A salt-free treatment of aluminum dross using plasma heating

The plasma dross treatment process is similar in operation and equipment to the conventional RSF process, but its elimination of salt fluxes solves the problem of corrosive gas evolution, and also results in salt-free by-products (NMP), which are recyclable and are a marketable raw material for other industries. Labor and equipment demands are about the same for both processes, but the new process dispenses with the costs of salt purchase and landfilling or recycling of salt cake. The new process is the first industrial application of plasma heating technology in the aluminum industry, and greatly reduces environmental risks, while providing a closed-loop, pollution-and waste-free dross treatment method.     

Issues in the melting and reclamation of aluminum scrap

The processing of aluminum scrap has been practiced for as long as aluminum has been produced due to the inherent value of the metal and the amount of energy required to produce primary aluminum from bauxite ore. Scrap can be remelted at a fraction of the expense. With the large-scale introduction of aluminum beverage containers in the 1970s, increases in energy costs, and the need to reduce solid waste, aluminum recycling has grown at an increasing rate. This article provides a overview of the technologies and issues that surround the melting and reclamation of aluminum scrap.     

Recovering aluminum from aluminum dross in a DC electric-arc rotary furnace

The recycling of aluminum scrap and dross yields significant economic and energy savings, as well environmental benefits. The recovery of aluminum depends on many factors. The aim of this work is to experimentally investigate aluminum recovery under different conditions. In this study, aluminum dross was processed in a direct-current electric-arc rotary furnace. The presence of crushing refractory bodies during processing was found to increase the degree of aluminum recovery by about ten percent.     

Sodium Treatment of Copper Dross

A new patented process for recovering lead from rough copper dross by sodium treatment was implemented at Asarcoys Glover Smelter in 1979. The basic metallurgical principles of the process are explained, and current plant operating procedures and results are described. The advantages of the sodium process, as compared to traditional dross treating in a reverberatory, and its possible application to treating complex lead blast furnace drosses are discussed.     

铝灰渣中AlN水解行为及其多元非线性回归分析

通过对铝灰渣水解反应过程中组分及其含量变化的研究,提出铝灰渣中AlN含量的修正公式;根据AlN含量和悬浊液pH值的测定,考察时间、温度、转速等水解参数对AlN水解速率的影响并对其进行多元非线性回归分析。结果表明:升高温度能降低铝灰渣中AlN含量并降低悬浊液pH值;延长时间可有效促进AlN的水解,同时在2h内悬浊液pH值迅速提升至高位;转速对AlN水解速率和悬浊液pH值无明显影响。总体而言,AlN含量比悬浊液pH值更能客观表征铝灰渣中AlN水解速率。对水解参数及修正后铝灰渣中AlN含量进行多元非线性回归分析并二次简化,发现理论值与实验值相对误差≤±8.65%。     

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.     

改革开放30年:中国铝罐料工业从无到有

评述了中国铝易拉罐制罐、制盖、罐身料、罐盖料工业和生产技术的发展过程,以及它们的产量和需求量.对今后中国这些产业的发展和产品的需求量进行了预测.     

Process of aluminum dross recycling and life cycle assessment for Al-Si alloys and brown fused alumina

In 2008, around 596 000 t of aluminum dross was generated from secondary aluminum industry in China; however, it was not sufficiently recycled yet. Approximately 95% of the Al dross was land filled without innocent treatment. The purpose of this work is to investigate Al dross recycling by environmentally efficient and friendly methods. Two methods of Al dross recycling which could utilize Al dross efficiently were presented. High-quality aluminum-silicon alloys and brown fused alumina (BFA) were produced successfully by recycling Al dross. Then, life cycle assessment (LCA) was performed to evaluate environmental impact of two methods of Al dross recycling process. The results show that the two methods are reasonable and the average recovery rate of Al dross is up to 98%. As the LCA results indicate, they have some advantages such as less natural resource consumption and pollutant emissions, which efficiently relieves the burden on the environment in electrolytic aluminum and secondary aluminum industry.     

铝底盖与马口铁电偶腐蚀行为研究

本文通过稳态极化曲线和电偶电流、电偶电位的测定,评价了在酸性饮料中铝底盖与马口铁电偶腐蚀倾向,结果表明:密封除氧酸性饮料液中Sn-Al电偶电位差远小于200mV,Sn为阳极,Al为阴极,属于弱电偶腐蚀行为,加之铝为阴极,且在这一体系中呈现钝化状态.因此,在酸性饮料罐状态下,腐蚀电化学行为仍以马口铁腐蚀过程为主,可以忽略铝底和罐体马口铁发生严重局部电偶腐蚀的可能性.     

Dross treatment in a rotary arc furnace with graphite electrodes

Aluminum baths are always covered with a layer of dross resulting from the aluminum surface oxidation. This dross represents 1–10% of the melt and may contain up to 75wt.% aluminum. Since aluminum production is highly energy intensive, dross recycling is very attractive from both energy and economic standpoints. The conventional recycling process using salt rotary furnaces is thermally inefficient and environmentally unacceptable because of the production of salt slags. Hydro-Quebec has developed a new technology using a rotary arc furnace with graphite electrodes. This process provides aluminum recovery rates of 80–90%, using a highly energy efficient, environmentally sound production method.     

