The behavior of rare-earth elements and major impurities during the nitric-acid decomposition of a lean yttrofluorite concentrate by the method of sorption conversion is studied. The decomposition conditions providing satisfactory extraction into the sorbent for rare-earth elements, especially yttrium and yttrium group lanthanides, are determined.

A hydrometallurgical technology for processing a titanomagnetite concentrate is proposed and substantiated. The technology includes the decomposition of the concentrate in a weakly concentrated sulfuric acid solution in the presence of a sulfonic cation-exchange resin in the H + form with the transition of the major portion of metals of the titanomagnetite concentrate to the sorbent and the formation of an ilmenite-enriched residue; the desorption of metals from the saturated sulfonic cation-exchange resin with a 5 M solution of sodium chloride; the fractional hydrolytic precipitation and separation of titanium hydroxide, iron hydroxide enriched in vanadium, pure iron hydroxide, and a mixture of iron and manganese hydroxides; and the regeneration of the sulfonic cation-exchange resin. The optimum parameters of the particular processes are determined. Sulfuric acid is weakly consumed and no liquid wastes are formed in the technology.

Представлены результаты исследований по разработке технологий утилизации кремнезолей, образующихся при переработке эвдиалитового концентрата методом сорбционной конверсии. В качестве перспективных направлений предложены и изучены: дополнительное извлечение содержащихся в кремнезолях ценных металлов сорбцией сульфокатионитом; разделение кремнезоля на обогащенный кремнеземом кремнегель и обедненный кремнеземом кислотный раствор последовательным замораживанием и размораживанием исходного кремнезоля; использование содержащегося в кремнезолях кремнезема для получения волластонита. Найдено, что из кремнезолей, полученных при 80 °С - оптимальной температуре разложения эвдиалитового концентрата методом сорбционной конверсии - сульфокатионитом может быть поглощено из содержащихся в кремнезолях, %: 58.6-70.3 Ti, 46-50 Zr, 24.7-29.9 Hf, 23.5-34.7 Nb; при этом натрий остается в кремнезоле. Низкая степень заполнения сорбционной обменной емкости сульфокатионита позволяет его дополнительно насыщать в процессе сорбционной конверсии. Показано, что в кремнегелях, полученных при последовательном замораживании и размораживании кремнезолей, концентрация SiO2 достигала 33.0 г/л. Удельная эффективная радиоактивность кремнегелей мала, что позволяет их использовать в производстве строительных материалов гражданского назначения. В обедненные кремнеземом кислотные растворы, объем которых составлял 72.5-81.2 % объема исходных кремнезолей, попадает до, %: 78.3 Ti, 56 Zr, 45.1 Hf, 76.4 Nb, 92.2 Na, 100 Th, 100 U и лишь 1.1-3.6 SiO2. Такие растворы после дополнительного укрепления пригодны для повторного использования для разложения эвдиалитового концентрата. Экспериментально доказана возможность получения волластонита из кремнезоля на основе азотнокислого раствора без использования автоклавного оборудования. Обсуждаются пути регенерации маточного раствора, полученного после осаждения прекурсора волластонита. The results of studies on the development of technologies for the utilisation of silica sols formed during eudialyte concentrate processing by means of sorption conversion are presented. As promising areas, the following directions have been proposed and studied: additional extraction of valuable metals from silica sols by sorption with sulphocationite; silica sol separation into silica-enriched silica gel and silica-depleted acid solution by successive freezing and thawing of the initial silica sol; the use of silica contained in silica sols to obtain wollastonite. The percentage of rare metals that can be absorbed by sulphocationite from silica sols obtained at a temperature of 80°C - the optimum temperature for the decomposition of eudialyte concentrate by sorption conversion - is found to be (%) 58.6-70.3 Ti, 46-50 Zr, 24.7-29.9 Hf, 23.5-34.7 Nb, while sodium remains in silica sol. The low degree of filling of the sorption exchange capacity of the sulphonic cation exchanger allows it to be additionally saturated in the process of sorption conversion. It is shown that the concentration of SiO2 reached 33.0 g/L in silica gels obtained by successive freezing and thawing of silica sols. The specific effective radioactivity of silica gels is low, which allows them to be used in the production of civil building materials. Acid solutions depleted in silica, the volume of which was 72.5-81.2 % of the volume of the initial silica sols, contain up to (%) 78.3 Ti, 56 Zr, 45.1 Hf, 76.4 Nb, 92.2 Na, 100 Th, 100 U, and only 1.1-3.6 SiO2. Such solutions after additional strengthening are suitable for reuse for the decomposition of eudialyte concentrate. The possibility of obtaining wollastonite from silica sol based on nitric acid solution without the use of autoclave equipment has been experimentally proven. The ways of regeneration of the mother liquor obtained after precipitation of the wollastonite precursor are discussed.

