Aluminum Scrap Research Articles

Environmental consequences of recycling aluminum old scrap in a global market

Nowadays, aluminum scrap is traded globally. This has increased the need to analyze the flows of aluminum scrap, as well as to determine the environmental consequences from aluminum recycling. The objective of this work is to determine the greenhouse gases (GHG) emissions of the old scrap collected and sorted for recycling, considering the market interactions. The study focused on Spain as a representative country for Europe. We integrate material flow analysis (MFA) with consequential life cycle assessment (CLCA) in order to determine the most likely destination for the old scrap and the most likely corresponding process affected. Based on this analysis, it is possible to project some scenarios and to quantify the GHG emissions (generated and avoided) associated with old scrap recycling within a global market. From the MFA results, we projected that the Spanish demand for aluminum products will be met mainly with an increase in primary aluminum imports, and the excess of old scrap not used in Spain will be exported in future years, mainly to Asia. Depending on the scenario and on the marginal source of primary aluminum considered, the GHG emission estimates varied between −18,140kg of CO2eq.t−1 and −8427 of CO2eq.t−1 of old scrap collected. More GHG emissions are avoided with an increase in export flows, but the export of old scrap should be considered as the loss of a key resource, and in the long term, it will also affect the semifinished products industry. Mapping the flows of raw materials and waste, as well as quantifying the GHG impacts derived from recycling, has become an essential prerequisite to consistent development from a linear toward a circular economy (CE).

Reprocessing of AW2007, AW6082 and AW7075 aluminium chips by using sintering and forging operations

Since its discovery in the late Nineteenth century aluminium becomes an important construction material due to its good mechanical properties such as sufficient strength at low density. Additional advantages are high corrosion resistance as well as low manufacturing forces. Apart from this, aluminium is still very expensive to produce. The energy consumption of the production process is at least twice as much as for steel. Most of the energy consumption takes place at the electrolyse process while aluminium oxide (Al2O3)—recovered from natural bauxite—is divided into unalloyed aluminium named “primary aluminium” and CO2. Contrary to the expensive production of primary aluminium the energy consumption of the recycling process of used aluminium also known as “secondary aluminium” is considerably lower. Given this huge effort in producing primary aluminium, the recycling of aluminium is an important economic and ecological approach. The common recycling method for aluminium is to melt it in a furnace. Except from small-sized scrap like chips, this is an overall efficient recycling method for most aluminium scraps. It can be observed that especially chips suffer high material losses mostly due to contaminants from the production process (cooling lubricant, oil etc.), fire losses (oxidation), slag and unadapted furnace settings. For this reason, several researches examine alternative recycling processes to avoid a melting process and minimize material losses. In this investigation a new non-melting aluminium recycling approach will be validated. For this purpose various chip pressings (turning, milling, sawing) are forged with an upsetting press. It will be shown that it is possible to generate a solid consolidation without pores in areas of high material movement. Furthermore, the effect of a previous sintering operation will be examined.

Analysis of anthropogenic aluminum cycle in China

Anthropogenic aluminum cycle in China was analyzed by the aluminum flow diagram based on the life cycle of aluminum products. The whole anthropogenic aluminum cycle consists of four stages: alumina and aluminum production, fabrication and manufacture, use and reclamation. Based on the investigation on the 2003–2007 aluminum cycles in China, a number of changes can be found. For instance, resources self-support ratio (RSR) in alumina production dropped from 95.42% to 55.50%, while RSR in the aluminum production increased from 52.45% to 79.25%. However, RSR in the Chinese aluminum industry leveled off at 50% in the period of 2003–2007. The respective use ratios of domestic and imported aluminum scrap in the aluminum industry of 2007 were 5.38% and 9.40%. In contrast, both the net imported Al-containing resources and the lost quantity of Al-containing materials in aluminum cycle increased during the same period, as well as the net increased quantity of Al-containing materials in social stock and recycled Al-scrap. Proposals for promoting aluminum cycle were put forward. The import/export policy and reducing the loss of Al-containing materials for the aluminum industry in China in the future were discussed.

