Ferrous Scrap and its Collection and Recycling
Ferrous Scrap and its Collection and Recycling
Ferrous scrap also referred to as, iron and steel scrap, or simply scrap comes from end of life products (old or obsolete scrap) as well as scrap generated from the manufacturing process (new, prime or prompt scrap). It is metal that contains iron. Iron and steel scrap can be processed and re-melted repeatedly to form new products. Due to the value of metal in the ferrous scrap, it is recycled or reused wherever it is possible. In fact, ferrous scrap is being recycled long before current awareness of environmental concerns started.
Ferrous scrap is generated during the production of iron and steel, fabrication or manufacture of iron and steel products, or when the product made of iron and steel reaches its end of life. Due to the high value of the metal, the ferrous scrap is largely being recovered. Given the chemical and physical properties of the material, iron and steel produced from ferrous scrap can, in almost all applications, compete with primary iron and steel produced from ore. However the amount of scrap collected and finally recovered depends on many factors, such as the collection system, the possibility and techniques used for the collection, etc. as well as a variety of legislation.
The main sources for ferrous scrap are those products, for which iron and steel is the main constituent. These are namely, vehicles (including ships and rail coaches and wagons), products of construction, machinery, electrical and electronic equipment, and packaging etc.
There is a difference between carbon steel scrap and stainless steel scrap since the carbon steel differs from stainless steel by composition and treatment. Carbon steel scrap is mainly used for the production of steel in induction furnace (IF), electric arc furnace (EAF) and partly in basic oxygen furnace (BOF) as well. Stainless steel scrap is used to produce new stainless steel in EAF.
Scrap is either distinguished as (i) home scrap, (ii) new scrap, and (iii) old scrap depending on when it becomes scrap in its life cycle. Scrap is further distinguished according to its specific source.
Home scrap is the internally generated scrap during the manufacturing of the new steel products in the steel plants and the iron and steel foundries. This form of scrap rarely leaves the steel-making production area. Instead, it is returned to the furnace on site and melted again. Technological advancements have significantly reduced the generation of home scrap.
New scrap (also called prompt or industrial scrap) is generated in steel-product manufacturing units and includes such items as turnings, clippings and stampings leftover when parts are made from iron and steel during the manufacturing processes. This material is typically sold to the scrap metal industry which processes it for recycling to steel plants and foundries. The composition of new scrap is well known and in principle new scrap does not need any major pre-treatment process before it is melted, although cutting to size may be necessary.
Old or post-consumer scrap results when industrial and consumer steel products (such as automobiles, appliances, buildings, bridges, ships, cans, railroad coaches and wagons, etc.) have served their useful life. Old scrap is collected after a consumer cycle, either separately or mixed, and it is often contaminated to a certain degree, depending highly on its origin and the collection systems. Since the life time of many products can be more than ten years and sometimes even more than 50 years (for example products of building and construction), there is an accumulation of iron and steel products in use since the production of the steel has started on a large scale.
Categories of ferrous scrap
Ferrous scrap usually includes (i) carbon steel scrap, (ii) cast iron scrap, and (iii) stainless steel scrap. Various categories of carbon steel scrap include (i) heavy melting steel, (ii) number 2 heavy melting steel scrap, (iii) number 1 and number 2 hydraulic bundles, (iv) number 1 and number 2 busheling – prepared, (v) plate and structural steel, (vi) hydraulic silicon bundles, (vii) number 1 bushelling (clips), (viii) short shoveling steel turnings (crushed), (ix) machine-shop turnings, (x) mixed turnings and borings, (xi) cast iron borings, (xii) number 1 machinery – cast, (xiii) mixed cast, (xiv) number 1 and number 2 shredded scrap, (xv) briquetted steel turnings – alloy free, (xvi) briquetted steel turnings – alloyed, and (xvii) foundry steel etc. Some of the common categories of carbon steel scrap are described below.
- Punchings and plate scrap – The desirable characteristics of these scraps are that they are generally clean, free from rust, melt with high yield and are of known composition. Materials from stamping plants are usually low in carbon, manganese, phosphorous and sulphur.
- Number 1 busheling scrap – This scrap is similar to punchings and plate. For the most part, this scrap category contains more steel clippings (up to 300 mm in length). The scrap is clean steel scrap and includes new factory busheling (e.g. steel clipping, stamping, etc.). It does not include old auto body and fender stock. It is free of metal which is coated, limed, vitreous enameled, and electrical sheet containing over 0.5 % silicon.
