A novel method for processing of Bangladeshi zircon: Part II: Leaching of zircon-caustic fused mass by hydrochloric acid

A thorough investigation on the leaching and kinetics of extraction of Zr(IV) from a semi-crystalline zircon–NaOH fused material by hydrochloric acid has been carried out. The fused material was produced by mixing NaOH/zircon at a wt. ratio of 1.8 (mole ratio 9) at 973° K for 15 min. Conditioning was done by water washing, drying, grinding and sieving. The optimum conditions for dissolution of Zr(IV) were leaching by 4 M HCl under reflux for only 5 min with a solid to liquid ratio of 1.41:10 w(g)/v(mL). By applying staged leaching it was possible to obtain a solution containing up to 112 g/L Zr(IV). The rate of leaching was found to be directly proportional to [HCl]2 and very dependent on the temperature. The rate constant at 382° K with a particle diameter of 48.5 ± 4.5 μm was determined to be 10− 1.91 g dm4/min mol2 and the activation energy, Ea, was 64.3 kJ/mol indicating chemical reaction control. Stirring had little effect on the rate of dissolution due to the high porosity of the conditioned fused material. However, the rate was inversely proportional to the radius of the particles used. The novelty of the process is the fast rate of dissolution of the caustic fused material to give a concentrated solution of Zr(IV).