Processing of Aluminum Dross: The Birth of a Closed Industrial Process

This is the history of a modern aluminum dross recycling company, from its beginnings in the last years of the twentieth century to the present day. The vision of the founders was to build a local recycling plant and take full responsibility for sensitive environmental issues by recycling aluminum dross locally rather than shipping it abroad. The paper tells the history of the company from the environmental perspective, and gives an overview of some of the challenges and the decisions that followed from this vision, for instance the selection of technology. The company developed a closed industrial process for the recycling of aluminum dross, and the paper discusses some of their laboratory experiments and industrial trials. An important milestone has now been reached as the process in its present form is recognized by the environmental authorities in the country. Furthermore, it seems realistic that in the near future the final product from this process will be comparable to the product delivered in the processing of salt cake in specialized chemical plants, but at a fraction of the cost.     

Alternative starting materials for the production of aluminum foam by the powder metallurgical process

In the past it has already been proven that aluminum foam is a construction material appropriate for numerous applications. Especially in domains such as machine tool manufacturing and vehicle construction the combination of lightweight design and vibration damping is of great importance and aluminum foam can unfold its full potential. The widespread use of aluminum foam is still hampered by the high production costs resulting from the expensive production process and starting materials. The present work focuses on studies of alternative, cheaper starting materials. The results of current investigations follow the idea that aluminum chips may be successfully used as base material instead of atomized powders, without negatively influencing the macroscopic foam structure. It could also be proven that good foaming rates can be achieved with calcium carbonate as foaming agent for aluminum. That's why already in the near future, it will be possible to use recycling materials like aluminum chips in the series production of aluminum foams by the powder metallurgical process (PM process). Since sorted aluminum chips cost less than 1 €/kg, and calcium carbonate costs only a fraction of titanium hydride, a distinct price reduction for aluminum foam, and the lowering of the inhibition threshold for its application should be possible. Further studies are required to examine the static and dynamic properties of the foams and to compare them with conventional aluminum foams.     

The Nondestructive Determination of the Aluminum Content in Pressed Skulls of Aluminum Dross

During production of primary and secondary aluminum, various amounts (in some cases up to 200 kg) of aluminum dross, a mixture consisting of molten aluminum metal and different oxide compounds (the nonmetallic phase), are skimmed per tonne of molten metal. To preserve the maximum aluminum content in hot dross for further extraction, it is necessary to cool the dross immediately after skimming. One way to do this is to press the skimmed hot dross in a press. In this process, the skimmed dross is transformed into so-called pressed skulls, with characteristic geometry convenient for storage, transport, or further in-house processing. Because of its high aluminum content—usually between 30% and 70%—pressed skulls represent a valuable source of aluminum and hence are in great demand in the aluminum recycling industry. Because pressed skulls are generally valued on a free-metal recovery basis, which is influenced by the yield of recovery, or in other words, by the quality of the recycling process, it was recognized as important and useful to develop a method of fast and cost-effective nondestructive measurement of the free aluminum content in pressed skulls, independent of the technology of pressed skulls recycling. In the model developed in this work, the aluminum content in pressed skulls was expressed as a function of the pressed skulls density, the density of the nonmetallic phase, and the volume fraction of closed pores. In addition, the model demonstrated that under precisely defined conditions (i.e., skulls from the dross of the same aluminum alloy and skimmed, transported, cooled, and pressed in the same way and under the same processing conditions), when other parameters except the pressed skulls density remain constant, the aluminum content in pressed skulls can be expressed as a linear function of the pressed skulls density. Following the theoretical considerations presented in this work, a practical industrial methodology was developed for nondestructive prediction of the amount of free aluminum in pressed skulls w _Al, based on nondestructive measurement of the density ρ of the pressed skulls. The pressed skulls density is measured by a fully automatic gas displacement pyknometer with a working volume large enough to enable the insertion of the whole pressed skull sample. An additional integral part of this methodology is the set of experimentally determined linear graphs w _Al-ρ, plotted in advance for all classes of pressed skulls existing in the plant, from the experimentally collected data on pressed skulls density and aluminum recovery by melting. After selecting the proper graph w _Al-ρ, which is usually performed on an aluminum alloy basis, the pyknometric measured density of the pressed skulls can be routinely related to the aluminum content sought, within a relative error of ±5%.     

