Recently, one of the main directions for increasing the extraction of uranium from difficult-to-hide ores is the use of intensifiers, which allow the most complete transfer of uranium from one valence state to another. In the article, the catalyst “M-1”, which is a compound of transition metals, is considered as an intensifier. Comparison of the kinetic dependencies of the sorption extraction of uranium by the ionites from the productive solutions of leaching of uranium-bearing ore in the presence of the “M-1” catalyst showed that they differ insignificantly. The possibility of sorption of uranium from productive solutions by natural sorbents in comparison with synthetic sorbents is investigated

A. N. Berkinbayeva

B. K. Kenzhaliyev

T. Yu. Surkova

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To the question of the intensification of the processes of uranium extraction from refractory raw materials

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75METALURGIJA 58 (2019) 1-2, 75-78B. K. KENZHALIYEV, T. YU. SURKOVA, A. N. BERKINBAYEVATO THE QUESTION OF THE INTENSIFICATION OF THE PROCESSES OF URANIUM EXTRACTION FROM REFRACTORY RAW MATERIALSReceived – Primljeno: 2018-06-26Accepted – Prihvaćeno: 2018-09-14Original Scientific Paper – Izvorni znanstveni radB. K. Kenzhaliyev (e-mail: bagdaulet_k@mail.ru) JSC “The Kazakh national research technical University after K.I. Satpaev”, T. Yu. Surkova, A. N. Berkinbayeva, JSC “Institute of Metallurgy and Ore Benefi cation”, Almaty, KazakhstanRecently, one of the main directions for increasing the extraction of uranium from difficult-to-hide ores is the use of intensifiers, which allow the most complete transfer of uranium from one valence state to another. In the article, the catalyst “M-1”, which is a compound of transition metals, is considered as an intensifier. Comparison of the kinetic dependencies of the sorption extraction of uranium by the ionites from the productive solutions of leaching of uranium-bearing ore in the presence of the “M-1” catalyst showed that they differ insignificantly. The possibility of sorption of uranium from productive solutions by natural sorbents in comparison with synthetic sorbents is investi-gated.Key words: uranium, ore, leaching, sorption, catalystINTRODUCTIONUranium is present in ores as part of a large number of mineral formations that differ in their physicochemi-cal properties. According to the literature, the main ura-nium ores are the minerals of the tetravalent uranium: oxides (nasturan, uranium black) silicates (coffinite). The most common in the ores of almost all genetic types are simple oxides of U (IV). Minerals of hexavalent uranium are of lesser industrial importance. The use of sulfuric acid as a leaching reagent allows the extraction of only uranium (VI) compounds, since uranium com-pounds (IV) in sulfuric acid do not dissolve. To convert uranium (VI) to uranium (IV), oxidizers are used in in-dustry, most often-ferric compounds. In this regard, the main problem of increasing the extraction of uranium in underground leaching is the transfer of uranium (IV) to a soluble state [1].The method of underground well leaching finds an increasingly wide application in the development of uranium deposits, which, due to complex bedding con-ditions, as well as high specific investments and operat-ing costs, can not be worked out by traditional methods.In Kazakhstan, underground well leaching is the only effective method of uranium mining. Sulfuric acid is used as a leaching reagent [2].Minerals of tetravalent uranium do not dissolve in sulfuric acid, unlike to hexavalent. To dissolve the min-erals of tetravalent uranium in dilute solutions of sulfu-ric acid, leaching is conducted with the addition of oxi-ISSN 0543-5846METABK 58(1-2) 75-78 (2019)UDC – UDK 546.791:669.051:66.066.1:66.097.5 = 111dizing agents. It is believed that the main problem of increasing the extraction of uranium from ore during underground leaching using existing technologies is the conversion of uranium (IV) to a soluble state. There-fore, at the heart of the overwhelming majority of re-search works is the question of the most complete trans-fer of uranium compounds into a soluble state, i.e. ura-nium (IV) in uranium (VI) [3].In this connection, the purpose of this work was to study the effect of the “Muhamedzhan - 1” (M-1) catalyst on uranium leaching and to assess the extent of its subse-quent extraction from the resulting productive solutions.In accordance with the complex chemical composi-tion of uranium-containing solutions of underground well leaching and low