Effect of slurry conditioning on flocculant-aided filtration of coal tailings studied by low-field nuclear magnetic resonance and X-ray micro-tomography

The present work aimed to study the effect of slurry conditioning on flocculant-aided filtration of coal tailings by the analysis of filtration kinetics and filter cake structure. Laboratory filtration tests of the coal tailings showed that both the shear rate and agitation time have significant effects on filtration rate and cake moisture. Moderate agitation at the shear rate of 92 s⁻¹ was favorable for fast filtration, but high cake moisture was encountered. The low-field ¹H nuclear magnetic resonance (NMR) measurements of the filter cake showed that the slurry conditioning has a significant effect on the residual water in large pores and a negligible effect on the residual water in small pores. The X-ray micro-tomography (XRM) measurements indicated that the filter cake formed at the shear rate of 92 s⁻¹ has more macro-pores and higher porosity than that formed at the shear rate of 53 s⁻¹, hence more residual water was entrapped in filter cake. The slurry conditioning in the presence of flocculant will change the structure of filter cake and affect the filtration performance. There was a paradox between fast filtration rate and low filter cake moisture. The findings enable better understanding of the effect of slurry conditioning on flocculant-aided filtration of coal tailings.     

Shear behavior of ultrafine magnetite tailings subjected to freeze-thaw cycles

To study the shear behavior of the ultrafine magnetite tailings subjected to freeze-thaw cycles,unconsolidated-undrained shear tests were conducted on ultrafine-grained tailings that were subjected to 1–11 cycles of freeze-thaw and defined as a type of clayey silt under confining pressures of 100, 200,and 300 kPa. Taking the number of freeze-thaw cycles, cooling temperature, initial dry density, and moisture content as the four main influencing factors of shear behavior of the tailings samples, the shear stress-strain curve, compression modulus, failure strength, cohesion, and internal friction angle were measured. The results show that the freeze-thaw cycle has an obvious weakening effect on the shear behavior of the tailings material, and the shear mechanical parameters are affected by a combination of confining pressure, freeze-thaw cycle condition, and initial physical-mechanical properties of the tailings samples. Through the microstructural analysis of the tailings samples subjected to freeze-thaw cycles, it shows that the freeze-thaw cycle mainly affects the porosity, bound water, and arrangement of the tailings particles. Subsequently, the macroscopic changes in shear strength indexes emerge, and then the stability of the tailings dam will decrease.     

An analytical solution to estimate the settlement of tailings or backfill slurry by considering the sedimentation and consolidation

A common and important task in mining industry is to estimate the settlement or final volume of the tailings or backfill associated with sedimentation and self-weight consolidation. Up to now however, most existing analytical solutions were developed by only considering the settlement induced by consolidation. In this paper, the process of shrinkage tests has been compared with those of sedimentation and consolidation. It was shown that the pore water and particles movement in the sedimentation are very similar to that in the normal shrinkage. The void ratio at the end of sedimentation is thus for the first time considered to be equal to the void ratio at desaturation onset of shrinkage tests. An analytical solution was then proposed to estimate the settlement of tailings or backfill by considering the sedimentation and consolidation. To validate the proposed analytical solution, tailing deposition tests were conducted in two molds to simulate the tailings impoundment and underground mine stope. The required parameters were obtained through shrinkage and consolidation tests. Good agreements were obtained between the measured settlements and those calculated by the proposed solution. The proposed solution can thus be considered as validated and used to evaluate the settlement of tailings or backfill slurry.     

高含水率吹填淤泥自然沉降规律

通过对4种不同吹填土开展室内自然沉降模型试验,探讨高含水率吹填土自然沉降规律。试验结果表明,随着初始含水率的增加,沉降曲线可分为固结沉降与沉积沉降;当泥浆的初始含水率大于土形成含水率时,泥浆在试验初始时刻处于沉积状态,泥浆的沉降过程经历絮凝、阻碍沉降、自重固结3个阶段;当泥浆的初始含水率小于土形成含水率时,泥浆在试验的初始时刻处于固结状态,并在自重作用下固结沉降。对于黏性土,阻碍沉降时的沉降速率随初始含水率及土样液限的增加而增加,土形成含水率为液限的9倍,自然沉降稳定时间则随相对初始含水率的增大而减小,随液限的增大而增大。对于粉质土,土形成含水率约为液限的3倍,并且自然沉降稳定时间显著小于黏性土的。     

