Abstract: A method is disclosed for fixing certain dangerous substances into recyclable waste foundry sand so that they are less likely to leach out into the environment. The method uses a roasting process which causes the dangerous substances to form insoluble compounds with the sand. One example is shown where hazardous waste foundry sand which contains acetic acid soluble lead contamination is treated by this method. In this example the lead is believed to react with the sand during the roasting process forming compounds such as lead silicate which are insoluble to acetic acid. The amount of lead which may be leached out into the environment is reduced to a safe level according to the currently accepted test methods promulgated by the U.S. Environmental Protection Agency. The method may be applied to the conversion of waste foundry sand into reusable sand or landfill which are less likely to leach dangerous substances into the environment.