Slag launder

The high lead slag from the smelting furnace is tapped continuously and transferred down a heated launder directly into the reduction furnace through a port in the side of the vessel. Lump coal for reduction is fed continuously to the furnace by conveyor and dropped direcdy into the bath. Heating for the endothermic reduction reactions is provided by oil injected down the lance. The combustion air stoichiometry is set at 95% of that required for complete oil combustion. Air is injected into the top of the furnace to afterbum the volatile materials from the coal and provide additional heat to the top of the furnace. Reduction temperatures range from 1170 to 1200°C to maintain slag duidity. 

The success of the process results from the fact that nowhere inside the furnace is heat extracted from the copper-saturated blast furnace buUion through a soUd surface. The problem of accretion formation (metal buUd-up), which has plagued many other attempts to estabUsh a copper dtossing operation of this type, does not arise. In the cooling launder, lead-rich matte and slag accumulate on the water-cooled plates, but these ate designed so that when they ate lifted from the buUion stream, the dross cracks off and is swept into the furnace via the cooled lead pot. 

Ausmelt s preferred approach to lead smelting is to use two furnaces where slag flows in a continuous manner from the smelting vessel (oxidising) to the reduction vessel (reducing) via weirs, siphons and launders, as shown in Figure 4. 

During the initial period of KIVCET operation, the most significant mechanical problems were external to the KIVCET fiomace itself These were related to the feed system, slag and bullion launders, and the slag granulation system. 

Figure 3 - Modification of the Launder for Liquid Slag Feeding...

Similarly, molten slag can be run into cast steel ladles or directly into a granulator. The usual form of granulator is a launder carrying a large flow of water into which the slag stream is directed. The slag stream is broken up by the water flow and chilled to form particles similar to coarse sand. The stream... 

Slag and bullion are tapped from the furnace hearth into a forehearth where they are separated. Slag flows from the forehearth into a granulation launder and lead bullion flows to a lead kettle of around 100 tonnes capacity either directly or via batch ladles. The bullion is allowed to cool in the kettle to separate a copper-lead dross, reducing the copper content to around 0.2 per cent. The resulting lead bullion is then cast into blocks of up to four tonnes each for transfer or sale to a lead refinery. 

The Outokumpu smelter operates in very much the same way as the Kiveet process. However, it consists of two separate furnaces, one for smelting and the other for electric slag cleaning. Between them is a short launder, through which directly reduced lead bullion and lead oxide slag flow continuously. The lead bullion can be separately tapped from the flash furnace, if required. 

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