Role of curing temperature in progress of lime-soil reactions

An expansive black cotton soil was used to assess if ambient temperature influences the progress of lime-soil reactions. Lime-soil mixes containing lime additions above the Lime Modification Optimum (or Initial Consumption of Lime value) of the expansive black cotton soil was cured for periods ranging from 1 hour to 400 days at 25°C. The curing temperature of 25°C is representative of mean temperatures occurring in semi-arid regions of Karnataka, India. The in situ progress of lime treatment was monitored by the use of electrical conductivity and pH measurements. The trend of decrease in conductivity and pH of the 4 and 7 lime-soil mixes suggested that pozzolanic activity commenced after 1 day of curing at 25°C. Comparatively, an earlier study by other researchers had reported that pozzolanic activity does not commence before 7 days of curing at 11.5°C for lime additions above the Lime Modification Optimum value of swelling clay. Combining the results of studies at 25°C and 11.5°C, it appears that higher ambient temperatures do accelerate the progress of lime-soil reactions.     

Adsorption of heavy metals in glacial till soil

The charged sites on soil particles are important for the retention/adsorption of metals. Metallic counterions can neutralize the intrinsic charges on the surfaces of soil particles by forming complexes. In this study, efforts have been made to determine the effect of surface potential, pH, and ionic strength on the adsorption of four metal ions, hexavalent chromium Cr(VI), trivalent chromium Cr(III), nickel Ni(II) and cadmium Cd(II), in glacial till soil. Batch tests were performed to determine the effect of pH (2–12) and ionic strength (0.001–0.1 M KCl) on zeta potential of the glacial till soil. The point of zero charge (pH _PZC ) of glacial till was found to be 7.0±2.5. Surface charge experiments revealed the high buffering capacity of the glacial till. Batch adsorption experiments were conducted at natural pH (8.2) using various concentrations of selected metals. The adsorption data was described by the Freundlich adsorption model. Overall glacial till shows lower adsorption affinity to Cr(VI) as compared to cationic metals, Cr(III), Ni(II) and Cd(II).     

Impact of small amounts of swelling clays on the physical properties of debris‐flow‐like granular materials. Implications for the study of alpine debris flow

The effect of the small fraction of clays on the rheological behaviour of alpine debris flow is poorly understood. This is partly due to the complexity of the debris flow mineralogy and the broad particle size distribution. This study has investigated this issue by simulating an alpine debris flow with a mixture of well characterized fractions and then varying the clay fraction composition. Four samples were tested, ranging from a clay fraction made up of only kaolinite (1:1 type clay) to samples where 80 per cent of the kaolinite is replaced by bedeillite (a 2:1 type clay similar to smectite). Changing the content of 2:1 type clay has a strong influence on the behaviour of the whole material, despite its low weight fraction of around 2 per cent. The tests carried out on these reconstituted materials were compared with the results obtained for natural debris flow materials and showed some common trends: in particular, the rheological parameters for materials with and without 2:1 clays with respect to yield stress as a function of solid content. Copyright © 2006 John Wiley & Sons, Ltd.     

氨基酸在改性黏土上的吸附机制研究

研究了四种氨基酸(赖氨酸、谷氨酸、甘氨酸、组氨酸)化合物在改性黏土的吸附特征, 考察了改性剂PACl 添加比例、介质pH 及离子强度对吸附过程的影响, 并探讨了吸附机制。结果表明, 在一定比例的PACl 改性能促进氨基酸在高岭土上的吸附, 最佳改性比例为5%, 赖氨酸、谷氨酸、甘氨酸、组氨酸的最大吸附量分别为827、712.56、723.14、732.56 μmol/g; 氨基酸在改性黏土上的吸附动力学符合伪二阶动力学模型; 利用Weber-Morris 模型测定四种氨基酸内部粒子扩散常数, 5%改性条件下赖氨酸、谷氨酸、甘氨酸、组氨酸的内部粒子扩散常数分别为0.847、0.567、0.780、0.603。热力学研究表明, 氨基酸在改性黏土上的吸附等温线是C 型等温线, 5%改性条件下四种氨基酸(赖氨酸、谷氨酸、甘氨酸、组氨酸)的热力学自由能分别为?1.99、?2.41、?3.16、?2.94 kJ/mol, 说明氨基酸在改性黏土上的吸附是一个自发的吸附过程。介质pH 及离子强度对吸附过程具有重要影响。     

Ocean wave attenuation due to soft seafloor sediments

Abstract

Ocean waves traveling over soft bottoms attenuate as a result of energy being absorbed by the soft bottom. This wave attenuation is important in the design of offshore facilities. The magnitude of wave attenuation can be predicted with an analytical model that couples wave and seabottom motions and realistically models the nonlinear stress‐strain behavior of soft sediments. An extensive parameter study was performed to develop wave attenuation behavior. Soil and wave characteristics typical of the Mississippi Delta were used for these analysis. Predicted results are compared with field observations, and good agreement is found.     

