Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
1999-02-01
2001-04-03
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C075S643000, C075S644000, C075S645000, C266S160000, C266S186000
Reexamination Certificate
active
06210463
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the production of copper. In one aspect, the invention relates to the pyrometallurgical production of copper while in another aspect, the invention relates to the pyrometallurgical production of copper using a continuous converting furnace. In yet another aspect, the invention relates to the pyrometallurgical production of copper using a continuous flash converting furnace equipped with a forebay.
The production of copper is ancient. Starting with finds of copper metal that were virtually ready for fabrication into various tools, man has learned over the millennia to recover essentially pure copper from ever more dilute ores (e.g. 0.2% or less copper). The two principal forms of copper production are pyrometallurgical and hydrometallurgical, the former the subject of this invention.
The pyrometallurgical production of copper is a series of multistep concentration, smelting, and refining procedures. Typically starting with an ore comprising one or more of a copper sulfide or copper-iron-sulfide mineral such as chalcocite, chalcopyrite and bornite, the ore is converted to a concentrate containing usually between 25 and 35 weight percent (wt %) copper. The concentrate is then converted with heat and oxygen first to a matte (typically containing between 35 and 75 wt % copper), and then to blister copper (typically containing at least 98 wt % copper). The blister copper is then refined, usually first pyrometallurgically and then electrolytically, to copper containing less than 20 parts per million (ppm) impurities (sulfur plus noncopper metals, but not including oxygen).
The conversion of copper concentrate to blister copper with heat and oxygen is known generally as smelting, and it comprises two basic steps. First, the concentrate is “smelted” to copper matte and second, the matte is converted to blister copper. Typically these steps are performed in separate furnaces, and these furnaces can vary in design. With respect to the first step, i.e. the smelting step, solid copper concentrates are introduced into a smelting furnace of any conventional design, preferably a flash smelting furnace, which is fired by the introduction of fuel and air and/or oxygen through a burner, and from which slag is tapped periodically and off-gases are routed to waste handling. In a flash smelting furnace, the copper concentrates are blown into the furnace through a burner together with the oxygen-enriched air. The copper concentrates are thus partially oxidized and melted due to the heat generated by the oxidation of the sulfur and iron values in the concentrates so that a liquid or molten bath of matte and slag is formed and collected in the basin (also known as the “settler”) of the furnace. The matte contains copper sulfide and iron sulfide as its principal constituents, and it has a high specific gravity relative to the slag. The slag, on the other hand, is composed of gangue mineral, flux, iron oxides and the like, and it has a low specific gravity relative to, and thus floats on top of, the matte.
The molten copper matte and slag are separated in any conventional manner, typically by skimming the molten slag from the matte through tap holes in the furnace walls. The slag tapholes are located at an elevation on the furnace walls that allows slag withdrawal from the furnace without removal of molten matte. Tapholes for the molten matte are located at a lower elevation on the furnace walls that allows the withdrawal of molten matte without the withdrawal of slag. The molten copper matte is then either transferred directly or indirectly (e.g. by way of a holding furnace) to the converting furnace by any conventional means, e.g. launder or ladle, or its converted to solid form, e.g. granulated, for storage and later use as a feed to a converting furnace.
Converting furnaces are basically of two types, flash (also known as suspension) and bath, and the purpose of both furnaces is to oxidize, i.e. convert, the metal sulfides to metal or metal oxides. Representative bath furnaces include those used by Noranda Inc. at its Horne, Canada facility, by Mitsubishi Materials Corporation at its Naoshima, Japan facility, and by Inco Limited at its Sudbury, Canada facility. Representative flash converting furnaces include that used by Kennecott Utah Copper Corporation at its Magna, Utah facility.
Regardless of its design, the converting furnace contains a bath of molten blister copper which was formed by the oxidation of copper matte that was fed earlier by one means or another to the furnace. The bath typically comprises blister copper of about 50 centimeters in depth upon which floats a layer of slag of about 30 centimeters in thickness. If the furnace is a rotary bath-type, then the molten metal and slag, separately of course, are poured from a mouth or spout on an intermittent basis. If the furnace is stationary, then outlets are provided for the removal of both the slag and blister copper. These outlets include tapholes located at varying elevations on one or more of the furnace walls and in a manner similar to that used with the smelting furnace, each is removed from the furnace independent of the other.
Alternatively, the bath contents (i.e. the metallurgical melt) of the converting furnace is removed through a forebay or syphon which is attached to the furnace. The forebay is in open communication with the settler of the furnace by a passageway that allows for the continuous removal of both slag and blister copper. The slag and blister copper maintain their phase-separated relationship as they enter the forebay.
The forebay comprises a slag skimming chamber or zone equipped with a weir on one end and at least one tapping or overflow notch on at least one sidewall. The notch or notches is or are located at an elevation on the sidewall such that only slag enters and is removed from the forebay. The bottom of the notch(es) is(are) above the top surface of the metal product.
The weir of the forebay is located downstream from the slag overflow notch, and it is positioned (usually attached to both forebay side walls) such that it acts as a dam to the slag but not the metal product which underflows the weir to a point beyond the weir in the forebay referred to as the riser chamber or zone. The metal overflows this riser chamber through a metal overflow notch(es) on the end and/or side walls. In this manner, the molten metal product continuously overflows the end wall of the forebay into any means, e.g. a launder, tundish, etc. for transfer to another vessel (e.g. a holding furnace, an anode furnace, etc.).
Unlike a forebay, only blister copper enters a syphon. The opening between the syphon and the settler zone of the furnace is sized and positioned such that only blister copper has access to the syphon, i.e. the opening is positioned below the bottom surface of the slag layer. In this manner, the settler endwall acts as a weir relative to the slag gaining entry to the syphon. In these types of arrangements, the slag is removed through tapholes in the settler side or end walls.
The physical and chemical separation that occurs between the slag and blister copper is not complete and as such, the slag contains copper (usually in the form of cuprous oxide, i.e. Cu
2
O, and copper metal, i.e. Cu
0
) and the blister copper contains various waste and unrecovered mineral values, e.g. sulfur (principally in the form of cuprous sulfide, i.e. Cu
2
S), ferrosilicates, cuprous oxide, etc. The copper in the slag is potentially lost metal value which is recovered by recycling the slag back to the smelting furnace. The waste and unrecovered mineral values in the blister copper are impurities which are eventually removed either in the anode furnace or through electrorefining.
The oxidation of copper sulfide at the interface of the slag and blister copper phases is known. However, the beneficial effect of this oxidation is minimized, particularly in stationary furnaces, by the relative quiescent state of the interface (because the activities of reacting sulfur and oxygen spe
Castle John F.
Gabb Philip J.
George David B.
Utigard Torstein
Andrews Melvyn
Kennecott Utah Copper Corporation
Whyte Hirschboeck Dudek SC
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