С целью развития технологии переработки эвдиалитового концентрата, основанной на применении метода сорбционной конверсии, исследованы закономерности извлечения металлов из насыщавшихся в процессе сульфокатионитов, а также регенерация сульфокатионита и используемых для десорбции растворов для повторного применения. Приведены составы насыщенных сорбентов, в которых содержатся щелочные (натрий, калий), щелочноземельные и редкоземельные металлы, титан, цирконий (гафний), ниобий (тантал), алюминий, железо, марганец, природные радионуклиды. Исследована десорбция различными растворами. Установлено, что наиболее трудно десорбируется ниобий (тантал). Рекомендовано проводить двухстадийную десорбцию при температуре 20 °С: сначала десорбцию раствором 5 М NaCl, при которой достигается перевод в раствор большинства содержащихся в сорбенте металлов, а затем десорбцию циркония и ниобия раствором 1 М Н2С2О4. Рассмотрены вопросы дальнейшей переработки полученных десорбатов. В соответствии с проведенными ранее исследованиями из десорбатов на основе раствора 5 М NaCl дробной нейтрализацией сначала до рН 4 осаждается и отделяется примесный кек, содержащий торий, железо, алюминий, титан, затем до рН 7.5 - концентрат редкоземельных элементов и, наконец, при рН ≥ 10 - щелочноземельные металлы и марганец. Из десорбатов на основе раствора 1 М Н2С2О4 нейтрализацией NaOH до рН 10 осаждается цирконий (гафний)-ниобиевый концентрат, из которого раствором Na2CO3 выщелачивается цирконий (гафний). Отмечено, что после десорбции раствором 1 М Н2С2О4 получается сорбент в Н+-форме, что позволяет его использовать повторно для разложения эвдиалитового концентрата методом сорбционной конверсии. Показано, что раствор 1 М Н2С2О4 может быть регенерирован методом электродиализа из раствора Na2С2О4, полученного при осаждении коллективного цирконий (гафний)-ниобиевого концентрата. In order to develop the technology of eudialyte concentrate processing based on the use of sorption conversion, the patterns of metal extraction from sulphocationites saturated in the process and the regeneration of sulphocationite and solutions used for desorption for reuse are investigated. The compositions of saturated sorbents containing alkaline metals (sodium, potassium), alkaline earth and rare earth metals, titanium, zirconium (hafnium), niobium (tantalum), aluminium, iron, manganese, natural radionuclides are presented. Desorption with various solutions is investigated. It is found that niobium (tantalum) is most difficult to desorb. It is recommended to carry out two-stage desorption at a temperature of 20 oC: at first, desorption with a 5 M NaCl solution, in which the majority of metals contained in the sorbent are converted into solution, and then desorption of zirconium and niobium with a 1 M Н2С2О4 solution. The issues of further processing of the obtained desorbates are considered. In accordance with previous studies, the impurity cake containing thorium, iron, aluminium, titanium is precipitated and separated from desorbates based on a 5 M NaCl solution through fractional neutralization, initially to pH 4, then the concentrate of rare earth elements is separated by neutralization to pH 7.5, and, finally, at pH ≥ 10, alkaline earth metals and manganese. Zirconium (hafnium) - niobium concentrate is precipitated from desorbates based on 1 M Н2С2О4 solution through neutralization with NaOH to pH 10, and then zirconium (hafnium) is leached from it using Na2CO3 solution. It is stressed that the sorbent in the H+-form is formed after desorption with a 1 M Н2С2О4 solution, which allows using it repeatedly to decompose eudialyte concentrate by sorption conversion. It is shown that the 1 M Н2С2О4 solution can be regenerated by electrodialysis from the Na2С2О4 solution obtained by precipitation of the collective zirconium (hafnium) - niobium concentrate.

