Page 167 - Materials Chemistry, Second Edition

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138 Waste Management Practices: Municipal, Hazardous, and Industrial
This material is known as processed, or furnace-ready cullet. In some situations, the containers are
not broken but sent directly to the manufacturer.
Manufacturers purchase whole and broken glass cullet and combine it with soda ash, limestone,
and silica to create new glass products for consumer, industrial, and other applications. Recyclers
in the United States utilize 10 to 80% cullet in glass manufacture. This compares with 80 to 90%
in Switzerland and Germany (Rhyner, 1995; Liu and Liptak, 2000).
Modern glass container manufacturing requires clean and uniform feedstock. There are four
requirements for cullet used in recycling:
● Must be separated by color
● Must be contaminant-free
● Must meet market specifications
● Must be container glass

6.8.4 COLOR
On separating glass by color, manufacturers can ensure the desired quality and color consistency of
new glass products. The preferred situation is for the individual consumer or business to separate
glass by color at the source. This is also the optimum location for removal of contaminants such as
food, labels, and dirt. Many community recycling programs will allow for the collection of mixed
glass. Although a convenient practice for the consumer, such mixing may actually hinder the mar-
ketability of the product.
If separation by color does not occur at the source of generation, colors and contaminants
should be sorted out early during processing. At a MRF or transfer station, cullet is almost always
color-sorted by hand. In some communities, intermediate processors known as glass benefaction
facilities receive glass from recycling programs and use sophisticated optical sorting machines to
separate the glass into three color types (CMI, 2002). Optical sorting equipment is capital-intensive;
therefore, hand-picking is typically the only feasible sorting mechanism.
If the cullet is not completely color-sorted and becomes thoroughly mixed, undesired colors are
difficult to remove and can ruin an entire load. Mixed cullet has significantly lower demand and
value. Glass manufacturers set limits on the amount of mixed cullet that is acceptable for manufac-
turing new containers. Many companies simply prefer not to buy mixed cullet. Other markets for
mixed glass are available (see below), but are limited.

6.8.5 CONTAMINATION
Contaminated cullet, probably the single greatest problem for glass manufacturers, is not suitable
for the production of new glass containers. Cullet can be contaminated at any point during the
recycling process: at home, during collection, processing, or shipping. Contaminated cullet
decreases quality and increases costs. Contaminants are a risk to the glass manufacturer and dis-
rupt production, cause injury to workers, damage manufacturing equipment, and produce a poor-
quality product.
Virtually all glass food and beverage containers, including food jars, soft drink bottles, juice
containers, beer bottles, wine and liquor bottles, are recyclable. However, household glass products,
such as light bulbs, drinking glasses, and window panes are not acceptable for producing glass con-
tainers. Such glass products vary significantly in chemical composition; furthermore, many possess
different melting temperatures. As a result, mixing these products with container cullet may cause
defects such as bubbles, cracks, or other weak points and imperfections in new containers.
Common materials that contaminate cullet include:

● Ceramic cups, plates, and pottery
● Crystal and opaque drinking glasses