Enhancement of insoluble residue removal from high-calcium sulfate sylviniteore via ultrasonic pretreatment

This study investigates the effect of low-frequency ultrasonic pretreatment on the removal efficiency of calcium sulfate (CaSO4) and clay-salt insoluble residue (IR) from sylvinite ores with elevated calcium sulfate content. Ultrasonic treatment was applied to both the flotation feed and the rougher concentrate to improve desulfation and desliming performance. Particle-size and mineralogical analyses revealed that the –0.1 mm fraction of the ore contains the highest concentration of impurities—up to 11.01 wt.% CaSO4 and 4.18 wt.% IR—primarily in the form of fine coatings on potassium and sodium chloride crystals. Additionally, CaSO4 is often present in semi-encapsulated forms located in microcracks, folds, and intergrowth zones, complicating its liberation during conventional processing. It has been established that ultrasonic treatment significantly enhances the removal of CaSO4 and IR due to the transient ultrasonic cavitation effect generated during acoustic energy exposure. At the maximum applied acoustic power of 420 W, the desulfation efficiency reached 34.36 %, while IR removal achieved 51.49 %. However, residual anhydrite persisted in isolated inclusions in inaccessible zones of the ore matrix, such as cracks, folds, and intergrowths. Ultrasonic pretreatment of the flotation feed increased the recovery of CaSO4 and IR to the slime fraction by 9.33 % during selective anhydrite flotation and by 3.98 % during combined anhydrite–sylvinite flotation. Treatment of the flotation feed and rougher concentrate, separately and in combination, resulted in reductions of CaSO4 and IR content in the final concentrate by 0.41 %, 0.58 %, and 1.15 %, respectively.