Component- and Alloy-Specific Modeling for Evaluating Aluminum Recycling Strategies for Vehicles

Previous studies indicated that the availability of mixed shredded aluminum scrap from end-of-life vehicles (ELV) is likely to surpass the capacity of secondary castings to absorb this type of scrap, which could lead to a scrap surplus unless suitable interventions can be identified and implemented. However, there is a lack of studies analyzing potential solutions to this problem, among others, because of a lack of component- and alloy-specific information in the models. In this study, we developed a dynamic model of aluminum in the global vehicle stock (distinguishing 5 car segments, 14 components, and 7 alloy groups). The forecasts made up to the year 2050 for the demand for vehicle components and alloy groups, for the scrap supply from discarded vehicles, and for the effects of different ELV management options. Furthermore, we used a source-sink diagram to identify alloys that could potentially serve as alternative sinks for the growing scrap supply. Dismantling the relevant components could remove up to two-thirds of the aluminum from the ELV stream. However, the use of these components for alloy-specific recycling is currently limited because of the complex composition of components (mixed material design and applied joining techniques), as well as provisions that practically prevent the production of safety-relevant cast parts from scrap. In addition, dismantling is more difficult for components that are currently penetrating rapidly. Therefore, advanced alloy sorting seems to be a crucial step that needs to be developed over the coming years to avoid a future scrap surplus and prevent negative energy use and emission consequences.

Evaluation of the Effect of Selected Alloying Elements on the Mechanical and Electrical Aluminium Properties

Abstract Modern industry expects aluminum products with new, unusual, and well-defined functional properties. Last years we are able to notice constant development of aluminium alloys. In food industry, power engineering, electrical engineering and building engineering, flat rolled products of 1XXX series aluminium alloys are used.8XXX series alloys registered in Aluminium Association during last 20 years may be used as an alternative. These alloys have very good thermal and electrical conductivity and perfect technological formability. Moreover, these materials are able to obtain by aluminium scrap recycling. Fundamental alloy additives of 8XXX series are Fe, Si, Mn, Mg, Cu and Zn. Aluminium alloying with these additives makes it possible to obtain materials with different mechanical ale electrical properties. In this paper, the analysis of alloy elements content (in 8XXX series) effect on chosen properties of material in as cast and after thermal treatment tempers has been presented.

Current efficiency of recycling aluminum from aluminum scraps by electrolysis

Extracting aluminum from aluminum alloys in AlCl3-NaCl molten salts was investigated. Al coating was deposited on the copper cathode by the method of direct current deposition using aluminum alloys as anode. The purity of the deposited aluminum is about 99.7% with the energy consumption of 3–9 kW·h per kg Al, and the current efficiency is 44%–64% when the deposition process is carried out under 100 mA/cm2 for 4 h at 170 °C. The effects of experimental parameters, such as molar ratio of AlCl3 to NaCl, cathodic current density and electrolysis time, on the current efficiency were studied. The molar ratio of AlCl3 to NaCl has little effect on the current efficiency, and the increase of deposition temperature is beneficial to the increase of current efficiency. However, the increase of current density or electrolysis time results in the decrease of current efficiency. The decrease of current efficiency is mainly related to the formation of dendritic or powder deposit of aluminum which is easy to fall into the electrolyte.

Classification and Reactivity of Secondary Aluminum Production Waste

Aluminum production wastes (APW) are produced during the recycling of aluminum scrap and dross. They are frequently disposed in dry form at Subtitle D nonhazardous waste landfills, where they may react adversely with liquids. Depending on the APW composition and landfill environment, the exothermic reaction can cause sustained temperature increases that inhibit normal anaerobic biodegradation. A constant pressure calorimeter test was developed to simulate the APW reaction in a basic environment and quantify the reactivity. APW reactivity was investigated under varying strengths of sodium hydroxide and particle size. Bench-scale calorimeter experiments show that concentrations greater than 4M NaOH oxidize metallic aluminum and increase temperatures rapidly to 100°C. Lower NaOH concentrations, such as 1M NaOH, are recommended to quantify the APW reaction in a constant pressure calorimeter. APW in neutral solutions was found to be stable, but reducing APW particles through ball-milling exacerbated reactivity.

Lightweight Concrete with Aggregates Made by Using Industrial Waste

The disposal and treatment of solid and hazardous industrial waste is quite expensive for any industry; therefore it brings challenges to find a solution that permits to obtain new, usable products by waste utilization in a technically and economically sustainable as well as environmentally friendly way.The production of lightweight concrete by using aggregates made by industrial by-products and hazardous solid waste such as expanded fly ash, slag, sludge etc. is well known. This research provides possibilities to reuse waste called non-metallic product (NMP) from aluminium scrap recycling factories for the manufacturing of lightweight expanded clay aggregates and lightweight concrete. Characterization of NMP is described in the preliminary publications (Bajare et al. 2012).The manufacturing cycle of lightweight expanded clay aggregates were simulated in laboratory by sintering the clay - waste mixes in the rotary furnace up to 1200°C. Lightweight expanded clay aggregates with rather different pore structure were obtained due to slight variations of mixture composition and sintering temperature. Produced aggregates were with bulk density from 320 kg/m3 to 620 kg/m3. Different types of lightweight aggregates were used to produce lightweight concretes. Mechanical, physical and thermal conductivity tests were performed for hardened concrete specimens according to standard procedures.DOI: http://dx.doi.org/10.5755/j01.sace.4.5.4188

