【作者】 刘剑；

【导师】 罗嗣海； 王观石；

【作者基本信息】 江西理工大学 ， 矿业工程， 2023， 博士

【摘要】 南方离子型稀土矿富含中、重稀土元素,是重要的战略资源。根据基岩出露情况的不同,离子型稀土矿可分为裸脚式和全覆式,其中全覆式稀土矿占比超过80%,该类矿山底板基岩基本为破碎状态。目前,离子型稀土矿主要采用原地浸矿工艺,而全覆式稀土矿由于底板基岩破碎,导致母液渗漏问题突出,使收液率降至70%以下。为提高收液率,本文提出了一种新型高效收液工艺,该工艺在上排导流孔侧壁以水射流冲击制作孔增透,下排孔以水射流切槽并注浆制作人造底板,以“上疏下堵”的方式提高原地浸矿收液率。该工艺实施过程中仍存重要技术问题,即深孔中的矿土强度多变,目前无法准确预测高压水射流冲蚀矿土的深度。因此本文针对此问题采用理论分析、重塑土试验及模拟试验相结合的方法,以准确预测高压水射流破土深度为目标,深入研究了固定高压水射流和移动高压水射流的破土机制,为离子型稀土矿高效收液工艺的设计和改进提供依据。本文主要工作及创新成果如下:(1)通过高压自由水射流试验,获得了射流滞止压力分布,并采用单相流模型研究射流速度分布规律,结果表明,射流轴心速度和射程呈反比关系,同时存在一个拐点使得速度二次骤降;此外,随着射流速度增大,射流的聚拢性要更加明显。因此以高速稀化模型建立了流体速度和湍流粘性系数之间的关系,依据高速稀化模型实现了高压自由水射流速度的计算,该模型计算结果与试验结果的平均相对误差不超过12.2%。(2)以两相流模型研究射流空化完全发展区的速度,依据单个空化气泡的功能原理和射流边界层内湍流时均等效作用,简化了Rayleigh-Plesset方程,提出了空化含气率的计算模型;依据射流速度的微分模型、动量通量守恒、射流的空化减阻效应,推导出水-气均相模型的射流速度方程;结合滞止压力试验,空化含气率、水-气均相模型的射流速度方程,建立了描述射流速度在各流体微元间传递的方程组,可用于射流的空化完全发展区速度计算。提出将高压自由水射流速度的计算按射程分为两段,前段以射流的两相流模型计算,考虑空化减阻效应对流速的影响,后段以射流单相流模型计算,考虑高速稀化作用对流速的影响,分段计算的方法可以更好模拟射流速度沿程变化。(3)通过固定高压水射流破土试验,分析了射流压力、喷嘴直径及靶距对破土深度的影响,发现固定高压水射流冲击破土的过程可分为剧烈冲击阶段、块体侵蚀阶段和表面冲刷阶段。采用侵蚀理论分析固定射流破土的机制,发现这三个阶段矿土破坏速度与剪应力、临界剪应力密切相关。提出以修正侵蚀模型计算各阶段的矿土破坏速度,其中关键参数为侵蚀系数的修正系数,该系数与矿土表面剪应力大小相关,采用步进式算法研究了时间迭代下破土深度的变化规律,提出了固定高压水射流破土深度的预测模型,为新型高效收液工艺中增透孔的施工设计提供理论支撑。(4)设计了一套可控制射流压力与喷嘴移动速度的射流破土试验装置,开展了针对矿土的高压移动水射流破土试验,分析了高压移动水射流破土过程中冲蚀面的演化特征;设计了一套狭缝壁面射流速度测试试验装置,用于测量冲蚀槽内移动水射流的速度分布情况,分析了高压移动水射流沿程速度的衰减规律,提出了计算高压移动水射流速度沿程分布的无量纲经验公式。依据修正侵蚀模型,进一步揭示了移动高压水射流作用下粘性矿土的破坏机理,揭示了喷嘴直径、射流压力、喷嘴移动速度三个射流关键参数对矿土冲蚀面形态和深度的影响机理,影响矿土冲蚀面形态和深度的机制。最后根据移动射流流速的衰减公式推算冲蚀面上沿程剪应力和压力分布,以此建立移动高压水射流破土的理论为新型高效收液工艺中人造注浆底板的施工设计提供理论支撑。(5)实际生产中,以一座即将开采的稀土矿山为目标矿山,考虑矿土强度的空间变异性,通过原位测试测得了不同深度矿土的强度,通过冲蚀试验确定了侵蚀的基本参数,作为增透孔和注浆槽射流施工参数优化设计的基础。基于固定高压水射流破土的机理研究结论,提出针对目标稀土矿山,制作增透孔射流参数的设计方法,并介绍了具体的实施流程;基于移动高压水射流破土的机理研究结论,提出针对目标稀土矿山,制作注浆槽射流参数的设计方法。更多还原

