Pigments from spent ammonium chloride zinc plating electrolytes

Abstract

BACKGROUND The volumes of discharged spent plating electrolytes comprise ≈2–3% of the total amount of wastewater from galvanic production. However, the concentration of heavy metal ions they contain is 100–150‐fold higher than in rinsing waters. The periodic nature of such discharges leads to a disruption in the operation of treatment facilities. At the same time, heavy metals could be separated as pigments. RESULTS The article presents the results of studies of the effect of brighteners included in the composition of spent zinc (Zn) plating electrolytes on the composition and structure of the resulting white pigments. The results confirmed the possibility of obtaining white pigments from spent Zn plating electrolytes. It was found that during the deposition of Zn(II) ions from the spent ammonium chloride (NH4Cl) Zn plating electrolytes with sodium phosphate, zinc phosphate predominantly is formed. It was found that the presence of brighteners in the spent NH4Cl Zn plating electrolytes practically did not affect the pH and the degree of deposition of Zn (II) ions, as well as the whiteness of the resulting pigments. CONCLUSION The presence of iron (Fe) ions in the spent zinc plating electrolytes leads to a decrease in the whiteness of the resulting precipitates; however, pigments of the required whiteness can be obtained with contents of Fe(III) of ≤170 mg L−1 and Fe(II) ≤1000 mg L−1. © 2021 Society of Chemical Industry (SCI).

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