The environmental management of selenium in aluminum processing

To identify the environmental fate and exposures with respect to selenium compounds in aluminum processing, total particulates and selenium concentrations at three U.S. aluminum facilities were assessed in October 2002. Site A was a reduction facility that utilized manganese alloys containing selenium, Site B was a rolling mill facility that used manganese alloys free of selenium, and Site C was a recycling facility that received aluminum dross and scrap from both Site A and Site B. Total selenium concentrations in process materials and waste materials were measured. Simultaneously, furnace stack emissions and occupational airborne exposures were monitored at each of the three facilities. Results indicated that the major environmental management issues were selenium particulates in the stack emissions from Site A and baghouse dusts classified as hazardous due to selenium from the rotary furnaces at Site C. For more information, contact K. Hagelstein, TIMES Limited, 1604 Leopard Street, Sheridan, WY 82801; (307) 674-4844; fax (307) 674-4843; e-mail aircaredoc@aol.com.     

The recycle of wrought aluminum alloys in Europe

Increasing demand for aluminum-based products and globalization of the aluminum industry have contributed significantly to the higher consumption of aluminum scrap for re-production of wrought aluminum alloys. The recycling of wrought auminum alloys not only fills market demand, but does so economically. It is a well-known fact that recycling wrought aluminum alloys from collected scrap consumes 15 times less energy than producing primary aluminum, and the cost of internal scrap is marginal. This paper examines opportunities for recycling scrap to solve the ongoing problem of raw material shortages for European producers of wrought aluminum alloys.     

Characterizing the physical and chemical properties of aluminum dross

In this article, the results of an investigation of granular and compact aluminum drosses are reported. The bulk density of granular drosses was determined according to DIN 52110-B, while DIN 52102-RE-VA was applied to compact drosses. The salt contents of the drosses were measured by applying the leaching test DIN 38414-S4; the metal contents by the salt-melting process were measured on a laboratory scale. In addition to the density data, the particle-size analysis, the distribution of elements in the different fractions, composition, metal content of recovered alloys, and gas evolution were compiled in a dross identity card characterizing each dross and simplifying the preanalysis for recovery.     

Relationship between plasma arc cutting acoustic and cut quality

Abstract

The tremendous acoustic signal exiting during the plasma arc cutting process includes a lot of information about this process and has a close relation with cut quality. To investigate the relationship between the plasma arc cutting acoustic and cut quality, a number of experiments have been carried out. In the present study, cut quality by plasma arc is described by top and bottom kerf widths, bevel angle, and attached dross state, and the relationship between the evaluation items for cut quality and the SPL (sound pressure level) of the cutting acoustic is investigated in detail. It is shown that the SPL reaches a maximum as the bottom kerf width equals the diameter of the plasma arc potential core. The attached dross and kerf widths in a state of free dross obviously affect the low and high frequency components of the plasma arc cutting acoustic, respectively. These results also suggest the possibility of designing an acoustic-based monitoring system for the plasma arc cutting process.     

铝灰中铝资源回收工艺现状与展望

铝灰是铝工亚一种重要的副产品,其中的铝含量约占铝生产使用过程中总损失量的1%～12%.回收铝灰中的铝资源能降低成本、保护环境、节约能源和提高资源利用率,有着巨大的经济和社会效益.本文总结了铝灰的来源、分类和组成,综述了铝灰中回收金属铝的回收工艺和利用铝灰合成材料工艺,展望了铝灰回收工艺的发展前景,提出了相关建议.     

An Industrial Method for Determining the Amount of Organics in Representative Samples of Aluminum Scrap

In recycling plants, especially those specializing in the recycling of low-grade aluminum scrap for wrought aluminum alloys, timely and accurate information about the amount of organics and other impurities in the incoming scrap is an important parameter in achieving both economic benefits and standard metallurgical quality of the recycled metal. To use aluminum scrap combined with organics as a source of aluminum for producing wrought aluminum alloys of standard quality, its metallurgical composition and the content of organic and other impurities should be quickly and cost-effectively analyzed on representative samples. In this work, an industrial thermogravimetric/differential thermal analysis of representative scrap samples was developed as an efficient analytical methodology for analyzing the humidity and organic impurities in incoming scrap. When performed in continuous mode, under a flowing atmosphere of argon with 1?wt.% of oxygen, this methodology enables a routine measurement of the humidity, the quantity of organics, and the carbon content in representative samples of incoming scrap in less than 15?min within an accuracy of ±0.5%.     

铝合金盘基片化学镀镍缺陷的形成机理

针对铝合金盘基片镀镍过程中产生的凹点型缺陷导致基片报废的问题,采用扫描电子显微镜、聚焦离子束显微镜对计算机硬盘用铝合金盘基片的微观组织缺陷进行分析,并通过实验室模拟化学镀镍前处理过程,观察前处理对铝合金盘基片表面形貌、相分布与表面润湿性的影响。结果表明:发现在前处理过程中铝合金表面析出相周围的铝基体发生溶解,造成析出相脱落,形成微孔。而深度较大的微孔由于气体难以及时排出,溶液难以浸没,造成微孔底部Zn覆盖较少。说明在镀镍过程中,基片浸入镀镍溶液时深度较大的微孔中的气体同样无法全部及时排除,造成微孔处无法发生镀镍反应,使得微孔处形成孔洞,最终造成镀层表面的凹点型缺陷。