湿法磷酸氨化料浆的流变性

本文用旋转粘度计测定了两种国产湿法磷酸氨化料浆的流变性。结果表明,含水高于50％的料浆属牛顿流体。随着料浆含水量的减少.则逐渐向假塑性流体转变,在一定剪切速率范围内,它们的流变性可用幂律方程描述。但在更高的剪切速率下又将转变成牛顿流体。本文还用实验数据计算了浓缩料浆通过蒸发器加热管的压力降。     

Rheological behavior of Shengli coal-solvent slurry at low-temperatures and atmospheric pressure

We report the results from systematic studies of Shengli lignite coal-solvent slurries. Solvent type, temperature, coal to solvent ratio, particle granularity, shear rate and shear time were investigated. The viscosity of the solvents is time independent. However, the slurries are thixotropic. A change from pseudo-plastic to Newtonian behavior occurs as the temperature, or as the solvent to coal ratio, increases. The solvent used in the slurry affects the point at which the theology changes from pseudo-plastic to Newtonian. The REC slurry changes at 1 : 1.2 coal to solvent ratio and at 40 ℃. The HAR slurry changes at a 1:1.5 ratio and at 60 ℃. The theology of the slurries is pseudo-plastic at low shear rates but Newtonian at high shear rates.     

红粘土抗剪强度的水敏性研究

为了研究红粘土的地域性特征及红粘土抗剪强度的水敏性,以广梧高速云浮段红粘土为试样,进行一系列基础试验,并绕过量测基质吸力,采用考虑不同含水率的变化研究其抗剪强度水敏性.试验结果表明,该红粘土具有高含水率、高液限、高塑性、缩胀性、裂隙性、高孔隙比、低压缩性和"假粉性"等特点;红粘土应力-应变曲线为强化型曲线,高含水率和低...     

开孔管桩真空固结提高承载力模型试验

为了研究桩基承载力的增长程度、桩周土的抗剪强度和含水率变化规律、桩周土排水量,开展真空固结模型试验,得到模型桩的Q-s曲线、桩周土的十字板强度和含水率的分布规律、排水量随时间的增长曲线. 结果表明,在该试验条件下,开孔管桩真空固结技术可以使桩基承载力提高2.7倍,使桩周形成厚4.5 cm、较高抗剪强度、较低含水率的致密层. 研究桩身开孔布置的影响,得出桩基承载力的增长程度受开孔层间距的影响较大,受孔径的影响很小.     

立体排水-电极联合体处理高含水率废弃土的试验研究

针对高含水率废弃土的自身特点,提出了一种适用于超软土加固的可回收立体排水-电极联合体,并根据立体排水-电极联合体空间布置情况,试验设计从过程中排水量、含水率与抗剪强度、沉降变化、电势分布、电流变化以及能耗情况出发,对比分析不同条件下的土体电渗固结性状,结果表明：（1）立体排水-电极联合体增加了横向排水通道之后,缩短了排水固结路径,使土体中部维持着一个较高的电势水平,相对于传统竖向电极排水量最大提高38%;（2）增加横向排水体后抗剪强度单层式与双层式联合体分别提高3.0倍和1.5倍,且土体强度更加均匀;（3）引入了统一能耗系数概念,增加横向排水体后能耗系数从0.163降低到0.154,体现了立体排水-电极联合体的优越性。     

尾矿土物理力学性质指标的相互关系

目的正确有效地确定尾矿土的抗剪强度,以保证尾矿库工程的稳定性．方法通过现场取样,然后在试验室进行土的物理及力学指标试验,研究尾粉砂、尾粉土、尾粉质黏土的含水率与孔隙比之间的关系以及含水率、孔隙比、干密度与抗剪强度指标之间的关系．结果随着含水率的增大,尾粉砂的孔隙比减小,尾粉土与尾粉质黏土的孔隙比增大;尾粉砂、尾粉土和尾粉质黏土的含水率与抗剪强度指标呈非线性关系;孔隙比、干密度与抗剪强度指标呈线性关系：随着孔隙比的增大,黏聚力与内摩擦角减小;随着干密度的增大,黏聚力与内摩擦角均增大．结论尾粉砂、尾粉土、尾粉质黏土的物理指标与抗剪强度指标之间存在相关性,在明确物理指标的情况下可以推断出相应的抗剪强度指标范围．     

