A new technique for extracting zirconium form Egyptian zircon concentrate

Zircon is the most important commercial source of zirconium, its compounds and alloys. Several methods are used for industrial processing of zircon for production of zirconium dioxide and tetrachloride. These methods include sintering of zircon with sodium carbonate or sodium hydroxide or calcium oxide or calcium carbonate and with potassium fluorosilicate, chlorination of zircon mixture with coal in blast furnace and carbidization of zircon in a mixture of coal in electric arc furnace. All these methods are carried out at high temperatures and have many disadvantages. The present work illustrates a study of a new technique for extracting zirconium from Egyptian zircon concentrate by its simultaneous ball-milling and pressure alkaline leaching, to improve the recovery of zirconium from zircon. Experiments were carried out in stainless steel ball-mills of cylindrical shape under different conditions of temperature, pressure and time. The ball-mills were heated and mechanically rotated in an electric furnace by means of roll mechanism. The filtrate after leaching of zircon, containing excess of sodium hydroxide was regenerated by its treatment with calcium hydroxide for purification from silicon impurity. Then, the solution was evaporated to the desired concentration (500 g/l Na2O) and recycled to the reactor of leaching. The results obtained show that complete recovery of zirconium from zircon (99.7%) by simultaneous ball-milling and alkaline leaching was attained at 250 degrees C within 3 h, using amount of sodium hydroxide 150% of theoretical requirement (satisfying favourable conditions of zirconate cake for subsequent acid leaching). The standard free energy (Delta F-o) and equilibrium constant (K) of the reaction of zircon with sodium hydroxide were calculated as-19.58 k cal mol(-1) and 2.29 (.) 10(14), respectively. The kinetics of the technological alkaline processing of zircon in ball-mail autoclaves was studied over the temperature range 150-275 degrees C. (c) 2005 Elsevier B.V. All rights reserved.