Synthesis of needle-like aragonite from limestone in the presence of magnesium chloride

Needle-like aragonite was synthesized with a reversible solution reaction from limestone without calcinations. Scan Electron Microscope (SEM) and X-ray Diffraction (XRD) were used to characterize the morphology and the crystal structure of aragonite. The synthesis of aragonite whisker involves two steps. At first GCC (Ground Calcium Carbonate) was dissolved in an aqueous solution of magnesium chloride with reflux and air flush. Then CO₂ was bubbled into the suspension at a low temperature to produce aragonite whisker. An in-house designed reactor and acid–base titration analysis were used to measure the remaining GCC content in the reaction mixture. A kinetics equation of GCC dissolution was developed, which showed a first-order kinetic feature to magnesium chloride concentration. A reaction rate constant of 0.04234 h^?1 was obtained. The dissolution rate of GCC in magnesium chloride is much higher than that in the magnesium sulfate solution. Some aragonite whiskers with a length of ca. 20 μm and an aspect ratio of 8–12 can be synthesized.     

Atmospheric acid leaching of nickel laterites review. Part II. Chloride and bio-technologies

Most existing hydrometallurgical processes for the leaching of nickel laterites employ sulphuric acid. Alternative technologies that utilise other leaching agents such as hydrochloric acid and various organic acids are currently being examined and developed, and are the topics of this review.The first section examines the hydrochloric acid leaching of nickel laterites, focusing on the reactivity of limonitic and serpentine ores. The recovery of iron oxides from chloride systems is then briefly reviewed. The next section examines some recently developed non-conventional processes such as the Atmospheric Chloride Leaching Process (ACLP) and Intec Process using strong magnesium chloride liquors whilst the final section considers the use of citric and oxalic acids commonly produced by heterotrophic organisms.     

Coherence and fragmentation of landscape patterns as characterized by correlograms: A case study of Estonia

The homogenization and fragmentation of landscapes caused by intensive management is an increasing problem worldwide. Therefore, there is need for development of methods that help to improve sustainable management and maintain the identity of landscapes. We proposed that landscape coherence is the similarity between soil pattern (potential landscape) and land use intensity (actual landscape), which may be investigated by means of correlograms. We studied the spatial autocorrelation (Moran's I) of raster format soil maps and land use maps (1:10,000; 10 m pixel size) in 35 study areas representing all landscape regions in Estonia. Various soil characteristics were taken into consideration in compiling the scale of contrast of 17 soil groups, whereas 19 land use types were ordered according to the intensity of human influence. We use a simple characteristic based on correlograms: a half-value distance lag, h_I = 0.5, a distance where Moran's I equals 0.5. According to the value of h_I = 0.5, in till-covered areas, the landscape structure is more fragmented in uplands than in lowlands. We found two study areas where the soil pattern was coherent with land use intensity, and detected a tendency that human influence makes the landscape pattern in uplands more homogeneous and in lowlands more heterogeneous, whereas the similarity between landscape patterns in lowlands and uplands is increasing due to human influence. This concept of coherence helps planners and decision makers to determine the optimal land use in landscapes by either reducing or increasing the fragmentation of the landscape pattern.     

Wear performance of spark plasma sintered Co/WC and cBN/Co/WC composites

The present study investigates the efficiency of spark plasma sintering (SPS) technique on the tribological behavior of tungsten carbide composites, and aims to develop the wear resistance of these composites by addition of cubic boron nitride (cBN). Wear tests of spark plasma sintered 6(wt.%)Co/WC, 25(vol%)cBN/6Co/WC and conventionally fabricated 6(wt.%)Co/WC as a reference sample were performed by ball-on-disk contact with dry and rotational sliding at room temperature in order to determine the friction coefficient and wear rate. Wear mechanisms were explained by using SEM observations and the wear rates were computed by a surface profilometer. In all cases, the major wear mechanisms were observed gradually in the form of microcraking, material removal by grain pull out, and generation and spalling of a tribochemical layer. Based on the experimental results, the addition of cBN considerably enhanced the wear resistance of tungsten carbides. In addition, these results revealed that SPS process has outstanding potential for the fabrication of tungsten carbides with high wear properties for tribological applications.     

