Micro-properties of coal aggregates: Implications on hyperbaric filtration performance for coal dewatering

The recovery of ultrafine coal can be enhanced significantly by flocculating the particles prior to dewatering. It is thus crucial to be able to quantify the effects of aggregated particles on the separation efficiency, of which they are still not fully understood. This study focused on the relationship between the micro-properties (size, structure, and strength) of flocculated coal particles and the characteristics of filter cakes obtained through hyperbaric filtration. Tools such as small angle light scattering and confocal scanning laser microscopy were used to determine the aggregate structure. The comparative bond strength of aggregates generated under different flocculation conditions was measured through a non-dimensional approach. The effects of these properties on specific cake resistance, saturation, and moisture content, as indicative of the filtration performance, were observed. It was found that flocs generated using a moderate amount of flocculant dosage (60–100 g of polymer/tonne of coal) for this ultrafine coal (97% < 35 μm) optimised the properties of dewatered filter cakes. Although cakes composed of larger and stronger aggregates with more flocculant were found to have higher porosity, the effects on specific cake resistance and cake saturation were detrimental, possibly due to the increasing proportion of intra-aggregate pores that were harder to dewater. The trend was less noticeable at low filtration pressures where most of the dewatering occurred within the larger capillaries of the inter-aggregate zones. In addition, the presence of polymer molecules was responsible in absorbing residual moisture that could not be removed through mechanical means. Through a series of tests using pre-formed filter cakes, the amount of moisture retained by the flocculant was quantified to be approximately 10.2 mg of water for every addition of 1 g of polymer/tonne of coal, calculated per 100 g of filter cake produced from hyperbaric filtration in this case.     

华北地区层状云微物理特性及气溶胶对云的影响

利用机载粒子探测系统(PMS,ParticleMeasurementSystem)对1990年9、10月和1991年4月的春秋两季层状云进行了云及降水的微物理特征探测,分析了云微观特征和垂直分布,初步探讨了气溶胶对云的影响。结果表明,华北地区层状云的基本特征为云滴数浓度79.2cm-3、液态含水量0.03g.m-3、有效直径11μm并有垂直差异;云下气溶胶数浓度与云滴数浓度两者之间存在正相关关系,但其定量关系还有待于进一步研究。     

全风化花岗岩孔径分布-颗粒组成-矿物成分变化特征及指标相关性分析

孔径分布、颗粒组成和矿物成分是全风化花岗岩微观和结构特征的3个主要方面,也是决定其工程地质性质的关键因素。理论研究和实际工程中,常用大、中小和微孔隙、角砾、砂粒和粉粘粒、三大矿物（石英、长石和粘土矿物）含量等指标表征这3方面的特征。3方面指标在一定范围上变化幅度多大？数值间相关性及作为土结构模型组份因子,它们相对权重多大？通过对香港九龙两处边坡51件全风化花岗岩试样压汞测试、颗粒分析和X射线衍射（XRD）等微观结构特征分析,结果表明：两处边坡粗粒和细粒结构全风化花岗岩有明显区别,前者主要属于砾石土和砂砾土,部分为含砾土,大孔隙多,石英和粘土矿物多,而后者部分属含砾土,部分为细砂土和亚砂土,微孔隙多,长石多;两者长石和粘土矿物含量变化正好相反。借助于多因素关系矩阵法,对3方面共9个指标作相关分析发现,相关性较好的指标是：角砾和砂粒 (0.948);大孔隙和微孔隙(0.846);石英和长石(0.827);长石和粘土矿物 (0.747)。从土结构因子角度考虑,权重从大到小指标是：微孔隙、长石、粘土矿物、砂粒、角砾、大孔隙、中小孔隙、粉粘粒和石英。其分析结果可为该类土微观结构特征细化及分类提供依据,为其微结构力学研究提供基础材料。