Mendeleev University of Chemical Technology, Moscow, Russia:

A. V. Kolesnikov, Associate Professor, Dept. “Innovative Materials and Corrosion Protection”, e-mail: artkoles@list.ru
Aung Pyae, Postgraduate, Dept. “Technology of Inorganic Substances and Electrochemical Processes”
T. V. Davydkova, Postgraduate, Dept. “Technology of Inorganic Substances and Electrochemical Processes”
V. A. Kolesnikov, Professor, Head of Dept. “Technology of Inorganic Substances and Electrochemical Processes”

The electroflotation process of extracting a mixture of Cu, Zn, Ni, Co, Fe hydroxides from wastewater containing NaNO₃, NaCl, Na₂SO₄, Na₂CO₃, Na₃PO₄, NH₄OH has been investigated. It was found that the maximum recovery rates of 97–99% are observed in the pH range from 8 to 11 for NaCl solutions. The electroflotation process is the least effective in Na₃PO₄ solutions with recovery rates of 10–20%. The cationic surfactant SeptaPAV-SKhV-70 (СептаПАВ-СХВ-70) added to the solution increases the extraction ratio in the presence of phosphates by 40–50%. Low efficiency of the electroflotation process in Na₃PO₄ is associated with a small particle size (about 20–30 μm) and a ζ-potential high negative value, what has an injurious effect on the formation of the flotation complex, negatively charged bubbles (H₂, O₂) and negatively charged particles. The addition of a cationic surface-active substance (SAS) reduces negative potential of the dispersed phase and increases particle sizes. All this contributes to the efficient passing of electroflotation process. Presence of a ligand (ammonia solutions) in the sewage reduces the recovery efficiency by 20–30%, especially for copper ions, which are strong complexing agents. Adding to the solution of small amounts (5 mg/l) of industrial surfactants STMs(a) (СТМх(а)) and Flon-1(c) (Флон-1(к)) at total concentration of hydroxides of 100 mg/l leads to a more efficient passing of the electroflotation process. A process flowsheet for removing suspended matters (a mixture of metal hydroxides) using an electroflotation cell and a microfiltration module is proposed. A model series of electroflotation devices with a capacity of 1–10 m³/h was proposed for application of the described technical solutions. The separation time in the devices does not exceed 10 minutes, power inputs is up to 0.6 kW·h per 1 m³ of the treated wastewater with a recovery rate of 97–99%. The cost of an installation for 10 m3/h does not exceed 1.5 million rubles.

The work was carried out with the financial support of the Mendeleev University of Chemical Technology (project No. Z-2020-004).

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