Dissolution kinetics of celestite ore with acid and base solutions and the production of SrCrO4 in the Sivas region

This thesis consists of four different studies, in which experimental studies were performed on leaching of raw celestite ore from Sivas province supplied by İstanbul Barit Maden A. Ş. a) in sodium carbonate (Na2CO3) solutions and b) in sodium hydroxide (NaOH) solutions; c) on the leaching of concentrated celestite in nitric acid (HNO3) solutions, and finally d) on the production of strontium chromate (SrCrO4) from the leachate obtained from nitric acid leaching. Temperature, solid-to-liquid ratio, particle size, stirring speed, and acid or base concentration were selected as leaching parameters. In the first stage, the leaching operation was not finished because strontium carbonate and calcium carbonate were difficult to separate in the solid phase of the pregnant leach solution of the sodium carbonate solutions at the end of the leaching of Na2CO3 with raw celestite ore. Kinetic modelling was not performed and activation energy was not calculated. In the second stage, strontium present in form of strontium hydroxide (Sr(OH)2) in the leachate obtained from leaching of raw celestite ore in NaOH solution was recovered in NaOH solution with 99.97% efficiency at a temperature of 90°C, a stirring speed of 500 rpm, 0.5 g/100 mL solid/liquid ratio, a range of 63–100 µm of particle size, and 4 mol/L NaOH concentration. The raw celestite ore dissolved in accordance with shrinking core model. The leaching operation was controlled by step of diffusion through ash layer for plate particles of constant size. The activation energy was calculated as 61.02 kJ/mol. In the third stage, leaching was applied to concentrated celestite ore in aqueous HNO3 solutions. Strontium in the shape of strontium nitrate was acquired (Sr(NO3)2) from leachate of nitric acid. The particle size was constant in a range of 125–250 µm during the leaching. A leaching efficiency of 91.10% was obtained under experimental conditions with a solid-to-liquid ratio of 0.5 g/100 mL, a stirring speed of 500 rpm, a temperature of 80°C and an acid concentration of 4 mol/L. The mineral leached in accordance with shrinking core model and leaching was controlled by diffusion through product layer for spherical particles. The activation energy was found to be 42.22 kJ/mol. In the final stage of the thesis, leachate of Sr(NO3)2, which was supplied from the leaching of concentrated celestite in HNO3 solutions, was reacted with sodium chromate dihydrate (Na2CrO7.2H2O) in the presence of sodium chloride (NaCl) salt at room temperature under optimized conditions of nitric acid leaching. The transformation of strontium to strontium chromate took place. Nanorod shaped strontium chromate (SrCrO4) crystals, which were dark yellow in colour, 1.72–5.56 μm long and 0.105–0.437 µm in diameter were obtained by the precipitation method. The effect of parameters such as the Sr+2/CrO4= ratio, NaCl concentration and reaction time between reaction system of Sr(NO3)2-Na2Cr2O7.2H2O and NaCl were investigated. As a result of this, SrCrO4 was produced with 78% efficiency at a stirring speed of 700 rpm, 0.25 Sr+2/CrO4= ratio (0.1164 mol/L Sr2+ and 0.4656 mol/L CrO4=), in a pH = 14 solution medium, 0.1 mol/L NaCl concentration, 60 minutes of reaction between Sr(NO3)2-Na2Cr2O7.2H2O system and NaCl and in 60 minutes of mixing of Sr(NO3)2-Na2Cr2O7.2H2O system before precipitation. The experiments were repeated to determine the effect of NaCl in the absence of NaCl. It was seen that NaCl changed the form of the product.