Recycling Aluminum Safely
Jun 9, 2014, 09:10 AM
November/December 2000
A host of contaminants can pose health and safety concerns in the aluminum melting process. Several educational and reporting programs are addressing this issue.
By Sey Epstein
Sey Epstein is technical director for the Aluminum Association Inc. (Washington, D.C.).
Aluminum plants are relatively safe, healthy workplaces, based on the injury/illness statistics gathered by the Aluminum Association. Virtually every industry, though, has potential hazards inherent to its processes and/or products, and the aluminum industry is no exception.
An important safety concern in the aluminum industry involves the handling of molten metal. The hazards associated with melting, casting, and transferring molten aluminum are well-recognized, and the industry has undertaken a number of programs to better understand and control the risks of burns and explosions. Under certain conditions, contact between any molten substance and water can result in an explosion. While millions of pounds of molten aluminum are produced and handled every day without incident, explosions can occur and, because of the chemical reactivity of aluminum, they can be violent.
The aluminum industry, through the Aluminum Association as well as individual company efforts, has spent the last 50 years studying these phenomena and how they can be prevented. The association has sponsored studies at research centers such as Battelle Memorial Institute, IIT Research Institute, Sandia National Laboratories, and the Alcoa Technical Center. In addition, several technology-exchange sessions have been held with scientists at Department of Energy National Laboratories, investigating steam explosions from molten metal-coolant interactions. Presently, the Aluminum Association has a program at the Alcoa Technical Center and the Oak Ridge National Laboratories to further enhance safety measures during direct-chill casting of aluminum, a widely used process.
Based on the results of these efforts, safety procedures have been developed and implemented, guidelines and training aids have been prepared and distributed, and a number of regional and international workshops have been held to provide pertinent information to those who handle molten aluminum. These efforts are continuing and, while explosions haven’t been eliminated, the industry has made great strides in better protecting its employees.
A major component of the Aluminum Association’s ongoing safety program is molten metal incident reporting. In 1985, following several explosions that caused a number of fatalities, a program was developed to formally obtain information on the incidents occurring in the industry. The program gathers the vital information to clarify the causes of incidents, fosters an awareness of the hazards at all levels of the work force, and provides insights into preventing similar occurrences in other facilities.
A simple, one-page reporting form was created and distributed to companies worldwide. The form allows companies to anonymously communicate information on their molten metal incidents. There’s no cost for participation, only a commitment to report incidents when they occur. In turn, the participants receive an annual summary report, plus bulletins and other timely information.
There are currently almost 240 participants in the program reporting for about 300 plants in 20 countries. The Aluminum Association receives about 60 to 125 reports a year. More than 1,400 reports have been submitted in the 15 years that the program has been in existence.
The Scrap Factor
One early finding from the reports is that the majority of the more severe explosions occur during the charging of scrap into the melting furnace. In addition, it appears that these charging explosions are caused not only by moisture, as would be expected, but by contamination in the charge. This was a difficult issue to address because many times the contaminants are hidden from view and not easily detected.
The incident-reporting program made it apparent that practices for receiving, handling, and charging metal, particularly scrap, needed attention in light of the greatly increased volume of recycling in the industry. To address the subject, the Aluminum Association held an ad hoc meeting that included a cross section of industry representatives and led to the formation of a task force on scrap charging safety. The task force—cochaired by Bob Hubbard of IMCO Recycling Inc. and Don Pierce of Reynolds Metals Co., with representation from 10 additional companies—has been an active group.
From the start, the task force worked with ReMA to improve the safety performance in scrap recycling. A workshop was conducted for ReMA members to show, through the incident reports and newscast videos, the effects of contamination in scrap charges going into remelt furnaces. With ISRI’s cooperation, the task force produced Guidelines for Aluminum Scrap Receiving and Inspection Based on Safety and Health Considerations, which was widely disseminated among members of ReMA and the Aluminum Association.
To further increase awareness of potential safety or health hazards in scrap loads, the task force developed a scrap rejection notification program based on the guidelines. The program works as follows: If a participating plant receives a load of aluminum scrap, inspects it, and rejects the load for reasons of safety or health, the plant fills out a one-page reporting form and faxes it to the Aluminum Association. The association reviews the form to check that it’s properly filled out, then faxes the form to the other participating plants. This program, implemented in mid-1997, has gleaned more than 100 reports from the 40 or so plants participating in the program.
