Evolution characteristics of mesoscopic pore structure of weathered crust elution-deposited rare earth ore under solution seepage
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摘要: 為研究風化殼淋積型稀土礦浸出過程中溶液滲流作用對孔隙結構的影響，以去離子水為溶浸液開展浸礦實驗。對浸出前后礦樣進行顯微CT掃描，獲取了試樣內部結構圖像，利用閾值分割算法得到了浸出前后稀土礦樣的孔隙結構圖像。進而，研究了溶液滲流作用下試樣孔隙結構的變化特征，分析了滲流作用對試樣孔隙率、孔隙體積、孔隙長度、孔隙寬度和孔隙方位角等參數的影響。結果表明：稀土礦孔隙形狀和尺寸在滲流作用下發生顯著變化，且在粗細顆粒接觸區最為明顯；溶液滲流作用使得稀土礦孔隙率增大，孔隙總數量減少，孔隙總體積增大。滲流作用下礦樣中小孔隙數量減少，大孔隙數量增多，各尺寸區間的孔隙數量變化率隨孔隙尺寸的增大呈現先增大后減小的趨勢。溶液滲流作用下孔隙長寬比分布更加集中，孔隙方位角在各角度區間的分布更加均勻，孔隙各向異性增強。Abstract: In-situ leaching is extensively used in the mining industry to recover rare earths from weathered crust elution-deposited rare earth ore. In the leaching system, the pore structure of rare earth ore is one of the most important factors that influence the leaching performance. A small column leaching experiment was performed with deionized water as a leaching solution to study the effect of solution seepage on pore structure evolution characteristics in the leaching process of weathering crust eluviation rare earth ore. Micro-computed tomography (micro-CT) was performed on the ore sample before and after leaching, and internal structure images of the sample were obtained. The pore structures of the rare earth ore sample were obtained using the threshold segmentation algorithm. The variation characteristics of pore structure of a rare earth ore sample under the action of solution seepage were then studied, and the effects of solution seepage on sample porosity, pore volume, length, width, azimuthal angle, and other parameters were analyzed. The results show that the pore shape and size of rare earth ore change significantly due to solution seepage, most notably in the contact area of the coarse and fine particles. The solution seepage increases the porosity of rare earth ore, decreases the total number of pores, and increases the total volume of pores. Besides, the number of small and medium-sized pores decreases, while the number of large pores increases due to seepage. The change rate of the number of pores in each size interval increases and then decreases as pore size increases. Compared with the initial state, the distribution of pore aspect ratio is more concentrated after the solution seepage. Moreover, the distribution of pore azimuthal angle is more uniform, and the anisotropy of pore structure is enhanced by solution seepage.
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圖 3 試樣內部結構圖像。（a）浸出前；（b）浸出后
Figure 3. Internal structure image of the sample: (a) before leaching; (b) after leaching
圖 4 預處理后試樣內部結構圖像。（a）浸出前；（b）浸出后
Figure 4. Internal structure image of the sample after preprocessing: (a) before leaching; (b) after leaching
圖 5 浸出前后孔隙三維圖像。（a）浸出前；（b）浸出后
Figure 5. 3D images of the pore structure before and after leaching: (a) before leaching; (b) after leaching
圖 6 試樣內部結構二維圖像。（a）浸出前；（b）浸出后
Figure 6. 2D images of the internal structure of the sample: (a) before leaching; (b) after leaching
圖 7 試樣三維獨立孔隙圖像。（a）浸出前；（b）浸出后
Figure 7. Images of 3D separated pores of the sample: (a) before leaching; (b) after leaching
圖 8 試樣二維獨立孔隙圖像。（a）浸出前；（b）浸出后
Figure 8. Images of the 2D separated pores of the sample: (a) before leaching; (b) after leaching
圖 9 浸出前后孔隙率變化特征。（a）分區示意圖；（b）不同區域孔隙率；（c）試樣不同高度各區域孔隙率增加率
Figure 9. Porosity variation characteristics of the sample before and after leaching: (a) diagram of regional division; (b) porosity of different regions of the sample; (c) porosity increase rate of different regions at different heights of the sample
圖 10 浸出前后面試樣的2D孔隙率分布特征
Figure 10. Distribution characteristics of the 2D porosity of the sample before and after leaching
圖 12 滲流前后不同體積孔隙數量變化特征
Figure 12. Variation characteristics of the number of pores with different volume sizes
圖 13 浸出前后孔隙長度和寬度分布特征。（a）孔隙長度；（b）孔隙寬度
Figure 13. Frequency distribution of the pore length and width: (a) pore length; (b) pore width
圖 14 浸出前后不同長度和寬度孔隙數量變化特征。（a）孔隙長度；（b）孔隙寬度
Figure 14. Variation characteristics of the number of pores with different lengths or widths: (a) pores with different lengths; (b) pores with different widths
圖 17 不同面積孔隙數量變化特征
Figure 17. Variation characteristics of the number of pores with different areas
圖 18 浸出前后孔隙方位角分布特征。（a）浸出前；（b）浸出后
Figure 18. Frequency distribution of the azimuthal angle θ: (a) before leaching; (b) after leaching
圖 19 浸出前后孔隙極角分布特征。（a）浸出前；（b）浸出后
Figure 19. Frequency distribution of the polar angle: (a) before leaching; (b) after leaching
表 1 浸出前后不同體積孔隙數量統計結果
Table 1. Statistical result of the number of pores with different volume sizes
Pore volume/mm3 10?6?10?5 10?5?10?4 10?4?10?3 10?3?10?2 10?2?10?1 10?1?100 100?101 101?103 Total The number of pores before leaching 30187 121818 93226 17208 1401 98 6 2 263946 The number of pores after leaching 7155 42762 70764 31437 4260 353 18 2 156751 The change in the number of pores ?23032 ?79056 ?22462 14229 2859 255 12 0 ?107195 
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表 2 浸出前后不同長寬比孔隙數量統計結果
Table 2. Statistical result of the number of pores with different aspect ratios
Aspect ratio 1 1?2 2?3 3?4 4?5 5?6 6?7 7?8 8?9 9?10 The number of pores before leaching 14171 163522 78077 7551 545 65 11 3 0 1 The number of pores after leaching 3123 104309 44409 4543 327 35 3 1 1 0 The change in the number of pores ?11048 ?59213 ?33668 ?3008 ?218 ?30 ?8 ?2 1 ?1 Rate of change in the number of pores/% ?77.96 ?36.21 ?43.12 ?39.84 ?40.00 ?46.15 ?72.73 ?66.67 ∞ ?100
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