Apatite–nepheline ore mill tailings – a source of functional materials

Abstract

The modern scheme of apatite–nepheline ore beneficiation is aimed at the extraction of apatite and partially nepheline. The remaining minerals are practically lost due to the lack of demand and, therefore, are stored in vast tailings dumps which worsen the ecological situation. Among the unused minerals, the practical interest is drawn by calcium titanosilicate— sphene which includes titanium. Given the current scale of ore mining, up to 200 thousand tons of TiO2 of this deficient element are lost annually. An original method has been developed for separation of the titanium-bearing minerals from waste in the form of the sphene concentrate. The method is based on treatment of the mineral with dilute hydrochloric acid (50 g×l-1 HCl). This allows separation of acid-soluble mineral components—apatite, nepheline, titanomagnetite, and production of sphene concentrate (CaSiTiO5) with the titanium dioxide content of 29–31.5%. Calcium is leached from sphene by thermal decomposition with concentrated hydrochloric acid. In this case, titanium and silicon are deposited in the form of the two-phase precipitate—SiO2 (silica)×TiO2 (rutile)×xH2 O, which is the parent subject for the synthesis of the functional materials. The efficiency of the high-energy shock–shear action on sphene particles and the titanosilicate parent subjects, which violates their structure and morphology, has been determined. The thermodynamic stability of the activated particles is achieved by chemisorption or firing to obtain the modified products. Due to the high degree loosening of the surface layer of sphene particles under mechanical activation, the ability of the materials to adsorb modifying substances increases. In preparation of mineral pigment, it is recommended to treat activated sphene particles with phosphoric acid. Hardly soluble calcium and titanium phosphates formed in this process improve the whiteness of the pigment product and its resistance to the moisture and temperature changes. The method for the production of hybrid fillers for special adhesives and sealants has been developed. In general, this article illustrates expediency of the use of the manmade waste in dressing of apatite–nepheline ores, in particular the froth product of nepheline flotation, to obtain deficient import-substituting titanium-containing products necessary for the development of the advanced industries, as well as to solve the acute environmental problems in mining, nonferrous metallurgy and defense facilities.