Plating operations usually generate four types of metal-bearing waste materials that may be regulated by local sewer authorities, or considered hazardous waste and require special handling. These materials include:
There are four general methods for managing metal-bearing waste materials. Applying these methods can help you:
These methods include:
The first thing to consider when evaluating a metal-bearing waste material is the process by which it is generated. The following questions need to be answered to determine if production of the waste material is unavoidable:
As the handling of metals becomes more regulated, the difficulty and cost of processing or recycling certain types of waste materials may increase. To avoid future problems, a process evaluation should be done on a regular basis. In addition, regular reviews of industry publications will provide information on changes and improvements in process technology.
Recovery of metals for reuse in the facility in which they are generated is usually the least expensive and most effective waste management method because it directly affects raw material needs and costs. Setting up a closed loop of chemical usage in the manufacturing process will require only a minimal input of raw material. If the material cannot be used in the process from which it came, it may be recovered for use in a different process within the facility.
One example of an on-site recovery system is the use of dragout tanks following a plating or process bath. Dragout tanks are filled with water in which processed parts are dipped to rinse off the process solution. When the plating solution levels in the process tanks need to be replenished, the rinse water in the dragout tank. Another example would be to maximize the drain or hang time of the parts over the process bath so that most of the plating solution goes directly back into the bath.
Before an on-site recovery system using dragout tanks is implemented, an evaluation should be made to determine its feasibility. In certain process baths (e.g., chrome and tin baths), using dragout water may not work because of chemical changes occurring in the dragout tank.
Two or more of these methods, along with dragout reduction techniques, can be used together to build an integrated system for reuse of metals, acids, and water. This is also true for the methods described below.
It may not be possible to use all the waste materials reclaimed on site. In this case, a market may exist where a facility's reclaimed materials could be used "as is" or as a feedstock. Examples include:
The characteristics of a company's operation or waste stream may make off-site recycling more practical. For example, cupric chloride etchant is a by-product best handled by an off-site recycler. Metal recyclers have restrictions for the materials they accept; therefore, be prepared to answer the following questions:
Recovery of the resources used in a plating operation is generally easiest when the metal-bearing waste streams are completely segregated from each other. This will usually result in solutions that contain only one metal, making it easier to handle and recycle.
NOTE: Be careful how your waste or by-product is handled and where it ends up, both within and outside the company. Before contracting for services, make sure the material will be recovered, not landfilled or stockpiled. Evaluate contractors for their reputation, cost, and reliability.
Regulations for recycling activities may very depending on your specific circumstance. For any recycling or reuse plan, consult with your local hazardous waste regulators. These are the county health departments in the metropolitan area or the Minnesota Pollution Control Agency representatives in greater Minnesota.
MnTAP has a list of metal recyclers available, along with other publications. If you would like to request this list, or if you have any other questions concerning resource recovery techniques, contact MnTAP at 612/627-4646 or 800/247-0015 is greater Minnesota.