Variations in pore structures and permeabilities of the ion-adsorption rare earth ores in the zones with different weathering degree before and after leaching
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摘要:
离子型稀土矿是典型的风化壳淋积型稀土矿，这类稀土矿浸出前后渗透性变化是反映稀土矿浸出率的重要指标之一，孔隙结构是控制其渗透系数的关键因素。以往对浸出前后稀土矿孔隙结构和渗透性研究主要集中于风化程度和丰度相对较高的全风化带稀土矿，对其他风化带稀土矿的研究较少。随着稀土资源日渐枯竭，其他风化带稀土矿的开发已受到产业部门的高度重视。研究以江西足洞矿区未开采段残积土、全风化带和强风化带内的原状稀土矿试样为研究对象，通过模拟原地浸矿试验，测试其浸出前后渗透系数，采用X射线计算机层析扫描技术获取浸出前后试样结构，采用三维成像技术构建其三维孔隙结构、提取孔隙结构参数，进而定量分析不同风化程度稀土矿浸出前后孔隙结构参数和渗透系数变化规律。结果显示：（1）浸出后，稀土矿渗透系数和孔隙结构参数中的孔隙度、连通性及平均配位数变化率随风化程度降低呈现减小趋势。其中，强风化带稀土矿的渗透系数和孔隙结构参数变化率最小，反映在丰度相近时，强风化带稀土矿较残积土稀土矿的浸出率更高；（2）浸出前后颗粒级配和矿物成分变化特征显示，不同风化带稀土矿浸出前后孔隙结构和渗透性变化率差异的内在机理是长石及云母颗粒分解作用、离子交换作用强度和团粒分散程度的差异以及由此导致的矿物成分和颗粒级配变化程度的差异。研究结果可为类似离子型稀土矿的充分开发利用提供参考。
Abstract:Ion-adsorption rare earth (RE) ore is a typical kind of rare earth ore derived from the weathering crust of igneous rocks. Variation in permeability of ion-adsorption rare earth ore is one of the indicative factors of mining efficiency. Permeability of the RE ore is controlled by its pore structure. Previous studies mainly kept on the RE ores in completely weathered zones, little on those in the zones with other weathering degrees. With the exhaustion of rare earth resources in the completely weathered zone, the extraction of the RE ore from the zones with other weathering degrees has gained more attention from the industrial sectors. This study shows a study on variations in pore structures and permeabilities of the RE ores in the zones with different weathering degrees, including the residual soil and completely weathered and highly weathered zones. The undisturbed samples were taken from an un-mining section of the Zudong mining area in Jiangxi province. Simulated in situ leaching experiments were conducted on the samples to measure their permeability coefficients before and after leaching. X-ray computer tomography scanning techniques were applied to the capture structure of the samples before and after leaching, and image processing techniques were used to construct their three-dimensional pore structure and extract their pore structure parameters. Variations in pore structure parameters and permeability coefficients of the RE ores from the zones with different weathering degrees were then carried out by a quantitatively comparative analysis. The results indicate that (1) the variation rate in permeability coefficient, and the pore structure parameters, including porosity, connectivity, and average coordination number, decrease with the decrease in weathering degree. Notably, these variation rates for the RE ores in the highly weathered zone are the smallest, indicating the RE ores in this zone are more leachable than those in residual soil if their abundance is not much different. (2) The mechanism leading to their differences was further investigated by the analyses of particle size distribution and mineralogical composition before and after leaching. The analysis results indicate that the differences in their variation of pore structure and permeability among the RE ore in the zones with different weathering degrees are caused by the differences in followings during leaching, including the chemical decomposition of plagioclase and mica, ion exchange, and disaggregation.The results can provide reference for the full development and utilization of similar ion-adsorption rare earth ore.
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表 1 稀土矿试样的基本物理性质
Table 1. Physical properties of the RE ore samples
编号 试样 天然含水率/% 孔隙度/% 干密度/（kN·m−3） 比重 1-1 残积土 7.33 22.58 17.04 2.71 2-1 全风化带 7.42 21.45 17.16 2.71 3-1 强风化带 7.42 21.07 16.68 2.71 
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表 2 稀土矿试样浸出前后矿物组成
Table 2. Mineral composition of the RE ore samples before and after leaching
编号 试样 全土矿物组成/% 石英 长石 云母 黏土矿物 1-1 残积土 浸矿前 52.5 22.7 11.3 13.5 浸矿后 52.5 20.4 9.9 17.2 2-1 全风化带 浸矿前 46.5 28.6 12.8 12.1 浸矿后 49.3 24.5 12.0 14.2 3-1 强风化带 浸矿前 41.1 31.4 16.3 11.2 浸矿后 45.2 28.5 12.4 13.9
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