D. Mendeleev University of Chemical Technology of Russia, Moscow, Russia:

T. V. Konkova, Professor at the Department of Inorganic Substances and Electrochemical Processes, Doctor of Technical Sciences, Associate Professor, e-mail: kontat@list.ru
Z. H. Than, Postgraduate Student of the Department of Inorganic Substances and Electrochemical Processes
T. A. Hein, Doctoral Student of the Department of Inorganic Substances and Electrochemical Processes, Candidate of Technical Sciences
A. D. Stoyanova, Senior Lecturer at the Department of Inorganic Substances and Electrochemical Processes, Candidate of Technical Sciences

The process of electroflotation is used for treatment of wastewaters carrying heavy and non-ferrous metals in the form of poorly soluble compounds if the concentrations of contaminants are too high to be handled by adsorption process. The problem of raising the efficiency of electroflotation process is currently of relevance. This paper examines how the composition of the medium, i.e. the nature of the electrolyte, surfactants and hardness salts, can influence the extraction of iron, aluminum and chromium hydroxides from aqueous solutions by electroflotation. It was found that the electrolyte (NaCl, Na₂SO₄) nature has no significant effect on the process. The hydroxide extraction performance can be impacted by the presence of calcium ions regardless of the electrolyte nature. It happens due to the adsorption of Ca²⁺ on the hydroxide surface, which makes it more hydrophilic. The degree of dispersed phase extraction can be increased due to the introduction of surfactants: didecyldimethylammonium chloride, sodium dodecyl sulfate and a mixture of primary oxyethylated synthetic alcohols. Sodium dodecyl sulfate, which is an anionic surfactant, proved to deliver the best result. The high process efficiency in terms of dispersed phase extraction is due to the hydrophobization of the particle surface by adsorbed sodium dodecyl sulfate and the stabilization of gas bubbles. The particle sizes of iron and chromium hydroxides vary in the range of 0.04 to 4 microns. At the same time, most of the aluminum hydroxide particles are bigger than 10 microns, which can be attributed to the high polymerization ability of aluminum ions and subsequent particle coagulation. The efficiency of electroflotation extraction of chromium, aluminum and iron hydroxides in the presence of calcium ions using anionic surfactant is at least 90%. Additional filtration is recommended to ensure the treated wastewater is in compliance with applicable standard.

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