Alternative Methods Used in the Beneficiation of Feldspar Minerals

Feldspar is a mineral composed of sodium, potassium, calcium and sometimes barium, cesium and aluminum silicate groups formed from the isomorphic composition of these minerals (Heyes et al., 2013; Zhang et al., 2018). It is one of the most abundant minerals in the world, comprising approximately 60% of the earth's crust (Vidyadhar et al., 2002). According to a report by the United States Geological Survey, Turkey ranked first globally in 2019 with 7,500 million tons of feldspar production. Feldspar minerals are named according to the K, Na and Ca ratios they contain. Na-feldspars are known as albite (NaAlSi3O8), K-feldspars as orthoclase/microcline and Ca-feldspars as anortite (Kangal et al., 2017). Due to their alkali and alumina content, they hold an important place in various industrial applications. Alkali feldspars (potassium feldspars) are widely used in the paints and coatings, glass and ceramics industries. Quality requirements for potassium and sodium feldspars used in the glass industry require that their Fe2O3 content be less than 0.2% and 0.3% respectively. On the other hand, in the ceramics industry, potassium feldspars are expected to have Fe2O3 content less than 0.5%. Feldspar is most commonly found in pegmatite and feldspathic sand deposits together with silica group minerals such as mica, quartz and spodumene. The flotation method with fatty acids is one of the most commonly used methods for the separation of silica group minerals accompanying feldspar (Xu et al., 2017).

Feldspar minerals carry a negative charge at many pH values. The point of zero charge has been observed to be approximately pH 1.5. This is due to the breaking of Si-O and Al-O bonds present in the crystal structure during grinding. The surface becomes negatively charged with the passage of ions such as Na+, K+ and Ca+ present on the surface into solution (Fuerstenau and Raghavan 1977; Gülgönül et al., 2007).

Enrichment methods based on magnetic susceptibility and specific gravity differences, as well as flotation utilizing the physicochemical properties of minerals and leaching techniques, which are a chemical method, are used to separate feldspar from the gangue minerals with which it occurs. By combining one or several of these methods together, high purity feldspar can be obtained. The staged flotation method is accepted and widely applied for the separation of feldspar from silicate group minerals and metal oxides accompanying it. Prior to the flotation process, slime-sized material is removed, preventing the negative effects caused by iron and clay minerals of this size from reducing flotation efficiency. Figure 1 shows the classical flotation process flow chart applied in feldspar flotation. [caption id="attachment_123299" align="aligncenter"] Figure 1: Feldspar flotation process flow chart (Demir, 2010)[/caption]   The slime-sized material (≤ 38 µm) separated before feldspar flotation contains, in addition to iron and clay minerals, a significant amount of feldspar. Therefore, to prevent the resulting loss, different flotation techniques for enriching fine-sized minerals are being conducted with laboratory-scale success (Karagüzel 2010). Industrial application is not yet widely practiced in Turkey.

References • Demir, C. (2010). Selective Separation of Na- And K-Feldspar from Weathered Granites by Flotation in HF Medium. Ceramics-Silikaty, 54(1), 60-64. • Fuerstenau, D.V., Raghavan, S., 1977. Proc. XII International Mineral Processing Congress. Nacional Publicacoes e publicidade S/C Ltda. 2, 3–8 September, pp. 368–415. São Paulo—Brazil. • Gülgönül, I., Karagüzel, C., & Çelik, M. S., (2008). Surface vs. bulk analyses of various feldspars and their significance to flotation. International journal of mineral processing, 86(1-4), 68-74. • Heyes, G. W., Allan, G. C., Bruckard, W. J., & Sparrow, G. J., (2012). Review of flotation of feldspar. Mineral Processing and Extractive Metallurgy, 121(2), 72-78. • Kangal, M. O., Bulut, G., Yeşilyurt, Z., Güven, O., & Burat, F., (2017). An alternative source for ceramics and glass raw materials: Augen-Gneiss. Minerals, 7(5), 70. • Karagüzel, C. (2010). Selective separation of fine albite from feldspathic slime containing colored minerals (Fe-Min) by batch scale dissolved air flotation (DAF). Minerals Engineering, 23(1), 17-24. • Vidyadhar, A., Rao, K. H., & Forssberg, K. S. E., (2002). Separation of feldspar from quartz: Mechanism of mixed cationic/anionic collector adsorption on minerals and flotation selectivity. Mining, Metallurgy & Exploration, 19(3), 128-136. • Xu, L., Tian, J., Wu, H., Deng, W., Yang, Y., Sun, W., & Hu, Y., (2017). New insights into the oleate flotation response of feldspar particles of different sizes: anisotropic adsorption model. Journal of colloid and interface science, 505, 500-508. • Zhang, Y., Hu, Y., Sun, N., Liu, R., Wang, Z., Wang, L., & Sun, W., (2018). Systematic review of feldspar beneficiation and its comprehensive application. Minerals Engineering, 128, 141-152.

 

Berivan Tunç Istanbul Technical University Faculty of Mines Department of Ore Preparation Engineering       Prof. Dr. Gülay Bulut Istanbul Technical University Faculty of Mines Department of Ore Preparation Engineering