The results of studies on the development of technologies for the utilisation of silica sols formed during eudialyte concentrate processing by means of sorption conversion are presented. As promising areas, the following directions have been proposed and studied: additional extraction of valuable metals from silica sols by sorption with sulphocationite; silica sol separation into silica-enriched silica gel and silica-depleted acid solution by successive freezing and thawing of the initial silica sol; the use of silica contained in silica sols to obtain wollastonite. The percentage of rare metals that can be absorbed by sulphocationite from silica sols obtained at a temperature of 80 C-degrees - the optimum temperature for the decomposition of eudialyte concentrate by sorption conversion - is found to be (%) 58.6-70.3 Ti, 46-50 Zr, 24.7-29.9 Hf, 23.5-34.7 Nb, while sodium remains in silica sol. The low degree of filling of the sorption exchange capacity of the sulphonic cation exchanger allows it to be additionally saturated in the process of sorption conversion. It is shown that the concentration of SiO2 reached 33.0 g/L in silica gels obtained by successive freezing and thawing of silica sols. The specific effective radioactivity of silica gels is low, which allows them to be used in the production of civil building materials. Acid solutions depleted in silica, the volume of which was 72.5-81.2 % of the volume of the initial silica sols, contain up to (%) 78.3 Ti, 56 Zr, 45.1 Hf, 76.4 Nb, 92.2 Na, 100 Th, 100 U, and only 1.1-3.6 SiO2. Such solutions after additional strengthening are suitable for reuse for the decomposition of eudialyte concentrate. The possibility of obtaining wollastonite from silica sol based on nitric acid solution without the use of autoclave equipment has been experimentally proven. The ways of regeneration of the mother liquor obtained after precipitation of the wollastonite precursor are dis-cussed.

The results of research on the development of the scientific foundations of the complex technology of processing Lovozersky eudialyte concentrate are summarized. The features of the concentrate composition are reported. The regularities of concentrate decomposition by sorption conversion with low-concentration solutions of mineral acids, desorption of metals from sulfocationite, stepwise hydrolytic deposition from eluates of concentrates of rare elements, the use of silicic acid transferred to solutions with simultaneous recirculation of acid solutions were studied. The outlines of the technology of complex processing of eudialyte concentrate are outlined, which provides for the production of concentrates of rare metals and the use of the main part of the silica and alkali metals contained in the concentrate.

A technology is proposed for processing of apatite concentrates by decomposition by phosphoric acid at 20°C in the presence of a sulfonic cation-exchange resin, defluorination of the obtained phosphoric acid, desorption of the sorbed cations with concentrated solutions of alkali metal salts, sequential hydrolytic precipitation of the thorium-enriched impurity cake and nonradioactive concentrate of carbonates of rare-earth and alkaline-earth elements, and regeneration of the sulfonic cation cation-exchange resin from the Na + form to the H + form. It is shown that the technology is also applicable for the processing of apatite concentrate with a high content of rare-earth elements and strontium. The technology ensures the recovery of all valuable components into commercial products while minimizing the consumption of reagents and energy, the amount of generated waste, and the environmental pollution.

Abstract—A technology is proposed to process ancylite-containing raw materials—ore or concentrate. The technology is based on their decomposition with 1 wt

It is proposed to process a titanium magnetite concentrate containing an increased concentration of titanium dioxide by 2–4 wt. % sulfuric acid solution in the presence of sulfocationite. Under optimal conditions, 85–87 % of the concentrate decomposes and ilmenite-based residues with an increased titanium content are obtained. The main part of the dissolved iron, titanium and vanadium is absorbed by the sorbent.

Представлены результаты исследований по переработке эвдиалитового концентрата с применением метода сорбционной конверсии, в котором концентрат разлагается разбавленными растворами минеральных кислот в присутствии сульфокатионита с получением насыщенного металлами сорбента и кремнезёмсодержащих кислотных растворов. Определены оптимальные составы используемых для разложения концентрата кислотных растворов и условия разложения, обеспечивающие высокое извлечение в сорбент редких металлов. Предложена схема переработки сорбентов с получением отдельных нерадиоактивных концентратов редких элементов: РЗЭ, циркония (гафния) и ниобия. Предложены методы утилизации кремнезёмсодержащих кислотных растворов, позволяющие использовать для получения товарной продукции значительной части нередкометалльных компонентов концентрата, в особенности кремнезёма и щелочных металлов, регенерировать для повторного использования растворы минеральных кислот. Исследовано поведение радионуклидов эвдиалитового концентрата. Обсуждаются преимущества изученной технологии. Монография адресована инженерно-техническим работникам химической и металлургической промышленности, научным работникам, предпринимателям, интересующимся проблемами получения редких металлов из минерального сырья. Она может оказаться полезной для обучающихся по соответствующим направлениям студентов высших учебных заведений.

The influence of the sorption conversion conditions for the eudialyte concentrate in low-concentration nitric and hydrochloric acid solutions (concentration and consumption of acid, temperature and duration of the process, sorbent consumption) on the valuable metals extraction efficiency (zirconium, hafnium, niobium, rare earth elements, titanium, manganese) into sulphocationite was studied. Optimal conditions for the process have been determined. It has been shown that sorption conversion in nitric acid solutions is more effective for separating valuable components from the silica component of eudialyte concentrate compared to both the traditional method decomposition by nitric acid and the method of sorption conversion in sulfuric and hydrochloric acid environments. The reasons for the loss of valuable metals and the behavior of natural radionuclides are discussed.

