Optimum Conditions for Applying the Magnetic Absorption Methodfor Decontamination of Ferrous Sulphate and Chromate-Containing Wastewater

The article deals with the acute issue of intensive contamination of surface and underground waters with iron and chromium ions, which reduces the amount of water suitable for consumption. It was noted that because of monitoring the state of transboundary rivers of Ukraine within the framework of bilateral agreements, an unacceptable excess of the content of heavy metal ions was recorded. The main polluters of the water environment are machinebuilding enterprises that discharge untreated or insufficiently treated metal-containing wastewater from the processes of steel etching, chrome plating, etc. Recently, the processing of these solutions to obtain a suspension of highly dispersed particles with magnetic properties–magnetite has been increasingly practiced. One of the directions of its use is the sorption of various pollutants in water environments, i.e., the application of the magnetic absorption method. Our study shows the advantages of using magnetite obtained from sulphate solutions in comparison with the traditional sulphate-chloride solution, the influence of the ratio of iron (II) and (III) ions, temperature, pH, nature of the precipitant, salinity on the dispersion of the obtained magnetic particles. When applying the magnetic absorption method, it was determined that hydrolyzed forms of iron (III) ions are best sorbed on magnetite, the removal process of which from aqueous solutions occurs quite intensively during the first two minutes. During the study of various samples of magnetite, it was established that in acidic solutions, with an increase in the ratio of iron (II) and (III) ions, the efficiency of iron ion removal decreases; in neutral and alkaline solutions, such a dependence is not observed. In the proposed technological scheme, purifying wastewater containing 10–100 mg/dm3 of iron ions is advisable by adding 100–1000 mg/dm3 of magnetite suspension and alkali solution to a pH of 8–9. The study showed that during the treatment of chromate-containing waters with magnetite, in addition to the processes of reduction of chromate ions, oxidation of surface Fe2+ ions to Fe3+, sorption of Cr3+ ions or Cr(OH)3 hydroxides, the reduction of chromate anions on its surface is observed, the basis of which may be the formation chemical compounds, as well as the sorption mechanism. The optimal conditions for removing chromium (VI) compounds from model solutions are to conduct the process at an elevated temperature and use magnetite with a 20 mg per 1 mg Cr6+ consumption.