![]() X-ray transmission (XRT) technology also faces limitations in its sorting efficiency as an alternative to the sink-float separation process. The remaining quantity-as much as two-thirds of the total fraction-remains unidentified because of surface contamination and therefore is unsorted within the heavy metal fraction. Only as little as one-third of the whole copper and brass fraction corresponds to the color definitions of these two nonferrous metals. Sorting tests and experience with different input materials also have shown that only part of the copper and brass fraction is optically recognizable in some instances. Sorting using a color camera also can be affected negatively by surface contamination and color impurities. All gray heavy metals, such as zinc, lead, nickel and stainless steels, may not be sortable from each other. Only fractions that are clearly distinguishable by color, such as copper and brass, can be separated. However, this form of separation can face limitations. Sorting by color using a color-detecting camera is one possibility offered by sensor-based sorting technology. The use of sensor-based sorting systems represents an economic and sometimes reasonable alternative to manual or density sorting. ![]() The aluminum recovered cannot be easily separated in all instances. Most heavy metals are exported to Asia for further manual sorting. The mix of heavy metals must be treated in another way or has to be sorted manually. The separation efficiency also is limited, but aluminum can be separated from heavy metals and low-density nonmetallic impurities (e.g., plastics and wood). This process can require large quantities of water and expensive additives, such as ferro-silicon. The sink-float process is used in many treatment plants to separate materials of different densities. Gray metals can only be sorted to a certain extent, and it can be difficult for stainless steel to be separated visually at all. While manual sorting results in high purity levels, the process is cost intensive in industrial countries and should therefore only serve as a final check for quality control purposes.įurthermore, not all metals can be sorted manually, as their difference is simply not discernible visibly. The practice of manual sorting is still considerably widespread. The current sorting method used for producing zorba, zurik and metals of similar composition includes sink-float separation processes and sensor-based sorting systems that use camera technology. (ISRI), Washington, has created terms and specifications for mixed shredded scrap metals, including zorba, zebra, zeppelin and zurik. The Institute of Scrap Recycling Industries Inc. Industrial production in all areas of daily life devours an enormous quantity of aluminum and other nonferrous metals, including copper, brass, nickel, tin, zinc and lead. Global demand for ferrous and nonferrous metals is increasing each year. On the environmental front, ore mining and the processes that follow can produce tailings and even “toxic red mud.” It also should be noted that the mining of many ores for primary production occurs in politically unstable regions and sometimes under unsafe working conditions. By using secondary raw materials in the production of aluminum, the energy-intensive electrolysis process is eliminated, thereby reducing the total energy costs to approximately 10 percent of primary production’s energy price. Of course, metals have to be separated from nonmetallic impurities, and different metals have to be sorted in pure fractions to be used as secondary raw materials.Īdditionally, the planet’s resources are exhaustible, making it more and more important to use secondary raw materials. Metal recycling knows no limits because metals can be remelted as scrap infinitely.
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