Sands used in the production of brass and bronze castings often pick up lead contamination and must be disposed of as hazardous waste. It has been reported (HazTECH News 1988) that Pittsburgh Mineral and Environmental Technology, Inc. has developed a process that can recover more than 90 percent of the metal value from the sand and render the sand nonhazardous.
Table 5-1 summarizes the waste reduction methods discussed in this chapter, and references concerning them. For more useful information on waste management in the foundry industry, refer to Nagle (1983), and Oman (1988).
WASTE MANAGEMENT FOR FOUNDRIES
Baghouse & Scrubber Wastes
Alter raw materials Induction furnace use Recycled to original process EAF dust recycling
Stabilization using iron filings Precipitation using magnesium hydroxide
USEPA 1985, Danielson 1973
Morris 1985, Chaubal 1982, Kellogg 1966, Krishnan 1982 and 1983, Miyashita 1976, Bounds 1983 Stephen 1984
Alter feed stock Alter desulfurization agent Alter product requirements Improve process control Recycle to process
Stephens 1988 Stephens 1988 Stephens 1988 Stephens 1988 Stephens 1988
WASTE MANAGEMENT FOR FOUNDRIES (continued)
Recycle/reuse in other processes Desulfurization slag quench tank
Stephens 1988 Stephens 1988
Spent Casting Sands
Use for construction material Reclaim Metals
ASM 1988 Smith 1982 HazTECH News 1988
SR = Source reduction R = Recycling T = Treatment
ASM. 1988. Metals Handbook. Ninth Edition Volume 15: Casting. American Society of Metals International, Metals Park, OH.
Bounds, C.O. August 1983. "The Modernization of the Monaca Electrothermic Zinc Smelter." Journal of Metals, pp.30-36.
Chaubal, P.C., O' Keefe, T. J., and Morris, A. E. 1982. "Sulphation and Removal of Zinc from Electric Steelmaking Furnace Flue Dusts". Ironmaking and Steelmaking. Vol. 9, No. 6. pp 258-266.
DHS. February 1989. Detoxifying Foundry Sand. California Department of Health Services, Toxic Substances Control Division, Alternative Technology Section. Prepared by California Cast Metals Association. Contract No. 86-T0106.
Nagle, D.L., Stanforth, R. R., Duranceau, P.E., and Kunes, T.P. 1983. 'Treatment of Hazardous Foundry Melting Furnace Dust and Sludges." American Foundrvmen's Society Transactions. 91:715-720. American Foundrymen's Society, DesPlaines, Illinois.
Danielson, J. A., ed. May 1973. Air Pollution Engineering Manual. 2nd Edition. EPA Office of Air Quality Planning and Standards. Research Triangle Park, NC. Publication No. AP-40.
Dressel, W. M., Barnard, P.G., and Fine, M.M. "Removal of Lead and Zinc and the Production of Pre-Reduced Pellets from Iron and Steelmaking Wastes." Bureau of Mines RI 7927.
HazTECH News. September 8, 1988. "A Process for Treating Lead-Contaminated Sand from Brass and Bronze Foundries." HazTECH News.
Kellogg, H.H. May 1966. "Vaporization Chemistry in Extractive Metallurgy." Trans. TMS-AIME. Vol. 236, pp. 602-15.
Krishnan, E. R. August 1983. "Recovery of Heavy Metals From Steelmaking Dust." Environmental Progress. Vol. 2, No. 3.
Krishnan, R. April 1982. Technical Assistance to the Missouri Department of Natural Resources-Heaw Metal Recycling. Penco Environmental Report, contract No.68-01-6007.
Miyashita, T. 1976. "Recovery of Zinc from Steelmaking Dust". World Mining and Metallurgical Technology. Proceedings of Joint MMIJ-AIME Meeting . Vol. 2, pp 622-9. AIME, New York, NY.
Morris, A, E., Cole, E. R., Neumeier, L.A., and O'Keefe, TJ. December 1985. Treatment Options for Carbon Steel Electric Arc Furnace Dust". Proceedings-Electric Furnace Steelmaking Conference.
