title: Final decontamination of the filtrates obtained after interaction of two ligand-containing Cu2+ and Zn2+ electroplating solutions.
abstract: A cheap and simple way to decontaminate two ligand-containing rinsing waters of metal finishing has been previously suggested. Both the copper diphosphate-containing rinsing wastewater and acidic zinc ammonium-containing rinsing wastewater may be decontaminated by mixing them which results in precipitation of solid solutions of copper-zinc-potassium-ammonium diphosphates. This way of decontamination requires no expensive reagents since only a small amount of H2SO4, is needed for pH adjustment. 80-99.5 % of environmentally dangerous substances, viz. zinc, copper and diphosphate, are removed from the mixture. However, Cu2+ and Zn2+ amounts in filtrates significantly exceed the discharge consent level (DCL). Besides, high concentrations of undesirable diphosphate and ammonium ions, which cause the eutrophication of natural water reservoirs, are present in the filtrates. There are relatively small concentrations of heavy metals: Cu2+ (approximately 0.4 mM dm-3) and Zn2+ (approximately 1 mM dm-3), and relatively large quantities of ligands: P2O7(4-) (approximately 20 mM dm-3) and NH4+/NH3 (approximately 500 mM dm-3) in these filtrates. Our investigation has shown, that decontamination may be easily achieved in industry by using cheap materials or industrial by-products: lime, MgO, phosphogypsum, extractive phosphoric acid and spent steel etching solution. Using lime, Cu2+ and Zn2+ ions may be removed below their DCL. After that, diphosphate ion concentration may be reduced approximately 1000 fold by addition of spent steel etching solution or continuous mixing with phosphogypsum. The amount of NH4+/NH3 may be reduced 20 to 30 fold, the concentration of soluble phosphates -- 5 to 40 fold and both c Cu2+ and c Zn2+ -- lower than their DCL by precipitating barely soluble fine crystalline MgNH4PO46H2O (struvite).
authors.affiliation: Institute of Chemistry, A. Gostauto 9, 01108 Vilnius, Lithuania.
authors.forename: A
authors.initials: A
authors.lastname: Pigaga
authors.forename: A
authors.initials: A
authors.lastname: Selskis
authors.forename: V
authors.initials: V
authors.lastname: Pakstas
authors.forename: A
authors.initials: A
authors.lastname: Selskiene
mesh_terms: D003300:Copper / Q000302:isolation & purification*; D004595:Electroplating; D005374:Filtration; D007220:Industrial Waste; D008024:Ligands; D010710:Phosphates / Q000737:chemistry; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D014865:Waste Disposal, Fluid / Q000379:methods*; D014873:Water Pollutants / Q000302:isolation & purification*; D015032:Zinc / Q000302:isolation & purification*
chemical_list: D007220:Industrial Waste; D008024:Ligands; D010710:Phosphates; D000644:Quaternary Ammonium Compounds; D014873:Water Pollutants; D003300:Copper; D015032:Zinc