uranium content, the most ac-ceptable method of their processing is sorption meth-ods, which are based on the use of ion exchange. Ion exchange has certain advantages over other methods (precipitation and extraction), since it allows to extract uranium from solutions of various concentrations [4].In the literature, there are data on the use of natural sorbents for the extraction of uranium from productive solutions with a low content [5]. The advantages of such sorbents are their low cost. Within the framework of the present work, the possibility of sorption of uranium from productive solutions by natural zeolite and schungite in comparison with synthetic sorbents is investigated.EXPERIMENTAL PARTMethod and work technologyExperiments on the leaching of uranium ore were conducted in a thermostated reactor according to a gen-erally accepted procedure. The maximum duration of 76B. K. KENZHALIYEV et al.: TO THE QUESTION OF THE INTENSIFICATION OF THE PROCESSES… METALURGIJA 58 (2019) 1-2, 75-78the process was 48 hours. The ratio of solid to liquid equals (S : L) = 1 : 4.Sorption of uranium was carried out on the anionites Purolite A500 and Ambersep 920 in a static mode ac-cording to the procedure described in [6] from the pro-ductive solution from leaching of uranium-bearing ore. The composition of the solution is given below.RESULTS AND ITS DISCUSSIONAs mentioned above, the main task of the vast ma-jority of research works is the question of the most com-plete transfer of uranium compounds into a soluble state, i.e. uranium (IV) into uranium (VI). In this con-nection, we chose the initial ore, in which the main min-eral is U [SiO4], which makes up about 95 % of the total uranium mineralization balance. Uranium-containing minerals are also represented by leucoxene, accompa-nying - native selenium, cobalt-nickel pyrite and sphal-erite. The composition of different rocks: quartz - 70 - 80 %, feldspars - 10 - 20 %, siliceous rocks - 5 -10 %. The average content of uranium is 0,03 %.At the first stage of the research, the effectiveness of the M-1” catalyst’s influence on the uranium extraction degree by agitation leaching with sulfuric acid was evaluated.The investigations were carried out in the presence of the “M-1” catalyst. Further, for comparison, in the presence of traditional oxidizing agents: ferric iron, am-monium nosulphate and sodium peroxoborate.Preliminary studies of the catalyst “M-1” are pre-sented in [7]. The catalyst “M-1” is a mixture of nitrates, sulfates, chlorides, bromides and iodides of transition metals (Fe, V, Cu, Mn). Data characterizing the extrac-tion of uranium by sulfuric acid in the presence of a “M-1” catalyst are presented in Table 1.Table 1  Results of sulfuric acid leaching of uranium in the presence of “M-1” catalystCatalyst content / g/dm3ORP / mVExtraction U / mg/dm3The acid consumption (СН2SO4 = 5,0 g/dm3), g/g of uranium0 378 35 39,10,3 388 80 14,20,6 396 82 12,80,9 402 84 11,11,2 408 86 9,7From the data presented, it can be seen that the use of the “M-1” catalyst in the leaching process leads to an increase in the extraction rate of uranium from the ore. The maximum increase in the concentration of uranium in the solution is observed at the site of the change in the catalyst content in the range 0 – 0,3 g/dm3.Table 2 shows the leaching of uranium-bearing ore by sulfuric acid in the presence of a catalyst in com-parison with oxidants.Table 2  Results of sulfuric acid leaching of uranium in the presence of “M-1” catalyst and oxidantsPresence of catalyst or oxidizerConcentration of uranium in solution / mg/dm312 h 24 h 36 h 48 hSulfuric acid without oxidizers and catalysts 35,2 36,0 37,5 38,4The catalyst “M-1” 84,6 86,2 87,4 88,3Ferric chloride 50,8 55,1 56,9 58,2Ammonium Sulfate 48,3 49,5 51,0 51,8Peroxoborate 39,2 39,7 40,1 40,9It can be seen from the table that the uranium con-tent in the leaching solution without catalyst and oxidiz-ers was 35,2 mg/dm3 after 12 hours of the experiment and increased to 38,4 mg/dm3 after 48 hours after the beginning of the leaching. In the case of using tradi-tional oxidants, an increase in uranium extraction was also observed with increasing leaching time. The use of ferric chloride during the leaching process allowed to increase the concentration of uranium in the solution from 50,8 mg/dm3 for 12 hours of leaching to 58,2 mg/dm3 for 48 hours, and for ammonium nitrate and sodium peroxoborate from 48,3 and 39,2 to 51,8 and 40,9 re-spectively. When the ‘M-1” catalyst was used after 12 hours of the experiment, 84,6 mg/dm3 of uranium ex-traction was achieved, with