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Pollution Prevention and Control Technologies for Plating Operations

Section 7 - Off-Site Metals Recycling


7.5.2 Basis of Off-Site Metals Recycling Costs

The price of waste recycling is generally non-standard because it is negotiated between the plating shop and recycling company. As such, there exists an undefinable cost element. However, there are certain factors that are known to contribute to pricing. These factors can be examined for a given situation, and in some cases, plating shops can change their processing operations to make their waste products more valuable to recycling firms, thereby reducing recycling costs. These factors are:

  • Metal Constituents of the Waste. Although some recycling processes and end uses are indifferent to the number of metals present in a waste stream, most metal recycling companies would prefer a mono-metal solution or sludge (ref. 23). Plating shops could segregate their sludges to increase the value of the material. However, this would require separate treatment of wastes which is not practical for most shops. This strategy was not used by any of the respondents to the Users Survey for F006 sludge (one shop, PS 246, operates separate filter presses for dewatering chromium and non-chromium sludges, but the dewatered sludge is sent to land disposal rather than off-site recycling). The preferred metal content of a sludge is generally a minimum of 5% to 10%.
  • Sludge Type. Hydroxide sludges are generally preferred to sulfide sludges because the later can make reclamation more difficult. Sodium hydroxide is usually preferred to lime as the alkali reagent because it adds the least amount of inert material to the waste. Sludges generated with anionic polymers used for flocculation are usually preferred to alum and ferric compounds, also due to a lower inert material content. The use of dithiocarbamate (DTC) is usually acceptable.
  • Tramp metals and Other Constituents. No recycling processes are designed to handle all possible constituents. The presence of some constituents (e.g., cyanide, arsenic, solvents) may preclude acceptance of the waste or significantly increase processing costs. The waste should be free of miscellaneous debris such as rubber gloves, cartridge filters, mop heads, etc. which add to the complexity of the treatment and handling process (ref. 420).
  • Moisture Content of the Waste. The preferred moisture content of a waste will vary from recycler to recycler and will depend on their material storage, handling and processing facilities and equipment.
  • Waste Volume. High volume waste streams are preferred by recycling companies. Small volume waste streams may be penalized. Also, unit transportation costs (see following) are impacted by volume.
  • Transportation. Hazardous wastes must be transported by RCRA permitted companies. The unit transportation costs ($/ton) depend on the quantity hauled per load and the distance. Some companies offer Òmilk runsÓ that collect small volumes of waste from different generators that may reduce a shopÕs transportation costs.
  • Chemical Consistency. Waste recycling firms prefer waste streams that are chemically consistent from shipment to shipment.

Relative to metal content and the presence of tramp metals and other unwanted constituents, the following example will help to demonstrate the cost impact of these factors.

  • The contract of one Southeast plater (PS 043) for recycling their zinc-bearing wastewater treatment sludge (F006) is charged a processing fee of $201 per ton (as received) with the following penalty fee structure:
    • Zinc content below 8.5%: $5.00 per one percent per ton
    • Lead and cadmium above 2.0%: $15.00 per one percent per ton
    • Oil and grease above 0.0%: $5.00 per one percent per ton

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