The principal hazards associated with a load of scrap and the principal reasons for rejecting a scrap shipment are described below. The numbers of rejected loads reported and the reasons for rejection are shown in the bar graph at left.
Powder Residues: Fertilizers, salt baths, and other materials containing nitrates, sulfates, or other oxidizing agents explode violently in molten aluminum. Some reports indicated that the explosions occurred even before the charge entered the molten metal in the furnace. In some instances, fertilizer was found inside bales of scrap and, fortunately, was detected prior to charging. Any powder found on metal, scrap, or ingot—or in the trailer or railcar transporting it—must be viewed with suspicion and analyzed prior to charging the load.
Closed Containers: Crimped tubing, bottles, cans, cylinders, and tanks can hold liquid that, if trapped in the charge and brought below the melt, will vaporize rapidly and cause an explosion. Aluminum sow or ingot with shrinkage cavities can also act as a closed container and must be preheated.
Flammable/Combustible Substances: Oil, grease, lubricants, and similar substances are often found in shipments of aluminum scrap at levels that can’t be safely processed at some facilities. Live ammunition and explosive detonators have been found in aluminum scrap and, in some cases, were believed to have caused furnace explosions. Aluminum fines can also burn or explode forcefully.
Toxic Substances: PCBs and other toxic substances must be avoided for health reasons. In some cases, depending on the product being produced, heavy metals such as lead and cadmium can’t be tolerated due to regulatory restrictions.
Radioactive Material: While aluminum itself doesn’t retain radioactivity, scrap shipments should be screened for radioactive contaminants. Many aluminum melting plants have radiation detectors at the receiving gate to prevent loads with radioactive contamination from entering the property.
Other Contamination: This category accounts for the greatest number of scrap rejection notifications. Specifically, hypodermic needles and syringes found in the shipment are the cause most frequently cited as the reason for rejection. There have been instances where entire loads of 30,000 to 40,000 pounds of scrap have been rejected because one needle was found. Receiving facilities can’t risk employee exposure to the hazards from contact with a used hypodermic needle. Most, if not all, of the shipments where needles and syringes were detected involved loads of UBCs, largely because of the practice of discarding these implements in aluminum cans. The Aluminum Association and ReMA have discussed this problem and will continue to review ways to alleviate this hazard.
The above list doesn’t encompass all contaminants that appear in loads of aluminum scrap, of course. Here are a few others (discussed during the UBC workshop at ISRI’s convention in March), with a short description of how they can adversely affect the consuming mill:
• Dirt, which creates dust in a mill’s shredder and generates dross during the melting process, posing a disposal burden for the mill.
• Steel cans, which prematurely wear down the blades and screens of a mill’s shredder and boost the iron content in the mill’s melt.
• Glass, which presents an employee safety hazard, gums up the shredder, and raises the silicon content in the melt.
• Paper/plastics, which gum up a mill’s shredder and act as combustibles in the delacquering kiln. In particular, these contaminants raise the temperature in the kiln to the point where it starts melting the aluminum rather than simply delacquering it, which can mean significant recovery losses.
• Wood, which can break a mill’s shredder and slow production.
• Base metals other than aluminum, which skew the chemistry of the melt.
While aluminum plants and scrap processors have made progress in the area of aluminum melting safety, both are committed to doing even more. Education and communication among aluminum mills, scrap suppliers, and other related parties are the keys to continued improvement in this area. By working together, these groups can achieve the goal of making scrap charging and molten metal handling as safe as possible. •
Editor’s note: Guidelines for Aluminum Scrap Receiving and Inspection Based on Safety and Health Considerations costs $10 for Aluminum Association members, $20 for nonmembers. To order, contact the association’s Publications Dept., Box 753, Waldorf, MD 20601; 301/645-0756 (fax, 301/843-0159). To review a complete list of the association’s publications and other resources, visit its Web site at www.aluminum.org.
A host of contaminants can pose health and safety concerns in the aluminum melting process. Several educational and reporting programs are addressing this issue.