Selective Recovery by Solubilization of Metals Ions of Chromium, Iron and Zinc from Electroplating Sludge to Develop Pigments for Ceramics Industry

Electroplating industries discharge large amounts of heavy metals, including chromium (Cr), iron (Fe) and zinc (Zn) ions, in the wastewater resulted from technological processes, as well as in the sludge from wastewater treatment. In this paper are reported the results of the scientific activity developed in laboratory to recover Cr(VI,III), Fe(III), and Zn(II) from the galvanic sludge by selective solubilization and to obtain metal salts which can afterwards be used as pigments in ceramics industry. Chromium recovery from the sludge was performed by alkaline sludge oxidation to obtain salts of Cr(VI). We aimed at obtaining two types of pigments based on chromium: chromium yellow pigments by precipitation of Cr(VI) in the form of lead chromate (PbCrO4) and chromium green pigments by reducing Cr(VI) and its precipitation in the form of Cr(III). Red pigment based on Fe(III) was obtained by solubilizing the resulting sludge after the recovery of chromium and iron precipitation at a pH corresponding to the complete precipitation. From the remaining solution by recovering Cr and Fe, Zn was recovered as zinc hydroxide [Zn(OH)2] that can be used as raw material in the ceramics industry. In the experiments performed at laboratory scale, optimal technological parameters were set for the selective recovery of the tested sludge metal ions