砂岩型铀矿床中铀矿物的形成机理

本文通过对砂岩型铀矿床中铀在不同地球化学环境中的行为、存在形式及铀矿物种类的分析，论述了主要工业铀矿物——沥青铀矿的形成机理：(1)铀是变价元素，在氧化环境中活化迁移，在还原环境中还原沉淀；(2)来自于氧化环境的UO2(CO3)3]^4-、UO2(CO3)2]^2-在氧化还原过渡带与有机质、硫化物及低价铁等还原剂发生反应，形成铀的简单氧化物——沥青铀矿；(3)有机质、粘土矿物等吸附UO2^2 ，加快了其被还原的速度，有利于铀的富集。因此认为：有机质还原UO2^2 形成H2S和H2S还原UO2^2 的作用是沥青铀矿形成的主要原因，这一反应在中性和弱碱性碳酸盐溶液中广泛和普遍存在。H2S等还原剂的存在是环境Eh值下降的主要原因，从而使水中的UO2^2 在氧化还原过渡带处于过饱和状态，加速了铀的吸附和沉淀。

Formation mechanism of uranium minerals at sandstone-type uranium deposits

By analyzing the behavior and existence form of uranium in different geochemical environments,existense form of uranium and uranium minerals species,this paper expounds the formation mechanism of main commercial uranium mineral--pitchblende:(1)uranium is a valence?changeable element.It is reactivated and migrates in oxidized environment,and is reduced and precipitated in reducing environment;(2)UO 2(CO 3) 3] 4- ,UO 2(CO 3) 2] 2- coming from oxidized environment react with reductants such as organic matter,sulfide and low?valenced iron at the redox front to form simple uranium oxide--pichblende;(3)the adsorption of uranium by organic matter and clay minerals accelerates the reduction and the concentration of uranium.Therefore,it is considered,that the reduction of SO 2- 4 by organic matter to form H 2S,and the reduction of UO 2 2 by H 2S are the main reasons for the formation of pitchblende.This reaction is extensively and universally available in neutral and weakly alkaline carbonate solubion.The existense of reductants such as H 2S is the basic factor leading to the decrease of Eh in environments and the oversaturation of UO 2 2 at the redox front in groundwater,thus accelerating the adsorption and the precipitation of uranium.