铀尾矿库中核素U(Ⅵ)的扩散迁移试验

Experimental simulated research on the diffusion migration of nuclide at the uranium mill-tailing

利用自制的设备,采用水平土柱吸渗法,测定了不同参数土壤中铀溶液的质量浓度,通过Fick扩散第二定律推导的公式计算其扩散系数。并对比氯离子迁移试验,探讨了时间、距离、土质、孔隙度等对铀扩散的影响,进而研究尾矿库中核素U(Ⅵ)的运移扩散规律。结果表明:铀和氯离子在砂质土壤中的扩散均比在黏质土壤中快,氯离子在黏土中的扩散系数D=0.354×10^(-3)m^3/d,在砂土中的扩散系数D=1.830×10^(-3)m^3/d,铀在黏土的扩散系数D=0.950×10^(-3)m^3/d,在砂土中的扩散系数D=1.623×10^(-3)m^3/d;铀在土壤中的质量浓度随扩散时间延长逐渐增大,且与扩散距离呈比例关系;铀在土壤中的扩散系数随土壤孔隙度增大而变大。

The present paper is intended to introduce the results of our experimental simulated research on the diffusion migration of nuclide at an uranium mill-tailing mine in hoping to disclose the migration diffusion regularity of the tailings of nuclide U（ Ⅵ）. For the said purpose,we have designed a special container for the simulated sewage of the uranium tailing impoundment somewhere in South China we have conducted the given experiment. The concentration of uranium tailing in the soil solution under the different parameters measured with the horizontal soil column infiltration absorption method whereas the nuclide U（ Ⅵ）diffusion coefficient has been calculated by using the derivation formula of the second law of Fick diffusion formula. When compared with the experiment of chloridion migration in the soil,we have also investigated the effect of the contact time,the distance,the soil texture and the porosity on the diffusion of uranium（ Ⅵ）.The experiment results we have gained through the experiment indicate that the chloride ion concentration tend to reach a stable value in the distilled water chambered for a period of 40 days and remain consistent with the initial concentration. However,the diffusion of uranium in the soil turns to get relatively faster,on the condition when the uranium concentration remains unchanged during the 25 days,though there can be found somewhat difference with the initial concentration. What is more,the chloride ions have been found bigger than the ones of the uranium diffusion in the soil with the time going on. We have also found that the uranium and chloride ions can be diffused faster in the sandy soil than in that of clay. Exactly speaking,the diffusion coefficients of chlorine ions in the clay are D = 0. 354 × 10^-3m^3/d,while in the sandy soil that account for D = 1. 830 × 10^-3m^3/d. In other words,the diffusion coefficients of uranium in clay are D = 0. 950× 10^-3m^3/d,whereas they are D = 1. 623 × 10^-3m^3/d in the sandy soil. In addition,the concentration of uranium in the soil has been found gradually increasing with the extension of time period and keeps a proportional relation with the diffusion distance.Nevertheless,in contrast,the diffusion coefficients of uranium in the soil tend to extend with the increase of the porosity of the soil.Thus,the study results of the paper has also proven that the contaminants of the uranium ions in the soil with bigger porosity tend to diffuse faster than in the soil with smaller porosity. Therefore,the comprehensive effect of the porosity of the soil and its texture has been confirmed with obviously greater on the uranium than the individual effect.