minerals Article Titanite Ores of the Khibiny Apatite-Nepheline- Deposits: Selective Mining, Processing and Application for Titanosilicate Synthesis Lidia G. Gerasimova 1,2, Anatoly I. Nikolaev 1,2,*, Marina V. Maslova 1,2, Ekaterina S. Shchukina 1,2, Gleb O. Samburov 2, Victor N. Yakovenchuk 1 and Gregory Yu. Ivanyuk 1 1 Nanomaterials Research Centre of Kola Science Centre, Russian Academy of Sciences, 14 Fersman Street, Apatity 184209, Russia; [email protected] (L.G.G.); [email protected] (M.V.M.); [email protected] (E.S.S.); [email protected] (V.N.Y.); [email protected] (G.Y.I.) 2 Tananaev Institute of Chemistry of Kola Science Centre, Russian Academy of Sciences, 26a Fersman Street, Apatity 184209, Russia; [email protected] * Correspondence: [email protected]; Tel.: +7-815-557-9231 Received: 4 September 2018; Accepted: 10 October 2018; Published: 12 October 2018 Abstract: Geological setting and mineral composition of (apatite)-nepheline-titanite ore from the Khibiny massif enable selective mining of titanite ore, and its processing with sulfuric-acid method, without preliminary concentration in flotation cells. In this process flow diagram, titanite losses are reduced by an order of magnitude in comparison with a conventional flotation technology. Further, dissolution of titanite in concentrated sulfuric acid produces titanyl sulfate, which, in turn, is a precursor for titanosilicate synthesis. In particular, synthetic analogues of the ivanyukite group minerals, SIV, was synthesized with hydrothermal method from the composition based on titanyl-sulfate, and assayed as a selective cation-exchanger for Cs and Sr. Keywords: apatite-nepheline-titanite ore; sulfuric-acidic decomposition; titanyl sulfate; hydrothermal synthesis; ivanyukite 1. Introduction The world largest apatite-nepheline deposits of the Khibiny massif (NW Russia) host complex ores containing five economic minerals are: Fluorapatite, nepheline, titanite, aegirine and titanomagnetite. However, at present, only two of them (fluorapatite and nepheline) are economically attractive, while the rest are accumulated in tailings ponds [1]. Titanite, CaTiSiO5, is the most important mineral among them because titanium and its compounds are widely used in different industrial technologies. In addition to titanite and titanomagnetite, the apatite-nepheline deposits contain numerous pegmatites with rare titanium minerals that have important functional properties, for example, ferroelectric loparite-(Ce) [2], molecular sieve chivruaiite [3,4] (Ca-analog of synthetic microporous titanosilicate ETS-4 [5,6]), cation exchangers kukisvumite and punkaruaivite [7–10] (respectively, Zn and Li analogues of synthetic titanosilicate AM-4 [11,12]), cation exchangers sitinakite [13] (natural analogue of synthetic titanosilicate Ionsiv IE-911 [14–16]), and minerals of the ivanyukite group [17–20]. Besides, these and other synthetic titanium-based compounds (ETS-2, ETS-10, JDF-L1, LHT-9, MIL-125, etc.) are utilized as agents for cation relocation, hydrogen storage and heat transformation, dehydrating agents, drug nanocarriers, adsorbents and membranes [20–25]. In particular, ivanyukite-Na and its synthetic analogue SIV described herein have pharmacosiderite- related crystal structure consisting of Ti4O24-clusters coupled into a framework by single SiO4 tetrahedra Minerals 2018, 8, 446; doi:10.3390/min8100446 www.mdpi.com/journal/minerals Minerals 2018, 8, 446 2 of 13 Minerals 2018, 8, x FOR PEER REVIEW 2 of 13 (Figure1). In this framework, there is a system of wide channels ( ≈6.1 Å), with extra-framework cations of K andsingle Na SiO and4 tetrahedra water molecules (Figure 1). inside In this that framework, can be easily there exchanged is a system withof wide Rb +channels, Cs+, Tl (+≈,6.1 Ag Å),+, Srwith2+, Ba2+, extra-framework cations of K and Na and water molecules inside that can be easily exchanged with Cu2+, Ni2+, Co2+, La3+, Ce3+, Eu3+, Th4+, etc. [18–20,26]. Moreover, (137Cs, 90Sr, 154Eu)-exchanged forms Rb+, Cs+, Tl+, Ag+, Sr2+, Ba2+, Cu2+, Ni2+, Co2+, La3+, Ce3+, Eu3+, Th4+, etc. [18–20,26]. Moreover, (137Cs, 90Sr, of ivanyukite can be transformed by heating into stable SYNROC-like titanate ceramics for long-time 154Eu)-exchanged forms of ivanyukite can be transformed by heating into stable SYNROC-like immobilizationtitanate ceramics of these for long-time radionuclides immob [20ilization]. of these radionuclides [20]. Figure 1. Crystal structure of ivanyukite-Na-T [17]: cubano-like clusters Ti4O24 consisting of four edge- Figure 1. Crystal structure of ivanyukite-Na-T [17]: cubano-like clusters Ti4O24 consisting of four shared TiO6 octahedra (dark-blue) are connected by vertexes SiO4 tetrahedra (yellow) to form the edge-shared TiO6 