Managing nickel processes to achieve operating compliance

TECHNlqLLY speal\.lng BY HUW WILLIAMS, SERFILCO EUROPE LTD., MANCHESTER, UNITED KINGDOM

Managing Nickel Processes to Achieve Operating Compliance Reducing fume emissions above tanks while minimizing occupational exposure to reclassified nickel salts.

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h is paper explores modern agitation and filtration methods that reduce occupational exposure to recently reclassified nickel salts while improving process efficiencies, reducing processing costs and minimizing energy requirements and filtration costs. The European Union recently announced plans to reclassify nickel salts commonly used in nickel plating processes, thereby limiting exposure to nickel mists above process tanks. This legislation is particularly relevant to metal finishing and aerospace companies, as the legislation includes soluble salts of nickel sulphate, nickel sulphamate and nickel chloride. Pumped flow eductor agitation is now widely used as a replacement to air agitation to reduce fumes to immeasurable levels above tanks. This paper covers this technology in detail, including design criteria as well as outlining other quality, cost and process benefits. Alongside fume emission controls, recommendations are also in place to minimize skin contact to soluble Nickel salts to prevent skin irritation. This paper outlines filtration and purification techniques that will reduce potential exposure whilst reducing filtration costs and improving quality. Environmental and health and safety issues have dominated agendas throughout the metal finishing

November 2008 I metalfinishing I 22

industries for several years. In Europe the implementation of IPPC legislation (Integrated Pollution Prevention and Control) certainly increased pressure on chemical processors in areas such as fume emissions and generally in the way that processes are managed. All platers and anodizers with 30m3 or more of chemicals for processing now need to operate with an IPPC license, which is audited on a regular basis. Alongside these environmental and waste management issues, the health and safety of operators in processing environments has also been considered. Legislation regarding the use of hexavalent chromium solutions was followed by further changes to permitted exposure levels to sulphuric acid mist. Soluble nickel compounds used in plating operations are now being reclassified, and some operational improvements are being recommended to control the potential health hazards identified. The legislation and recommendations consider the inhalation of nickel mist and also potential problems associated with skin contact. Nickel mist through inhalation is to be reclassified as a Class 1 carcinogen and Control of Substances Hazardous to Health (CoSHH) requires that skin exposure to nickel is prevented or adequately controlled in the workplace. The substitution of nickel plating operations is not an option and , therefore, exposure cannot be pre-

vented; the law now requires that exposure is adequately controlled, meanmg:

-The process is totally enclosed unless this is not reasonably practicable - Exposure is less than the work place exposure limit (WEL) of 0.1 mg/m3 (as nickel as an a-hour time weighted average) • Exposure is reduced to as low as is reasonably practicable As total enclosure is not an option, the Health & Safety Executive (HSE) recognizes that the use of eductor agitation in nickel processes is a proven method of solution agitation that reduces fume emissions above tanks to immeasurable levels. This paper highlights this technology, alongside filtration methods that remove any manual intervention, thereby reducing skin contact when changing filters.

PART 1-S0LUTION AGITATION Agitation is required in nickel-plating operations to: 1. Provide a mass movement of solution around the tank to generate a completely homogenous solution. 2. Provide a constant supply of plating ions along with other brighteners and wetting agents to the substrate. 3. Disperse hydrogen away from work interface, thus preventing gas pitting. 4. Disperse heat away from work to prevent burning and produce continuity of surface properties. 5. Eliminate temperature stratification-generating constant temperature throughout the tank 6. To encourage dissolution of anode materials.

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solution. Foam and noxious chemical fumes are produced, which creates an unpleasant and potentially dangerous working environment as well as increasing the need for extraction.

Figure 1: TypicaL arrangement of an air-agitated tank.

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Eductor agitation installation on plating tank with 2 x cathode stations.

Common Methods of Solution Agitation. (Air Agitation). Compressor or blower generated air distributed through tank via an arrangement of sparge pipes (Figure 1).

Some Inherent Problems with Air Agitation. Heat and chemical losses to air are increased due to the explosion of air bubbles at the solution surface and the increased surface area of the

• As the air bubbles explode, latent heat leaves the tank, thereby increasing the energy requirements to maintain operating temperature-which has a significant impact on the operating costs of a plant and is particularly relevant when considering the climate change levy. • Air agitation is often very uneven as the sparge pipes block. It is very common to see plating tanks

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that are highly turbulent in one corner yet static in other areas. • Air is inherently non-conductive. thereby reducing the efficiency of the electrolyte • Brightener usage is increased through oxidation Cathode Rod Agitation. Side-to-side or up-and-down movement of cathode bar. This type of agitation can be conside red as compliant with current h ealth and safety requirements although the re are technical limitations in terms ofuse with nickel solutions.

