强风化强氧化砂岩铀矿工艺矿物学与浸出性能

Process Mineralogical Characteristics and Leaching Performance of Heavily Weathered and Oxidized Sandstone Uranium Ore

以采自某急倾斜疏干型砂岩铀矿床的强风化强氧化砂岩铀矿石为研究对象,先将其破碎至-10 mm,分成5~10,3~5,1~3,0.5~1和0~0.5 mm这5个粒级;然后分析各粒级铀矿石的质量和品位;再分析其铀矿物的赋存形态,观测铀矿石和铀矿物的微观形貌和结构;最后开展这类铀矿石的搅拌浸出-堆浸组合试验。结果表明:该铀矿石由砂岩、砾岩和泥岩组成,其结构松散,裂隙发育,破碎至-10 mm后,-0.5 mm粒级的铀矿石占比较高,导致破碎矿石渗透性差,不适合直接堆浸;铀矿物赋存状态较简单,以独立矿物和二连体赋存为主,易解离,占铀矿物总量的80%~85%;铀矿石破碎至-10 mm后,-0.5 mm粒级的铀矿石搅拌浸出3 h,+0.5 mm粒级的铀矿石柱浸4 d后,即可浸出85%左右的铀,余下15%左右的铀浸出相对较慢,搅拌浸出-堆浸组合工艺可高效浸出矿石中的铀;柱浸浸出率(R)随时间的变化可采用经验公式R=k_(1)(1-e^(-k_(2)t))×100%进行拟合,其中参数k_(1)为矿石中可回收铀的质量分数,参数k_(2)为与浸出速率有关的常数,t为浸出时间。

