Key Technologies And Theories On In-situ Leaching Of A Sandstone Uranium Deposit In Xinjiang

Aiming at the insufficiency of leaching rate and leaching efficiency of sandstone-type uranium mine in China,and the lack of predictive control theory and technology in production process,this paper takes a low-permeability sandstone uranium mine in Yili,Xinjiang as the research object,firstly using micro-radiography and electron probe test.Experimental methods such as XRD,XRF,SEM/EDS and mercury intrusion method are used to analyze the overall situation of the ore in the mining area,and the geological and geochemical characteristics of the mining area are obtained.Then the high-efficiency compounding surfactant CSH combined with acid leaching was proposed.The preliminary selection,optimization,formulation and binary compounding theory of surfactants were systematically studied.The kinetic mechanism of CSH combined with acid leaching was investigated by stirring leaching,horizontal column immersion,resin adsorption and leaching experiments.Finally,the innovative uranium occurrence form and ²³⁴U/²³⁸U activity ratio were used as tools to study their Indication,prediction and control of the practice of in-situ production.The main findings and conclusions are as follows:Firstly,the overall characteristics of sandstone uranium deposits are characterized by low permeability and an average permeability coefficient of only0.133 m/d.Uranium minerals are mainly in the form of bituminous uranium ore,with a small amount of uranium and titanium uranium minerals.The uranium is still adsorbed in the cement and distributed between the ore particles and inside the particles.It is demonstrated that the chemical composition is generally beneficial to acid leaching.The coarse-grained uranium ore accounts for the largest proportion,also with high uranium content,but the path required for the leaching solution to enter the core is long,and the uranium is difficult to be leached by wetting.the medium-grain size accounts for a larger proportion than the fine-grained grade,but the uranium content is lower than the fine-grained grade.The uranium ore is complex in shape and not too low in porosity,but the pore size is small and the proportion of tiny pores is large,which limits the free flow and penetration of the solution inside.As a result,the permeability of the ore layer is low,and improving the permeability of the ore layer becomes a difficult problem and key technology for the in-situ mining of such low-permeability uranium mines.Measures should be taken to improve the wettability and permeability of the leachate,in which surfactants being the preferred admixture.Secondly,the study on the compounding mechanism of surfactants shows that when the molar fraction is 0.47,the synergistic effect of mixing FS-3100 with OP-10is the most obvious,and the surface tension of sulfuric acid solution can be as low as17.9mN./m,this binary hybrid system is defined as CSH.The critical micelle concentration CMC^exp measured by CSH is lower than the CMC^ideal calculated by the ideal mixed solution theory,and the two are not ideal mixtures.Thermodynamic analysis showed that FS-3100 and OP-10 acted spontaneously when the molar fraction was moderate,forming a new structure by nesting between molecules.The performance of CSH surfactants is affected by the amount of surface adsorption and molecular structure,and there is a certain gap with the theory of informal solutions.The mechanism of CSH assisted uranium leaching shows that the overall performance of assisted uranium leaching is coarse grain grade>medium grain grade>fine grain grade,which mainly acts by wetting and osmosis.At a concentration of 9 mg/L,CSH can increase the leaching rate of uranium by stirring leaching to 92.7%,the permeability coefficient by 90.2%,the column leaching uranium concentration by 18.9%,and the uranium leaching rate by 31.6%.CSH does not adversely affect resin adsorption and leaching,and can improve rinsing efficiency.The result of kinetic analysis shows that CSH can change the kinetic mechanism of the leaching reaction,and convert the diffusion control leaching reaction into the joint control of diffusion and chemical reaction.The apparent rate constant is increased from 0.0023/d to 0.0082/d,which is 3.6 times higher,and the chemical reaction controlled leaching apparent rate constant was 0.0077/d.The method of using the new compound surfactant CSH for in-situ leaching is useful for low-permeability sandstone uranium deposit,it can also be used to resume the production of mines with reduced permeability.Thirdly,the role of the chemical fraction in the prediction of in-situ leaching of uranium is mainly reflected in the gradual extraction by the improved Tessier method.There are five occurrences of low-permeability sandstone uranium deposits acording to chemical fractions,of which F2>F3>F1>F4>F5.They are classified into three types:easysily leachable uranium?F1-F3?,leachable uranium?F4?,and hardly leachable uranium?F5?.The eassily leachable uranium has an absolute dominant position,the proportion of leachable uranium is high,and the hardly leachable uranium accounts for a relatively small proportion.The uranium ore with high easily leachable uranium has a high grade,and the chemical fractions of uranium can directly reflect the difficulty of uranium ore leaching.The uranium leaching rate K_d in the diffusion control stage increases logarithmically with the grade of uranium in F1.The chemical reaction control stage K_r increases linearly with the total percentage of uranium in the F1-F4 fractions.The overall variation characteristics of uranium concentration in in-situ leaching can be divided into two categories according to the uranium content of F1.The variation of uranium monitoring concentration in time is consistent with the fourth-order polynomial relationship.The predicted model equation is as follows:y_i,x=a_ix⁴+b_ix³+c_ix²+d_ix+e_i,and the parameters of which can be solved by regression analysis using uranium chemical fractions.At the same time,an index correlation model between the peak value of uranium concentration and the total grade of F1-F4 was established.After validity test,the accuracy of the model is qualified,and they can be used for precision mining and CSH combined with sulfuric acid leaching uranium in actual production.Fourthly,through the measurement and analysis of the ²³⁴U/²³⁸U activity ratio ARS of the uranium isotope during the gradual extraction of each phase and column leaching process,the following ARS characteristics are indicated for the in-situ leaching of uranium:ARS are higher?1.293-1.348?in exchangeable fraction?F1?and easily acid soluble fraction?F2?,which decrease to 1.204-1.229 in acid soluble fraction?F3?and then reduce to the minimum 0.917-0.934 in oxidation fraction?F4?.After that ARS increases to 1.018-1.142 in hardly soluble fraction?F5?.Three phases of uranium leaching were identified according to the ARS.The first phase was characterized by the relatively high ARS in the range of 1.217-1.318,and the leaching uranium is mainly U?VI?in fraction F1,F2 and F3.The second phase was represented as the decrease of ARS,up to 1.016,and the leaching uranium is mainly U?IV?partly in F3 and primarily in F4.The third phase was characterized by the fluctuant ARS of 1.070-1.118,and the few leaching uranium is mainly the hardly soluble uranium in F5.