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Geochemistry journal homepage: www.elsevier.com/locate/chemer
Geochemical aspects of the mining and processing of the large-tonne mineral resources of the hibinian alkaline massif V.M. Sizyakova, R. Kawallab, V.N. Brichkina,
Sankt-Petersburg Mining University, St Petersburg, Russia TU Bergakademie Freiberg, Germany
Handling Editor: Astrid Holzheid
This article presents an analysis of the influences of nature and production factors relating to the chemicalmineralogical composition of products that formed at the stages of mining and processing apatite-nepheline ores in the Khibiny Mountain Massif. It is shown that all main production processes are connected to the formation of dump waste products that are subject to further changes under the influence of exogenous factors, which include conditions of outdoor storage in dumps and sludge accumulators. According to the dead tails (stale tails) of apatite production, the characteristic changes in the chemical-mineralogical composition and grain-size distribution are determined and have a significant effect on the indicators of their mineral processing. The experimental study of dead tails includes processing a set of technological operations, and their flowsheets are also determined. These flowsheets provide a nepheline concentrate of the required composition with indicators no worse than when processing the tailings of the current composition. It is shown that the existing flowsheets for apatite or nepheline concentrate processing lead to the accumulation of significant amounts of mulls associated with the separation of less valuable components of raw materials into the dump waste products, including calcium and silica. The experimental work also demonstrates the conversion process of gypsum wastes produced during the production of phosphoric acid and shows the importance of additional hydrochemical treatment of belite mull to achieve an economically justified ratio of the main and by-products in the processing of aluminosilicate raw materials.
Keywords: Alkaline aluminosilicates Apatite-nepheline ores Concentrates Enrichment Processing Waste products Geochemical regularities Ecology
1. Introduction The Khibini Mountains alkaline massif, or Khibini tundras, from the Sami word “tundr” which means massif upper forest belt, is a wellknown and detailed geological formation. The Khibini Mountains alkaline massif is located far beyond the Arctic Circle in the centre of the Kola Peninsula. From the north, east and south the Khibini Mountains alkaline massif is surrounded by the Barents Sea and White Sea, and in the west, it surrounded by Norway and Finland (Voytekhovsky et al., 2014). Geologically, Khibiny is a multiple-phase intrusive massif with an area of 1327 km2, which formed approximately 350 million years ago. Khibiny consists of nepheline syenites of different compositions and geological structures that crystallized from magmas penetrating through conical faults. Rock complexes nested into each other in the form of arcs open to the east and determined the style of the geological map (Voytekhovsky et al., 2014). Magmatism ended with the emplacement of the dikes of phonolites and tinguaites into the faults, which
caused a large variety of minerals giving world-wide fame to the Khibiny alkaline massif. Of the approximately 4000 known minerals on Earth, more than 1000 occur here, of which a total of 115 are described for the first time. This number of minerals is a world record for one geological site. The industrial importance of the Khibiny region is determined by the unique combination of the minerals in alkaline rocks and favourable geographic position. In the first instance, this unique combination is due to the extraction and processing of apatite-nepheline ores, which began in 1929 and continue to present day (Glubokyi, 2014). At the same time, the ongoing mining operations and associated industrial technologies are comparable in scale to geological processes, and considering existing transport links, cover significant areas of the northwest of Russia. These activities cause a significant redistribution of elements and lead to the formation of new technogenic objects with geochemical regularities. The study of the new technogenic objects is an integral part of the work to improve the regional ecological situation, based on effective technological solutions for the prevention of
Corresponding author. E-mail addresses: [email protected]
(V.M. Sizyakov), [email protected]
(R. Kawalla), [email protected]
https://doi.org/10.1016/j.chemer.2019.04.002 Received 1 June 2018; Received in revised form 11 April 2019; Accepted 12 April 2019 0009-2819/ © 2019 Published by Elsevier GmbH.
