Amber glass melt with ZnO added shows desired blue-green color.

Amber Color Removable from Recycled Glass

In her CEER-sponsored summer research, Melissann Ashton-Patton explored ways to chemically remove the amber color of container glass so that it can be recycled.

Recycling of glass is currently limited by problems associated with the remelting of waste glass, called cullet in the glass industry. Cullet consists of an unsorted mixture of amber, green, and colorless glasses. The remelting problems are due to the presence of amber glass in the mix. Green and colorless glasses are compatible for remelting, but even small amounts of amber glass in cullet causes unacceptable brown streaks in the product. In addition, remelting mixtures of amber and green glasses results in massive foaming of the melt due to changes in the redox of the melt. This foaming can shut down a commercial glass tank, resulting in the loss of millions of dollars. As a result, the industry will not use cullet containing any amber glass. This problem needs to be solved in the near future because members of the European community are being required to use 70% recycled glass in container production by 2006.

Various methods of eliminating the amber color were examined in Ashton-Patton’s research. Since the amber color is due to the presence of an iron sulfur compound, FeS, she explored replacing the iron with another element and removing the sulfur.

Ashton-Patton found that the addition of a small amount of ZnO was very successful in eliminating the amber color. Addition of as little as 1 wt% of ZnO converted the glass to a yellow green. Larger additions converted the glass to the desired blue-green, with very uniform color distribution. It is believed that zinc ions replace the iron ions in the FeS compound, thus eliminating the source of the amber color. Ashton-Patton’s research was presented at the Fusion of Glasses Conference in July and will be published in the Proceedings of that conference.

CEER is funded in large part by the United States Environmental Protection Agency.

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