 41K raised the ratio of bone 41K/(39K+41K) to 9.8+/-0.5% on the surface (ratios of counts per second of detected secondary ions, mean+/-95% confidence interval) but did not alter the ratio in the interior (6.9+/-0.4%), indicating biological incorporation of the 41K into the mineral surface. The ratios of 41K/40Ca on the surface of Ctl calvariae was 14.4+/-1.2, indicating that bone mineral surface is rich in K compared with Ca. Compared with Ctl, Ac caused a marked increase in the net Ca efflux from bone that was blocked by CT. Ac also induced a marked fall in the ratio of 41K/40Ca on the surface of the calvariae (43+/-0.5, p < 0.01 vs. Ctl), which was partially blocked by CT (8.2+/-0.9, p < 0.01 vs. Ctl and vs. Ac), indicating that Ac causes a greater release of bone mineral K than Ca which is partially blocked by CT. Thus, bone mineral surface is rich in K relative to Ca, acidosis induces a greater release of surface mineral K than Ca, and osteoclastic function is necessary to support the enriched levels of surface mineral K in the presence of acidosis.     

DSC and FIB/TEM investigation of calcium and yttrium additions in the sintering of magnesium powder

Powder metallurgy can be used to produce near-net-shape magnesium parts and also allows unique chemical compositions to be achieved that can lead to new alloys with novel properties. However, the surface layer formed on the magnesium powders during processing acts as a barrier to diffusion and sintering is less effective. The layer, formed by reactions with the atmosphere, contains oxides, hydroxides and carbonate hydrates of magnesium. To overcome this barrier, small additions of calcium or yttrium metal powders were made to the Mg matrix. The oxides of Ca and Y are thermodynamically more stable than magnesium oxide, and will disrupt the surface layer. The present work reports the results of investigation by differential scanning calorimetry, and focussed ion beam (FIB) microscopy and transmission electron microscopy (TEM), on the effect of calcium and yttrium additions during the sintering of magnesium powder. FIB examination of sintered Mg–1?wt-% Ca show that secondary phases are located along grain boundaries as well as inside porosity, which confirms the characteristic mechanism of magnesium sintering. A TEM specimen made by a FIB liftout process was also examined by TEM and EDS and indicates that the sintering process was successful, with the elemental distribution being as predicted by sintering.