- New black steel sheet clippings – This scrap is for direct charging with maximum size 2.5 m by 0.5 m. It is free of metal which is coated, limed, vitreous enameled, and electrical sheet containing over 0.5 % silicon.
- Shredded clippings – These represent another factory grade of scrap. They resemble shredded automobile scrap (ferrous fraction) with similar density.
- Number 1 scrap bundles – They are also known as hydraulic bundles and are tightly compacted bales of light gauge scrap produced in hydraulic baling machines. The material is collected from press shops, and it consists of clean sheets, strips, and trimmings which can also be sold as punchings and plate scrap or as number 1 busheling scrap. These bundles may also include new black steel sheet scrap, clippings or skeleton scrap, compressed to charging box size, and have a density of not less than 1.2 ton/ cum. The bundles are tightly secured for handling with a magnet. The bundles can include tightly secured mandrel wound bundles or skeleton reels, chemically de-tinned material, old auto body and fender stock. The scrap bundles are free of metal which is coated, limed, vitreous enameled, and electrical sheet containing over 0.5 % silicon.
- Number 2 scrap bundles – These bundles are also produced in hydraulic baling machines and contain significant amount of steel sheets which have been galvanized or otherwise coated with zinc. With these bundles, not only do the contaminants result in a poor quality melt, but also the yield is poor (around 70 %). These bundles consist of old black and galvanized steel sheet scrap, hydraulically compressed to charging box size and have density not less than 1.2 ton/cum. The bundles do not include tin coated or lead coated material or vitreous enameled material.
- Number 3 scrap bundles – These bundles are also produced in hydraulic baling machines and contain old steel sheet, compressed to charging box size. The bundles have density not less than 1.2 ton/cum. It can include all coated ferrous scrap not suitable for inclusion in number 2 bundles.
- Electric furnace bundles – These bundles are simply smaller version of number 1 bundles and are so named because of their better suitability for charging through the smaller doors of electric arc furnaces.
- Prompt silicon grades – This scrap category consists of punchings, trimmings and skeletons from high silicon electrical sheet. These represent very pure scrap categories in terms of tramp elements but are high in silicon, which restricts their use.
- Flashings – This scrap category is also called forging scrap and consists mainly of croppings, and frequently includes defective forgings. This category of scrap shows the effect of forging temperatures, mainly in the form of scale.
- Heavy home scrap from steel plants – This scrap includes items such as ingot butts, billets, blooms, slab crops and rail crops.
- Railroad wheels and track materials – Railroad wheels and track materials represent a class of scrap where impurities are generally low. Users of this scrap are also to consider that railroad wheels and track materials are being alloyed increasingly with chromium and molybdenum. Also, it is to be remembered that most of the earlier cast iron wheels are being replaced with medium carbon steel forgings.
- Cut plate and structural scrap – This type of scrap is covered under several different codes, depending on the size of the pieces. These categories are more commonly used for charging large electric furnaces than for cupolas.
- Number 1 heavy melting scrap – This scrap category is characterized by a higher percentage of impurities than is found in cut plate and structural scrap, as well as higher alloy content since it generally consists of high-strength low-alloy (HSLA) steels. It is usually available in lengths under 1.5 m for charging into BOFs and large electric arc furnaces. It can also include wrought iron and/or steel scrap of 6 mm and above in thickness. Individual pieces are normally not above 0.6 m x 1.5 m (charging-box size) prepared in a manner to ensure compact charging.
- Number 2 heavy melting scrap – This scrap category differs from number 1 heavy melting scrap mainly in that the lower limit of thickness is 3 mm, and more coated steel is allowed. It includes wrought iron and steel scrap, black and galvanized steel, 3 mm and above in thickness. The scrap is of charging-box size and includes material not suitable as number 1 heavy melting scrap.
- Shredded scrap – It is usually similar to shredded clippings except that shredded scrap is likely to contain more shreddings from auto bodies, and may contain more plastics, aluminum and other contaminants. It includes homogeneous iron and steel scrap, magnetically separated, originating from automobiles, unprepared number 1 and number 2 steel, miscellaneous baling and sheet scrap. Average density of the category of scrap is 0.8 ton/cum.
