De Wet Process for the Beneficiation of Zircon:  Optimization of the Alkali Fusion Step

Abstract

Milled zircon, d 50 ≈ 9 μm, was fused with caustic soda pearls in open reaction vessels at temperatures between 650 and 850 °C. Fusion times of 1, 2, 4, 24, and 336 h (with intermittent milling) were investigated. The fusion products were characterized by X-ray diffraction and by wet-chemical analysis. For prolonged fusion times, the fusion products approached equilibrium compositions. However, the phases Na2ZrSiO5 and Na4Zr2Si3O12 observed at 850 °C did not form at 650 °C. Because these compounds do not hydrolyze completely in water, they limit the recovery of alkali in the sodium silicate product stream. With short fusion times (2 h), a nonequilibrium product spectrum is obtained. It is dominated by sodium zirconates and sodium silicates, allowing reasonable zirconia yields and high alkali recovery in a sodium silicate product stream. This allows efficient fusion of two moles of NaOH per mole of zircon at 850 °C with a zirconia yield of ca. 57% and an alkali recovery of ca. 78%.

Novel decomposition method for zircon

“…El-Yamani et al [15] choose 650 • C and 60% of excess NaOH at 2 h as the optimum conditions and obtained 97.6% zircon decomposition but they used commercial grade sodium hydroxide. The complete dissociation observed by El-Barawy et al was also confirmed by the treatment of other zircon concentrate around the world as reported by Focke et al [11] for Richards Bay (South Africa) zircon, Saha and Chandran [16] for Indian zircon, and recently by Naher and Haseeb [17] for Bengaline zircon. All these workers used extensive reaction conditions and relatively small amount of zircon as a started reaction materials.…”

“…The melting point of KOH is 406 • C [11], G for this reaction at 298 • K is expected to be more negative than that of reaction (2) and hence one can expect that the former has slightly more decomposition effect on zircon than NaOH. Therefore, when the mixed alkalis used, the competition of KOH is longer than that of NaOH, which mean that the molar percent of KOH may decrease than that of the eutectic ratio.…”

“…El-Barawy et al [4] and Focks et al [11] reported the presence of water insoliuble compounsd such as Na 2 ZrSiO 5 , and Na 4 Zr 2 Si 2 O 12 specially when the less coustic (Na 2 Co 3 ) have been used. These compound will dissociate ducring the acid leaching of the product and increase the silica content in the produced zirconium componds.…”

A two-step zircon decomposition method to produce zirconium oxychloride: alkali fusion and water leaching

“…The chemical inertness of zircon renders its processing a difficult task, and a large number of studies were carried out on this problem; several methods are used for industrial processing of zircon, including chlorination [7][8][9], sodium hydroxide fusion [10][11][12][13][14][15][16][17], sodium carbonate fusion [11,12,17], mixed alkali fusion [18][19][20], liming fusion or other alkali metal oxides [21][22][23], sodium hydroxide solution leaching [24,25], fluorosilicate fusion [26], plasma thermal dissociation in the presence of carbon [27,28]. Alkali fusion with NaOH is the most commonly used method in China due to the advantages of technically simplicity and low reaction temperature.…”

Calciothermic Reduction of Zirconium Oxide in Molten CaCl2

“…The production of pure zirconium dioxide through zircon fusion with alkali at temperatures between 600 and 850°C, [8][9][10] followed by wet chemical treatments can solve many problems at the first stage. The authors have studied these pyro-and hydro-metallurgical steps.…”