In a metal recycling plant in the Yangtze River Delta, Mr. Wang, an operator, can identify the type of
scrap on the conveyor belt just by the sound of metal impacts. When iron and stainless steel tubes
are mixed into the same batch of waste, this wisdom of discrimination from production practice reveals
a subtle and profound technical division between ferrous and non-ferrous metal waste.
Genetic differences in the metal family
The essential difference of metal waste begins with the deep code of the periodic table. Ferrous metals
to iron as the core of the gene, its crystal structure has a typical body-centered cubic characteristics.
This atomic arrangement gives the material strong magnetism, but also brings the inherent defect of easy
oxidation. The reddish-brown rust layer commonly found on the surface of steel scrap is the chemical
imprint of the continuous interaction of iron with the water and oxygen in the environment.
Non-ferrous metals form a more complex spectrum of elements. The unique face-centered cubic structure
of copper atoms allows its scrap to remain electrically conductive even after oxidation; the silvery-white
luster of aluminum scrap originates from the dense alumina protective film on its surface; and the grayish
appearance of lead scrap hides a natural barrier against acid and alkali corrosion. This elemental diversity
determines the non-ferrous metal waste treatment of special process needs.
Practical identification of physical properties
Physical identification occupies a central position in the operation manual of metal sorting site. Strong magnet
adsorption test is the most intuitive means of initial screening - can be firmly adsorbed by the magnet scrap iron,
scrap steel belongs to the ferrous metal camp, while non-ferrous metals such as copper and aluminum show
complete antimagnetism. This difference stems from the way the spins of the free electrons are arranged within
the metal, building very different magnetic field response mechanisms at the microscopic scale.
Weight perception is the second dimension of discrimination for experienced recycling workers. Holding an
equal volume of metal scrap in the hand, the heaviness of cast iron pieces contrasts with the lightness of
aluminum alloys. The density of pure copper scrap (8.96g/cm³) is almost 1.13 times that of 304 stainless steel
(7.93g/cm³), and this quality difference will produce a significant difference in sorting efficiency in batch processing.
The technological gap in the recycling process
Regeneration of ferrous metal scrap melting like precision surgery. In the high temperature environment of 1600 ℃
in the electric arc furnace, the scrap steel and the precise proportion of carbon, manganese elements in the
metallurgical reaction, through the oxygen slag blowing technology to remove phosphorus and sulfur impurities.
Modern steel mills are able to achieve a 98% reutilization rate of scrap, and each ton of regenerated steel reduces
carbon dioxide emissions by 1.6 tons.
Non-ferrous metal regeneration is a complex elemental purification project. Mixed copper scrap needs to go through
seven processes such as eddy current sorting and X-ray identification, and the redox atmosphere needs to be
precisely controlled during smelting to prevent metal volatilization. Recycled aluminum consumes only 5% of
the energy used in primary aluminum production, but requires the addition of silicon and magnesium to
compensate for the loss of performance. The recovery of precious metal wastes relies more on electrolytic refining
and other special processes, and the separation precision of gold, silver and palladium needs to reach more than 99.99%.
Dynamic scales of the value system
The price fluctuation curve of the metal recycling market clearly outlines the difference in the commercial value of the
two types of scrap.2023 market shows that the price of No.1 bright copper scrap continues to stabilize at 58,000 yuan/tonne,
while the price of heavy scrap steel oscillates at the level of 2,800 yuan/tonne during the same period. This nearly 20-fold
difference in value stems from the dual drive of non-ferrous metal scarcity and industrial demand.
Value assessment system presents multi-dimensional characteristics: copper scrap according to the copper content of
four levels of pricing, aluminum scrap to distinguish between deformed alloys and casting alloys, stainless steel scrap,
nickel content of each 1% price fluctuation of 1,500 yuan. In contrast, ferrous metal scrap pricing mechanism is more
uniform, mainly based on carbon content and residual elements for division.
The invisible battlefield of environmental protection game
Metal regeneration process of environmental costing reveals deep differences. Iron and steel regeneration, although
lower energy consumption, but each ton of steel scrap processing will still produce 18kg of dust emissions, need to
be equipped with bag dust removal and activated carbon adsorption system. The control of dioxin emissions from
non-ferrous metal smelting requires that the flue gas stays above 850°C for 2 seconds for decomposition, which
puts higher demands on the waste gas treatment equipment.
Resource scarcity gives non-ferrous metal waste strategic value. China's dependence on foreign copper resources
for a long time to maintain more than 70%, 2 million tons of copper waste recovered each year is equivalent to less
mining 80 million tons of copper ore. Nickel, cobalt and other strategic metal recycling, directly related to the safety
and stability of the new energy industry chain.
The technological revolution of intelligent sorting
Spectral analysis equipment is rewriting the traditional sorting model. Laser Induced Breakdown Spectrometer (LIBS)
can recognize the elemental composition of metal scrap on the conveyor belt within 0.8 seconds, and accurately
distinguish copper-zinc brass from silicon bronze through machine learning algorithms. This technological breakthrough
has increased sorting accuracy from 75% to 98% by hand, with a processing capacity of up to 20 tons per hour.
Eddy current sorter shows unique advantages in non-ferrous metal recycling. High-speed rotation of the magnetic
rollers produce alternating magnetic field, so that aluminum, copper and other non-ferrous metal wastes produce
induced currents, to achieve automatic separation from plastic, rubber and other impurities. This physical sorting
method avoids secondary pollution caused by water washing, and water saving efficiency is increased by 90%.