High-effective technology for the neutralization of Cr (VI)-containing washwater of electrochemical plants

The protection of aquatic environment from pollutions, the most dangerous of which is wastewater containing heavy and non-ferrous metals is one of the most important environmental issues. The processes of electrochemical chromium plating are accompanied by the formation of sewage and washwater containing compounds of highly toxic Cr^{6 +}. However, chromium is of great value in industrial wastewater, and its extraction and reuse in manufacturing can have a significant economic impact. The discharge of such water into surface water bodies without prior purification to the maximum permissible concentrations is prohibited. At present, there are no universal methods of cleaning industrial wastewater from chromium. Various methods, such as: reagent, electro- and galvano-coagulation, ion-exchange, electrodialysis, sorption, membrane separation, biological ones, etc. are used for wastewater treatment. Each of these methods has its own advantages and disadvantages. The analysis of existing methods for the neutralization of chrome-containing spent solutions is described. The work is devoted to the development of technology for the neutralization of Cr (VI)containing washwater of electrochemical plants. Aqueous solution of barium (II) hydroxide as a precipitating reagent is proposed to be used. The temperature of the purification process and the excess reagent-precipitator to obtain a residual concentration of Cr (VI) in purified water at the level of MPC and the maximum rate of delamination of the suspension are experimentally substantiated. Considering that the highest rates of suspension separation are observed in the temperature range 30÷50 °С, the temperature 25÷35 °С and the excess of precipitant 40÷50 % should be considered the most optimal regime for the process of purification of solutions from Cr⁶⁺ compounds