Oman, D.E. 1988. "Waste Minimization in the Foundry Industry." USEPA/Journal of the Air Pollution Control Association series Waste Minimization. Vol. 38, No. 7:932940.
Smith, M. E., Stephens, W. A., and Kunes, T. P. May 1982. "Making your Foundry's Waste Work for You: Constructive Use and Reclamation." Modern Casting.
Stephens, W. A., Oman, D. F., and Stolzenburg, T. R. September 1988. Waste Minimization Options for The Ferrous Foundry Industry. RMT, Inc. Madison, WI.
Stephens, W.A., Stolzenburg, T.R., Stanforth R.R., and Etzel, J.E. May 1984. "Use of Iron to Render Sludge from Ferrous Foundry Melting Furnace Emission Control Waste Nonhazardous." Presented at the 39th Annual Purdue Industrial Waste Conference. West Lafayette, Indiana.
Stolzenburg, T. R., et al. May 1985. "Analyses and Treatment of Reactive Waste: A Case Study in the Ductile Iron Foundry Industry." Purdue Industrial Waste Conference Transactions. West Lafayette, Indiana.
Turpin, P.D. et al. 1985. "Methods to Treat EP-Toxic Foundry Wastes and Wastewaters." American Foundrymen's Society Transactions. 93:737-740. American Foundrymen's Society, Desplaines, Illinois.
USEPA, September 1985. Compilation of Air Pollutant Emission Factors. Volume 1. Stationary Point and Area Sources. Fourth Edition. EPA, Research Triangle Park, NC. Publication No. AP-42. Also include Supplement A to this publication, October 1986.
WASTE MANAGEMENT IN METAL CLEANING AND STRIPPING
Parts cleaning and stripping are integral process operations for industries that repair, maintain, or manufacture parts and equipment. Manufacturing groups generating metal wastes include metal furniture manufacturers, metal fabricators, machinery manufacturers, electric and electronic equipment manufacturers, instrument manufacturers, and many others.
While the science of parts cleaning and stripping is complex, its aims are relatively simple -to prepare workpieces for subsequent operations, and to avoid the generation of rejects during subsequent use or processing steps by removing contamination such as soil and old plating or paint from the surfaces of the parts being cleaned. Cleaning and stripping methods that generate metal wastes include chemical reactions and mechanical actions.
Chemical reactions often involve the dissolution of the contamination and some metal into the cleaning media. Popular systems include alkaline de-rusters containing organic sequestrants which solubilize metal oxides, acidic pickling baths which yield soluble salts by reaction with oxides and sulfides, and electropolishing, which causes dissolution of the metal substrate at the anode. In addition to metal dissolution, some of the cleaning and stripping solutions contain metal-bearing compounds such as chromic acid.
Mechanical action might involve such activities as abrasion, deformation, heat or flame cleaning, and electrocleaning, which involves direct current hydrogen scrubbing at the cathode. Metal-bearing wastes associated with these actions would be due to the metal-bearing contamination removed in the process as well as any of the metal substrate removed.
The recommended strategy for developing effective waste minimization options for parts cleaning operations relies on systematic exploration of the following sequence of steps:
need to clean.
least hazardous medium for cleaning.
recycling and reuse.
This strategy is consistent with the multi-media approach and general emphasis of reducing the waste at the source. Each step is discussed in the following sections.
In many instances, by controlling the factors that contribute to surface contamination of the parts, the need for cleaning can be reduced or eliminated altogether. Control of parts contamination starts with a study of contamination sources. Sources can be incoming soils applied by metal vendors or soils applied in house.
