Chemistry: electrical and wave energy – Processes and products
Patent
1989-10-13
1991-10-15
Niebling, John F.
Chemistry: electrical and wave energy
Processes and products
204 68, 75 1054, 75 1065, C25C 306
Patent
active
050571940
DESCRIPTION:
DESCRIPTION
DETAILED DESCRIPTION
The process of the present invention represents a continuous deep salt metal reclamation technique designed and developed primarily for melting high surface area, dirty aluminum scrap. Used beverage cans are an example of such an aluminum scrap, and the process of the present invention is suitably tailored to the high volume of such used beverage cans being recycled today. Aircraft plate and sheet trimmings are examples of aluminum-lithium alloy scrap. However, the process of the present invention is not limited to used beverage cans or aircraft plate and sheet, and also can be applied to most any aluminum or alloy containing oxide impurities including skim or dross formed in melting processes wherein molten aluminum metal or alloy comes into contact with oxygen in the air.
The continuous metal scrap reclamation process of the present invention involves a molten salt maintained continuously in the molten state and providing a chemical composition and oxide composition such that metal recovery is achieved at improved levels continuously.
The process of the present invention operates to control and maintain the chemical and physical composition of the salt continuously at levels consistent with the maximum recovery of aluminum (and alloying agent, e.g., lithium) metal through reaction of the oxides with chlorine and carbon or carbon monoxide to form chlorides of two general types: volatile and non-volatile. The volatile chlorides, e.g., such as titanium tetrachloride and silicon tetrachloride, are removed from the continuous salt-based melting process as part of the reaction sequence in the carbon monoxide/dioxide vapor waste stream. Small amounts of all chlorides present, including aluminum chloride, are removed in the off gas stream, but most remains in the molten salt. Aluminum chloride (AlCl.sub.3) in the pure state has a vapor pressure much higher than one atmosphere at aluminum melting temperature. However, AlCl.sub.3 forms readily low vapor pressure complexes with most other metal chlorides, i.e., NaCl AlCl.sub.3.
Non-volatile chlorides, e.g., such as aluminum chloride, lithium chloride and magnesium chloride, are removed in a process step by electrolysis. The process provides a continuous melting operation in which recovery of molten aluminum is maximized by controlling the integrity of the salt-based melting medium continuously.
Referring now to FIG. 1, a continuous scrap remelt process involves a superheated molten salt (the term superheated means a temperature sufficiently high to accommodate the contemplated metal charge without freezing) melt medium circulated throughout the continuous process of the present invention beginning, for purposes of illustration, in heat bay 1. Salt is heated in heat bay 1 to a temperature to maintain a molten charge in the heat bay, e.g., such as in the range of about 1400.degree.-1450.degree. F. The salt is pumped from heat bay 1 by pump 2 to charge bay 3 where the salt is mixed with aluminum (or alloy) scrap through an appropriate agitation in a swirl motion. In one aspect, scrap enters charge bay 3 continuously via a fume-controlling lock chamber (not shown). As the heated salt mixes with, and melts, the aluminum scrap, coalesced molten metal originating from the scrap collects in a lower portion of a collection bay depicted here as collection bay 4 where an optional coalescer is located to ensure substantially metal-free salt/oxide passage to chlorination bay 6. Chlorine and carbon or carbon monoxide, alternatively phosgene, is introduced to the salt stream in chlorination bay 6 to convert the required amount of oxides into chlorides to maintain a steady-state oxide concentration. In the chlorination bay 6, several gas species are provided such that carbon dioxide is the main reaction by-product as well as titanium tetrachloride and silicon tetrachloride if titanium dioxide or silicon dioxide is present as scrap contaminant which, together with excess chlorine and carbon monoxide, are withdrawn from chlorination bay 6 and passed through a sc
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Hornack Thomas R.
LaCamera Alfred F.
Parkhill James O.
Pierce Thomas V.
Stewart Donald L.
Aluminum Company of America
Marquis Steven P.
Mueller Douglas P.
Niebling John F.
Sullivan Jr. Daniel A.
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