Scholarly record

INFLUENCE OF SURFACTANTS ON PHYSICAL AND CHEMICAL PROPERTIES AND EFFICIENCY OF ELECTROFLOTATION REMOVAL PROCESS OF THE DISPERSE PHASE OF SLIGHTLY SOLUBLE METAL COMPOUNDS FROM CONCENTRATED ELECTROLYTE SOLUTIONS

V. А. Brodskiy, Yulia Malkova, Roman Yakushin, Ekaterina Kondratieva, Ekaterina Bandina

Abstract

The present study has been dedicated on the removal process of heavy metal ions from electrolyte solutions by using methods of electroflotation and subsequent filtration in a multi-component system with the presence of various surfactants of different nature. The research was conducted in a five-component system comprising ions of iron (II), nickel (II), copper (II), plumbum (II), and zinc (II) (the total concentration of metal ions is 200 mg/l). The research was conducted in a highly concentrated electrolyte solution (the mixture of NaCl and Na2SO4 salts with a concentration of 100 g/l in the mass ratio of 1:1). The samples of solutions selected for the study are similar by composition to the waste technological solutions and wastewater from electroplating facilities, mechanical engineering enterprises and non-ferrous metallurgical industry. The mentioned solutions contain significant amount of toxic heavy metal ions that are dangerous for the environment and human health. The study was conducted in the system with pH = 10. The metals used in the study are characterized by various pH-values for hydrates formation and solution. This finding allowed evaluating the contribution of mutual sorption of hydroxides to the efficiency of electroflotation and filtration processes. The first stage of the work included the investigation of the effect of various surfactant of anionic, cationic, nonionic and amphoteric types related to the electrokinetic potential (?-potential) formation mechanism and the average hydrodynamic diameter (dav) of heavy metal dispersed phase particles in the multi-component system. It was established that in a system without surfactants, the electrokinetic potential of the dispersed phase had a negative value (-7 mV). This can be explained by high concentration of sulfate anions in the solution. It?s identified, that addition of the anionic surfactant (sodium dodecyl sulfate) to the solution causes an increase the ?-potential of slightly soluble heavy metal compounds (Fe(III)-Ni(II)-Cu(II)-Pb(II)-Zn(II)), and brings its value closer to the isoelectric point (± 0 mV). In the case when the cationic surfactant (alkyldimethyl (2-hydroxyethyl) ammonium chloride) was added an increase of the ?-potential of particles to a positive value equal to 5,3 mV has been observed. The percentage ratio of fine and coarse particle fractions was identified during the study of dispersed phase particle size of slightly soluble metal compounds in the multi-component system. It was shown that the ratio varies depending on the nature of the surfactant. For example, with the addition of a cationic surfactant, small particles with a size of fewer than 2 microns (75% of the total number of particles) prevailed. However, the contrary situation is being observed with the addition of an anionic surfactant, i.e. an enlargement of the dispersed phase up to 105 ?m is noted, but the amount of such particles does not exceed 40% of the total amount. It is noted that nature and functional group of a surfactant both play the main role in the stable foam layer formation during the electroflotation process. The second stage of the work included the investigation of the effect of the surface characteristics for the dispersed phase and composition of the solution on the efficiency of electroflotation removal of slightly soluble compounds of iron (III), nickel (II), copper (II), plumbum (II), and zinc (II) in the multicomponent system. Results of the work show that the anionic surfactant addition increases the efficiency of the electroflotation treatment of concentrated electrolytes from heavy metal compounds by to 97 ? 98% for all the metals in the system with an optimal pH = 10. The subsequent filtration of the solutions allows to reduce the residual metal concentration to the following values: 0,05 mg/l for Fe (III), 0,01 mg/l for Ni (II), 0,05 mg/l for Cu (II), 0,05 mg/l for Pb (II) and 0,14 mg/l for Zn (II). Cationic, nonionic, and amphoteric surfactants addition to the solutions does not enhance the efficiency of the electroflotation process and complicates the electroflotation process in systems with amphoteric and cationic surfactants. This effect can be explained by the positive charge of dispersed phase in the presence of a cationic surfactant. In this case an enlargement of the dispersed phase is rather difficult and the smaller particles can?t adsorb on the surface of the larger particles. The addition of the amphoteric surfactant leads to a significant enlargement of 40% of particles (up to 110 ?m). At the same time, difficulties are observed during the formation processes for both foam layer and flotation complex that are caused by the dispersed phase negative charge.

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