【Abstract】 The ion-adsorption type rare earth ores in southern China are rich in medium and heavy rare earth elements and are an important strategic resource.According to the different outcrop situations of the bedrock,ion-type rare earth deposits can be divided into barefoot and full-cover types,with the latter accounting for over 80%.The bedrock of full-cover rare earth deposits is generally in a broken state.Currently,in situ leaching technology is mainly used to extract rare earth from iontype deposits.However,the leakage of the leaching solution from the broken bedrock of full-cover deposits results in a low liquid collection rate of less than 70%.To improve the liquid collection rate,this paper proposes a new and efficient liquid collection process.The process creates holes with increased permeability by using water jets to impact the sidewalls of the upper drainage holes,and creates artificial bedrock by cutting grooves and grouting the lower holes with water jets,thereby improving the liquid collection rate of in situ leaching through the "upward drainage and downward blocking" method.However,there are important technical issues during the implementation of this process.The strength of the ore in the deep holes is variable,and it is currently impossible to accurately predict the depth at which the high-pressure water jets erode the ore.Therefore,this paper adopts a method that combines theoretical analysis,remolded soil tests,and simulation experiments to accurately predict the depth of the high-pressure water jet erosion.The study focuses on the erosion mechanisms of fixed and moving high-pressure submerged water jets,providing a basis for the design and improvement of efficient liquid collection systems for iontype rare earth deposits.The main work and innovative achievements of this paper are as follows:(1)Through high-pressure submerged free water jet experiments,the distribution of stagnation pressure of the jet was obtained,and the velocity distribution law of the jet was studied using a single-phase flow model.The results show that the axial velocity of the jet and the range are inversely proportional,and there is a inflection point where the velocity drops sharply for the second time.In addition,as the velocity of the jet increases,the convergence of the jet becomes more obvious.Therefore,a high-speed thinning model was used to establish the relationship between fluid velocity and turbulent viscosity coefficient.Based on the high-speed thinning model,the calculation of the velocity of high-pressure submerged free water jets was realized.The average relative error between the calculation results of this model and the experimental results was no more than 12.2%.(2)The velocity of the fully developed cavitation zone of the jet was studied using a twophase flow model.A cavitation gas content calculation model was proposed based on the functional principle of a single cavitation bubble and the effect of turbulent flow in the jet boundary layer under time averaging.The velocity equation of the water-air homogeneous model was derived based on the differential model of jet velocity,momentum flux conservation,and the cavitation drag reduction effect of the jet.Combined with the stagnation pressure experiment,cavitation gas content,and water-air homogeneous model velocity equation,an equation group describing the transfer of jet velocity among various fluid elements was established for the calculation of the velocity of the fully developed cavitation zone of the jet.The calculation of the velocity of high-pressure submerged free water jets was divided into two stages according to the range.The velocity was calculated using the two-phase flow model of the jet in the first stage,considering the effect of cavitation drag reduction on velocity.The velocity was calculated using the single-phase flow model of the jet in the second stage,considering the effect of high-speed thinning on velocity.The method of segmented calculation can better simulate the variation of jet velocity along the distance.(3)A fixed high-pressure water jet excavation test was conducted to analyze the effect of jet pressure,nozzle diameter,and stand-off distance on the excavation depth of high-pressure fixed water jets.It was found that the process of high-pressure water jet impacting and breaking the soil can be divided into three stages: violent impact,block erosion,and surface erosion.The mechanism of fixed jet excavation was analyzed using erosion theory,which revealed a close correlation between the rate of soil failure in each stage and shear stress and critical shear stress.A modified erosion theory was proposed to calculate the rate of soil failure in each stage,with the key parameter being the modification coefficient of the erosion coefficient,which is related to the shear strength of the soil surface.The variation of excavation depth under time iteration was studied using a stepping algorithm,and a predictive model for the excavation depth of fixed high-pressure submerged water jets was proposed to provide theoretical support for the construction design of new efficient liquid collection technology with increased permeability.(4)A jet excavation test device was designed to control jet pressure and nozzle movement speed,and a high-pressure mobile water jet excavation test was conducted on soil to analyze the evolution characteristics of the erosion surface during the process.A slit wall jet velocity test device was designed to measure the velocity distribution of the moving water jet in the erosion groove,and the attenuation law of the velocity of high-pressure mobile water jet along the path was analyzed.An empirical formula for calculating the non-dimensional distribution of high-pressure mobile water jet velocity along the path was proposed.Based on the modified erosion theory,the mechanism of destruction of viscous soil under the action of mobile high-pressure submerged water jets was further revealed,and the effects of nozzle diameter,jet pressure,and nozzle movement speed on the morphology and depth of the erosion surface of the soil were studied.The distribution of shear stress and pressure along the erosion surface was calculated based on the attenuation formula of the jet flow velocity,which provided theoretical support for the construction design of the artificial grouting bottom plate in new efficient liquid collection technology.(5)In practical production,a rare earth mine that is about to be mined was chosen as the target mine.Considering the spatial variability of soil strength,the strength of soil at different depths was measured by in-situ testing,and the basic erosion parameters were determined through erosion tests,which served as the basis for optimizing the design of jet construction parameters for increased permeability holes and grouting trenches.Based on the research conclusions of the mechanism of fixed high-pressure submerged water jet excavation,a design method for the jet parameters of increased permeability holes for the target rare earth mine was proposed,and the specific implementation process was introduced.Based on the research conclusions of the mechanism of mobile high-pressure submerged water jet excavation,a design method for the jet parameters of grouting trenches for the target rare earth mine was proposed.更多还原