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Table 2: Relation of Chamber Size to Length of Filtration Process

Pumped Flow Eductor Agitation. Eductor agitation is now firmly established as the alternative method of agitation to the use of air, and its use in nickel plating operations is recommended by the health and safety execu tive in UK as a means of complying with new legislation. Principal ofOperation. Eductor nozzles use the Venturi principle to amplify and direct solution flow from the pump to the required area of the tank (Figure 2). For one liter of solution pumped through the eductor at the required pressure, the discharge flow from the nozzle will be five liters. In simple terms, a very high tank turnover rate of solution can be achieved from a relatively small pump. Solution can be d irected easily within the tank with strategic positioning of the nozzles . H ere the ed u cto rs are fitted to a manifold along the middle of the tank flo or and will gen erate a rolling agitation as the flow deflects from the tank wall and circulate around the wo rk. This arrangement would often be used where direct impingement needs to be avo id ed (e.g. electroless nickel and alkaline non-cyanide zinc). Generally, systems a re considered on a case-bycase basis and any arrangement of eductors can be used to generate the best results. Another example, for instance, November 2008 I metalfinishing I 24

Flow Characteristics of Eductors. Table 1 shows the flow and pressure requirement of the different sizes of eductor. The minimum flow and pressure is the point at which the Venturi principal works, generating the extended net flow from the nozzle . You can see that to apply the multiple of five for the relationship

would be a tank plating stacked wheel rims. Here, the positioning of the eductors would need to be specific to ensure fresh solution can pass between the gaps between the rims and also generate a circular motion around the outside. Here, eductors placed on vertical manifolds in the tank corners would be used. 10 _ "'-_1111

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between flow in and out of the eductor the pressure increases in line with the flow. Improvements reported in nickel processes where eductors have replaced air:

• Reduced noxious fumes above the tank to immeasurable levels • Reduced evaporation of chemicals • Improved solution conductivity generating power savings of upto 2S% • Reduced brightener consumption www.metalfinishing.com

• Improved distribution leading to metal savings • Improved temperature distribution (± o.s-c) • Reduced heating costs • Reduction in gas pitting • Improved filtration • Improved throwing power PART 2-FILTRATION AND PURIFICATION SYSTEMS DESIGNED TO MINIMIZE OPERATOR EXPOSURE TO NICKEL SOLUTIONS

In the guidance notes regarding nickel, filtration maintenance has been highlighted as a function that can lead to operators' skin in contact with nickel. It is estimated that approximately 1%of males and up to 10% of women are allergic to nickel and once one has become sensitized, any further exposure can put an operator at risk of an allergic reaction. Therefore, a sensible choice of filtration system would be a unit that requires little or no maintenance and can, therefore, either be an automatic permanent media type, or contain a sufficient dirt-holding capacity to provide for extended change-out periods.

Filter Systems with Consumable Media. To provide for extended change-out schedule, a cartridge system is recommended with an oversized chamber to provide maximum dirt-holding capacity (see Table 2). The chart demonstrates that by oversizing the filter chamber, a much longer period of filtration is provided as the flow velocity per cartridge is significantly lowered. In many cases, changing from a disc system, for instance, being changed twice a week, a cartridge system could be provided for change-out only once in six weeks. Automatic Backwash Permanent Media Filtration Systems. For larger process tanks, the use ofan automatic permanent media filter should be considered. A PLC-controlled permanent media filter, once commissioned, is maintenance free. There is no consumable filter media required and, therefore, no disposal costs or any exposure risks. The filter vessel contains the support media and filter media along with the filter and air laterals and manifold systems that together control the filtration and backwash flow while preventing any migration of the media. The system maintains a high flow rate and, therefore, crystal clear electrolytes by automatically backwashing the media based on a preset low flow relay. Sequence ofoperations (Figs. 3a-3d): • Filtration • Blowdown #1 - air purge solution back to tank November 2008 I metalfinishing I 25

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• Backwash • Blowdown #2 - air purge water to effluent • Filtration CARBON PURIFICATION Historically, powdered carbon was used with nickel solutions to remove organics generated through chemical breakdown and drag-in. Powdered carbon techniques are very messy indeed and often result in downtime, solution loss and clearly exposure risks. Achieving organic control by employing bypass methods with activated granular carbon is proven to be successful and present the plater with a user friendly, clean and easy method of organic removal. The carbon is held on a separate chamber downstream ofthe main filter and a percentage of filter flow is directed to the carbon. This is achieved by simply opening a valve

and to maximize the usefulness of the carbon only "just filtered" solution passes through. For complete avoidance of exposure risk, a mobile carbon chamber can be linked with a permanent media filter via a quick release valve system. When the carbon is spent, the whole chamber can be moved to the effluent plant and connected to a water supply to thoroughly rinse the carbon prior to opening the chamber. Benefits of combining bypass carbon treatment with automatic permanent media filter:

• Reduces operator exposure to nickel salts • Reduces downtime and filtration costs • Produces crystal clear electrolytes by maintaining a high average flow rate • Reduces roughness and improves quality • Provides for uniform ductility • Provides for the most cost-effective and user-friendly organic removal

SUMMARY It is clear that legislators continue to

reassess chemicals widely used in the metal finishing industries and changing legislation can create some problems for platers and anodizers. However, in many cases, employing innovative technologies in various aspects of the finishing process can actually be very cost effective. While the justification is driven by legislation, there are many added benefits that can be achieved by making the investment.

810 Huw Williams works out of SERFILCOJs Manchester; U.K, offtce. He may be reached via e-mail at [email protected].

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