有机质含量对水泥土强度影响的室内定量研究

采用对盐城泻湖相软土掺入不同含量的有机质作为试料土,进行了大量的水泥加固室内试验。对试验结果进行了分析,提出了不同有机质含量软土水泥加固后的室内无侧限抗压强度的预测公式,同时建立了不同有机质含量的试料土经水泥加固后的室内强度比与有机质含量之间的定量关系,该定量关系式可以有效地对有机质含量在5.5 %～17.5 %的水泥加固后的无侧限抗压强度进行定量的预测。     

超固结非饱和土的试验研究

Farulla等[1]通过固结仪对不同轴应力下的超固结非饱和土进行了湿化变形研究,试验结果表明超固结非饱和土的湿化变形随轴应力的不同而不同,其规律与Alonso等[2]的假设并不完全相符。为了进一步验证这个试验现象,利用双压力室非饱和土三轴仪,在同一个前期固结压力下对不同程度的超固结非饱和土进行了湿化试验,研究其湿化变形特性;对某一吸力下的超固结非饱和土进行三轴排水剪切试验,研究其体变和强度特性。试验结果证明了Farulla等试验的正确性,最后用文中所提的模型进行了预测,其结果与试验现象一致     

两种改性粘土去除群体状铜绿微囊藻的比较

实验采用壳聚糖和聚合氯化铝改性高岭土,进行以铜绿微囊藻为优势种的水华蓝藻去除的比较研究,研究采用动力学手段,通过去除效率的比较,得到线性方程:壳聚糖改性高岭土投加量(y)与藻细胞浓度OD68(x)和叶绿素a含量(x)之间的关系分别为:y=0.0349x-0.0019、y=0.0524x-0.009;聚合氯化铝改性高岭土投加量(y)与藻细胞浓度OD68(x)和叶绿素a含量(x)之间的关系分别为:y=0.0351x+0.0065、y=0.0676x-0.0059,壳聚糖改性粘土除藻的最适pH范围为5-8,聚合氯化铝改性粘土除藻的最适pH范围为5-9,pH范围相对较宽,电子传递速率分析表明壳聚糖改性粘土处理后1个月内藻趋于死亡,聚合氧化铝改性牯土处理过的藻,一周内藻开始黄化,衰老.     

Concentration and association of minor and trace elements in Mukah coal from Sarawak, Malaysia, with emphasis on the potentially hazardous trace elements

The ash yield and concentrations of twenty-four minor and trace elements, including twelve potentially hazardous trace elements were determined in Mukah coal from Sarawak, Malaysia. Comparisons made to the Clarke values show that Mukah coal is depleted in Ag, Ba, Be, Cd, Co, Mn, Ni, Se, U, and V. On the other hand, it is enriched in As, Cr, Cu, Pb, Sb, Th, and Zn. Among the trace elements studied, V and Ba are associated predominantly with the clay minerals. Manganese, Cr, Cu, Th, and Ni are mostly bound within the aluminosilicate, sulphide and/or carbonate minerals in varying proportions, though a portion of these elements are also organically bound. Arsenic, Pb and Sb are mostly organically bound, though some of these elements are also associated with the sulphide minerals. Zinc is associated with both the organic and inorganic contents of the coal. Among the potentially hazardous trace elements, Be, Cd, Co, Mn, Ni, Se, and U may be of little or no health and environmental concerns, whereas As, Cr, Pb, Sb and Th require further examination for their potential health and environmental concerns. Of particular concern are the elements As, Pb and Sb, which are mostly organically bound and hence cannot be removed by physical cleaning technologies. They escape during coal combustion, either released as vapours to the atmosphere or are adsorbed onto the fine fly ash particles.