Please cite this article as: V.M. Sizyakov, R. Kawalla and V.N. Brichkin, Geochemistry, https://doi.org/10.1016/j.chemer.2019.04.002
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generation and processing of accumulated waste. The existing flow of mining and treatment of apatite-nepheline ores includes a number of industries, each of which is associated with geochemical changes in natural and man-made formations, including the formation and accumulation of industrial wastes. The change that occurs at the mining step is the accumulation of overburden in dump storages. The overburden amount is determined by the overburden ratio. Usually, the overburden amount is more than the volume of mined ore. It is clear that the extracted rock is subject to exogenous processes under the conditions of the Earth's surface and is a potential source of drift of the most mobile elements (Yevdokimov et al., 2011). The resulting overburden in the future is considered a raw material for the production of alumina and by-products because it is predominantly composed of ijolite-urtites (Bazhin et al., 2017). More complex and dynamic processes occur at the stage of apatitenepheline ore processing, which is due to the grinding and the implementation of a number of separation processes that provide the production of apatite concentrate with a recovery of 32%. The remaining rock mass, representing the tails of apatite production, enters the sludge collectors. These tails are now partially subjected to additional enrichment to produce a nepheline concentrate suitable for the production of alumina and by-products. According to experts, in the long term, this waste will become a notable source of aluminium, alkaline batteries, and other products. It is well known that profound changes occur at the stage of chemical treatment of apatite concentrate, while the corresponding chemical plant may be located at a considerable distance from the processing factory of apatite ore. The main technological process of apatite treatment is an acid decomposition with nitric or sulfuric acid. At reaction of apatite matter with sulfuric acid during the production of phosphoric acid using the dihydrate method:
CaSO4(sol) + H3PO4(sol) + 2NH3(g) + хH2O(l) = CaHPO4·xH2O(s) + (NH4)2SO4(sol); Al2(SO4)3(sol) + 2H3PO4(sol) + 6NH3(g) = 2AlPO4(s) + 3(NH4)2SO4(sol); Fe2(SO4)3(sol) + 2H3PO4(sol) + 6NH3(g) = 2FePO4(s) + 3(NH4)2SO4(sol). which makes it possible to obtain chemically precipitated calcium carbonate and a solution of ammonium sulfate, suitable for its precipitation by the method of polyhydric crystallization. In this paper, technical waste utilization will be described and possibilities to include those wastes into the production sequence will be discussed. 2. The method The main part of the paper is devoted to the technical treatment of the alumina-silicate raw material, thus different kinds of alumina-silicate raw materials were chosen for the investigation. The analysis of the chemical and mineralogical compositions was carried out in analytical centre of mining university by a tow of X-ray fluorescence spectral and X-ray spectral methods. This combination of these methods of analysis allow the establishment the phase composition of the samples and the distribution of the elements in separate phases. For X-ray fluorescence spectral analyses, the XRF spectrometers Epsilon 4 PANalytical and XRF -1800 Shimadzu were used, and for XRD-analysis, the XRD-6000 (Shimadzu) was used. The sampling of dead tails was prepared by the Kola Mining Company by drilling the tail field in accordance with the manufacturing methodology. The sample weighed approximately 200 kg. The laboratory investigation involved grain-size analysis using a laser analyser of particle size distribution, the Horiba LB-550, and the chemical analysis of the composition, especially for the following oxides: SiO2, Al2O3, TiO2, P2O5, CаO, MgO, Na2O, and К2O. The content of hygroscopic moisture ranging from 5 to 14% was performed by the gravimetric method using a moisture analyser MOC – 120 H (Shimadzu). The main purpose of this investigation was to obtain data about the coarse grain size, mud fraction, and element distribution between these samples. In addition, several types of nepheline ore concentrates were investigated. These concentrates were obtained after the flotation of apatite-nepheline ores, which were either collected in the vicinity of the mineral processing factory or from dead tails treatment. One of the materials that was given special interest in the study was potassium-enriched alkaline aluminosilicate ores, named Rischorrit, located in the primary location on Mount Rischorr. The bedding of these ores is revealed near the existing mining enterprises and even adjacent to mining enterprises. Rischorrites are massive, grey-green rocks consisting mainly of large crystals of feldspar, nepheline, with an admixture of coloured minerals - egirine-augite, mica, astrophyllite, enigmatite, sphene and lamprophyllite. In the process of a drilling test, rischorrit samples were selected from the explored and processed apatite-nepheline deposits of Kukisvumchorr, the Sami quarry, Gakman gorge, the Rasvumchorr plateau. Phosphogypsum, a by-product of phosphoric acid production, contains 92% of gypsum. It should be noted that in phosphogypsum contains from 0.4 to 0.6% rare Earth element oxides, including the most valuable neodymium, samarium, terbium, ytterbium, erbium, and dysprosium. Table 1 presents the chemical composition of phosphogypsum obtained during processing of apatite concentrate.