octahedra (dark-blue) are connected by vertexes SiO4 tetrahedra (yellow) to form the microporous framework, with Na (cyan), K (pale green), and H2O (magenta) in channels. microporous framework, with Na (cyan), K (pale green), and H2O (magenta) in channels. There are a lot of studies related to titanite concentrate chemical processing [27–29]. Among the There are a lot of studies related to titanite concentrate chemical processing [27–29]. Among the known technologies, sulfuric-acidic ones are the most perspective because they enable to obtain a knownwide technologies, spectrum of sulfuric-acidicmaterials including ones titanium are the mostpigments, perspective fillers, adhesives, because theytanning enable agents, to obtainsorbents a wide spectrumand molecular of materials sieves. including High titanite titanium content pigments,is a typical property fillers, adhesives,of apatite-titanite tanning and nepheline-titanite agents, sorbents and molecularrocks, which sieves. are High currently titanite stockpiled content in is dumps a typical due propertyto difficulties of apatite-titanitewith titanite separation and nepheline-titanite from apatite rocks,and which nepheline are by currently flotation. stockpiledWe would like in to dumps show he duerein tonew difficulties perspectives with for production titanite separation of synthetic from apatiteivanyukite-type and nepheline compounds by flotation. and Weother would materials like me to showntioned herein above newwith perspectives sulfuric-acidic for cleaning production of syntheticfollowed ivanyukite-type by hydrometallurgical compounds processing and of other ground materials apatite-titanite mentioned and abovenepheline-titanite with sulfuric-acidic ores. cleaningThis followedapproach byfeatures hydrometallurgical better productiveness processing in relation of ground to a conven apatite-titanitetional technologies and nepheline-titanite of titanite ores.extraction This approach by flotation features and better titanosilicate productiveness synthesis from in relation compositions to a conventional based on titanium technologies chlorides. of titanite extraction2. Geological by flotation Setting and titanosilicate synthesis from compositions based on titanium chlorides. 2. GeologicalThe world’s Setting largest Khibiny alkaline massif (35 × 45 km) is situated in the West of the Kola Peninsula (Murmansk Region, Russia), at the contact between low-metamorphosed volcano- sedimentaryThe world’s rocks largest of the Khibiny Proterozoic alkaline Imandra-Varzuga massif (35 greenstone× 45 km) belt isand situated the Archaean in the ultra- West of the Kolametamorphic Peninsula rocks (Murmansk of the Kola-Norwegian Region, megablock Russia), at(Figure the contact2). Its age betweenis 380–360 low-metamorphosedmillion years [30]. volcano-sedimentaryThe main rock of the rocks massif of theis coarse-grained Proterozoic Imandra-Varzuganepheline syenite (foyaite) greenstone that forms belt funnel-shaped and the Archaean ultra-metamorphichomogeneous body rocks divided of the into Kola-Norwegian two parts by the Main megablock Ring intrusion (Figure of2 ).foidolite Its age (melteigite–urtite is 380–360 million yearsrock [30 ].series), The with main related rock poikilitic of the massif (kalsilite)-ne is coarse-grainedpheline syenites nepheline (rischorrite syenite and lyavochorrite) (foyaite) that and forms funnel-shapedfine-grained homogeneous alkaline syenite bodywith xenolites divided of into feinitized two partsvolcano-sedimentary by the Main Ring rocksintrusion [31,32]. The of Main foidolite (melteigite–urtiteRing thickness rockon the series), day surface with varies related from poikilitic 0.1 to 10 km, (kalsilite)-nepheline and rapidly decreases syenites with depth. (rischorrite Within and the outer part of the foyaite body, there is another one semi-ring zone of foidolites, alkaline syenite lyavochorrite) and fine-grained alkaline syenite with xenolites of feinitized volcano-sedimentary and fenite. In addition, monchiquite–carbonatite veins and explosion pipes occur in the Eastern part rocks [31,32]. The Main Ring thickness on the day surface varies from 0.1 to 10 km, and rapidly of the Main Ring. decreasesThe with rock-forming depth. Within minerals the outer of foyaite part include of the foyaitenepheline, body, microcline, there is anotherorthoclase, one albite, semi-ring aegirine, zone of foidolites,augite, alkaline Na–Ca- syeniteand Na-amphiboles, and fenite. In addition,aenigmatite, monchiquite–carbonatite titanite, eudialyte, lamprophillite, veins and and explosion annite. pipes occur in the Eastern part of the Main Ring. The rock-forming minerals of foyaite include nepheline, microcline, orthoclase, albite, aegirine, augite, Na–Ca- and