increasing leaching time this value varies 88,3 mg/dm3.Thus, the highest concentration of uranium in the solution is achieved when the ore is leached with sulfu-ric acid in the presence of a catalyst and decreases in the series: the catalyst “M-1” - ferric chloride III - ammo-nium perchlorate - sodium peroxoborate - sulfuric acid in the absence of oxidants and catalyst.It should be noted that the catalyst “M-1” was suc-cessfully tested under production conditions and rec-ommended for use.Unlike other methods, uranium sorption is charac-terized by the possibility of achieving high purification factors and a degree of concentration, high selectivity, the possibility of flexible regulation of selectivity by changing pH, oxidation-reduction conditions, compl-exation, simplicity and compactness of instrumentation, and a wide variety of artificial and natural sorbents.Sorption of uranium together with the process of leaching is a kind of indicator of its extraction from this type of raw material.Sorption of uranium was carried out in a static mode on Purolite A500 and Ambersep 920 anion exchangers. The selected anion exchangers - strongly basic ma-croporous Purolite A500 anionite on the basis of styren-edivinylbenzene matrix and macroporous strongly ba-sic anionite Ambersep 920 based on cross - linked poly-styrene are effectively used in uranium mining enter-prises of Kazakhstan.In the course of the experiment, a productive solu-tion was used from the leaching of uranium-bearing ore with sulfuric acid in the presence of the “M-1” catalyst. The concentration of uranium in the initial solution was 77B. K. KENZHALIYEV et al.: TO THE QUESTION OF THE INTENSIFICATION OF THE PROCESSES…METALURGIJA 58 (2019) 1-2, 75-7888,3 mg/dm3. The kinetic dependencies of extraction of uranium from the productive solution by Purolite A500 and Ambersep 920 ion exchangers were determined in comparison. The results of the experiment are shown in Figure 1, from which it can be seen that the ion ex-changers practically equally sorb uranium from the so-lution. The degree of extraction of uranium on ion ex-changer Ambersep 920 reaches 88,3 %, Purolite A500 – 89,1 % for 8 hours of contact.In addition, studies have shown that increasing the duration of the process over 8 hours is ineffective.The rate of ion exchange is usually determined by diffusion processes: either by the rate of diffusion of ions inside the ionite grain (gel diffusion), or by the rate of passage of these ions through a liquid film adjacent to the grain surface (film diffusion) [8].If the process is limited by diffusion in the film (film kinetics), the following simplified formulas are used: where, F - degree of achievement of equilibrium in frac-tions, %; – constant rate of ion exchange, s-1;D – diffusion coefficient in the film, cm2/sec;r0 – the average grain size of the ion exchanger, cm;σ – the thickness of the film, cm;t – time, s;λ – the distribution coefficient.To determine the limiting stage of the uranium sorp-tion process, the dependence “ln (1-F) on t” was con-structed and shown in Figure 2.In Figure 2 confirms the predominance of gel kinet-ics in this region.Experiments on the influence of temperature were carried out in the interval of 15 - 45 °C in a thermostated reactor. Figure 3 shows the degree of extraction of ura-nium as a function of temperature on Purolite A500 and Ambersep 920 anion exchangers.It follows from the figure that the temperature has a positive effect on the sorption of uranium. With an in-crease in temperature to 45 °C, the uranium recovery rate rises: on the ioniser Ambersep 920 up to 91,6 %, Purolite A500 up to 95,7 %. However, the temperature of the solutions should not be more than 50 - 60 °C, because when heated above this temperature, the de-struction of the sorbent grains, the cleavage of the ac-tive groups and, as a consequence, the decrease in the capacity of the resin, is possible. Based on the studies carried out, the values of the activation energy and the diffusion coefficients of uranium were calculated. The results are shown in Table 3.Table 3 Kinetic parameters of the sorption processSorbent T / K Diff usion coeffi  cient / cm/s2Activation energy / kJ/molPurolite А500 298 6,338·10-96,94308 8,574·10-9318 8,015·10-9Ambersep 920 298 2,649·10-111,53308 1,086·10-8318 1,73·10-8It follows from the table that the calculated values of the diffusion coefficients of uranium are of the order of 10-8 - 10-11 m2/s and indicate a diffusion mechanism in-side. The calculated activation energies for uranium sorption on Purolite A500 and Ambersep 920 anionites are