Ca3(PO4)2 + 3H2SO4 + 2H2O = 3CaSO4⋅2H2O + 2H3PO4 A significant amount of gypsum waste is produced. In the dumps of each plant, 10–12 million-ton phosphogypsum accumulate, the amount of which continues to increase by 0.81 million tons per year. A similar situation exists in any phosphate fertilizer plants. The world accumulation of such wastes exceeds 170 million tons/ year, and their utilization is one of the most serious problems in the chemical industry. In worldwide practice, there are known technologies for the conversion of phosphogypsum to ammonium sulfate and calcium carbonate, developed by OSAG (Austria), FACT (India), Maru-beni Jida (Japan), TVA (USA) and Continental Engineering. Most of the implemented flowsheets based on the so-called” fluid” method, which includes the stage of conversion and maturation of carbonate pulp in cascaded reactors as the main technological process (Sizyakov et al., 2012). A number of chemical interactions occur, which include the formation of ammonium carbonate: 2NH3(g) + CO2(g) + H2O(l) = (NH4)2CO3(sol), reactions of gypsum with ammonium carbonate: CaSO4·2H2O(s) + (NH4) (NH4)2SO4(sol) + 2H2O(l);
2CO3(sol) = CaCO3(s) +
CaSO4·0,5H2O(s) + + 0,5H2O(l);
= CaCO3(s) + (NH4)2SO4(sol)
and reactions with residual phosphoric acid: Ln2(SO4)3(sol) + 2H3PO4(sol) + 6NH3(g) + 2хH2O(l)=2LnPO4·xH2O(s) + 3(NH4)2SO4(sol);
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Table 1 Chemical composition of phosphogypsum obtained during processing of apatite concentrate of Kola and Kovdor deposits. Apatite deposit
Chemical composition, % CаO
0.50-0.06 0.14- 0.15
– 0.03- 0.08
3. Results and discussion The possibility of involving the apatite producing dead tails in the production cycle was investigated using a canned tailing dump that formed during the work of the apatite-nepheline processing factory (ANPF-1) in 1930–1940 and 1950–1969. According to preliminary estimations, the total volume of the field is approximately 40–50 million tons. By technological origin, the mineral mass is the flotation tails from apatite-nepheline ore processing, and geographically, it is located in the valley of the Belaya River between the cities of Apatity and Kirovsk in the Murmansk region. The sample analysis of dead tails indicates that is the main part of minerals exist in an open state. The fraction of crystalline aggregate is not more than 7%, and the main part of crystalline aggregate is a submicroscopic aggregate of nepheline and aegirine. The main fraction of aegirine beans both free and as an aggregate with nepheline cover a size grade of −200 + 125 μm and -100 + 63 μm. Sphene in the form of almost completely opened beans is concentrated in fraction -200 + 125 μm and with a decrease in the grain-size to –63 + 40 μm, the portion of dark-coloured minerals increases due to the increasing content of aegirine and titanomagnetite. The quantity of the fine fraction (dust-like) −100 + 63 μm of dead tails ranges from 65 to 70%. The mineral composition identification of this fraction is very difficult. This difficulty is the result of the destruction and intensive changes (oxidation, sericitization, and zeolitization) of all the available minerals with conversion into thin-scale, clay-hydromic aggregates together with zeolites (Yevdokimov et al., 2011). The large-size −200 + 125 μm fraction mainly includes fragments of nepheline, with the development of secondary mineral formation of cancrinite, sericite and zeolites, which, in a large number of cases, almost completely replaces nepheline. Single grains of nepheline, overcrowded with micro-inclusions of aegirine, are also noted. In addition to nepheline, and its effects in a large-size fraction, there are free grains of intensely altered feldspars and individual grains of apatite and sphene. There are crystalline aggregates of aegirine with biotite and free inclusions of aegirine beans, as well as its aggregates with feldspar over cleft cleavage cracks. Consequently, fractional and mineralogical-petrographic analysis testifies to extremely unfavourable characteristics of the sample associated with the development of exogenous processes in the tailings mineral mass of apatite production. As consequence, there is an increase in the fine fractions and a redistribution of the constituent composition, which contributes to significant losses of P2O5 and A12O3 during desliming, in both the -40 μm and−20 μm types. The obtained results allow for the specification of the requirements for the ore preparation and the correction of the reagent consumption considering the increased specific surface area of the mineral mass. (Sizyakov et al., 2016) studied the production of nepheline concentrate from the old tailings of apatite production using a standard set of
Fig. 1. Qualitative-quantitative scheme for obtaining nepheline concentrates from dead tails of apatite-nepheline ore flotation.
techniques and laboratory equipment, which allowed substantiating the following qualitative and quantitative schemes for obtaining nepheline concentrate that agree with the requirements of the existing metallurgical complex, Fig. 1. Nepheline ore concentrate obtained from the flotation of components of apatite-nepheline ore, and subsequent processing of dead tails of apatite production, is a valuable raw material for the production of alumina, soda, gallium, and Portland cement. At the same time, the process of high-temperature sintering of limestone-nepheline charge used as the leading technological process, which describes in the first approximation by the following reaction: Na2O⋅Al2O3⋅2SiO2 + 4(CaO⋅CO2) = Na2O⋅Al2O3 + 2(2CaO⋅SiO2) + 4CO2.
