The pH and medium composition impact on the efficiency of electroflotation-based extraction of slightly soluble iron, chromium and manganese compounds from water solutions and physical-chemical properties of these compounds

Abstract

The study demonstrates the pH and solution ion composition impact on the average hydrodynamic diameter dm and electrokinetic potential (ζ-potential) of the dispersed phase of slightly soluble ferrous metals compounds. We examined formation dispersed phases of slightly soluble Fe (III), Cr (III), and Mn (II) compounds in the presence of OН–, CO32–, PO43– ions as precipitating agents and anionic, cationic, and non-ionic flocculating agents. The electroflotation-based extraction of slightly soluble ferrous metals compounds was found to be directly linked to dispersity and electrokinetic potential of particles, that depend on acidity and ionic medium composition. The maximal hydrodynamic diameter of dispersed phases of the slightly soluble Fe (III), Cr (III), and Mn (II) compounds were observed at isoelectric point and corresponded with pH value of the minimal dispersed phase solubility. In this case, electroflotation-based extraction was more efficient, the iron (III), manganese (II), and chromium (III) removal α reached 98, 96, and 83 %, respectively. Cationic flocculating agent additives increased the iron, manganese, and chromium extraction up to 99, 98, and 94 %, respectively. If carbonate and phosphate ions were added, the electrokinetic potential of compounds of all examined slightly soluble metals changed to negative values: –(12–19) mV in the presence of CO32– ions and –(35–43) mV in the presence of PO43– ions. This shift hindered coagulation and decreased electroflotation-based extraction of the dispersed phases, especially in case of manganese compounds (α ≤ 10%). Cationic and non-ionic flocculating agents additives balanced the high negative charge of the dispersed phases of slightly soluble ferrous metals compounds, enlarged the removal up to 98 % depending on the dispersed phase and flocculating agent. The research was conducted under financial support of the Mendeleev University of Chemical Technology of Russia within the frame of investigations on strategic development directions, project No. 3-2020-033.