Pore network model of tailings thickener bed and water drainage channel evolution under the shearing effect
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摘要: 剪切作用是膏體重力濃密制備的基礎要素, 本文研究了濃密床層孔隙和喉道的變化對導水通道的影響, 揭示了水分排出的來源與比例. 開展半工業實驗并結合計算機斷層掃描(CT)與孔隙網絡模型(PNM)提取床層微觀孔隙結構, 利用最大球搜索算法識別并分析剪切前后孔隙與喉道的演化規律. 結果表明, 添加轉速為2 r·min-1的剪切作用將尾砂底流濃度(即底流的固相質量分數)由55.8%提升到58.5%, 孔隙率由43.05%降低到36.59%, 孔隙率降低的比率為15%. 通過PNM技術將孔隙空間劃分為"球體"儲水孔隙與"棍體"喉道; 剪切后球體和棍體數量分別增加了16.5%和22%, 球體平均尺寸小幅下降, 球體半徑多集中在40~60 μm之間. 棍體平均半徑由9.83 μm降低至8.58 μm, 降低了12.7%, 棍體長度變化較小. 剪切作用下的球體配位數在5~10的部分從25.73%增加至44.58%, 配位明顯增多, 顆粒接觸緊密. 本文提出"球棍比"的概念用于孔隙結構的定量表征. 剪切后球體體積占比由14.14%降低至12.75%, 球體體積減少的比率達到9.83%;棍的體積由28.91%降低至23.84%, 棍體積減少的比率為17.54%. 球棍比由48.91%增加至53.48%, 球棍比提升的比率達到了9.34%, 與球體體積減小相比, 棍的體積減少的幅度更大, 導致球棍比上升. 本文從孔隙結構變化的角度揭示了全尾砂重力濃密剪切排水機理; 剪排水過程中主要排出的是喉道中的水分, 孔隙中的水分排出較少.Abstract: Shearing is the basic factor involved in gravity thickening of paste. This work focuses on the influence of pores and throats characteristics on water drainage channel evolution, and determines the proportion of discharged water in tailings thickener bed. Pilot-scale experiment combined with computed tomography (CT) and pore network model (PNM) technology to determine the micropore structure. The maximum ball algorithm is used to analyze the evolution of pores and throats with and without shearing. The results show that the tailings underflow concentration increases from 55.8% to 58.5% under 2 r·min-1 rake shearing and the porosity decreases from 43.05% to 36.59%, the decrease rate of porosity is 15%. The pore structure can be divided into two types, i.e., "balls" and "sticks, " by the PNM technology. The quantity of "balls" and "sticks" increases by 16.5% and 22%, respectively. However, the average radius of balls decreases slightly in the range of 40-60 μm under shearing. The average radius of sticks decreases from 9.83 μm to 8.58 μm, i.e., by 12.7%. Nevertheless, the length of sticks exhibits only a slight change. The coordination number of balls increases significantly from 25.73% to 44.58% in the range of 5-10 under shearing, and the particles are in close contact. The concept of "the volume ratio of pores to balls" is proposed for the quantitative characterization of the pore structure. The volume fraction of balls decreases from 14.14% to 12.75%, the decrease rate of volume fraction is 9.83%, and volume fraction of sticks decreases from 28.91% to 23.84%, the decrease rate of volume fraction is 17.54%. The volume ratio of balls to sticks increases from 48.91% to 53.48%, and increase rate of it is 9.34%. When the volume decrease of balls is more than that of sticks, the volume ratio of balls to sticks increases. This work reveals the shearing drainage mechanism of unclassified tailings gravity thickening from the perspective of pore structure change, i.e., the drainage is mainly discharged from the throat more than the pore from the tailings thickener bed shear dewatering process.
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Key words:
- paste filling /
- gravity thickening /
- shearing /
- porosity /
- water drainage channel /
- volume ratio of ball to stick
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表 1 有/無剪切作用下PNM參數對比
Table 1. Comparison of pore network model parameters with and without shearing
試驗條件 模型尺寸/(mm×mm×mm) 孔隙率/% 孔隙數量 吼道數量 無剪切 2×2×1 43.05 206 827 有剪切 36.59 240 1009 表 2 不同濃度下的屈服應力與指數m值
Table 2. Yield stress and index m under different concentrations
料漿濃度(料漿固相質量分數)/% 屈服應力/Pa 指數m值 50 24.01 2.7296 55 30.55 2.1391 60 41.71 0.552 65 75.62 0.3717 70 129.65 1.2251 75 214.93 1.0164 259luxu-164 -
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