Acid Decomposition Of Transformation Mass(TFM) And Desilication By Flocculation In Zirconium Oxychloride Production

Abstract:The zirconium oxychloride (ZrOCl2·8H2O) is one of the most important raw materials to produce zirconium metal, zirconium oxides and other zirconium compounds. It has wide application in ceramics, textiles, electronics and nuclear industry. China is the most powerful producer in the world. Alkali fusion of zircon sand concentrate is the key method to produce zirconium oxychloride, in which the desilicication process is complex and with long operating period. To solve above problems, a novel desilicication process consisting of acid decomposition and flocculation was proposed. The major reserch content and results are as follows:(1) The transformation mass (TFM) prepared by water and acid washing of zirconNaOH fused material was used as raw materials for the novel acid decomposition. The effects of main parameters during acid decomposition and flocculation processes on removal of silicon were investigated and the optimal conditions were obtained. The5litre-scale expansion experiments were carried out at the optimal conditions, and the silica content in the zirconium oxychloride solution after purification were stable to35-50ppm. Meanwhile, Zr(Hf)O2concentration of115-125g/L is20%higher than that of conventional technology. The cooling crystallization and the continued dissolution units in the traditional technologies are eliminated. Thus, the production process and period are shorten, and the steam consumption in following evaporation unit is reduced.(2) The mechanism of polymerization and removal by flocculation of silicic acid was analyzed and verified. The polymerization state of silicic acid during transformation, acid decomposition and flocculation processes were characterized by both IR and NMR. The polymerization of silicic acid has taken place in the transition process, and is further enhanced during the acid decomposition. The polymerized silicic acid is removed in the flocculation process through the bridging role with polyer flocculant added.(3) The orthogonal experiments of silica residues washing to recover zirconium were carried out. The impact factors of zirconium recovery are determined in order of liquid-solid ratio, slurry time, pH, and the temperature. The optimal conditions of silica residues countercurrent washing are further achieved, providing the basic data for the industrial implementation.