Aluminum dross

Table 1. Aluminum Dross Treatment Using Three Rotary Furnace Technologies ...

Another method of secondary aluminum recovery uses aluminum drosses as the charge instead of scrap. Traditionally, the term dross was defined as a thick liquid or solid phase that... 

Secondary aluminum Aluminum dross, water Particulates Wastewater, salts ... 

This air-oxy/fuel burner concept was first tried in 1989 at a Canadian aluminum dross reclamation plant where drosses and skimmings are smelted.2 The dross, with 10% salt, is charged through the burner end of a 25,000 lb (11,000 kg) rotary furnace, fired by a dual-fuel burner of 20 x 106 Btu/h (6 MW) capacity for melting. The... 

From Aluminum Dross Tailings Chemical Waste Leaching with NaOH and precipitation with different agents. Calcination of the precipitate at 600"C for 3 h. 

PZC/IEP of Alumina from Aluminum Dross Tailings Chemical Waste... 

El-Katatny, E.A. et al., Surface composition, charge and texture of active alumina powders recovered from aluminum dross tailings chemical waste. Powder Technol., 132, 137, 2003. 

Secondary Aluminum Production and Recycling of Aluminum Drosses... 

Aluminum dross comes either from skimmed product during primary aluminum smelting or from the melting of aluminum scrap such as used beverage containers, aluminum siding, castings, and the like and treating the melt with salt fluxes. 

Aluminum dross is especially recalcitrant, i.e., only about 30 wt.% can be recovered using conventional processes the remaining fraction is buried in landfill. Approximately one milhon tonnes of aluminum dross and salt cake materials are landfilled annually in the United States. Usually, the free aluminum metal, which is considered the most valuable component, is recovered from the solidified dross by first crushing and grinding it, for example, by ball milhng. 

Table 3.5. Annual capacity for major aluminum dross recyclers Company Annual recycling capacity (/tonnes)...

Lead alloys containing 0.09—0.15 wt % calcium and 0.015—0.03 wt % aluminum are used for the negative battery grids of virtually all lead—acid batteries in the United States and are also used in Japan, Canada, and Europe. If the molten alloy is held at too low a temperature, the aluminum precipitates from solution, rises to the surface of the molten alloy as finely divided aluminum particles, and enters the dross layer atop the melt. 

Lead—antimony or lead—arsenic ahoys must not be mixed with lead—calcium (aluminum) ahoys in the molten state. Addition of lead—calcium—aluminum ahoys to lead—antimony ahoys results in reaction of calcium or aluminum with the antimony and arsenic to form arsenides and antimonides. The dross containing the arsenides and antimonides floats to the surface of the molten lead ahoy and may generate poisonous arsine or stibine if it becomes wet. Care must be taken to prevent mixing of calcium and antimony ahoys and to ensure proper handling of drosses. 

If the temperature of a molten lead—calcium (tin)—aluminum ahoy is not kept sufficiently high, finely divided aluminum particles may precipitate and float to the top of the melt. These may become mixed with oxides of lead in the dross. The finely divided aluminum particles can react violently with the oxides in the dross if ignited. Ignition can occur if attempts are made to melt or bum the dross away from areas of buildup with a torch. The oxides in the dross can supply oxygen for the combustion of aluminum once ignited. 

Scrap that is unsuitable for recycling into products by the primary aluminum producers is used in the secondary aluminum industry for castings that have modest property requirements. Oxide formation and dross buildup are encountered in the secondary aluminum industry, and fluxes are employed to assist in the collection of dross and removal of inclusions and gas. Such fluxes are usually mixtures of sodium and potassium chlorides. Fumes and residues from these fluxes and treatment of dross are problems of environmental and economic importance, and efforts are made to reclaim both flux and metal values in the dross. 

The dross is removed and fed into a dross furnace for recovery of the nonlead mineral values. To enhance copper recovery, dressed lead bullion is treated by adding sulfur-bearing materials, zinc, and/or aluminum, lowering the copper content to approximately 0.01%. 

As mentioned above, approximately 7% of the total sulfur present in lead ore is emitted as S02. The remainder is captured by the blast furnace slag. The blast furnace slag is composed primarily of iron and silicon oxides, as well as aluminum and calcium oxides. Other metals may also be present in smaller amounts, including antimony, arsenic, beryllium, cadmium, chromium, cobalt, copper, lead, manganese, mercury, molybdenum, silver, and zinc. This blast furnace slag is either recycled back into the process or disposed of in piles on site. About 50 to 60% of the recovery furnace output is slag and residual lead, which are both returned to the blast furnace. The remainder of this dross furnace output is sold to copper smelters for recovery of the copper and other precious metals. 

The nonvolatile residues (iron, lead and aluminum in the case of dross from smelting and casting) accumulate in the retort or in the muffle furnace and must be removed at intervals. This is facilitated by tipping the retorts. 

A typical charge for an aluminum rotary furnace contains mixed scrap, such as sheets, foils, castings, turnings, and dross. The aluminum producer would like to recover as much of that aluminum as possible to maximize the yield. There has... 

Scrap aluminum, earlier used for a new product, must be re-melted and refined. This technology consists of melting aluminum under a molten salt mixture in order to prevent oxidation and to enhance the coalescence and recovery of the molten metal. In this process, the interfacial tension between aluminum and the salt mixture plays a significant role in terms of both metal recovery and dross de-wetting. Since scrap metal always has an oxide layer, it is required, by either mechanical or chemical means, to break this layer to allow the metallic droplets to coalesce. 

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