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時間–速率雙因素下全尾砂膏體的屈服應力易變行為

Variability behavior of yield stress for unclassified tailings pasted under measurement time?velocity double factors

  • 摘要: 以往對全尾砂膏體屈服應力的研究局限于理想屈服應力流體框架內,認為一定材料配比條件下,膏體的屈服應力是確定的,即認為屈服應力是膏體料漿固有的一個物理屬性值。通過開展不同質量分數全尾砂膏體屈服應力測量實驗,分析了測量速率與測量時間對不同濃度膏體屈服應力的影響,發現屈服應力值的大小與測量過程相關。對比分析峰值屈服應力、動態屈服應力、靜態屈服應力,發現全尾砂膏體屈服應力隨測量時間–測量速率在一定條件下的變化規律,即峰值屈服應力、靜態屈服應力正比于膏體的測量速率,動態屈服應力反比于測量時間,以變異系數Cv評價料漿屈服應力的離散程度,其中74%質量分數膏體動態屈服應力變異系數最大,Cvmax=27.07%,而66%質量分數膏體靜態屈服應力變異系數最小,Cvmin=2.33%。進而從細觀層面分析了膏體屈服過程中顆粒間作用力、顆粒網絡結構隨測量時間–測量速率的變化規律,解釋了全尾砂膏體屈服應力易變性機理。

     

    Abstract: The rake torque of deep cone thickener, pipeline resistance, and paste accumulation slope were important technological parameters for the efficient paste backfill process, which are to be solved or optimized for the practical application in mines. The yield stress of paste was considered as an important rheological parameter for solving these technological parameters. In the past, the research of yield stress of the materials for unclassified tailings paste was limited to the concept and analysis of yield stress fluids used. For example, the fluids such as Bingham fluid, H–B fluid, and Casson fluid were commonly used. When the shear stress of the paste was less than yield stress, the slurry paste remained stationary, and the paste started to flow when shear stress was greater than yield stress. So it concluded that the yield stress was an important parameter in the transition from solid state to flow state. It was considered that yield stress of paste with a certain ratio of material had a unique value, which was regarded as inherent physical property of paste. At present, most rheological studies of concentrated suspensions had found that the evolution of particle structure in suspensions resulted in thixotropy, which increased the difficulty of measuring yield stress of suspensions. Considering the unclassified tailings as specific experimental sample, experiments with different mass fractions paste were carried out and yield stresses were measured. The influence of measuring velocity and measuring time on yield stress of paste was analyzed. It is found that the yield stress value is correlated with measuring protocol. By comparing and analyzing peak yield stress, dynamic yield stress, and static yield stress, the variations in yield stress of paste with measuring time and measuring velocity under certain conditions were obtained. It is observed that the peak yield stress and static yield stress are proportional to measuring velocity of paste, and the dynamic yield stress is inversely proportional to measuring time. The coefficients of variation of degree of yield stress with discreet features are evaluated. The dynamic yield stress of 74% mass fraction paste has the largest Cv, which is 27.07%, while the static yield stress of 66% mass fraction paste has the smallest Cv, which is 2.33%. Further, the variation of particle interaction force and particle network structure with measuring velocity and measuring time during paste yielding was analyzed from the mesoscopic level. The mechanism of variation in yield stress of paste was elucidated based upon the analysis and the results and the necessary values of parameters were obtained for the efficient backfill process.

     

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