X hits on this document

PDF document

SURVEY OF U.S. MINERAL AND METAL PROCESS - page 4 / 12

26 views

0 shares

0 downloads

0 comments

4 / 12

The product of flotation, copper mineral concentrate, contains

60-80%

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

state.

>1 which

nrocessinq nlassv

Gas cleaning sludge

Waste gases

from

the smelting operation are separated from flue dust at 1250°C in the

off-

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

include sulfites

sulfates

and chlorides. Trace quantities of hydrocarbons and

(SO3),

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,

*some

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.

Lead process

ORNL engineers evaluated and prepared a flow diagram of lead-mining operations

[8],

and

identified process residues with by-product recovery potential (Figure 2). The U.S. lead

commodity sector generates

Some minerals (e.g.,

30% lead. Ore

galena) bgeneficiation

metric tons per year of process residues

contain

to

lead while other lead minerals contain only

up 3,000,000-3,200,OOO 86%

by sizing and froth flotation

soncentrates

lead while

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,

fine

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

c

I

Document info
Document views26
Page views26
Page last viewedSat Dec 03 12:23:06 UTC 2016
Pages12
Paragraphs496
Words4139

Comments