Low-temperature desiliconization of activated zircon concentrate by NH4HF2 solution

Abstract

The demand for zirconia concentrates significantly exceeds the supply, which causes a significant difference in their cost, which raises the question of removing silicon from zircon to obtain a zirconium dioxide concentrate. The article presents the development of a low-temperature technology for processing activated zircon concentrates with the production of a baddeleyite concentrate used for the manufacture of high-temperature ceramics, including the possibility of regenerating the main reagent. The optimal conditions for desiliconization were established as follows: concentration of NH4HF2 solution – 30 %, duration – 60 min, temperature – 90 °C; the ratio of solid to liquid – 1:5. Under these conditions, more than 99 % of silicon goes into solution. During the leaching process, zirconia partially reacts with the leaching agent to form ammonium heptafluorozirconate, which has lower water solubility than ammonium fluorides and ammonium hexafluorosilicate. Subsequent calcination allows the heptafluorozirconate to be converted back into zirconia. The resulting solution of ammonium hexafluorosilicate can be used to obtain amorphous silicon dioxide and ammonium fluoride solution, which serves as a raw material in the process of regeneration of the leaching solution with its reuse for processing a new batch of raw materials. Based on the work results, it was possible to achieve more than 99 % degree of desiliconization of zircon concentrate. The appropriate waste-free technological scheme for obtaining baddeleyite concentrate was proposed.