characteristic for a mixed external and internal dif-fusion process type.Figure 1  Kinetic curves of sorption of uranium from the productive solutionFigure 2  Change of ln (1-F) in time for the uranium sorption reactionFigure 3 Dependence of uranium extraction on temperature78B. K. KENZHALIYEV et al.: TO THE QUESTION OF THE INTENSIFICATION OF THE PROCESSES… METALURGIJA 58 (2019) 1-2, 75-78During the research, sorption extraction of uranium was tested with natural sorbents. Chemical composition of schungite, %: C - 10; SiO2 - 26,0; Al2O3 - 6,5; Fe2O3 - 3,8; MgO - 2,5; CaO - 13,5; Na2O - 0,6.The results of uranium sorption from productive so-lutions are presented in Table 4.Table 4  Results of sorption of uranium from productive solutionsSorbentUranium content / mg/dm3The extraction of U into the sorbent / %Content of U in the sorbent / % wt.Shungite 0,85 90,9 0,193Zeolite 0,97 90,1 0,165It states in the table that the degree of extraction of uranium by natural sorbents is quite comparable with the synthetic ones (the ratio of solid to liquid equals (S : L) for synthetic sorbents 1 : 500, and for natural sorb-ents 1 - 1,2 : 25), but their sorption capacity is low. The main disadvantage of synthetic sorbents is their high cost, and therefore, the use for uranium sorption from solutions with low concentrations (usually for pre-ex-traction) is unreasonable. To extract uranium from pro-ductive solutions, or from liquid waste of uranium chemical-metallurgical industries, it is more profitable to use natural sorbents. However, due to the low sorp-tion capacity, their use is limited. At present, we are working to increase the sorption capacity of natural ion exchangers for uranium.CONCLUSIONThe technology of uranium mining by the method of borehole underground leaching mainly uses aqueous so-lutions of mineral acids or salts of alkali metal carbon-ates. From the practice of conducting the process of un-derground uranium leaching, it follows that the choice of the type of solvent for the working (leaching) solutions depends on the form of the uranium mineralization, the material composition of the ores and host rocks, and on the chemical nature of the uranium minerals.When poorly soluble uranium ores containing main-ly tetravalent uranium by sulfuric acid is leached, the main task is the most complete oxidation of uranium (IV) to uranium (VI). Uranium (IV) in sulfuric acid is insoluble. In this connection, the study of the effect of new intensifiers on the process of uranium leaching is of great interest.The influence of “M-1” catalyst on uranium leach-ing from persistent uranium-containing ore is studied and its advantage over traditional oxidants is shown.Sorption methods are used to extract uranium from productive solutions. The concentration of uranium on Purolite A500 and Ambersep-920 ion exchangers and natural sorbents - zeolite and shungite was studied. In view of the low cost of natural sorbents, their priority use is considered for the extraction of uranium from productive solutions and liquid waste of uranium chem-ical and metallurgical industries.AcknowledgementsThe work was carried out under the budget program “Grant financing of scientific research” on the topic: “Development of innovative technologies for selective uranium mining from uranium-containing solutions us-ing new modified sorbents based on natural minerals of Kazakhstan.”REFERENCES[1]  A. Susan, E. Barbara, B. Joël, D. Grant, E. Katy. Characte-rization of uranium redox state in organic-rich Eocene se-diments, Chemosphere 194 (2018), 602-613. doi.org/10.1016/j.chemosphere.2017.12.012[2]  M. Panfilov, B. Uralbekov, M. Burkitbayev. 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Bobrova, A.S. Sharipova. Sorption technology of rhenium extraction from uranium-containing solutions using we-akly basic anion exchangers, Complex Use of Mineral Re-sources 3 (2011), 8-16.[7]  Y. Aibassov, S. Aibassova, G. Aibassov, Zh. Aibassov, M. Aibassov, B. Abenov, Method of catalytic oxidation of U+4 to U+6 using a catalyst Muhamedzhan-1. United States Pa-tent No. 2013/0104698 A1 (02.05.2013)[8]  P. Abbasi, B. Kevitt, D. Dreisinger, The kinetics of nickel recovery from ferrous containing solutions using an Imi-nodiacetic acid ion exchange resin, Hydrometallurgy 175 (2018), 333-339. doi.org/10.1016/j.hydromet. 2017.11.002Note:  The responsible translator for the English language is D. Imanku-lova, JSC “KBTU”, Kazakhstan.

To the question of the intensification of the processes of uranium extraction from refractory raw materials

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