- Shredded clippings – They consist of shredded low carbon steel clippings or sheets. This scrap category is to have an average density of 1 ton/cum.
- Shredded tin cans for re-melting – This scrap category includes shredded steel cans (tin coated or tin free) and can include aluminum tops but is to be free of aluminum cans, non-ferrous metals except which is used in can construction, and non-metallics of any kind.
- Auto slabs – Auto slabs have essentially the same chemical composition as number 2 scrap bundles but they provide more yield since they contain less trash.
- Briquetted steel turnings – Briquetted steel turnings are classified in accordance with several codes including a number of types (and grades of purity) which depends on whether or not the turnings are mixed with cast iron borings.
- Steelmaking slag scrap – Steelmaking slag scrap is normally considered to be a low grade melting material. This material consists of irregular steel nuggets that have been separated magnetically from crushed slag. Melting yield with this category of scrap usually ranges from 70 % to 80 %.
- Machine shop turnings – These include clean steel or wrought iron turnings, free of iron boring, non-ferrous metals in a ‘free state’, scale, or excessive oil. It does not include badly rusted or corroded material.
- Machine shop turning and iron borings – These are the same as machine shop turnings but include iron borings.
- Shoveling turnings and iron borings – These are the same as shoveling turnings but include iron borings.
- Fragmentized scrap from incineration – Fragmentized incinerator scrap is loose steel scrap which is processed through an incinerating plant for household waste followed by magnetic separation, fragmentized into pieces not exceeding 200 mm in any direction and consisting partly of tin coated steel cans. This scrap is required to be prepared in a manner to ensure direct charging. The scrap is to be free of excessive moisture and rust and must be free of excessive metallic copper, tin, lead (and alloys) and steriles to meet the aimed analytical contents.
Some of the common categories of cast iron scrap are given below.
- Broken ingot moulds and stools – This category of scrap is derived from worn-out ingot moulds. This is not very suitable for BOF steelmaking, most of it is used in the foundries. This grade is comprised of fairly high-quality cast iron that is generally low in tramp metals.
- Drop broken machinery cast – This category of scrap is also called number 1 machinery cast. This category by definition is machinery cast and is to show evidence of having been machined. Thus it is designated as a good scrap category of relatively soft iron.
- Auto cast – This scrap category is comprised normally of the powertrains from trucks and buses. For the most part, the steel components are removed for their inclusion in steel scrap.
- Cupola cast – Cupola cast iron scrap is a designated category which can contain virtually any grade of iron except stove plate, burnt iron or brake shoes. It is also frequently known as ‘mixed cast’.
- Briquetted cast iron borings – These briquetted cast iron borings have become a prominent category of cast iron scrap. Various grades of borings are available under this category.
- Stove plate – Stove plate consists of thin sections which had been purposely cast from high fluidity iron, and thus contains much silicon and phosphorus.
- Burnt iron – Burnt iron consists of burnt stove plate, grates, furnace parts, fire pots and annealing boxes and tubes. It represents the lowest category of cast iron scrap.
Some of the common categories of stainless steel scrap are given below.
- 200 series stainless steel scrap solids – This type of scrap includes all types of clean 200 series of stainless steel scrap solids, which contain a maximum of 0.5 % copper.
- Stainless steel scrap – Stainless steel scrap consists of clean 18-8 type (300 series) stainless steel clips and solids containing a minimum of 16 % chromium, 7 % nickel, a maximum of 0.5 % phosphorous, and 0.03 % sulphur and is otherwise free of harmful contaminants. Typical scrap comes from the manufacture of sinks, tanks, pipes, etc.
- Stainless steel turnings – Stainless steel turnings consist of clean 18-8 type (300 series) stainless steel turnings containing a minimum of 16 % chromium, and 7 % nickel, and are free of non-ferrous metals, non-metallics, excessive iron, oil and other contaminants.
- 400 series stainless steel scrap – This scrap category consists of clean 400 series stainless steel containing no nickel and 10 % to 17 % of chromium, and is otherwise free of harmful contaminants.
A major challenge in recycling scrap is to maintain the quality of steel products and minimize contamination with other metals. Potential residual element contamination can come from the recycling of automobiles and municipal scrap. Use of recycled scrap steel in steelmaking processes has been increasing, and this trend is expected to continue and grow because of the increased availability of cheap automotive scraps. As a result, levels of residual impurity elements entering the steelmaking process from scrap feed are increasing with increased scrap use and repeated recycling. The ability to control the detrimental effects of these residual elements, and the need for more efficient refining technologies to recycle future scrap feed, are major concerns.
