Pollution Prevention and Control Technologies for Plating
Section 7 - Off-Site Metals Recycling
7.5.OFF-SITE RECYCLING COSTS
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
- 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
- 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
- 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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