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Sources, Effects and Treatment of Effluents in Electroplating Industry

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Electroplating Industry

ELECTROPLATING INDUSTRY:SOURCES, EFFECTS AND TREATMENTOF EFFLUENTS CleaningRemoval of Grease, due to machining, stamping, polishing.Organic grease removed by saponification with alkaliPetroleum & Mineral grease benzene, gasoline, carbon tetrachloride used Most commonly employed method is emulsification with alkalisspent cleaning solutions are discharged as waste water. StrippingRemoval of rust and scaleFor articles made of iron, H2SO4 or HCl usedelectrolytic method is also being used increasinglyFine sand particles remaining on the surface due to sand blasting can be removed separately by hydrofluoric acidspent acid solutions and rinse waters constitute the waste water Platingpickled articles are placed in wooden or mild steel vats with special liningOr in tanks made entirely of polymer materialmetal to be plated is made the cathode in an electrolytic cell.Plating baths are acidic in nature and generally contain H2SO4 , HCl or HNO3 Alkaline baths containing sulphide, carbonate, cyanide and hydroxide are also used.concentration of chemicals normally used in some of the common plating baths is shown

RinsingAfter plating, objects are rinsed with water.First dipped in stationary water baths, which are allowed to drain.Then dipped in running water baths to remove the adhering plating solution.Stationary baths are utilized to make solution for the plating operations.Running water baths are discharged into the drains.

Cleaning Solution Spent Alkaline and Rinse waters Acid Pickling and Rinse Waters Cyanide Concentrates Chromate Wastes Metal wastes from Plating baths Floor Washes Regeneration Wastes from Ion-Exchange Columns Other Wastewaters Composite Wastewaters

Composite WastewatersCyanide TreatmentAlkaline ChlorinationpH = 10.52NaCN + 5Cl2 + 12NaOH N2 + 2Na2CO3 + 10NaCl + 6H2O

Two methods are suggested:Batch TypeContinuous Type

Batch treatment for Cyanide wastes

Continuous treatment of Cyanide wastes

Ferrous Sulphate TreatmentpH = 7.5 to 9.0Formation of dark blue sludgeLarge sludge and odor produced

6NaCN + FeSO4 Na2SO4 + Na4Fe(CN)6

Chromium TreatmentChromates, dichromates and chromic acid occur in the waste waters generated from chromium plating, anodising, and other metal finishing operations.Hexavalent chromium ions in these wastes are highly toxic even in very low concentrations.treatment involves reduction to trivalent state and subsequent precipitation with an alkali.Ferrous sulphate along with sulphuric acid is commonly used.Maximum reduction occurs in the pH range 2.0 to 2.5.

H2Cr2O7 + 6FeSO4 Cr2(SO4)3 + 3Fe2(SO4)3 + 7H2O + 6H2SO4

Cr2(SO4)3 + 3Ca(OH)2 2Cr(OH)3 + 3CaSO4

Fe2(SO4)3 + 3Ca(OH)2 2Fe(OH)3 + 3CaSO4

Batch Treatment of Hexavalent Chromium Wastes

Continuous Treatment of Hexavalent Chromium wastes

Treatment of Other Metal bearing Wastescommon holding tank is normally used for all the metal wastes.Precipitation occurs in the holding tank if the pH is on the alkaline side.To prevent settling and to ensure proper mixing, agitation is provided.Almost all the metals precipitate completely in the pH range of 9.5 to 10.5.

Batch Treatment of metal wastes not containing hexavalent chromium

Continuous treatment of metal wastes not containing hexavalent chromium Metal Recovery by Soluble ConcentrationIn large electroplating industries, chrome, nickel and copper in acid type plating solutions are reclaimed from the rinse tank by evaporation in glass-line equipment or other suitable evaporators and the concentrated solution returned to the plating system. This process appears to be economically feasible, where chemical quantities involved are relatively large and would justify recovery

Overall Flow Sheet for treatment of various wastes from electroplating worksStandards by CPCB

Abhishek Koul13201001M.E Environmental EnggThank You