The main sources of ferrous scrap are the construction and transportation sector. Engineering products, tubular products and metal ware are the sources of old scrap.
Steel has been used as beams, reinforcement bars, and other structural parts in building and construction. Large amounts of steel scrap get generated during the demolition of a building however the amount varies greatly from the type of building and its geographical location. On average, steel accounts for slightly less than 1 % of the mass of a residential building. Almost all steel parts are recovered, with good quality beams for direct reuse and the rest for recycling in a steel plant.
Large equipment and machinery covers the industrial and agricultural machinery and structure, such as earthmoving and quarrying equipment, cranes, farm vehicles and machinery, storage tanks, tools etc. At the end of their life, these equipment and machinery become source of old scrap.
In the case of electronics and electrical equipments, on an average, steel accounts for almost half of the content on a weight basis in electrical equipment and these electronics and electrical equipments have the potential of generating quite a good amount of old steel scrap at the end of their life cycle.
Steel packaging materials includes food cans, beverage cans, aerosols, and steel straps etc. After their use steel packaging materials become old scrap.
Wherever, when ferrous scrap containing products cannot be easily collected separately then the majority of these products go into mixed waste. Recovery of ferrous scrap from mixed waste is difficult as well as costly and hence results in some potentially recyclable ferrous scrap getting lost.
The various sources and forms of ferrous scrap require the use of several scrap sorting and preparation techniques to remove the contaminants and/or recover other valuable materials (i.e. non-ferrous metals) prior to entering the steelmaking process.
In general, ferrous scrap recycling consists of collection, sorting, shredding and/or sizing, and final melting at the steel plants. This process can be summarized as given below.
- Ferrous scrap is collected either separately or mixed and then sorted in the scrap yard and then sent to either scrap treatment plants or directly to the steel plants.
- In case of the scrap treatment plant, different types of ferrous scraps are further separated and prepared for shredding/sizing. Shredding and sizing is often needed for a further stage of separation. While shredding and cutting, magnetic separation normally single out the ferrous metal (carbon steel). If shredded scrap metal needs to be dried or to be further cleaned of possible contaminants such as oil, grease, lubricants, lacquers, rubber, and plastic laminates, this is usually done at the scrap treatment plant but for thermal treatment, it is more energy efficient to perform this at the steel production furnace and avoid double heating.
- At the steel plants, iron and steel scrap are often charged directly to the steelmaking furnaces.
The following is the description of the processes carried out for scrap recycling (Fig 1) under waste regulation.
- Collection – The ferrous scrap is usually collected at the scrap generating source and then transported to the scrap yard for processing.
- Sorting – This is mainly a manual process to pick out the scrap metal, according to the type of metal and sources, from the mixed waste.
- Separating – When there is the risk of mixed ferrous and non-ferrous metal scrap, magnetic separation is to be done through a simple magnetic device, such as magnetic conveyor, via mechanical or manual separation.
- Cleaning and de-polluting – If necessary, the sorted scrap is required to be washed and then dried to have minimal moisture or pre-treated (e.g. thermal treatment) to eliminate residues such as oil and paint etc.
- Compacting – Baling is to be done with baling machine or when sizing is taken place using a shredder such that the resulting material is naturally compacted.
Fig 1 Processes carried out for scrap recycling
While a small proportion of unprepared old ferrous scrap can be directly used by consumers, the vast majority of old iron and steel scrap is sorted and processed by the scrap recycling industry. Scrapyards use a variety of processes including sorting, shearing, shredding, torching and baling to sort and prepare ferrous scrap to commodity-grade specifications. The process of shredding, which was developed in the late 1950s, allows for whole cars, appliances and other end-of-life products to be quickly shredded into fist-size pieces of scrap, greatly increasing scrap processors´ ability to handle large items and to separate nonferrous material.
These days for an example, when a passenger car reaches its end of life, it is brought to a specific collection point, which in some cases can also be a generic scrap treatment plant. The car is treated (depolluted) according to a certain procedure. It is first decontaminated by removing various fluids and parts. The rest of the car, including the body, the interior, etc. is fed into a shredder. In the shredding process, magnetic separation is used to remove the magnetic ferrous fraction, leaving non-ferrous metals and non-metallic materials to pass to further stages, i.e. dense media separation and eddy-current separator, for the segregation of one type from another. The separated ferrous part contains as much as 98 % ferrous metal.