Fracture surface of recycled AlSi10Mg cast alloy

Recycled aluminium alloys are made out of aluminium scrap (new or old) and workable aluminium garbage by recycling. Due to the increasing production of recycled aluminium cast alloys is necessary to ensure their strict metallurgical control. The mechanical properties and the microstructure character depends on the chemical composition; melt treatment conditions, solidification rate, casting process and the applied thermal treatment. The mechanical properties depend on the morphologies, type and distribution of Si, Cu, Mg and Fe-phases, on the grain size, DAS and porosity distribution. Improvement of mechanical properties and structure of Al-alloys can often significantly increase the using lifetime of a casting. Different elements are added to achieve the optimum casting and mechanical properties. Modification can be achieved by several methods as faster solidification, mould vibration, melt agitation in mushy state and melt inoculation by using chosen elements like Sr, Na, Sb etc. Present work is focused on study of the effect of Sr-modification on the structure and mechanical properties of recycled AlSi10Mg cast alloy. For study and identification of intermetallic phases' was utilized standard (HF), colour (MA) and deep etching (HCl) in order to reveal the three-dimensional morphology of the silicon particles and intermetallic phases. For element composition of the specimen was used X-ray (EDX) analysis. Finally, the effect of modification on silicon morphology and fracture surface was examined.

Conversion of aluminum foil to powders that react and burn with water

In the US, the total amount of aluminum scrap and waste, including foil, is outpacing efforts to recycle it into conventional aluminum materials. It would be attractive to develop technologies for converting aluminum foil scrap and waste to useful products and energy carriers. The present paper focuses on the feasibility of converting foil to activated Al powders that chemically split water, releasing hydrogen. As a method for this conversion, high-energy ball milling of Al foil with sodium chloride is investigated, with removing NaCl from the obtained powder by dissolution in cold water or methanol. The powders are characterized using BET specific surface area analysis, laser diffraction particle size analysis, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The obtained micron-sized Al powders readily react with warm (35–80°C) water. Hydrogen evolution is studied using water displacement, while solid byproducts are examined by X-ray diffraction and thermal analysis. The powders are also mixed with gelled water at various mass ratios and combustion of these mixtures is studied in argon environment. With increasing Al concentration, the combustion front velocity increases despite the decrease in the combustion temperature. The burning rate of the stoichiometric mixture of the activated Al powder with water is comparable with the values reported previously for the mixtures based on nanoscale aluminum, while the content of active Al in the obtained micron-sized powder is significantly higher.

Microstructural and Vickers Microhardness Evolution of Heat Treated Secondary Aluminium Cast Alloy

Secondary aluminium alloys are made out of aluminium scrap and aluminium-processable waste by recycling. These alloys contain different alloying elements such as Al, Cu, Fe, Si and Mg that form intermetallic phases in aluminium matrix and influence on the microstructure, basic mechanical properties and microhardness evolution in aluminium cast alloy. As experimental material was used secondary aluminium cast alloy AlSi9Cu3. Material was subjected to heat treatment (age-hardening) consisting of a solution treatment at temperature 515 °C with holding time 4 hours, than water quenching at 40 °C and artificial aging by different temperature 130 °C, 150 °C and 170 °C with different holding time (2, 4, 8, 16 and 32 hours). The age-hardening led to changes in the morphology of structural components, but also leads to precipitation of finer hardening phases in the material substructure. As optimal age-hardening mode for secondary aluminium cast alloy AlSi9Cu3 was determined mode consisting of solution treatment at temperature 515 °C with holding time 4 hours and artificial aging at temperature 170 °C with holding time 16 hours. After this heat treatment cast alloy shows the best changes in microstructure and mechanical properties. These changes are comparable with changes by primary AlSi9Cu3 cast alloy.

Aluminium flows in vehicles: enhancing the recovery at end-of-life

The transportation sector constitutes the major end-use market for aluminium-containing products and expectations for the future do indicate that aluminium will increase at 140 kg per vehicle. Moreover, up to 75 % aluminium recycled in Europe is used in transportation: thus, metal scrap recovered from ELVs is a key lever to act for closing material cycles. However, although the management chain of ELVs has an established procedure and aluminium scrap is usually recovered in shredding plants, a considerable fraction of the metal particles ends up in the light fraction called car fluff and is then landfilled. In this study we investigated potential of enhancing the recovery of aluminium scrap from the light fluff treatment. With this goal, the quantity of aluminium embedded in the Italian transport sector in the last 62 years was estimated, and a campaign of characterization in size and shape distribution of aluminium particles in the light fluff output has been carried out. The results estimated up to about 560,000 tons of metal are potentially recoverable from the treatment of light fluff at current operating conditions, but relevant improvements may be achieve when size and shape distribution criteria are adopt to implement eddy currents separation for a quantitative metal recovery.