Experimental study on the energy conversion of food waste via supercritical water gasification: Improvement of hydrogen production

In this study, the model food waste was gasified to hydrogen-rich syngas in a batch reactor under supercritical water condition. The model food consisted of rice, chicken, cabbage, and cooking oil. The effects of the main operating parameters including temperature (420–500 °C), residence time (20–60 min) and feedstock concentration (2–10 wt%) were investigated. Under the optimal condition at 500 °C, 2 wt% feedstock and 60 min residence time, the highest H₂ yield of 13.34 mol/kg and total gas yield of 28.27 mol/kg were obtained from non-catalytic experiments. In addition, four commercial catalysts namely FeCl₃, K₂CO₃, activated carbon, and KOH were employed to investigate the catalytic effect of additives at the optimal condition. The results showed that the highest hydrogen yield of 20.37 mol/kg with H₂ selectivity of 113.19%, and the total gas yield of 38.36 mol/kg were achieved with 5 wt% KOH addition Moreover, the low heating value of gas products from catalytic experiments with KOH increased by 32.21% compared to the non-catalytic experiment. The catalytic performance of the catalysts can be ranked in descending order as KOH > activated carbon > FeCl₃ > K₂CO₃. The supercritical water gasification (SCWG) with KOH addition can be a potential applied technology for food waste treatment with production of hydrogen-rich gases.     

Surface and Groundwater Quality Evolution in the Agrio and Guadiamar Rivers After the Aznalcóllar Mine Spill (SW Spain): Lessons Learned

Mine Water and the Environment - The failure of the tailing dam at the Aznalcóllar mine (SW Spain) in 1998 released ≈ 6 million m3 of pyrite sludge and acidic...     

Cellulose supported copper nanoparticles as a versatile and efficient catalyst for the protodecarboxylation and oxidative decarboxylation of aromatic acids under microwave heating

Cellulose supported copper-nanoparticles is a versatile catalyst for the protodecarboxylation of aromatic and vinylic carboxylic acids to corresponding arenes and alkenes without using base or ligand is disclosed. The same nanoparticles catalyze the oxidative decarboxylation of phenylacetic acids to aromatic aldehydes in oxygen atmosphere and protodecarboxylation of phenylacetic acid to alkyl benzene in the absence of O₂ atmosphere. Decarboxylation reactions were performed in acetonitrile or water solvent under microwave heating. The conditions are mild enough to tolerate a wide range of different functional groups. The catalyst gives high yield and it is reusable up to four times, and hence green.     

Delimiting the urban growth boundaries with a modified ant colony optimization model

Delimiting urban growth boundaries (UGBs) has been generally regarded as a regulatory measure for controlling chaotic urban expansion. There are increasing demands for delimiting urban growth boundaries in fast growing regions in China. However, existing methods for delimiting UGBs mainly focus on intrinsic dynamic processes of urban growth and ignore external planning interventions. Delimiting UGBs to restrain chaotic expansion and conserve ecological areas is actually a spatial optimization problem. This study aims to develop an optimization-based framework for delimiting optimal UGBs by incorporating dynamic processes and planning interventions into an ant colony optimization (ACO) algorithm. Local connectivity, total utility values and quantity assignment were integrated into the exchange mechanism to make ACO adaptive for the delimitation of UGBs. The core area of Changsha-Zhuzhou-Xiangtan urban agglomeration, a very fast growing area in Central China was selected as the case study area to validate the proposed model. UGBs under multi planning scenarios with given combinations of weights for urban suitability, high-quality farmland protection, and landscape compactness were efficiently derived from the ACO model. Hypothetic datasets were initially used to test the performance of ACO on global optimum and its ability to optimize complex landscape patterns. Compared with experts' planning scenario, the optimal UGBs delimited by ACO model is practical. Results indicate that spatial optimization methods are plausible for delimiting optimal UGBs.     

An R package for assessment of statistical downscaling methods for hydrological climate change impact studies

Due to inherent bias the climate model simulated precipitation and temperature cannot be used to drive a hydrological model without pre-processing – statistical downscaling. This often consists of reducing the bias in the climate model simulations (bias correction) and/or transformation of the observed data in order to match the projected changes (delta change). The validation of the statistical downscaling methods is typically limited to the scale for which the transformation was calibrated and the driving variables (precipitation and temperature) of the hydrological model. The paper introduces an R package ”musica” which provides ready to use tools for routine validation of statistical downscaling methods at multiple time scales as well as several advanced methods for statistical downscaling. The musica package is used to validate simulated runoff. It is shown that using conventional methods for downscaling of precipitation and temperature often leads to substantial biases in simulated runoff at all time scales.     

结构面影响下的岩质边坡稳定性计算方法探讨

岩质边坡的稳定性主要受岩体内结构面的控制,研究含节理岩质边坡的稳定性分析方法具有重要的理论意义和工程价值。以工程实例为背景,首先,基于现场测试和室内试验,给出了岩石和结构面计算参数的取值过程和方法;其次,基于强度折减理论,运用FISH语言编写了强度折减程序,并把其推广应用到Ubiquitous-Joint模型中;再次,提出了用薄层材料来模拟结构面,进而运用极限平衡计算出结构面作用下边坡安全系数的方法。最后,分别运用有限差分法、离散单元法和极限平衡法计算了含1组优势结构面的岩质边坡的稳定性,计算结果显示3种方法计算的边坡安全系数以及潜在破坏模式具有一致性。研究成果为类似工程边坡的稳定性评价提供了有效的方法。