陕西泾阳南塬黄土滑坡滑带土残余剪切强度特性

为探求陕西泾阳南塬高速远程黄土滑坡的复活机理,从大型黄土滑坡滑带采集原状黄土试样、古土壤试样(原状土),部分制备重塑试样(重塑土),进行不同体积含水率下的反复剪切试验,从而获得滑带土残余剪切强度指标与体积含水率、黏粒含量之间的关系。结果表明:原状土和重塑土的剪应力-位移曲线均为硬化型; 在不同的垂直压力下,原状土和重塑土的残余剪切强度差值变化较大; 当剪切强度达到峰值强度以后,随着剪切位移的继续增大,原状土和重塑土的残余剪切强度都有一定程度的损失,这种损失因垂直压力的不同而不同; 对同类土,通过反复剪切试验获得的内聚力和内摩擦角随体积含水率的增加而降低; 相关性分析表明,该区滑带土的黏粒含量较低,对残余剪切强度的内摩擦角影响很小,尤其是当天然体积含水率较低时,体积含水率的变化对残余剪切强度的影响远远大于黏粒含量的影响。     

PHD-PVD真空预压联合电渗法处理工程废浆试验研究

为了改进传统真空预压法的缺陷,提出一种PHD-PVD真空预压联合电渗处治工程废浆的方法。通过6组大型室内模型试验,对工程废浆固结过程中的排水量、电流强度、沉降值等进行监测,通过测量土体含水率及十字板抗剪强度并结合压汞试验宏微观分析土体的加固效果,研究真空泵和电源的间歇断开处理对PHD-PVD真空预压联合电渗法加固工程废浆效果的影响。试验结果表明,联合电渗法有效提升了PHD-PVD真空预压法后期的排水效率,远端土体固结程度得到提高,强度显著提升;对真空泵和电源的间歇断开式处理使土中产生新的排水通道,一定程度上缓解了排水板附近的淤堵,使得试验后期也保持了较快的排水速率,排水总量得到提升。压汞试验结果表明,采用间歇断开式的PHD-PVD真空预压联合电渗法处理的工程废浆,其峰值孔径更小,土体微观结构更加致密。     

真空预压联合逐级动力压实和电渗法处理疏浚淤泥试验研究

真空预压联合电渗法常用于疏浚淤泥地基处理,但存在排水板淤堵及电极腐蚀严重、能耗大等问题,导致该方法在实际应用中受限。提出利用真空预压-逐级加能动力压实联合电渗法,克服传统联合法的缺陷,通过5组室内模型对比试验,采用孔压消散比PPDR确定动力压实启动时间,研究最优动力压实启动时间点。试验过程中监测土体的孔隙水压力、排水量、土表沉降和电流强度,在试验前后测量土体含水率、十字板剪切强度及阳极腐蚀量。结果表明：与真空预压联合电渗法相比,在真空预压阶段启动动力压实可使淤堵土柱开裂,有效提高真空预压的排水效率;动力压实后土体表面裂缝减少,更加平整,电渗固结过程产生的阳极腐蚀量和能耗降低;在PPDR为70%时启动动力压实,土体的排水量最大,土表沉降增幅最大,处理后的十字板剪切强度达到65 kPa,获得了更好的处理效果。     

攀钢马家田尾矿化学固结机理初探

通过对马家田尾矿堆积坝水化学场的分析,初步探讨水化学场的变异对尾矿的力和压缩性的影响,以及非饱和－饱和的氧化还原状态下Ｃａ＾２＋,Ｍｇ＾２＋,ＳＯ４＾２－离子和Ｆｅ（ＯＨ）３凝胶在尾矿颗粒间产生化学胶结的尾矿化学固结机理,并划分了３个不同的化学因结分区,即化学固结增强区、化学固结相对稳定区和化学固结削弱区。     

基于坍落度测试的粗骨料充填料浆流动性检验

针对某矿充填法开采,为使充填料浆的流动性满足长距离管道输送形成的充填体力学强度满足采矿生产,需对其流动性进行坍落度测试以确定合理的输送浓度。由试验测试可知,对于相同表观流动性的料浆,随着戈壁料用量比例的加大其浓度也得到提高,戈壁料∶分级尾砂为2∶1、1∶11、∶2的各灰砂比料浆制备输送浓度分别为82%-78%、80%-76%、78%-74%时的管输性能好,相应的坍落度约为25-27 cm、24-27 cm、24-26.5 cm,形成的充填体强度可满足采矿需要。     

初始含水率对城市污泥压缩及强度特性的影响

城市污泥具有含水率高、有机物含量高等特点,对污泥的处理及资源化利用影响较大.本文对不同初始含水率的污泥进行标准固结与无侧限抗压强度试验,研究初始含水率对污泥一维固结及强度特性的影响.结果表明:污泥的初始含水率越高,压缩性越大;初始含水率低于最优含水率(约45％)时,压缩指数随含水率增大显著增大;含水率超过最优含水率后,...     

