Recycling Process Developed for Smelting Waste Product
Melbourne, Australia - A world-first in treating a waste product from the aluminium smelting industry has been developed at Portland Aluminium in Australia in Victoria's south west.
The waste, spent pot lining (SPL), has been the subject of an eight-year $26 million research and development program that harnessed technology and expertise developed by Portland Aluminium, Alcoa Inc., Ausmelt Ltd, and Australia's CSIRO.
The Alcoa Portland SPL Process treats the hazardous waste and renders it harmless. The process produces aluminum fluoride and a granulated vitreous material referred to as "synthetic said."
The aluminum fluoride decreases the overall cost of the Portland Aluminum operations by reducing the quantity of the expensive imported aluminum fluoride required for the aluminum smelting process.
The synthetic sand has been given approval for unrestricted use by the Environment Protection Authority of Victoria (EPAV), as long as it continues to have fluoride leachability measures of less than 15 parts per million. The Alcoa Portland SPL Process achieves this standard.
The EPA's approval opens up opportunities for the end product to be used in commercial applications such as road making and concrete. Both products will conserve natural resources.
SPL is a waste product of the electrolytic process in the smelting of aluminum.
Prior to treatment SPL is considered to be a hazardous waste in various countries because it contains significant quantities of absorbed fluoride along with traces of cyanide.
The EPA's acceptance for these end uses means the Alcoa Portland SPL Process has treated the hazardous waste material SPL successfully and converted it into non-hazardous useful products.
The disposal of SPL primarily has been in landfill because of difficulties in the development of a successful techno-economic SPL treatment process.
Increasing concern about SPL land-filling practices is resulting in regulations in some countries to ban this form of disposal. As a consequence, stock-piling of SPL is occurring in an increasing number of countries pending the development of a successful treatment process.
Co-author of a paper to the conference, and Manager Spent Pot Lining Project, Ken Mansfield, says the unique gas treatment process converts hydrogen fluoride in the furnace off-gases to aluminum fluoride in a multi-stage fluidised bed reactor, designed by Portland Aluminum.
"The aluminum fluoride produced in the reactor has been tried successfully in Alcoa's aluminum smelting process as a replacement for imported aluminum fluoride," Mr. Mansfield said.
"The installation in mid 2001 of a granulation system has enabled a granulated vitreous product with excellent leachability qualities to be produced."
Work on the Alcoa Portland SPL Process began in 1992 and involved investigations into the suitability of Ausmelt's submerged lance technology furnace process for treating SPL. Portland Aluminium, Alcoa and Ausmelt subsequently worked together on trials in Ausmelt's Dandenong premises until 1994.
Separate development work by Portland Aluminium, involving the CSIRO, resulted in small scale production of aluminum fluoride from typical off-gases from the pyrometallurgical process and agreement was reached to go ahead with the $26 million research and development program at Portland.