Characterization by EBSD of antimony-calcium rich phases formed during purification of aluminum scrap

We studied the influence of antimony on the modification rate of the silicon eutectic with sodium and/or strontium for casting of Al-Si alloys, and introduced controlled Ca and Sb to the system and studied the resulting compounds, which were determined to be Ca2Sb and AlSb. Scanning electron microscopy together with the complementary technique of electron backscatter diffraction (EBSD) were used to characterize the materials. The experimental results provided the basis for us to establish that antimony removal from Al occurs mainly through the reaction (Sb)Al + 2Ca = Ca2Sb + Al.

Modeling of Alternative Compositions of Recycled Wrought Aluminum Alloys

Nowadays, a significant part of postconsumed wrought aluminum scrap is still used for the production of comparatively cheaper cast alloys, in that way losing an important part of the potential added value. The share of postconsumed scrap in wrought aluminum alloys could be increased either by sorting to fractions with the required chemical composition and/or by broadening the standard compositional tolerance limits of alloying elements. The first solution requires hand or automatic sorting of postconsumed scrap as alloys or groups of alloys to the degree of separation sufficient to enable the blending of standard compositions of wrought alloys; the second solution is much more radical, predicting changes in the existing standards for wrought aluminum alloys toward nonstandard alloys but yet having properties acceptable for customers. In this case, the degree of separation of incoming postconsumed scrap required is much less demanding. The model presented in this work enables the design of optimal (standard and nonstandard recycling-friendly) compositions and properties of wrought aluminum alloys with significantly increased amounts of postconsumed scrap. The following two routes were modeled in detail: (I) the blending of standard and nonstandard compositions of wrought aluminum alloys starting from postconsumed aluminum scrap sorted to various degrees simulated by the model and (II) changing the initial standard composition of wrought aluminum alloys to nonstandard “recycling-friendly” ones, with broader concentration tolerance limits of alloying elements and without influencing the selected alloy properties, specified in advance. The applied algorithms were found to be very useful in the industrial design of both procedures: (I) the computation of the required chemical composition of the scrap streams obtained by sorting (or, in other words, the postconsumed scrap sorting level), necessary for achieving the standard wrought alloy composition and (II) the transformation of standard to nonstandard (recycling-friendly) compositions with the key alloy properties (e.g., tensile strength and elongation) remaining the same.

Aluminium recovery from waste incineration bottom ash, andits oxidation level

The recovery of aluminium (Al) scraps from waste incineration bottom ash is becoming a common practice in waste management. However, during the incineration process, Al in the waste undergoes oxidation processes that reduce its recycling potential. This article investigates the behaviour of Al scraps in the furnace of two selected grate-fired waste-to-energy plants and the amount recoverable from the bottom ash. About 21-23% of the Al fed to the furnace with the residual waste was recovered and potentially recycled from the bottom ash. Out of this amount, 76-87% was found in the bottom ash fraction above 5 mm and thus can be recovered with standard eddy current separation technology. These values depend on the characteristics and the mechanical strength of the Al items in the residual waste. Considering Al packaging materials, about 81% of the Al in cans can be recovered from the bottom ash as an ingot, but this amount decreases to 51% for trays, 27% for a mix of aluminium and poly-laminated foils and 47% for paper-laminated foils. This shows that the recovery of Al from the incineration residues increases proportionally to the thickness of the packaging.

Elemental analysis of lightweight metal scraps recovered by an automatic sorting technique combining a weight meter and a laser 3D shape-detection system

To verify the effectiveness of a new automatic sorting technique that combines a weight meter and a laser 3D shape-detection system, elemental analysis of lightweight metal scraps generated in end-of-life vehicle (ELV) shredder facilities was conducted using a handheld XRF analyzer. According to their 3D shape and chemical composition, aluminum scraps were classified into cast alloy (Alc) and wrought alloy (Alw) fragments, and magnesium scraps were classified into irregularly shaped and rod-like fragments. The average chemical composition of a group of fragments was estimated before and after the separation test using the developed automatic sorting technique. The results show that the production of wrought aluminum alloy from the mixture of Alc and Alw fragments is not realistic because the contents of some alloying elements greatly exceed the standard values, although these alloying elements greatly decrease after the Alc fragments are separated out. For the magnesium scraps, after the rod-like magnesium fragments originating from the steering column were separated from the irregularly shaped fragments, the average chemical compositions of the rod-like products and the irregularly shaped products clearly approached the standard compositions of AM60B and AZ91D alloys, respectively. Thus, it was confirmed that the developed automatic sorting technique contributes to recycling of lightweight metal scrap in the automobile industry.

