Ефективність інгібіторів корозії металів у водних середовищах різної мінералізації

Abstract

EFFECTIVENESS OF INHIBITORS OF METAL CORROSION IN AQUEOUS ENVIRONMENTS WITH VARYING SALINITYThe main reason for the growing problem of water quality in Ukraine is the increase of anthropogenic impacts on water resources caused by intense chemical, biological and radiation contamination of existing and potential sources for industrial and communal water supply. Especially polluted rivers in Donbass and Krivbas area, that turned into collectors of saline wastewater. Especially hard environmental conditions is observed in areas of location of major coal mines and coal processing factories, steel plants, machinery and coal chemistry enterprises. The mining activity impacts the water basin in form of changes in the water regime, adds up to water pollution and contamination. Mine water is derived from groundwater and surface water penetrating into the mine working. Flowing into openings and in rocks, they become contaminated by bacteria, suspended matters, including radioactive and soluble chemicals. The mineralization level and chemical composition of mine water are very diverse and depend on the type of mined ore or coal, the depth of mines, composition of groundwater and other factors. To prevent corrosion of equipment due to use of substandard water with high salinity variable chemical composition of mine water requires special treatment, which reduces the corrosion activity of mine water to highly corrosive action of drinking water quality.The tap water (Kyiv) and artesian water, that comply with requirements to drinking water, were used for comparison. For the experiments, clarified water from colliery group «Pokrovsky» and a model solution with salinity ~ 30 g/dm3 were used. Corrosion largely dependends on water salinity. Anions in solution can be adsorbed onto metal surface and significantly affect the corrosion, accelerating or reducing it. For example, most of iron alloys corrode in seawater much faster than in water with the same concentration of oxygen and the absence of chlorides. This is due to the adsorption of chloride-ions onto the iron surface that prevent the formation of protective layers composed of corrosion products.When using polyphosphates and phosphonates in the presence of zinc ions in the model solution, the impact of inhibitors on the corrosion rate of steel St. 3 was not observed. This applies to sodium o-phosphate, sodium hexametaphosphate (SHMF), sodium tripolyphosphate (STPP), oxyethylidenediphosphonic acid (OEDFA) neither individual nor in the presence of zinc ions.In highly mineralized media – the model solution and clarified water from colliery group «Pokrovsky», oxygen passivation film was not formed, so for none of the studied metals corrosion rate was decrease when applying corrosion inhibitor – OEDFA, Zn2+. In case of highly mineralized solution, when passivation or diffusive oxide-hydroxide protective film is not formed on the metal surfaces, the best way to prevent corrosion is to reduce the oxygen concentration in the water. This can be achieved by adding a reducing agent to the solution, for example, sodium sulfite. This reagent decreases the corrosion rate of alloy-free and stainless steel to the values, lower than not only in the model solution, but also in tap water. The corrosion protection for the steel St. 3 reaches 91 % compared to the model solution and 85 % compared to tap water..