Elimination of the contaminant fluoride ions from plant zinc sulfate electrolytes by aluminum sulfate

Based on the literature data, the most used chemical element for the removal of the contaminant fluoride ions from different water systems was the Al followed by the Zr, Mg, Fe, C, and several others elements that form stable Me–F complexes. The application of mixed composite adsorbents is a modern tendency, but in this study, the dry aluminum sulfate was tested for direct chemical elimination of the fluoride ions from real industrial zinc sulfate electrolytes. The behavior of the used fluorine ion-selective electrode (FISE) was tested in the presence of sodium fluoride and aluminum sulfate. For suppression of the negative role of the aluminum ions on the FISE potential citrate total ionic strength adjustment buffer (TISAB) was used for appropriate ex situ analytical measurements of the fluoride ions in the real zinc electrolytes from the different hydrometallurgical purification stages. The elimination of the free fluorine ions was tested at room temperature (18–27 °C) and by heating up to 40 °C. The obtained results show that at room temperature, the efficiency of the reaction between F − and Al 3+ ions was not very satisfied. Maximum 13% from the initial fluoride concentration was reduced at real conditions. By heating the process was intensified up to 75–95%, but in excess of non-reacted aluminum ions that additionally contaminated the electrolyte for zinc electrowining. The experimentally proven advantages and disadvantages revealed that the elimination reaction needs further optimizations before any applications at plant conditions. Factors as temperature was beneficial, whereas pH was hard for operation since the dry aluminum sulfate acidified the plant electrolytes and the zinc sulfate matrix precipitated easy by titration from acid to neutral conditions. Graphical abstract