The cake leaching leads to the separation of valuable components from raw materials (alkali metals and aluminium) in the form of watersoluble sodium aluminate (potassium) and practically insoluble calcium orthosilicate. The last component is used for Portland cement production. It should be note that not only the nepheline concentrates but also other rocks of the Khibiny massif could be a valuable raw material for this technology, which at this time will be considered as ore material. Mineralogical analysis of samples indicates they are composed mainly from the following minerals; nepheline, kalsilite, potassium feldspar and aegirine. The comparative mineralogical characterization of aluminosilicate raw materials of a different mineralogical composition is given in Table 2 (Gorbunova et al., 2011; Bazhin et al., 2017). It is clear that the content of alumina in the feedstock and the molar ratio of SiO2/Al2O3 are very important for achieving high parameters of this technology, especially the factors that determine the amount of Portland cement clinker that formed during the white sludge utilization. In the first approximation, the amount of clinker of alitic composition determined by the following stoichiometry: 2CaO⋅SiO2 + CaO⋅CO2 = 3CaO⋅SiO2 + CO2,
which is an economically justified technical solution (Sizyakov
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Table 2 Chemical composition of alumina-silicate raw materials of the Khibiny massif valuable for the alumina production. Name
Mass fraction of a component in oxide form, %
Nepheline ore concentrate Urtite Rischorrite
Molar ratio of component oxides
Na2O+K2O Al2 O3
Fe2 O3 Al2 O3
28.5 21.06 22.10
45.3 42.0 47.0
2.56 5.40 5.00
0.81 6.1 4.0
12.3 10.4 8.8
8.49 5.30 9.80
1.03 1.09 1.14
2.68 3.39 3.62
0.06 0.16 0.14
et al., 2017). Nepheline slurry is used as a raw mix component for Portland cement production due to the considerable chemical, mineralogical and grain-size composition properties of this material for clinker formation because of their formation at the stage of alumina production. Such a process of alkali alumina-silicates treatment with the production of alumina and Portland cement clinker directly affects the amount of byproducts produced per 1 ton of alumina. Fig. 2 shows the dependence of the theoretical yield of Portland cement clinker with alite composition on the Al2O3 content in the feedstock. The first and last points of the lines on Fig. 2 are calculated with reference to the processing of nepheline and albite of the theoretical composition, determining the yield of slime of the belitic composition according to reactions (1) and (3), alite by reaction (2):
SiO2 = 3, and the theoretical degree of conversion of CaO to the compound not containing SiO2 is 1/3 or 33.3%. Thus, the need to add additional amounts of limestone is eliminated, and accordingly, the yield of clinker decreases, which makes the processing of the alumina-silicate raw materials less dependent on Portland cement consumers. The dependencies shown in Fig. 2 allow us to set tasks aimed at increasing the Al2O3 content in the feedstock via the extraction and conversion processing of belite sludge. Experienced industrial tests of the technological conversion of phosphogypsum to produce calcium carbonate and ammonium sulfate at JSC (PhosAgro-Cherepovets) showed the possibility of achieving the required values for the degree of conversion of gypsum to final products of a specified composition, as in Table 3. The analysis of the obtained results show the concentration of all the rare-earth elements in the conversion chalk, which makes it available for extraction. The mass fraction of calcium carbonate in the conversion chalk equals 95–96 %. The high dispersion of the chalk, with an average particle diameter ringing from 16 to 17 μm, allows the user to consider this product an available material for liming the soil and as a reagent for a number of chemical and metallurgical processes, including the production of alumina, Portland cement, and other many products. It is not difficult to assess the additional effects arising from the regeneration of the lime component by the technology of the conversion processing of phosphogypsum and nepheline sludge. In the first case, we propose replacing natural limestone with chemically obtained calcium carbonate in agriculture and chemical-metallurgical technologies, which makes complete use of the elements in the composition of apatite concentrate. In the second case, the need for lime materials (natural limestone or artificially derived carbonate materials) is reduced; therefore, carbon dioxide emissions into the atmosphere are reduced, which in accordance with equations 1 and 2, are at least 2.6 tons per 1 ton of Al2O3.
