A green method for decomposition of scheelite under normal atmospheric pressure by sodium phytate

Abstract

As a critical metal, tungsten is in widespread use and high demand. Most traditional tungsten smelting processes use a NaOH decomposition method. However, there are deficiencies with the traditional method, such as the high cost of leaching agents and environmental pollution. In this paper, sodium phytate, a phosphate-rich ester salt, was evaluated for the first time as a green leaching agent for the extraction of tungsten from scheelite. In the leaching process, sodium phytate was used to precipitate Ca2+ while transferring WO42− from the mineral to the water phase. The results of FTIR showed that the solid product in the leaching residue of scheelite was calcium phytate. The highest tungsten leaching extents of 96.89% and 97.12% were achieved with 1.5 times of the theoretical amount of sodium phytate, 150 g/L NaOH, and an L/S ratio of 10:1 at 363 K for 10 h. Sodium phytate is regenerated by leaching tungsten slag with H2SO4, and the solid product, CaSO4, can be repurposed as a building material to avoid environmental pollution caused by leaching residue. In this sodium phytate leaching system, impurities such as silicon, molybdenum, and phosphorus in scheelite were leached to different degrees, and then entered the leaching liquid. This innovative process features leaching tungsten under mild conditions using reusable sodium phytate. These advantages contribute toward the sustainable characteristics of this process, which can be considered as a sustainable and efficient agent to scheelite leaching.