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By JenCartmell *

The aqueous waste generated by the

plating industry is being disposed in many ways including incineration, but modern treatment methods developed by the waste management industry are able to extract and recycle

many of the valuable metals contained in the wastes.

And even non- recoverable wastes

such as cyanide and chromic acid can be treated to remove the hazardous properties and made safe for disposal to sewer.

Twoofthe main metals inherent in electroplating aqueous wastes which are being recovered in bulk are nickel and copper but silver,chromium, cadmium, iron and zinc are frequently present and are also capable of being recovered.

As specialists in the treatment of both hazardous and non-hazardous wastes Cleansing Service Group is involved in both developing and operating new processes for the recovery of materials from aqueous wastes.

One of the main breakthroughs made recently is the development of aprocess to recover valuable nickel from spent electroless nickel solutions.

Electroless nickel is most commonly used in eng- ineering coating applications where excellent wear resistance, hardness and corrosion protection are required although there is avery wide range of other applications including use as acoating in electronics printed circuit board manufacturing.

Produced by achemical process alone without the need for an electric current, the electroless process relies on the presence of areducing agent, for example hydrated sodium hypopho- sphite, which reacts with the nickel ions to deposit metallic nickel. This plating technique prevents corrosion and wear and has several advantages over electroplating.

Waste electroless nickel contains up to 5g/litre of nickel, but due to the complexity of chemical reactions occurring during the electroless nickel plating process ahost of contaminants are also present such as complexing agents, solids (suspended & dissolved),

52 SURFACEWORLD april 2013

organics &contamination from handling in tanks, tankers, containers etc.

It has been possible for along time to use electrolysis to recover nickel from solution but, as the electrolyte needs to be relatively pure to achieve any degree of success, recovery of waste nickel solutions on acommercial scale has remained elusive.

The purpose-built plant developed by CSG recovers valuable metal, particularly nickel, but also copper,from metal bearing waste solutions using amulti-stage pre-treatment process centred on IEX (Ion Exchange) technology to concentrate and purify the waste solutions, followed by Electrowinning to recover the pure metal.

It is the development of an extensive intermediate process rather than ‘off-the-shelf’electrolysis technology that makes CSG’s process unique.

The first treatment step is through an Ion- Exchange Unit that selectively retains the nickel whilst allowing other contaminants to pass through. Following removal of the metals through the Ion Exchange the aqueous effluent undergoes further treatment to make it suitable to be discharged to asewer.

The nickel sulphate solution resulting from the pre-treatment process then goes to the Electro- winning plant. This consists of 15 cylindrical cells, each capable of plating up to 25 Kg of metal.

Each cell produces acylinder of pure metal 1200mm long and weighing about 25 Kg.

The recovered metal is up to 99.9 percent pure and the very low final concentration in the means that 99.9 percent of the metal has been recovered.

The plant is also being used to recover copper at 99.9 percent purity.This is asimpler operation with none of the tight variables experienced in developing the nickel recovery process.

Whether it is nickel or copper being recovered, or any of the other valuable metals, the company

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