Establishment of regularities of electroflotation extraction of non-ferrous metal (Cu, Ni, Zn, Co, Fe) hydroxides from wastewater of various compositions in the presence of industrial surfactants

Abstract

The electroflotation process of extracting a mixture of Cu, Zn, Ni, Co, Fe hydroxides from wastewater containing NaNO 3 , NaCl, Na 2 SO 4 , Na 2 CO 3 , Na 3 PO 4 , NH 4 OH 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 Na 3 PO 4 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 Na 3 PO 4 is associated with a small particle size (about 20-30 μm) and a ]-potential high negative value, what has an injurious effect on the formation of the flotation complex, negatively charged bubbles (H 2 , O 2 ) 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 m 3 /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 m 3 of the treated wastewater with a recovery rate of 97-99%. The cost of an installation for 10 m 3 /h does not exceed 1.5 million rubles.

Electrochemical Techniques Applied for Industrial Wastewater Treatment: A Review

“…It gets its name from the bubbles generating process it employs, which is electrolysis of the aqueous medium. Some of the technique's advantages should be highlighted: the electrode grids may be set to give adequate coverage of the whole surface area of the flotation tank, resulting in homogeneous mixing of the wastewater and gas bubbles (Kolesnikov, 2021).…”