高钙粉煤灰固化重金属污染土的工程性质试验研究

高钙粉煤灰是燃煤电厂排出的固体废物,其堆放不仅需占用大量土地,而且对周围环境存在严重威胁。通过系统的室内试验,着重研究了高钙粉煤灰固化铅与锌污染土的工程性质,揭示了其作用机制,探讨了利用高钙粉煤灰固化重金属污染土的可行性。试验结果表明,土体受到重金属离子污染后其无侧限抗压强度降低,掺入高钙粉煤灰可提高土体强度,并能抑制重金属离子的滤出;污染物浓度较低时,固化污染土中的Pb2+和Zn2+均能得到有效固化,污染物浓度较高时,Zn2+的固化效果优于Pb2+。干湿循环试验结果表明,高钙粉煤灰固化污染土的强度随干湿循环次数的增加,先增大后减小;固化土体中重金属离子浓度较低时,滤出液中金属离子浓度随干湿循环次数增加而增大;重金属离子浓度较高时,滤出液中金属离子浓度基本保持不变。     

干湿循环作用下压实黄土湿陷特性试验研究

压实黄土作为重要的填筑材料,广泛应用于我国西北、华北公路、铁路、机场等基础设施建设中.由于降雨及蒸发的周期性变化,黄土路基及基础经历着强烈的干湿交替作用.基于此,开展压实黄土风干干燥-滴水增湿条件下的干湿循环试验,利用双线法测试最佳含水量条件下不同初始压实度的黄土土样干湿循环前后的湿陷系数.结果表明：没有经历干湿交替作用的土样,湿陷系数随着压实度的增大而快速减小,当压实度达到90%,提高压实度对于黄土湿陷变形特征的影响较小;5次干湿循环作用后,不同压实度下的试样的湿陷系数均明显增大,且压实度越大,干湿作用对其湿陷变形的影响越显著;压实度K=95%试样在经历5次干湿循环作用后土样上部出现肉眼可见的细微孔隙,体积膨胀,有可溶盐析出,湿陷系数达到0.017,土样出现二次湿陷.     

微波炉法测定遗址土含水率的可靠性研究

古代土遗址病害发展与土的含水率变化密切相关,但土遗址保护现场快速准确测定土的含水率不是一件容易的事。选择遗址土、含盐土、黄土等进行对比试验,研究分析微波炉烘干法（简称微波炉法）测遗址土含水率结果的可靠性。在测定试验土样界限含水率和易溶盐含量的基础上,对比分析微波炉法、烘箱法两种方法测定土含水率的误差来源。试验结果表明,土的塑性对微波炉法的测定有一定影响,但测定误差均在2%以内;土的含盐量影响水分的蒸发速度,不影响微波炉法的测定结果;微波法测定遗址土含水率准确,且具有快速、便捷等优势,值得在土遗址保护工程中推广使用。     

Relative contribution of various climatic processes in disintegration of clay-bearing rocks

The climatic processes of heating and cooling, wetting and drying, and freezing and thawing affect the disintegration characteristics of clay-bearing rocks (shales, claystones, mudstones, and siltstones) to varying degrees. Although heating and cooling, wetting and drying, and freezing and thawing are known to be the main processes responsible for physical disintegration of rocks under natural conditions, most of the previous investigators have used methods based only on water content variations (e.g., jar slake, slake index, and slake durability index tests) to assess the disintegration of clay-bearing rocks. Such assessments may not be adequate to explain the field behaviour of clay-bearing rocks subjected to a full range of climatic processes. In order to evaluate the combined effects as well as relative contributions of various climatic processes on the disintegration behaviour, samples of selected clay-bearing rocks, consisting of 5–6 particles, each weighing 85–150 g, were subjected to multiple cycles of heating and cooling, wetting and drying, and freezing and thawing. These treatments resulted in fragmentation of samples with fragments ranging from 50 to 2 mm and finer in dimensions. A new approach, referred to as the disintegration ratio, and defined as the area under the grain size distribution curve of the disintegrated material to the total area encompassing all grain size distribution curves of the samples, was used to account for fragmentation into varying sizes. Statistical analyses were performed to investigate the relationship between fragmentation, mineralogical composition, and physical properties.     

