1. 1996; Macmillan et al., 2012). Leaching is

1.

Introduction Strontiumis found at a concentration of 0.04% on average in the Earth’s crust and istherefore the 15th element in abundance. It is thetenth most abundant element and has a concentration of 8×10–4 in seawater (Chegrouche etal., 2009). The major reservesin the world are found in Turkey, Spain, Mexico, Britain and Iran, and the mostimportant strontium beds known in Turkey are the basins of Ulas, Hafik, Kabali,Budakli, Demirci, Akcamescit, Tahtakeme and Karayun in Sivas province (Palmer et al., 2004). The mostimportant compound of strontium is strontium nitrate, which is used inpyrotechnology as a component of signalingdevices.

Strontium nitrate givesthe desired bright red color and is used in large quantities in military andnon-military applications such as pyrotechnic devices. Strontium is used inmilitary pyrotechnic applications involving, ammunition, military cartridges,and marine hazard signals. Non-military applications include warning devicesand fireworks. The strontium content in military flares can be up to 40% byweight and is about 20% in Roman candle fireworks (Harben et al., 1996; Macmillan et al.,2012).

Leaching is one ofthe most commonly used metal production methods in metallurgy. It has a numberof advantages such as low energy consumption, reduced environmental pollutionand the ability to treat low grade ores(Ajemba and Onukwuli, 2012). Numerousstudies have been conducted during the past decades on the dissolution ofcelestite with the aim of understanding, controlling, and optimizing theeffects of process parameters on the dissolution rate to other strontiumcompounds.Inassorted studies, celestite concentratecontaining 97.24% strontium sulfate has been converted to strontium chloride(SrCl2) in acidic barium chloride (BaCl2) (Aydogan et al.,2006). Celestite concentrate containing 96.

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5% strontium sulfatewas washed in dilute HCl solution for purification of the ore before leachingwith Na2S. A product of over 97% SrS product was obtained. Thekinetic model was determined to be controlled by diffusion to the product layer (Erdemogluet al., 2006).

Orduna et al. studied thekinetics of dissolution of celestite concentrate with a grade of 96.8% suppliedfrom Coahuilla, Mexico in sodium carbonate solution by a leaching processcarried out in a pressurized autoclave. The kinetic model of the pressurizedleaching process fitted to the shrinking particle model (Suarez-Orduna et al., 2007). Strontium carbonatewas obtained by leaching celestite concentrate containing 95.69% of strontiumsulfate in sodium carbonate solution. The kinetic model was found to be anartificial neural network model (Bingol et al.

, 2010). Celestiteconcentrate containing 95.30% strontium sulfate was subjected to a leachingprocess in solutions of HNO3, HCl, HClO4, Na2CO3and (NH4)2CO3, and the leaching yields weredetermined to be 91.35, 99.56, 93.57, 79.70 and 79.66% respectively (Ermis, 2011).

Strontium karbonate was obtained by the leaching of 96.79% SrSO4in solutions of ammonium carbamate and ammonium bicarbonate. The kinetic modelof the leaching fitted to the shrinking particle model. The leaching kinetics of celestite containing 96.79% SrSO4in oxalate solutions were investigated, and 98.55%SrC2O4.H2O was determined (Zoraga andKahruman, 2014).

In a patent taken out by deBuda, SrCO3 was obtained from low and medium quality celestite orecontaining 60-80% celestite (De buda, 1987).     The leaching agents Na2CO3,HCl+BaCl2 and (NH4)2CO3 + NH4CO2NH2have been used in studies of celestite dissolution kinetics in theliterature. No studies on the leaching kinetics ofcelestite ore in nitric acid solutions were found in the literature.      The aim of this work was to investigate anew dissolution method of extracting strontium from celestite concentrate in the presence of nitric acid. Theeffects of nitric acid concentration, stirring speed, solid-liquid ratio andtemperature parameters on the dissolution rate of selestite were investigated. Dissolutionkinetics were studied using homogeneous and heterogeneous reaction models.

Theequation which best fitted the experimental data was determined, and theactivation energy was calculated using Arrhenius’ Law.