Extraction of tungsten from scheelite using hydrodynamic and acoustic cavitation

Abstract The primary purpose of this study is to investigate the effects of hydrodynamic and acoustic cavitation (HAC) on the leaching efficiency of tungsten. The aim is to reduce energy use and to improve the recovery rate. The goal is also to carry out a leaching process at a much lower temperature than in an autoclave process that is currently used in the industry. Energy-efficient initiation and collapse of cavitation bubbles require optimization of (i) vibro-acoustic response of the reactor structure, (ii) multiple excitation frequencies adapted to the optimized reactor geometry, and (iii) hydrodynamic cavitation with respect to orifice geometry and flow conditions. The objective is to modify and apply a previously in house developed high power cavitation reactor in order to recover tungsten by leaching of the dissolution of scheelite in sodium hydroxide. In this process, various experimental conditions like dual-frequency excitation, different orifice geometry have been investigated. The numerically optimized reactor concept was excited by two frequencies 23 kHz and 39 - 43 kHz in various flow conditions. The effects of leaching time, leaching temperature, ultrasonic power and geometry of orifice plates have been studied. The leaching temperature was varied from 40°C to 80°C. The concentration of leaching reagent sodium hydroxide (NaOH) was 10 mol/L.The results were compared to conventional chemical leaching. Energy supplement with acoustic cavitation of 130 kWh/kg concentrate resulted in a leaching recovery of tungsten (WO3) of 71.5 %, compared to 36.7 % obtained in absence of ultrasound. The results confirm that the method developed is energy efficient and gives a recovery rate potentially better than current autoclave technology.