Adsorptive extraction of chromium (VI) ions from corrosive aqueous solutions

Abstract

Chromium is one of the most effective metals used for protection and decorative coating of various products. However, chrome plating typically occurs in a strongly acid medium, thus involving the formation of dangerous and corrosive solutions. In this article, we investigate the possibility of removing chromium from such solutions using carbon adsorbents, which allow for almost complete extraction of the metal from production solutions up to a residual content of no more than 0.05 mg/dm3. A significant advantage of carbon adsorbents is their ability to extract chromium (VI) ions without chromium reduction to the trivalent state. It was established that the sorbent under study exhibits the maximum sorption capacity in a strongly acidic medium at pH = 1.2–2.5. This medium causes the formation of a Cr2O7 2- dimer in the solution, which is an adsorbed ion. A scheme of a production unit for chromium adsorption from solutions of electrochemical production was proposed. The choice of an adsorber with a fluidized bed was determined by the maximal interaction of the flow with the adsorbent in such reactors. The adsorber design in the form of a cylindrical column with tapered upper and lower parts assumes installation of distribution grids inside the apparatus. It is proposed to forward the chromium-containing solution of electrochemical production remained after the averaging tank directly to the adsorber with the loading of the carbon adsorbent. In order to ensure the continuity of the extraction mode, it is necessary to apply two parallel working adsorbers, whose technical parameters were calculated to be as follows: the diameter of 1.2 m; the height of 7.5 m; the loading volume of 5.9 m3; and the loading height of 6 m. The calculated process parameters were determined: the linear flow rate along the walls of the adsorber – 12.75 m/h; the duration of the apparatus operation before coal regeneration – 21 days. The proposed scheme can be recommended for recycling water supply.