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FACILITY CONCEPT The six heavy metals used by electroplating and printed circuit board firms which are currently discharged into the sewer and are now subject to pretreatment standards are copper, chromium, nickel, cadmium, zinc and lead. These metals along with cyanide, which is also present in some of these waste waters, will be treated at the Facility so that participating firms can comply with discharge regulations. A preliminary Facility concept has been developed as part of a proposal submitted by MRC to the MWCC, as well as the conceptual feasibility work done for the Metropolitan Councils' Resource Recovery Task Force. While certain components of the Facility's scope may change as a result of pilot scale testing and preliminar.•y design work, major components described in this section are expected to be incorporated into the Facility's final design. Explicit in the Facility's design is treatment and recovery. The treatment technologies include those processes which render the aqueous inorganic wastes received by the Facility more amenable to recovery, less expensivue to handle and/or less hazardous to manage. The use of these treatment processes may occur as in -plant modifications in the electroplating or printed circuit shops participating in the project, or done at the Facility itself. The recovery ;systems, on the other hand, are those processes designed to extract raw materials (chrome, nickel, zinc, etc.) from appropriately treated wastes. A general process flow sheet is presented in Figure 1. This shows the overall relationship of the incoming feed stocks to the Facility's various treatment technologies and recovery systems. The incoming feedstock includes Yon exchange canisters, metal -specific waste water solutions (batch dumps) and solids (metal -specific and mixed metal sludges). The following individual treatment and recovery systems that are to be involved in the proposed Facility are described in detail. Ion Exchange The ion exchange process is a stoichiometric chemical reaction whereby an ion from a solution is exchanged for a similarly charged ion that is attached to an immobile solid particle. These particles make up a granular solid called an ion exchange resin. This process is utilized in the metals pre-treatment process to concentrate the metals present in the waste water at the plant so that transportation of the metals to the Facility for recovery will be more economical. Ion exchange may also be used to treat spent plating baths as an end of pipe treatment but its greatest value is in the recovery applications. A-2