水平联合竖直排水板真空预压处理工程废浆试验研究

传统真空预压法(VP)在加固工程废浆时存在预制竖向排水板(PVD)易淤堵、周围土体形成土柱以及真空度随深度衰减等问题,考虑到预制水平排水板(PHD)在真空预压法处理软土地基中的特点,提出一种水平联合竖直排水板真空预压(PHD-PVD-VP)处理工程废浆的方法。通过4组大型室内模型试验,对工程废浆加固过程中的排水、沉降以及孔隙水压力进行监测,并借助扫描电镜得到的排水板滤膜微观图片,分析不同初始PHD真空压力下PHD-PVD-VP对工程废浆的加固效果。试验结果表明,PHD-PVD-VP处理工程废浆时减少了土颗粒径向移动速率,延缓“土柱”的形成及缓解土颗粒嵌入排水板滤膜的淤堵效应,提升了土体整体固结效果;40 kPa的初始PHD真空压力使PHD-PVD-VP对工程废浆的排水固结效果最佳,处理后土体的平均含水率和十字板剪切强度分别为40.9%和25.5 kPa,有效地缓解了PHD和PVD的淤堵并改善了土体固结的均匀性。通过微观结构分析发现,PHD初始真空压力的大小同时影响着PHD与PVD滤膜的淤堵情况,从而影响其排水性能,40 kPa的初始PHD真空压力使得两种排水板的排水性能都得到充分发挥。     

Influence of surface state on moisture sensitivity of carbon fiber and its composite interfacial properties

The influence of surface state on the moisture sensitivity of carbon fiber was analyzed by applying a T800 grade carbon fiber with five different surface conditions, namely, with and without surface oxidation, in the presence or absence of sizing agent. The interfacial properties of their composites in the presence of two epoxy matrices (respectively EP07 and EP10) were also characterized by micro-droplet tests. The overall results show that both oxidized and sizing-coated fibers have higher moisture equilibrium content than that of the pristine unsurface-treated fiber, due to higher amount of activated carbon groups. After moisture absorption of the carbon fibers, almost all the fiber/epoxy systems show decrease in the interfacial shear strength and the unsurface-treated fiber system exhibits the largest decline. Moreover, both interfacial shear strength and interlaminar shear strength of carbon fiber/EP10 composite demonstrate better water resistance performance than that of the carbon fiber/EP07 composite, consistent with DSC results of the two resins.     

含水率对下蜀土抗剪强度的影响

为研究不同剪切方式中,含水率对下蜀土抗剪强度的影响,选取下蜀土为研究对象,进行多组原状土样的快剪、慢剪和反复直剪试验。试验结果表明:下蜀土试样含水率在19%~28.2%之间变化时,随着含水率的增加,土的抗剪强度总体呈下降趋势,但不同剪切方式中影响规律不同。快剪试验中,含水率对土体抗剪强度的影响较大,当含水率增加到23.5%附近时,黏聚力和内摩擦角均急剧下降;慢剪和反复直剪试验中含水率对土体的抗剪强度影响较小。快剪和反复直剪试验中,土的抗剪强度主要受黏聚力控制;慢剪试验中,土的抗剪强度主要受内摩擦角控制。快剪、慢剪和反复直剪分别模拟下蜀土滑坡中的快速滑动、缓慢滑动和古滑坡的再次滑动,试验结论可为不同类型下蜀土滑坡的防治工程提供参考。     

城市固体废弃物剪切强度参数的研究

为了在填埋场稳定性分析时合理地选取城市固体废弃物剪切强度参数，参照杭州天子岭填埋场城市固体废弃物的主要成分，人工配制固体废弃物试样，利用大型三轴剪力仪进行固结排水剪试验，延伸岩土工程中研究土体的概念和方法，研究城市固体废弃物的剪切强度特性.城市固体废弃物的黏聚力和摩擦角随着轴向应变的增加逐渐增大，摩擦角增长较为平缓，应变较大时达到峰值，黏聚力主要由纤维状加筋相所产生，增长趋势较快.结合国内外大量的强度参数资料，提出了两种典型城市固体废弃物成分的强度参数，可以用于成分相近的填埋场稳定分析中.