A kind of steeply inclined dry sandstone uranium ore body was recently found in Northwest China.It was evolved from the original horizontal in situ leachable sandstone uranium deposit under the long geological process,the groundwater in the deposit was drained due to seepage to the deep ground,and the sandstone uranium ore in it became a heavily weathered and oxidized one due to its long-term connection with the atmosphere.In order to develop an efficient process for extracting the uranium from ore,induction coupled plasma-mass spectrometry(ICP-MS)was used to analyze its chemical elements,mineralliberation analyzer(MLA)system was used to determine its main mineral composition,its uranium mineral dissociation and its uranium mineral symbiosis with other minerals,and scanning electron microscope(SEM)was used to observe the micro morphology and analyze the element composition.Sandstone,conglomerate and mudstone were found to compose the sandstone uranium ore,they contained 0.2%,0.15%and 0.1%uranium,and their original mass proportions were 57%,25%and 18%,respectively.They were taken from the ore body,weighed on their original mass proportions,crushed to-10 mm particles,and were sieved into 5~10,3~5,1~3,0.5~1 and 0~0.5 mm particle groups,respectively,their particle size distribution curves were determined,and the-0.5 mm particle groups of the crushed sandstone,conglomerate and mudstone accounted for nearly 50%.The uranium grades in their-0.5 mm particle groups were 0.20%,0.15%and 0.10%,respectively,and they decreased a little with the increase of the particle size of the particle group,with the grade in-0.5 mm particle group being the highest in all the particle groups.The sandstone uranium ore contained 78.40%SiO_(2),10.84%Al_(2)O_(3) and 10.84%other elements,and its chemical composition was simple,and its average uranium grade was 0.124%.It contained U(IV)and U(VI)compounds,with U(VI)compounds accounting for 96.8%,indicating that ore was of good oxidizability and was easy to leach.The ore minerals were mainly the pyrite and uranium minerals.The main uranium minerals included pitchblende,hydrouranite,aluminosilicate and uranium bearing clay minerals which accounted for 0.81%,0.01%,0.27%and 3.30%of ore,respectively.The gangue minerals included quartz,muscovite,diorthosite,rutile,etc.,and ore was of silicate and was suitable for acid leaching.There was no obvious difference between the parameters of uranium mineral dissociation state,and the monomer proportions of asphaltic uranium and uranium bearing clay minerals were large,while those of hydrosiliceous and silicoaluminic uranium minerals were small.The dissociation degrees of other uranium minerals and their associated bodies were all more than 50%except for hydrosilicalite mineral.82.22%of the total uranium minerals had a dissociation degree of more than 50%.In addition,the occurrence state of uranium minerals was mainly in the form of independent minerals and dimers,which accounted for more than 80%in total.The uranium minerals in ore were mainly in the form of independent uranium minerals,and they coexisted with pyrite or feldspar minerals.The micro cracks and pores in the sandstone uranium ore particles were well developed,and the uranium minerals were exposed to air in the cracks and pores.Agitation leaching tests were performed on dry sieved-0.5 mm ore particles,which were prepared by crushing the sandstone uranium ore samples to-10 mm particles,and passing them through 0.5 mm sieve.The leaching test conditions were:ore particle size was-0.5 mm,ore mass of 3 kg,ore grade of 0.077%,liquid solid ratio of 2∶1,sulfuric acid concentration of 10 g·L^(-1),and leaching time of 2 h.The ore particles and the leach solution were put into the conical flask,the magnetic agitation device was used to agitate until the end of leaching,and the leaching rate reached 85%.Column leaching tests were performed on dry and wet sieved ore samples,which were prepared by crushing the sandstone uranium ore samples to-10 mm particles,and dry or wet sieving them by 0.5-or 5-mm sieve.Column 1 leaching test:ore sample was the dry sieved one(70%sandstone+30%conglomerate),particle size of 0.5~10 mm,initial sulfuric acid concentration of leach solution of 30 g·L^(-1),and 3 d later it was changed to 20 g·L^(-1).Column 2 leaching test:ore sample was the wet sieved one(70%sandstone+30%conglomerate),and the rest conditions were the same as those for Column 1 test.Column 3 leaching test:ore sample was the dry sieved comprehensive one(57%sandstone+25%conglomerate+18%mudstone),and the rest conditions were the same as those for Column 1.Column 4 leaching test:ore sample was the wet sieved comprehensive one(57%sandstone+25%conglomerate+18%mudstone),and the rest conditions were the same as those for Column 1 test.Column 5 leaching test:ore sample was the drysieved comprehensive one,particle size of 0.5~10 mm,and sulfuric acid concentration of10 g·L^(-1).Column 6 leaching test:ore sample was the wet sieved comprehensive one,particle size of 0.5~5 mm,and sulfuric acid concentration of 10 g·L^(-1).The sulfuric acid concentration of leach solution was adjusted except for Column 5 and 6 tests.The adjustment was conducted because when pH value of leach solution was stabilized at about 1.0,it was conducive to uranium leaching.Column 1~4 test results showed that dry or wet sieving had little influence on leaching rate.Column 1 and 3,2 and 4 test results showed that uranium leaching rate was slower for ore sample with mudstone than for that without mudstone,indicating that mudstone affected leaching of uranium from ore due to the blocking of the pore of ore resulted from the disintegration and sliming of mudstone in leach solution.Column 5 and 6 test results showed that the influence of particle size on leaching was negligible,indicating that the pores and fissures of ore itself were well developed,and it was not necessary to crush ore too fine,which could reduce the cost of the ore breaking.Column 4 and 5 test results showed that the influence of sulfuric acid concentration of leach solution on leaching rate was not obvious,and better leaching effect could be obtained by using 10 g·L^(-1) sulfuric acid concentration,which could decrease the amount of sulfuric acid.After 12 d of column leaching,leaching rate reached about 90%.The dynamics for column leaching could be fitted by empirical formula R=k_(1)(1-e^(-k_(2)t))×100%,in which R was leaching rate,%;t was leaching time,d;k_(1) was mass fraction of recoverable uranium in the ore,and k_(2) was a constant related to leaching rate.It could be concluded that the uranium could be efficiently extracted from the heavily weathered and oxidized sandstone uranium ore in the following hybrid leaching process,which included producing-0.5 mm ore particles and 0.5~10 mm ore particles by crushing the sandstone uranium ore to-10 mm particles and passing them through the 0.5 mm sieve,and treating the-0.5 mm ore particles by agitation leaching and 0.5~10 mm ore particles by column leaching.