Green recovery of potassium and aluminum elements from alunite tailings using gradient leaching process

In this work, a gradient leaching process is proposed to treat alunite tailings in order to recover potassium and aluminum. Thermodynamic analysis on the reactions of alunite tailings with potassium hydroxide in the leaching process over the temperature range of 30-120 °C is accomplished. In the gradient leaching process, the main mineral of potassium alunite from alunite tailings is extracted into the concentrated potassium hydroxide solution, while kaolinite and quartz are still remained in the leaching residues. The proposed leaching process is demonstrated to be feasible based on the leaching ratio of potassium, aluminum, silicon elements in the leaching solution by ICP-OES and the mineralogical characterizations of the leaching residues by XRD, IR and Raman spectrometers. Furthermore, the gradient leaching conditions, such as alkali-to-ore mass ratio, leaching temperature, leaching time and potassium hydroxide concentration, are optimized using the response surface method to recover potassium and aluminum from alunite tailings as many as possible and to extract silicon as small as possible. Under the optimal leaching conditions of alkali-to-ore mass ratio 3.3, temperature 81.8 °C, time 41.6 min, and potassium hydroxide concentration 53.9 wt%, the leaching ratio of potassium and aluminum reaches 99.5% and 84.0%, and the leaching ratio of silicon is controlled in 5.6%, respectively. All the obtained results could contribute to affording a green and closed-loop recovering process for potassium and aluminum elements from alunite tailings.