In order to develop the technology of eudialyte concentrate processing based on the use of sorption conversion, the patterns of metal extraction from sulphocationites saturated in the process and the regeneration of sulphoca-tionite and solutions used for desorption for reuse are investigated. The compositions of saturated sorbents con-taining alkaline metals (sodium, potassium), alkaline earth and rare earth metals, titanium, zirconium (hafnium), niobium (tantalum), aluminium, iron, manganese, natural radionuclides are presented. Desorption with various solutions is investigated. It is found that niobium (tantalum) is most difficult to desorb. It is recommended to carry out two-stage desorption at a temperature of 20 degrees C: at first, with a 5 M NaCl solution, in which the majority of metals contained in the sorbent are converted into solution, and then desorption of zirconium and niobium with a 1 M H2C2O4 solution. The issues of further processing of the obtained desorbates are considered. In accordance with previous studies, the impurity cake containing thorium, iron, aluminium, titanium is precipitated and sepa-rated from desorbates based on a 5 M NaCl solution through fractional neutralization, initially to pH 4, then the concentrate of rare earth elements is separated by neutralization to pH 7.5, and, finally, at pH >= 10, alkaline earth metals and manganese. Zirconium (hafnium) - niobium concentrate is precipitated from desorbates based on 1 M H2C2O4 solution through neutralization with NaOH to pH 10, and then zirconium (hafnium) is leached from it using Na2CO3 solution. It is stressed that the sorbent in the H+-form is formed after desorption with a 1 M H2C2O4 solution, which allows using it repeatedly to decompose eudialyte concentrate by sorption conversion. It is shown that the 1 M H2C2O4 solution can be regenerated by electrodialysis from the Na2C2O4 solution obtained by precipitation of the collective zirconium (hafnium) - niobium concentrate.

A new method of purification of rough sphene concentrate from phosphorus impurities has been developed, based on its treatment with low-concentrated solutions of orthophosphoric or sulphuric acids in the presence of sulphocationite. It is shown that this method provides effective purification of sphene concentrate and makes it possible to increase the efficiency of the technology through significant reduction of the consumption of acids, elimination of the formation of liquid waste, and due to the possibility of using aluminium, which is formed during the decomposition of nepheline contained in the initial concentrate.

A new technology has been considered to process monazite concentrate by treating it by a phosphoric acid solution in the presence of strong acid cation exchange resin. The end products are a carbonate of hydroxide concentrate of rare-earth elements (REEs), orthophosphoric acid, and thorium concentrate.

This paper summarizes the findings of the research aimed at the development of a new method for the integrated processing of naturally occurring and anthropogenic rare-earth raw materials based on the decomposition of rare-earth element (REE) concentrates in the presence of sulfocationite. Sorption and desorption of REE cations on a strongly acidic ion exchanger, sorbent regeneration, and REE recovery from eluates are discussed. A virtually zero-waste integrated process for apatite concentrate is proposed. The generalization of the research findings is aimed at demonstrating the prospects and universality of the proposed resource-saving and environmentally safe approach to the processing of various types of naturally occurring and anthropogenic rare-earth mineral feeds. The new methodology made it possible to develop a number of new hydrochemical processes united by a single approach, providing a qualitative increase in the processing performance of various types of rare-earth mineral feeds. The theoretical foundations of a unified approach to the processing of a wide range of minerals can significantly accelerate and cheapen the implementation of specific process circuits, significantly reduce reagent consumption and waste generation, simplify the separation of rare earth elements and impurities, and the separation of rare earth elements from naturally occurring radionuclides, fluorine, and phosphorus. The study was funded by the Kolarctic CBC 2014-2020 program, Project KO1030 SEESIMA — Supporting Environmental Economic and Social Impacts of Mining Activity.

