Studies on extraction of potassium values from nepheline syenite S.K. Jena a , N. Dhawan a , D.S. Rao a , P.K. Misra b , B.K. Mishra a , B. Das a, ⁎ a CSIR-Institute of Minerals and Materials Technology, Bhubaneswar751013, India b CSST, School of Chemistry, Sambalpur University, Jyoti Vihar768019, India abstract article info Article history: Received 7 May 2014 Received in revised form 22 July 2014 Accepted 16 September 2014 Available online 28 September 2014 Keywords: Nepheline syenite Beneficiation Acid leaching Roast-leach method Nepheline syenite is a complex rock consisting of different mineral phases such as nepheline, alkali feldspar, and biotite. It is a promising source for the recovery of potassium and alumina values. India is importing most of its potassium demand from the global market. An attempt is therefore made to extract potassium values from nepheline syenite available in the state of Odisha. It contains 2.8% Fe 2 O 3 , 19.9% Al 2 O 3 , 55.5% SiO 2 and 5.4% K 2 O as its prime constituents. Magnetic separation and flotation techniques are found unsuitable to recover apprecia- ble amounts of potassium values. Chemical leaching with dilute sulphuric acid could recover only ~40% of the potassium values. The potassium values present in nepheline syenite are unlocked through roasting with calcium chloride followed by water leaching. In this approach, it is possible to recover ~ 99.6% K 2 O value at 900 °C temper- ature and 30 min of roasting time. The results indicate that the use of planetary mill grinding prior to roasting is favorable for potassium extraction due to mechanical activation of the potassium bearing phases. The different mineral phases present in the feed and the leach residue have been characterized by using optical microscope, XRD and SEM-EDX which shows a phase conversion of locked potassium into sylvite which is soluble in water. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Potassium is an essential element for plant nutrition. Its demand for agricultural use is growing steadily at 3–3.5% per annum (Manning, 2010). Since India does not have any commercial resources of potash, a large quantity is imported every year from the global market to meet the agricultural demand. It is expected that India's potash import would be likely to go up to 3.6 million tons in the future from the present import level of 2.4 million tons per annum. Under such circum- stances, the recovery of potassium (K) values from different indigenous sources is highly essential. In general, K values in the earth crust are as- sociated with silicate minerals such as feldspar, mica, biotite, muscovite, and nepheline. Some of the mineral sources available in India containing 3–14% K 2 O are glauconitic sand, feldspar, muscovite, and nepheline syenite [Indian Minerals Yearbook, 2011]. Out of various feldspars, po- tassium feldspar is the most common and contains up to 13% K 2 O(Rao et al., 1998). Glauconite sand contains around 4–8% K 2 O and has been used as a source of potash fertilizer worldwide (Majumder et al., 1995; Yadav et al., 2000). In eastern India, some potential resources of nephe- line syenite containing ~5–12% K 2 O are available. However, no commer- cial plant has been established to recover the potash values from the available mineral resources. The main potassium mineral reserves for fertilizer prospects are soluble K-chlorides or sulfates such as the minerals sylvite, kainite, carnallite and polyhalite. Solution mining or leaching in closed dissolvers are applied to these minerals in which heated brine preferentially dis- solves the potassium values. Recently, a pilot plant operation has been developed to produce fertilizer grade potassium sulfate from polyhalite (K 2 Ca 2 Mg(SO 4 ) 4 ·2H 2 O). The process claims to be less expensive com- pared to mined sylvite, which is a naturally occurring mineral composed of KCl. The process involves crushing, calcination in a fluidized bed reac- tor, leaching, hybrid crystallization, drying and granulation (Potash, 2013). Literature shows that not much research efforts have been made to make use of alternative low grade mineral resources due to the avail- ability of highly soluble potash salts of marine origin in many countries, with a K 2 O concentration varying up to 63% in the pure mineral sylvite. In this context, some effort has been made to recover potassium values from glauconitic sandstone widely available in India. Yadav et al. (2000) have reported nearly complete recovery of potassium from glauconitic sandstone by leaching with hydrochloric, nitric, and sulphuric acids. Similarly, more than 90% potassium dissolution from glauconitic sandstone has been reported via calcium chloride assisted roasting at a temperature of 750–900 °C followed by water leaching at a particle size of 90–240 μm(Majumder et al., 1995). Yadav et al. (2000) have also reported 96% extraction of the potash from glauconite sand by using 6 M hydrochloric acid leaching at 105 °C for 3 h (Yadav and Sharma, 1992; Yadav et al., 2000). Similarly, several experiments were carried out on phosphate rocks (22–25% K 2 O) and glauconite sands (~ 6% K 2 O) available in Argentina for direct use in fertilizers (Castro and Tourn, 2003). Kleiv and Thornhill (2007) reported the use of International Journal of Mineral Processing 133 (2014) 13–22 ⁎ Corresponding author. E-mail address: bdas@immt.res.in (B. Das). http://dx.doi.org/10.1016/j.minpro.2014.09.006 0301-7516/© 2014 Elsevier B.V. All rights reserved. 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