The product of flotation, copper mineral concentrate, contains
water that is filtered
before processing in a smelter. Roasting may be used to prepare sulfide concentrates for subsequent pyrometallurgical or hydrometallurgical operation by decreasing the sulfur content prior to smelting. Smelting of sulfur-containing, copper concentrate produces two immiscible molten phases: a heavier sulfide phase containing most of the copper, the matte, and an oxide phase, the slag. Matte is an intermediate phase in the copper pyrometallurgical processes because of the extractive metallurgy of copper. The pyrometallurgical process separates three main chemical species: crude copper, iron (II) silicate slag, and sulfur dioxide. Modern copper smelting processes produce high-grade mattes-the short residence time of the materials in the reaction chamber does not allow chemical equilibrium. These factors contribute to
produce a high concentration of copper in the slag, generally would be -required to recover copper from slag
wt %. Aggressive is in a
Gas cleaning sludge
the smelting operation are separated from flue dust at 1250°C in the
take shaft and pass through a waste boiler that generates steam, and subsequently to an electrostatic precipitator to separate the bulk of the flue dust, which is recycled to the feed.
The sulfur dioxide gas contains
and inorganic metals. Common ionic species
and chlorides. Trace quantities of hydrocarbons and
X3% SO:! (SO.+),
precious metals are present in the gas stream. Impurities are removed from the gas stream; typically, gases are routed through bag-houses to remove coarse entrained particulate matter (i.e., bag-house dust). The flue dust consists chiefly of’sulfates of copper, lead, and zinc and other sulfates, as well as some volatile compounds of arsenic, antimony, bismuth, and
selenium. The cleaned off-gas is usually processed to form sulfuric acid.
Sulfur dioxide generated by the smelting process is retained and processed to make commercial-grade sulfuric acid by-product. The gas cleaning section of an acid plant scrubs these gases with dilute sulfuric acid using venturi scrubbers, wash towers, and electrostatic
precipitators. The process re-circulates scrubber water; however,
of the stream must be
purged periodically to prevent buildup of solids and to minimize corrosion. Filtered wet solids can be processed for recovery of by-products such as copper, gold, lead, and silver.
ORNL engineers evaluated and prepared a flow diagram of lead-mining operations
identified process residues with by-product recovery potential (Figure 2). The U.S. lead
commodity sector generates
Some minerals (e.g.,
30% lead. Ore
metric tons per year of process residues
lead while other lead minerals contain only
up 3,000,000-3,200,OOO 86%
by sizing and froth flotation
p r o d u c i n g d u s t , t i n e p a r t i c l e s , a n d t a i l i n g s . S i n t e r i n g a n d b l a s t f u r n a c e s a r e u s e d t o p r o d u c e lead bullion and also generate slag waste. The processes that generate dust and particles,
tailings, slag waste, and gas cleaning sludge are described below. It should be noted that lead recycling accounts for a large fraction of the lead market.
Dust. fine particles. and tailings
Lead most often occurs in association with the sulfide mineral group. Lead ore deposits usually form with other minerals and the host rock. These crude ores cannot be directly smelted-beneficiation must be used to concentrate the lead. Ore beneficiation normally