The decomposition of eudialyte concentrate was studied by means of sorption conversion in the 2 mass % solution of sulphuric acid. It was shown that eudialyte decomposes at a temperature of 80 degrees C with the formation of silica gel, while silica sol is formed at 20 degrees C. The efficiency of the sorption of refractory rare elements by the sorbent in the mode of silica sol formation increased in comparison with the mode of silica gel formation from 52.5 to 89.4 for zirconium, from 60.1 to 89.2 for hafnium, from 7.4 to 85.1 for niobium, from 0 to 67.1 for tantalum, from 27.6 to 80.0 for titanium. respectively, with the provision of a high degree of extraction of rare earth elements (REE) - 82.9 To, including REE of yttrium and medium groups up to 86-89 %. The major part of the losses of niobium, tantalum, titanium and REE is determined by their inclusion in loparite and other accessory minerals that are untreatable under the studied conditions. It is assumed that a substantial increase in the sorption of rare elements of IV and V groups at 20 degrees C (in comparison with the results obtained at 80 degrees C) is due not only to the formation of silica sol but also to a decrease in the hydrolysis of the cations of these metals with the formation of their forms that are not sorbed by the sulphocationite. The features of decomposition of the eudialyte concentrate by the low-concentrated solutions of nitric and sulphuric acids were compared. The reasons providing the formation of silica sol during the low-temperature sulphuric decomposition of eudialyte are discussed. It is stressed that the studied method may be the basis of an efficient technology of eudialyte concentrate processing because the application of this method results in a decrease in acid consumption by a factor of 3-5 in comparison with traditional acid procedures. As a consequence, the amount of liquid wastes subjected to utilization is reduced, the effective specific radioactivity of the silica residue and the consumption of energy resources decrease.

The nitric acid decomposition of an eudialyte concentrate by sorption conversion is studied. This method is based on the interaction of the concentrate with a low concentrated solution of HNO3 in the presence of sulfonic cation-exchange resin. During sorption conversion, the target metals are predominantly sorbed by a sorbent, which is easily separated from the solution and silica gel-containing residues. When the solution containing 2% HNO3 is used, the extraction of rare elements is comparable and the acid consumption is 6–8 times lower than that in the case of the traditional decomposition of an eudialyte concentrate using concentrated nitric acid. The procedure simultaneously produces a nonradioactive silica gel product appropriate for the production of qualitative building materials. The possibility of the further increase in the degree of extraction of rare elements is discussed. A route for the processing of the sorbent saturated with rare metals is proposed to produces salt concentrates of these elements.

The aim of the work is the continuation of the development of a new efficient hydrochemical technology for the processing of apatite concentrate, which makes it possible to produce phosphoric acid with a reduced content of impurities as a product, to use all the valuable components of apatite concentrate. The dependence of the efficiency of decomposition of apatite concentrate with a phosphate acid solution at a temperature of 20 and 50 °C in the presence of sulfate cationite КУ-2-8чС in Na+- and K+ - forms was studied. The influence of the decomposition conditions (expense and form of sorbent, the ratio of liquid: solid, the interaction temperature) on the degree of decomposition of the concentrate, the completeness of absorption by the sorbent of the metallic cations of the concentrate, the content of impurities in the resulting phosphate-acid solution, and the composition of undissolved residues are studied. The possibility of achieving a high degree of decomposition of the concentrate (up to 99.5 %) is established. High sorption efficiency of calcium and strontium (up to 90.2 and 93.4 % respectively) is shown. The sorption of REE of the cerium group was better than the REE of the middle and yttrium groups. Increasing the temperature from 20 to 50 °C reduced REE sorption by 14-170%. Aluminum, thorium and uranium were the most difficult to sorb. It has been found that effective purification of phosphoric acid from the impurity of fluorine is achieved directly in the process of decomposition. The efficiency of purification from fluorine when using a sorbent in the K+ - form is greater than when using a sorbent in the Na+- form. It is shown that the obtained acid can be purified from sodium or potassium by the electrodialysis method in a two-chamber electrodialyzer equipped with a cation exchange membrane. It is found that before electrodialysis, preliminary purification of the phosphate solution from calcium, which is obtained during the decomposition of apatite concentrate, is necessary. To this purpose, an additional purification of the phosphoric acid solution by sulphocathionite sorption has been investigated. The lower sorption from the phosphoric acid solution of Al, Ti, Fe, Th, and U is explained by the formation of stable anionic complexes or undissociated molecules by these elements. The developed technology for the production of phosphoric acid from the apatite concentrate does not require the use of sulfuric acid, has a number of other advantages. The content of impurities in the resulting phosphoric acid is much less than in the extraction phosphoric acid produced by the sulfuric acid processing of apatite concentrate.

The possibility of using sorption by sulfocationite in order to extract zirconium from nitrate and sulfuric acidic solutions has been shown. The sorption of zirconium from sulfuric solutions is much more effective than from nitrate solutions. Zirconium can be desorbed by concentrated solutions of ammonium salts; at the same time, ammonium sulfate is a more effective desorbing solution when compared with ammonium nitrate. The acidification of desorbate based on ammonium nitrate decreases the efficiency of the desorption of zirconium.