The plating industry

Transcription

1 The plating industry

2 Environmental issues by electroplating Wastewater (from rinsing processes) Waste (liquid waste, sludge) Air pollution (extraction from hot and toxic process baths) Resource consumption (Energy, chemicals, water, raw material) Soil and groundwater pollution (Spillage and leakages of toxic chemicals) Occupational health and safety Occupational health and safety OHS (toxic vapours, handling of chemicals, noise)

3 Cleaner Production Strategy - The 5 R - Rearrange (processes, equipment, routines, etc) Reduce (pollution, consumption, waste, etc) Reuse (water, chemicals, waste, etc) Replace (chemistry, process, raw material, etc) Recycle (Water, chemicals, waste, etc)

4 Input Water, cleaner salt, NaOH, energy Water Process Metal item Degreasing C Water rinse Output (waste) Sludge, oil, spent bath, water vapour Wastewater with oil, NaOH, cleaner salt HCl or H2SO4, water Water Pickling % Acid Water rinse Sludge, spent bath, acid-vapour Wastewater with acid, Fe, Zn, Cu Water, cleaner salt, NaOH, energy Water Electro cleaning C Water rinse Sludge, oil, spent bath, water vapour Wastewater with oil, NaOH, cleaner salt Acid, water Water Conditioning Acid Water rinse Spent baths with metals Wastewater with acid and metal Chemicals, metal anodes, water Water Process chemicals Electroplating bath Water rinse Chemical treatment Spent process baths, sludge, vapour Wastewater with bath chemicals Spent bath with Cr, Fe, Zn, Al Water Water rinse Wastewater with Cr, Fe, Zn, Al Plated item

5 Automatic nickel-chrome line

6 Technical silver line (encapsulated)

7 Degreaser tank with cover and extraction

8 Anodising of aluminium items

9 Racks for small items

10 Double barrels for zinc plating

11 Checklist for electroplating Consumption of chemicals per m 2 production is a very important key figure Maintenance procedure and lifetime for process baths Water consumption and rinsing procedures Waste generation and waste minimisation Wastewater treatment and monitoring of wastewater discharge Occupational health and safety

12 Rinsing strategy to save water and money and improve quality Define rinse water quality (Dilution, concentration, conductivity, hardness, etc.) Control water flow (Flow-meter, restrictor, magnetic valve, etc.) Minimise drag-out (dripping time, withdrawal speed, hanging) Use rinsing system correct (agitation, air, inlet/outlet, tank design, etc.) Change of rinsing system (Drag-out, counter current, spray, ion-exchanger, reuse treated wastewater, etc.)

13 Dilution factor Dilution factor F is the dilution ratio of process bath and last rinse in a rinse system. In a nickel bath Ni = 70 g/l. By F = 10,000 the final concentration in the rinse is 7 mg/l Rinsing process After cleaning and pickling Before electroplating bath After bright chrome Final rinse after other plating baths Typical dilution factor 100 1, ,000 5,000 10,000 1,000 5,000

14 Rinsing between two process baths Rinsing is important to stop remove drag-out chemicals to stop reaction and avoid contamination of next process bath Item transport Item transport Process bath 1 Rinse Process bath 2 Wastewater Wastewater

15 Counter current rinse By counter current rinse you may save 90-99% water. Many tanks are needed and the plating line will be very long. It is the most usual water saving method Item transport Item transport Item transport Water Process bath Rinse 1 Rinse 2 Rinse 3 Wastewater

16 Drag-out rinse tank A drag-out tank (static rinse) will save 25-75% chemicals and water. A drag-out should also be used as a pre-dip after cold process baths. Evaporation loss DI-water Process bath Drag-out rinse Rinse 2 Tap water Wastewater

17 Water recycling using ion-exchanger Ion-exchangers are very useful for saving water. Normal two rinse tanks are sufficient to run optimum. By regeneration the chemicals are removed from the resin in the ion-exchanger. Evaporation loss Process bath Drag-out rinse Rinse 2 F Cat An Ion-exchanger plant

18 Ion-exchangers for rinsing

19 Controlling the water flow

20 Transport of rinse water by air-lift pumps

21 Transport of rinse water by air-lift pumps

22 How to save chemicals Ensure a good pre-treatment Control of bath chemistry to obtain a good quality and to avoid reject and rework Minimise drag-out Use drag-out tanks Use low-concentrated electrolytes if possible Train the operators to work proper Good maintenance of the process bath to prolong the lifetime of the bath Avoid unauthorised persons to control the process (Management system)

23 Analysis of process baths

24 Filtration of process baths

25 Wastewater treatment principles Wastewater inlet Detoxification (chromate, cyanide, complex) Neutralisation and Precipitation Separation of sludge Post-treatment Outlet to sewer

26 Chemical treatment processes Reduction of chrome(vi) Cyanide oxidation with chlorine or hydrogen peroxide Oxidation of ammonia with chlorine Destruction of complexing agents Chemical destruction of oil emulsions Precipitation of heavy metals as metal hydroxides Precipitation of heavy metals with sulphur chemicals Precipitation of phosphate with Fe, Ca or Al Precipitation of fluoride as calcium fluoride

27 Precipitation and settling

28 Precipitation and settling

29 Wastewater plant overview

30 Wastewater plant overview

31 Wastewater filtration in sand filter

32 Sludge drying in air

33 Sludge dewatering in filter press