SCANNING ELECTRON MICROSCOPY IDENTIFICATION OF INTERMETALLIC PHASES IN Al-Si CAST ALLOYS

Al-alloys are preferred in the automotive industry because of theirs lightweight. European Union has on the present big interest of share recycling aluminium, and so increase interest about recycled (secondary) aluminium alloys and castings from them. Recycled aluminium alloys are made out of aluminium scrap and workable aluminium garbage by recycling. Due to the increasing production of recycled aluminium cast alloys is necessary their strict metallurgical control. The mechanical properties and the microstructure are dependent on the composition, melt treatment conditions, solidification rate, casting process and the applied thermal treatment. The mechanical properties depend, besides the morphologies, type and distribution of Si, Cu, Mg and Fe-phases, on the grain size, DAS, porosity distribution or profile. Therefore, study the microstructure of Al alloys is very important. Analysis of microstructure in the AlSi9Cu3 alloy was performed on the SEM. For study and identification of intermetallic phases’ was utilized standard (Dix-Keller, 0.5% HF) and deep etching. Deep etching consists of dissolving the alpha-matrix in the reagent (30 s in HCl) in order to reveal the three-dimensional morphology of the silicon particles and intermetallic phases. For elemental composition of the specimen were used x-rays analysis (line, point and surface - mapping). Finally the fracture surfaces of Al-Si alloy after impact test in the as-cast state were observed.

Functional properties of glass–ceramic composites containing industrial inorganic waste and evaluation of their biological compatibility

Abstract A study has been carried out on the feasibility of using Latvian industrial waste (peat cool ash, fly ash, aluminium scrap metal processing waste, metallurgical slag and waste cullet glass) and raw mineral materials (limeless clay) to produce dense, frost resistant, chemically durable glass–ceramic materials by powder technology. Highly crystalline and dense products (density: 2.50–2.94 g/cm 3 , water uptake: 1.3–4.3%) were fabricated from different mixtures by sintering at temperatures in the range of 1060–1160 °C. Glass–ceramics were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and four point bending strength test. Chemical durability, soluble salt crystallization as well as biological tests were carried out in order to evaluate the environmental stability and possible toxicity of the materials. The novel glass–ceramics developed here can find applications as building materials, such as wall tiles and for manufacturing industrial floors.

Aluminium recovery during black dross hydrothermal treatment

The purpose of present research work was to present a process for the recovery of Al, by treating aluminium black dross (ABD), a by-product formed during aluminium scraps melting. The proposed process consists of the following four (4) unit operations:a.Crushing the initial ABD by a jaw crusher to “−1mm” and recovery of metallic Al by sieving and screening (distorted or flattened particles).b.Further grinding of the material by ball mill to “−100μm”, and recovery of the residual metallic Al. The total quantity of metallic Al recovered was estimated at 10.25% of the ABD.c.Recovery of soluble salts (NaCl, KCl), at atmospheric pressure, by water leaching of the grinded ABD at 90°C. During leaching, about half of the nitrides were also decomposed.d.Aluminium recovery from the water leached residue, by pressure leaching at 240°C, with NaOH strong solution (260g/L). The total aluminium leaching efficiency on the basis of ABD weight reached 57.5%.

Preparation of Ultrafine Al(OH)<sub>3</sub> Powders from Scrap Aluminum

The homogeneous precipitation pathway was explored to synthesize ultrafine powders of Al(OH)3. In the experiment, the scrap aluminum were used as raw material . The effects of reaction time, reaction temperature, stirring speed, concentration of sulphuric acid and dispersant on the preparation process were investigated. The results showed that ultrafine Al(OH)3 powders can be yielded and well-controlled under the following optimal conditions: the concentration of sulphuric acid 3.0 mol•L-1, reaction temperature 0-4 °C, stirring speed 900 r.min-1 and reaction time 15 min. The diameter less than 100nm of sphericity Al(OH)3 particles with the narrow distribution were successfully obtained. The Al(OH)3 powders was analyzed with scanning electron microscopy , infrared spectrometer. The Al(OH)3 powders have good dispersancy and purity is more than 90%. The operation of the experiment was very simple, and the particles were separated easily.