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