Metal Finishing Guide Book


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environmental controls WASTE MINIMIZATION AND RECOVERY TECHNOLOGIES BY W. J. MCLAY DEDIETRICH PROCESS SYSTEMS INC., UNION, N.J.; AND F. P. REINHARD CH2M HILL, EAGAN, MINN. The surface-finishing industry is a chemical-intensive industry. A special category of chemical processes, characterized primarily as electrochemical processes, are used to treat and condition, or ���finish,��� the surfaces of a variety of manufactured goods and components to either enhance visual appeal, improve corrosion resistance, or to increase product durability or serviceability. Some providers of finishing services, and most manufacturers with in-house finishing operations, are understandably inclined to view themselves as purveyors of finishing services for the end products that they process or as producers of the products that are manufactured, rather than as operators of chemical plant and chemical producing processes. Surface-finishing processes certainly fall under the definition of chemical processes. As such, they are no less subject to the limitations and laws of chemistry and physics and to good process design and chemical engineering practice. The similarity of chemical production processes and surface-finishing processes is strong. At the heart of electroplating and waste-treatment operations, one finds many of the classic chemical unit operations and process techniques common to chemical production: mass and energy transfer, fluid flow, mixing, evaporation, reaction, sorption, crystallization, concentration/dilution, solid/liquid separation, etc. A broad variety of chemicals is used by the finishing industry; however, only a small fraction of the chemicals purchased for bath make-up and operation is ultimately incorporated in the finished goods. While chemical manufacturing processes generate more hazardous waste on a tonnage basis, surface-finishing processes lose a disproportionate quantity of purchased chemicals as byproduct hazardous waste. The value associated with this wastage, plus the added cost of treatment and disposal, constitute major pressure on operating margins and profit. In addition, finishing operations also require equally disproportionate quantities of process water per unit of production for parts cleaning and preparation, for bath make-up and maintenance and, of course, for rinsing. In many parts of the country the availability of quality process water is becoming a major concern to the finishing industry. The price and conditioning costs of raw water are also increasing. Many finishers are looking for practical ways to limit water usage and to recover and reuse as much process water as possible. Some firms have achieved, or are approaching, the elusive goal of zero liquid discharge. Also, the added incentive of potentially not requiring an effluent discharge permit has strong appeal. In addition, finishing processes cannot be operated with the same degree of control common to many chemical production processes. By definition, many 637

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