地浸过程中铀迁移特征及条件的实验研究

An Experimental Study of Migration Characteristics and Conditions of Uranium during the In-situ Leaching Process

通过室内模拟试验,对地浸过程中铀的迁移规律进行了研究。结果表明:①溶浸液中铀浓度值在达到饱和浓度前,随地浸路径延长而逐渐增大;②铀的存在形式及其含量与水文地球化学条件相关,当1.9<pH<4.4时,为UO_2SO_4和UO_2^(2+) ;当4.4<pH<5.1时,为UO_2SO_4和(UO_2)_3(OH)^(5+);③随着水文地球化学条件的变化,铀迁移经历了溶解迁移、水解沉淀、再溶解迁移的多次旋回,即当pH>4.6、Eh<420mV时,溶解状态的铀产生沉淀;当2.0<pH<4.6,420mV<Eh<650mV时,U^(6+)溶解迁移;当pH<2.0、Eh>650mV时,U^(4+)溶解迁移;④根据溶浸液中铀浓度和pH、Eh临界值,铀地浸路径可划分出充分浸出带、有效浸出带、铀沉降带和未浸出带,不同特征的浸出带随浸出时间的变化而有序移动。

Through experiments of solute migration and geochemical modeling, this paper reveals the characteristics and conditions of uranium transport during the in-situ leaching process. Firstly, with the extension of the in-situ leaching flow-path, the uranium content increases gradually until reaching saturation in the acid leaching solution. Secondly, the form and concentration of uranium are closely related to the hydrogeochemical conditions of the solution. The predominant uranium forms are UO2SO4 and UO22+ when the pH values range from 1. 9 to 4. 4, and UO2SO4 and (UO2)3 (OH)5+ when the pH values are in the range of 4. 4 to 5. 1. Thirdly, uranium migration during the in-situ leaching process has experienced multiple cycles of dissolution, precipitation and re-dissolution. On the one hand, uranium (U6+) begins to transport when 2. 0<pH<4. 6 and 420 mV<Eh<650 mV, and uranium (U4+) begins to transport when pH<2. 0 and Eh>650 mV. On the other hand, the dissolved uranium can be precipitated when pH>4. 6 and Eh<420 mV. Lastly, in terms of uranium concentration and the pH and Eh values of the leaching solution, the whole flow-path of uranium migration can be divided into four leached zones: the completely leached zone, the effectively leached zone, the uranium precipitation zone and the non-leached zone. The four leached zones move orderly and all the zones finally become completely leached zones when the in-situ leaching process is over.