Na2O⋅Al2O3⋅6SiO2 + 12(CaO⋅CO2) = Na2O⋅Al2O3 + 6(2CaO⋅SiO2) + 12CO2. (3) The dashed line shows the plant composition of the nepheline concentrate with an Al2O3 content of 28.5%. Line 3 was calculated by taking into account the increase in the lime module of nepheline sludge to alite composition with the SiO2 separation as an individual product by the reaction: 2CaO⋅SiO2 = [2/3(2CaO⋅SiO2) + 2/3CaO] + 1/3SiO2.
In this case, the lime-containing residue has a molar ratio of CaO/
4. Conclusions 1 The extraction and complex processing of apatite-nepheline is an important factor in the redistribution of elements in the Earth’s crust under the influence of natural and production factors that lead to the accumulation of less valuable components of the raw materials in the form of gypsum and silicate sludges with the formation of new technogenic deposits. 2 Under the influence of exogenous factors, the mineral components of waste apatite-nepheline ore beneficiation products undergo significant destructive and intensive alteration of all the available minerals into fine-scale clay-hydromyous aggregates together with
Fig. 2. Theoretical yield of alumina clinker: 1 – per 1 ton Al2O3 in raw material; 2 - during through extraction Al2O3 85%; 3 – per 1 ton Al2O3 in the feedstock, taking into account the production of a one-component raw meal.
Table 3 The content of impurities in the chemically precipitated chalk during the liquid conversion of gypsum from the processing of the Kola apatite concentrate. Component
Conversion chalk Component Conversion chalk Component Conversion chalk
< 0.01 Y% 0.011 ± 0.002 Lu % < 0.001
< 0.0001 Ce % 0.27 ± 0.03 Nd % 0.031 ± .0.005
0.014 ± 0.003 Dy % 0.0026 ± 0.005 Pr % 0.016 ± 0.003
0.32 ± 0.04 Gd % 0.018 ± 0.004 Sm % 0.005 ± 0.001
< 0.001 Er % < 0,001 Tb % < 0.001
< 0.001 Eu % 0.0020 ± 0.005 Tm % < 0.001
2.0 ± 0.2 Ho % < 0,001 Yb % < 0.001
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zeolites. This alteration causes a noticeable increase in the share of difficult to diagnose small fractions and the redistribution of the component composition with significant losses of P2O5 and А12O3 during desliming. 3 Despite the negative changes that occur with the dump products of apatite production under the influence of endogenous factors and the high thermodynamic strength of slurries for the chemical and metallurgical processing of apatite and nepheline concentrates, there are acceptable technological solutions for their processing and for the reduction in the environmental load associated with the large-tonnage of technogenic formations.
treatment of a nepheline charge using additives of natural and technogenic origin. Metallurgist 1 (61), 147–154. Glubokyi, S.S., 2014. Correction of the strategy of geological study of reserves of apatitenepheline ores of the Khibiny massif in connection with intensive development of deep horizons of deposits. Min. J. 10, 25–27. Gorbunova, Е.S., Zaharov, V.I., Alishkin, А.R., 2011. Chemical-processing technology of complex processing of Riccorrites. Obogaschenie Rud 4, 12–16. Sizyakov, V.M., Nutrihina, S.V., Levin, B.V., 2012. Integrated technology phosphogypsum processing conversion method with ammonium sulfate, phosphomel and new products. Lournal Min. Inst. (197), 239–244. Sizyakov, V.M., Nazarov, U.P., Brichkin, V.N., Sizyakova, E.V., 2016. Enrichment of the stale tails of flotation of apatite-nepheline ores. Obogaschenie Rud 2, 33–40. Sizyakov, V., Brichkin, V., Litvinova, T., Kurtenkov, R., 2017. Lime component regeneration and recycling in chemical-metallurgical technologies, international multidisciplinary scientific GeoConference surveying geology and mining ecology management. SGEM 17 (41), 185–192. Voytekhovsky, Y.L., Peter Johansson, P., Lauri, L.S., Miroshnichenko, T.A., Raisanen, J., 2014. Khibiny Tundra. Geological Outdoor Map and Guidebook. AO «Grano» 56 P. http://geoksc.apatity.ru/images/stories/Print/ABCG/Khibiny%20large%20pdf.pdf. Yevdokimov, G.A., Gershenkop, A.S., Mozgova, N.P., Fokina, N.V., 2011. Biogenic destruction of aluminium-containing minerals on the example of nepheline and kyanite. Non-Ferrous Met. 11, 13–16.
Acknowledgement The study carried out with the financial support of the Ministry of Education and Science of the Russian Federation (registration number of the project 11.4098.2017 / PP (ПЧ) of 01.01.2017). References Bazhin, V.Y., Brichkin, V.N., Sizyakov, V.M., Cherkasova, M.V., 2017. Pyrometallurgical