Determination of Abundances of Fifty‐Two Elements in Natural Waters by ICP‐MS with Freeze‐Drying Pre‐concentration

To precisely determine the abundances of fifty‐two elements found within natural water samples, with mass fractions down to fg g^?1 level, we have developed a method which combines freeze‐drying pre‐concentration (FDC) and isotope dilution internal standardisation (ID‐IS). By sublimation of H₂O, the sample solution was reduced to < 1/50 of the original volume. To determine element abundance with accuracy better than 10%, we found that for solutions being analysed by mass spectrometry the HNO₃ concentration should be > 0.3 mol l^?1 to avoid hydrolysis. Matrix‐affected signal suppression was not significant for the solutions with NaCl concentrations lower than 0.2 and 0.1 cg g^?1 for quadrupole ICP‐MS and sector field ICP‐MS, respectively. The recovery yields of elements after FDC were 97–105%. The detection limits for the sample solutions prepared by FDC were ≤ 10 pg g^?1, except for Na, K and Ca. Blanks prepared using FDC were at pg‐levels, except for eleven elements (Na, Mg, Al, P, Ca, Mn, Fe, Co, Ni, Cu and Zn). The abundances of fifty‐two elements in bottled drinking water were determined from five different geological sources with mass fractions ranging from the fg g^?1 to μg g^?1 level with high accuracy.     

冻结岩石钻进空气洗井时压缩空气的冷却和干燥问题

在冻结岩石中钻进时,使用压缩空气作为冲洗介质较之使用钻井液有很多优点。给出了冷却空气洗井钻进时井内温度的简化计算公式,按照这些计算公式可以确定空气洗井时井内任何时间、任何深度的温度和代表性关系曲线。井内温度的分布与进入钻杆柱内空气的初始温度有直接的关系,从空气压缩机中出来的压缩空气的温度很高,因此必须对其进行冷却和干燥,给出了冷却和干燥的方法和手段,提出了相应的建议。     

共沸蒸馏置换干燥法制备纳米氧化镁粉体的研究

以六水氯化镁和尿素为原料,采用均匀沉淀法制备出氢氧化镁沉淀,利用不同共沸蒸馏置换干燥法除去沉淀中的湿分,再将干燥的氢氧化镁粉体经马弗炉煅烧得到纳米氧化镁粉体;通过透射电子显微镜和X射线衍射仪的表征与分析,研究不同共沸蒸馏置换干燥法对纳米氧化镁粉体形貌、颗粒尺寸和团聚情况的影响;探讨了共沸蒸馏置换干燥的基本原理、操作方法和置换剂的选择原则。     

A flux-limiting wetting–drying method for finite-element shallow-water models,with application to the Scheldt Estuary

We present a flux-limiting wetting–drying approach for finite-element discretizations of the shallow-water equations using discontinuous linear elements for the elevation. The key ingredient of the method is the use of limiters for generalized nodal fluxes. This method is implemented into the Second-generation Louvain-la-Neuve Ice-ocean Model (SLIM), and is verified against standard test cases. The method is further applied to the wetting and drying of sand banks in the Scheldt Estuary, which is located in northern Belgium and the southern Netherlands. The results obtained for both the benchmarks and the realistic problem illustrate the accuracy of the method in describing the hydrodynamics in the vicinity of dry areas. In particular, the method strictly conserves mass, and there is no transport through dry areas.     

Photosynthetic performance of Setaria viridis to soil drought and rewatering alternations

The ability of psammophyte(a plant that grows in sand or sandy soil) to withstand and recover from severe droughts is crucial for desertification control and restoration of degraded vegetation in semi-arid sandy land in northern China.Responses of the photo-synthetic gas exchange and chlorophyll fluorescence of an annual(Setaria viridis) were measured through three cycles of soil drying and rewatering.Results showed that the net photosynthesis rate(Pn) decreased by 95 percent,91 percent,and 61 percent at end of three drought periods;the stomatal conductance(gs) decreased by 72 percent,73 percent,and 53 percent;the transpiration rate(Tr) decreased by 70 percent,69 percent,and 37 percent;and water-use efficiency(WUE) decreased by 83 percent,69 percent,and 38 percent.At the same time,the trapping probability with no dark adaptation(FV’/FM’) decreased by 70 percent,12 percent,and 10 percent,while the electron transport per cross-section(ET0’/CS’0) decreased by 80 percent,45 percent,and 13 percent.The intercellular CO2(Ci) increased by 1.77,1.02,and 0.66 times,and the dissipation per cross-section(DI0’/CS0’) increased by 98 percent,28 percent,and 22 percent.These results indicated that S.viridis was subjected to photoinhibition and some nonstomatal limitation of photosynthesis under drought.However,the above photosynthetic characteristics were restored to control values after three or four days of rewatering.The capability to recover from drought may contribute to the plant’s use of water as efficiently as possible.Furthermore,during the subsequent drought spells,suppression of Pn,gs,Tr,FV’/FM’,and ET0’/CS0’ decreased or slowed down following the drying and rewatering alternations,especially in the third drought spell.