Secondary smelting processes

The Isasmelt technolt has been described in Chapter 5. However, given its successful introduction at Britannia Refined Metals Northfleet secondary plant, some discussion of the relative advantages of the Isasmelt furnace compared with other secondary smelting processes is in order. 

QSL [Queneau-Schumann-Luigi] A submerged smelting process for extracting lead from its ores and secondary sources. Pellets of sulfide ore concentrate are fed into a bath of... 

Once bullion lead has been recovered via the various primary and secondary smelting operations, it must undergo a refining process to remove impurities. Bullion... 

Modern industry practice can be extremely effective in limiting lead emissions from recycling facilities. Facility emissions have been a cause of historic concern, with speculation that increased use of lead-acid batteries in electric and/or hybrid electric vehicles might result in unacceptable levels of lead contamination. For example. Lave et al. [23] estimated that emissions to water and air associated with primary lead production, secondary lead production, and battery prodnction were 4, 2, and 1%, respectively, of the total amount of lead processed. In contrast, Socolow and Thomas [24] estimated that secondary smelting and refining were associated with system losses of up to only 0.01% of material processed. 

The unwanted automobile is collected by the scrap dealer, partially disassembled by a recycler (e.g., lead battery, aluminum rims, radiator, variety of parts), and is then reduced in size by a shredder. Steel and nonferrous metals are sent to secondary smelting plants, while nonmetallic components are further processed. The lead battery... 

The Kivcet process is able to treat a wide variety of raw materials. The reported ratio of primary to secondary materials was 73 27 in one plant (Portovesme) and reversed in the second (Cominco). At the Cominco plant, the bulk of the secondary material consists of zinc leach residues. The flash smelting process, however, requires drying the feed material, prior to its being charged into the furnace, to a moisture content of less than 1%. 

These studies, associated with pilot-plant trials, indicated that Sirosmelt technology, because of its flexibility, versatility and simplicity, was the most suitable process to replace the conventional sinter machine-blast furnace. The process has been optimized since the start-up of the furnace based on increased industrial experience and pilot plant trials at the Metaleurop Research Centre. Improved automation and expert systems are necessary to stabilize the process because of the short residence times involved. The bath smelting process operates with a large range of primary and secondary feed materials, and carries out different metallurgical operations in the same reactor.The exhaust gases produced are processed in a sulfuric acid plant, and final SO2 conversion efficiencies of more than 99.5 % are achieved. All the emissions have been drastically reduced CO2 emissions have decreased by 60 %. 

A substantial proportion of the lead used at present is recycled lead, produced from lead scrap and residues by secondary smelting. Emission factors for the processes used, and annual US emissions from secondary lead smelting are given in Chapter 2. In the US, about two thirds of the output of the secondary lead industry is produced using blast furnaces or cupolas, although reverberatory and pot furnaces are also used [1]. A typical blast furnace, with pollution control equipment is shown in Fig. 5.2. The furnace is charged from the top, whilst air... 

Moriya, K, 1989. Achievement in lead smelting during a quarter century at Mitsubishi-Cominco s Naoshima smelter, in Proceedings Primary and Secondary Lead Processing Symposium, Halifax, August, pp 71-86. 

This part of the text covers the preparation of secondary feed materials and the smelting processes used for iead extraction. This predominantly covers the treatment of scrap lead-acid batteries. 

The TBRC is represented by the Kaldo process, developed and operated by Boliden in Sweden and detailed in Chapter 7. This process is suitable for both primary and secondary smelting and can accept whole batteries if required. The Kaldo system at the Ronnskar smelter has adequate facilities for the capture of sulfur and paste desulfurisation is unnecessary. 

To address the problems associated with slags, environmental emissions and occnpational health issues from secondary smelting operations, a nnmber of hydrometaUurgical processes involving the electrowinning of lead from battery pastes have been developed. One or two only have been operated... 

While pyrolysis of coal plays an important role in the production of blast furnace coke on a large industrial scale (approximately 600 Mt of coal/year), it is of minor importance for biomass today. Around 50 Mio.t charcoal are used especially in South America as blast furnace coke. However, modem iron smelting processes would allow for substitution of coke by secondary reduction media and fuels produced from biomass and organic waste. Nonmetallurgical production of carbon is estimated at 18 Mt/year, approximately 600 000 t/year being used as adsorbent with its diverse applications. The latter is prepared mainly from coke, charcoal, and coconut shell coke. 

It has special features which set it apart from other direct smelting processes. It is unsuitable for large-scale production, but is flexible in operation and can treat a range of secondary materials (including scrap batteries) and recycled dusts and residues (containing lead, zinc and copper), as well as lead concentrates. It utilises one rotating furnace, which is completely enclosed in a vented enclosure, into which batches of dry, fine feed and oxygen are introduced. 

The lead-bearing components ate released from the case and other nordead-containing parts, followed by the smelting of the battery plates, and refinement to pure lead or specification alloys. The trend toward battery grid alloys having Httle or no antimony, increases the abiHty of a recovery process to produce soft lead (refined). As requited in the production of primary lead, each step in the secondary operations must meet the environmental standards for lead concentration in ait (see Air pollution Lead compounds, industrial toxicology). 

---