In case of used beverage cans which are made both from steel and aluminum, they are collected and then steel cans are separated from the aluminum cans. The cans are then processed by baling before being sent to the steel plants for melting in the steel production shops.
The electronics and electrical equipment waste covers a wide variety of end of life products mainly from households and offices. These products require that hazardous components, such as batteries, printed circuit boards, liquid crystal displays, etc., to be removed with proper technologies. This is done at different stages of the treatment process. After this de-pollution step, the electronics and electrical equipment waste consists chiefly of a mixture of metal, plastics and glass. From here, the treatment of the electronics and electrical equipment waste in general has the following steps, though the process can vary with different combinations of shredding, granulating (more than once), magnetic separation, and eddy current separation (more than once), there is also the possibility of density separation on the separation table and/or hand separation. The stainless steel, aluminum and copper fractions are separated from other ferrous metal and other nonferrous metal during these processes and can be sent directly to the steel plants or refineries.
In case of demolition of the civil construction, metal scrap is separated whenever possible along the dismantling process and is sold for direct reuse or to traders or treatment plants. Since by weight aluminum and steel have different prices, further separation is often performed on site. Steel elements inside concrete is generally first be sent to recycling centres for crushing and separation with magnets before being returned to the ferrous scrap industry.
Environmental, health and safety considerations during handling of scrap
The safety related issues are as follows.
- All categories of scrap are to exclude (i) pressurized, closed or insufficiently open containers of all origins which can cause explosions. Containers are to be considered as insufficiently open where the opening is not visible or is less than 10 cm in any one direction, and (ii) dangerous material, inflammable or explosive, fire-arms (whole or in part), munitions, dirt or pollutants which may contain or emit substances dangerous to human health or to the environment or to the steel production process.
- All scrap categories are to be checked, within the limitations of accessibility and in strict compliance with appropriate detection equipment for radioactivity, to identify (i) material presenting radioactivity in excess of the ambient level of radioactivity, and (ii) radioactive material in sealed containers even if no significant exterior radioactivity is detectable due to shielding or due to the position of the sealed source in the scrap delivery.
The cleanliness related issues are as follows.
- All scrap categories are to be free of all but negligible amounts of other non-ferrous metals and non-metallic materials, earth, insulation, excessive iron oxide in any form, except for nominal amounts of surface rust arising from outside storage of prepared scrap under normal atmospheric conditions.
- All scrap categories are to be free of all but negligible amounts of combustible nonmetallic materials, including, but not limited to rubber, plastic, fabric, wood, oil, lubricants and other chemical or organic substances.
- All scrap categories are to be free of larger pieces (brick-size) which are non-conductors of electricity such as tyres, pipes filled with cement, wood or concrete.
- All categories are to be free of waste or of by-products arising from steel melting, heating, surface conditioning (including scarfing) grinding, sawing, welding and torch cutting operations, such as slag, mill scale, bag house dust, grinder dust, and sludge.
The residual and other metallics elements related issues are as follows.
- Copper- All categories of scrap are to be free of visible metallic copper which means free of copper wound electric motors, sheets and copper coated materials, bearing shells, winding, and radiator cores. All categories of scrap are to be free of all but negligible amounts of wire, insulated wire and cable tubing, and other copper, brass items mixed with, attached to, or coating ferrous scrap. All categories of scrap are to be free of materials with high dissolved copper content such as rebars and merchant bars which will be grouped in the high residual scrap categories.
- Tin – All categories of scrap are to be free of tin in any form such as tin cans, tin coated materials etc. as well as bronze elements such as rings, bearing shells etc.
- Lead – All categories of scrap are to be free of lead in any forms such as batteries, solder, wheel weights, terne plate, cable ends, bearings, bearing shells etc.
- Chromium, nickel, and molybdenum – All categories of scrap are to be free of alloyed steels and stainless steels as well as of mechanical parts (which mainly contain these elements) such as motors, drive gears for trucks, axles, gear boxes, gear wheels, tools and dies as well as non-magnetic pieces.
The maximum levels of the above metallic elements in different scrap categories are to be indicated in the specification.