arger effective furnace capacities. Because Li2O can lower the required processing temperature by as much as 25°C (77°F), it provides a 5-10% reduction in energy use and can also decrease NOx emissions. Additional benefits include improved glass quality and an increased melt-to-pack ratio as a result of fewer checks and tears, as well as a potential increase in refractory life due to lower operating temperatures.
With growing competition from plastic and aluminum packaging materials, glass container producers are seeking to develop lighter weight containers by reducing the glass thickness. Lithium can help glass producers achieve this goal by enhancing the mechanical strength of the glass, as well as its hydrolytic and chemical resistance. It also increases the working range of glass, thereby improving the thickness uniformity (from top to bottom) of glass bottles.
According to Anand Sheth, technical marketing manager for Sons of Gwalia Ltd., West Perth, Australia, only a small amount of lithium is needed to reap the benefits. The normal addition rate in glass containers is only 0.1 to 0.17 wt% Li2O or 3 wt% spodumene concentrate (glass grade).
What Evidence Exists?Using lithium to reduce energy requirements in glass manufacturing is not a new concept. In 1968, Thatcher Glass Manufacturing Co. performed production tests using spodumene, a lithium-bearing ore, as a batch additive. The company concluded that lithium increased the melting rate and lowered melting temperature and fuel usage.1 However, little or no additional production-scale research was reported on lithium's effect in a glass batch until the early 1980s, when Glass Containers Corp. decided to run two tests, one in Jackson, Miss., and the other in Hayward, Calif., with the assistance of Lithium Corp. of America in Gastonia, N.C. (now FMC Corp., Lithium Division). The results were similar to what had been achieved in Thatcher Glass over a decade earlier-adding lithium carbonate to the glass batch resulted in a 40-50°F reduction in furnace temperature, a 12% increase in pull rates, increased machine speeds averaging one to two bottles per minute, and a slight increase in pack, as well as an increased surface brilliancy and sheen of the final product.2
In other parts of the world, glass manufacturers were also starting to realize the benefits of lithium. In the late 1980s and early 1990s, trials at container glass manufacturing plants in Asia, the UK, Germany, Switzerland, Italy and France all showed that lithium additions between 0.03 and 0.20% by weight provided energy savings in the range of 4-10%, as well as increased production speed and reduced defects. In 1990, Kirin Brewery in Japan reported a 7.5% increase in pull without increased energy consumption using 0.2 wt% glass-grade spodumene.3 In 1994, trials at a container glass manufacturing plant in Central America showed that production was increased 11% with a 3% reduction in energy and equivalent quality compared to the glass without the lithium addition, while trials at a North American container glass manufacturing plant showed increased quality (decreased checks) along with a 5% savings in energy consumption at the same production levels used prior to the lithium addition.4
More recent trials at glass container and tableware manufacturing plants have further substantiated the idea that lithium can provide energy savings, increased product quality, higher throughput and other benefits in glass manufacturing.
Over the last several years, a number of glass container and cosmetic glass manufacturers in Asia have begun using spodumene in production and have increased their furnace capacities by 20 to 25%, reduced their rejection rates and eliminated the problem of weathering in glass. These manufacturers have also achieved enhanced glass brightness and a lower seed count, which has enabled them to increase sales.
According to Sheth, 0.1 wt% Li2O can provide approximately the same melting effect as a 10% cullet addition to the glass. With the unavailability of high-quality cullet in some countries, lithiu