Preliminary Studies on Metal Adsorption by Waste Foundry Sand

In the casting industries, sand is typically reused through the production cycles. Since sand for itself do not have the necessary properties to this process, it’s necessary to introduce binders to force the sand grains to hold their shape during the casting process. When the casting sand cannot be reused it considered a residue, and it is formally called waste foundry sand. Worldwide, China is the larger producer with 35.3 million tonnes (in 2009), followed by North America with 9.6 million tonnes per year and finally Europe with 12 million tonnes. In Europe, this value is 75% of sand waste. Europe as a producer, has Germany as the largest producer of foundry casting. In 2006 total casting production was 5.5 million tonnes divided between ferrous (82.3%) and non-ferrous foundries (17.7%). At present Germany is the 6th largest producer of cast components. Available in large quantities, and considered an inert residue, waste foundry sand presents good characteristics to adsorption processes. The adsorption of metals by waste foundry sand is a key parameter to be considered in the application of passive barriers. Special attention was given to Antimony and Germanium. Antimony, is commonly used in alloys, batteries, cable sheathing, flame-proofing compounds, paints, and glass, among others. Germanium is a very important semiconductor material, doped with arsenic, or gallium, it is used as a transistor element in electronic applications, as PET catalysts in the plastic bottling industry, in infrared spectroscopes, glass and in fiber optics. In this work, sophisticated nanoscale techniques were used to identify and characterise this material. Adsorption studies were carried out with positive results and the time evolution was analysed. In this dissertation its proved that sand grains were covered partially by a clay layer, and that germanium is well adsorbed by waste foundry sand. In the first 5 minutes of reaction an adsorption of Ge of 10% is observed, followed by an increase up to 22% at 90 minutes of reaction. It is also shown that equilibrium is reached after 30 minutes of reaction. It is possible to conclude that there is an increase in the efficiency of adsorption with time, and it stabilizes at a level of 22%.