Moisture which can lead to rust can often be reduced or eliminated by allowing the parts to dry more thoroughly between operations or by storing the parts indoors to avoid condensation and/or rain. Sufficient moisture exists in almost any atmosphere, however, for iron iron oxide to form, unless a protective coating has been applied. A material that forms a good surface barrier protective coating for metals is benzo-toly-triazole, marketed by Sherwin Williams under the trade name Cobra-Tec (Egide 1989). It is important for a shop to determine whether use of a surface barrier film will interfere with subsequent operations. It is also important to thoroughly analyze any potential environmental or worker hazards that might be generated through use of organic chemical protective coatings.
Frequently, by making plating processes more efficient and monitoring them more closely, rejects and rework can be minimized, thus reducing the need for stripping and replating, and reducing the wastes generated from these operations.
Also of importance is the location of cleaning and stripping operations in the manufacturing sequence. Articles to be cleaned prior to finishing should only be cleaned at the point in time when they are ready for coating. Parts should not be cleaned and conversion-coated and then warehoused or staged for subsequent batch coating. During storage, the parts can become contaminated by air-borne oils or by handling. These contaminants will interfere with ultimate finish quality and increase the rate of rejects.
The choice of cleaning or stripping medium for a given parts cleaning operation is determined by a number of factors. Some of these factors include:
o physical and chemical properties of contaminants, substrate surface, and cleaning media o the amount of contaminant to be removed o the required degree of cleanliness and product quality o size, shape, and complexity of part to be cleaned o volume or number of parts to be cleaned per unit time o costs of raw materials, equipment, and labor o worker protection required o quantity of waste generated o environmental protection required
The relative importance of these factors can change considerably over time. For example, while "wet" stripping using aqueous solutions has been standard in the industry for many years, the high costs of sludge disposal, as well as the liability, have caused some shops to phase out aqueous stripping in favor of "dry" methods such as sand or bead blasting.
In looking for a new cleaning or stripping medium or procedure, a company should consider the least toxic or most environmentally acceptable medium, and then, if this is not satisfactory, progress to more toxic or less environmentally desirable alternatives. Ideally, the method of choice would involve the shortest process sequences, employing the least toxic medium, generating the least amount of wastes, and still providing the necessary minimum level of cleaning or stripping to the part at minimum cost. For facilities attempting to change from one medium to another, the impact on subsequent operations must be considered. Any proposed changes to the process requires careful evaluation of potential effects of the chemicals on the substrate that might affect the integrity of downstream processes such as plating, painting, etc. The impact of drag-out on the life span of downstream process solutions should also be addressed.
If a cleaning or stripping step cannot be eliminated, and the least hazardous cleaning material that is effective is already being employed, then it should be used as efficiently as possible. From a waste reduction point of view, this means using the least amount of cleaning medium to achieve an acceptable level of cleanliness. This could involve ensuring that rinse tanks are clean, for example, or could involve minimizing dragout, or instituting a process or equipment modification.
The cleaning waste that cannot be eliminated through substitution or more efficient use should be considered for recycling or reuse. The segregation of different types of cleaning waste may be required for such recycling or reuse. Specific examples of recycling and reuse are discussed for specific media in later sections.
Although organic solvents have excellent cleaning properties and do not contribute to the metal-bearing waste problem by attacking or etching the metal substrate, many of them are considered hazardous to human health and the environment. Some negative environmental and health-related attributes of various solvents include toxicity, flammability, ability to dissolve and serve as a carrier to other toxic organics, high volatility, photochemical reactivity, and resistance to biodégradation.
Solvent wastes were among the first to be banned from land disposal by EPA. The 1984 RCRA amendments specify five categories of solvent waste (F-001 to F-005) which were banned from land disposal effective November 1986 (RCRA 3004 (e)(1)). Due to the diverse problems associated with solvent use, solvents should be used only when no other cleaner is suitable for the job.
Many firms have been successful in substituting less toxic cleaning media for solvents. Solvent substitution is discussed in detail in DHS (1989). Alternatives to solvent use that can generate metal wastes include:
o substitution of solvents with aqueous cleaners o substitution of solvents with mechanical and/or thermal methods
Discussion of each substitution approach is provided below. Most emphasis is given to aqueous cleaners, since this is the major and often most effective alternative.
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