Situ desulfurization scrubbing process for refining blister...

Details Situ desulfurization scrubbing process for refining blister... Situ desulfurization scrubbing process for refining blister...

2001-03-19

2002-05-28

King, Roy (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Processes

Free metal or alloy reductant contains magnesium

C075S651000

Reexamination Certificate

active

06395059

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for refining high impurity blister copper to anode quality. The process utilises alkali oxides and a solution containing sulphates to effectively remove sulphur and other impurities, such as As and Sb as well as Pb, Ni, Bi, Se and Te, from blister copper.
BACKGROUND OF THE INVENTION
The production of blister copper from copper sulphide concentrates can be accomplished using two main pyrometallurgical systems: flash-smelting and bath-smelting. The number of stages within each system may vary from a single stage copper production to two stage smelting and converting processes.
A conventional two-stage smelting and batch converting process has the following major disadvantages: (i) the process is not energy efficient; (ii) the slag must be periodically skimmed from the converter; and (iii) the matte produced in the smelting furnace must be physically transferred to the converter furnace. During this transfer, high levels of fugitive emissions of SO
2
are generated. Due to these drawbacks, there is a need to develop environmentally acceptable single stage smelting and converting systems that are both cost-efficient and energy-efficient.
Single stage blister copper production systems offers environmental and energy-efficiency advantages over the conventional two-stage copper smelting and batch converting processes. The Noranda continuous smelting and converting process is capable of producing blister copper from chalcopyrite concentrates in a single vessel. Likewise, the Noranda continuous converter is able to produce blister copper from mixtures of liquid and solid matte as well as from slag and copper concentrates. The Outokumpu flash smelting process can also produce blister copper from chalcocite concentrates in a single stage.
A significant drawback of all single-stage copper production systems is that they produce blister copper containing high levels of impurities, specifically sulphur, arsenic, antimony, and bismuth (e.g. ,1.3 wt % S, 0.5 wt % As, 0.5 wt % Sb, 0.03 wt % Bi). By comparison, blister copper produced in a conventional two-stage copper smelting and batch-converting process typically contains about 0.02-0.1 wt % sulphur, and only trace amounts of precious and other minor elements. However, as the grade and quality of copper ores decreases with time, even blister copper from conventional two-stage smelting-converting processes may contain high levels of these undesirable elements. Thus, in both cases, to produce molten “anode quality” copper, an extra “blister copper refining” stage is needed.
Blister copper refining, which is the subject of this invention, is conventionally carried out in three steps: i) de-sulfurization; ii) fluxing-skimming; and iii) de-oxidation. In the first step, batches of molten blister copper are introduced into modified Pierce Smith converters or cylindrical “anode furnaces”. Oxygen-enriched air is injected to remove the sulphur as SO
2
. As the sulphur content is lowered to about 0.003 wt % sulphur, the oxygen content reaches a level of about 0.8 wt %. Fluxing is practised by injecting basic materials such as mixtures of soda ash-CaO to combine with the acidic oxides of As and Sb, forming a slag that must be removed from the vessels prior to commencing de-oxidation. The oxidised molten copper thus produced is then de-oxidised to an oxygen level of about 0.1 wt % by injecting a reducing gas, such as natural gas.
Currently, various copper refining techniques exist for removing some of the impurities. The removal of arsenic by soda ash fluxing at about 1 wt % oxygen dissolved in copper is discussed by Eddy (1). The effectiveness of using soda ash fluxing to remove As and Sb is also described by Themelis (2). Stapurewicz et al. (3) provides a study of the thermodynamics of Sb removal from blister copper by soda ash fluxing. Taskinen (4) describes the distribution equilibrium of As, Sb and Bi between copper and soda ash. Peacey et al. (5) discusses the equilibria resulting from fluxing copper with soda ash and limestone. Riveros et al. (6) describes kinetic aspects observed during the operation and optimisation of the soda ash fluxing process practised at the Chuquicamata smelter.
In U.S. Pat. No. 3,561,952, the use of alkali oxide-silicate slags as well as alkali oxide phosphates and/or borates for the removal of lead and tin from copper scrap is described. In U.S. Pat. No. 3,262,773, a refining process for the removal of arsenic, antimony, tin and other acidic oxide forming elements from molten copper is presented. It teaches that removal may be accomplished by combining the acid oxides of such elements with basic materials such as alkaline earth oxides, in particular CaF
2
and CaO, present in the slag. This patent suggests the use of 4 to 12 wt % calcium oxide based on the weight of the crude copper while the process temperature is maintained at between 1250 and 1300° C. U.S. Pat. No. 4,316,742 describes a method of refining copper by melting the copper scrap in the presence of a flux that comprises a mixture of calcium oxide and sodium oxide in a weight ratio of CaO/Na
2
O of from 1:1 to 4:1 while bubbling oxygen into the copper bath. A process for the production of high-grade copper from an inexpensive starting material such as blister copper or copper scraps by adding a mixture of CaO and other oxides is disclosed in U.S. Pat. No. 4,055,415. U.S. Pat. No. 4,211,553 presents a method and apparatus for refining a melt using a pulverous solid material and a carrier gas, where the solid material may be CaO. U.S. Pat. No. 5,849,061 describes a stepwise injection of mixtures of air, oxygen and Na
2
CO
3
followed by a simultaneous injection of hydrocarbons and SF
6
as a process for refining high-impurity copper to anode quality copper.
While the above methods relating to the use of alkali oxides for the removal of impurities from molten copper have been described, they are not used in combination with a solution containing sulphates.
The concept of scrubbing SO
2
and forming sulphates in pyrometallurgical systems is not new. For example, U.S. Pat. No. 4,034,036 describes a process for controlling SO
x
emissions from copper smelter operations involving pyrometallurgical reduction of copper ores to elemental copper, in which the gases from reverberating furnaces, roasters, and/or converters are scrubbed with a sodium alkali sorbent to produce sodium sulphate and sulphite wastes. This patent teaches the scrubbing of SO
2
in flue gases. Conventional wet or dry scrubbing of SO
2
in flue gases using sodium alkali, either using a regeneration type of scrubbing or a double alkali process, presents high capital and operating costs as well as environmental issues involving the disposal of a thixotropic sludge of the end product (i.e., calcium sulphate-sulphide).
A copper flash smelting process in which part of a sulfidic copper feed is roasted in the presence of a calcareous SO
2
scavenger to produce a calcine containing calcium sulphate and an oxidic copper product is described in U.S. Pat. No. 4,615,729. This is referred to a sulphate roasting process where the sulfidic copper material is roasted at a temperature of about 850 to 1000° C. The well-mixed feed therein is reacted with air to provide a calcine comprised mainly of solid calcium sulphate and copper ferrite and an off-gas rich in CO
2
and poor in SO
2
. Thus, the concept of using an SO
2
scavenger selected from the group of lime and limestone is established.
U.S. Pat. No. 5,180,422 describes a copper smelting process in which copper concentrates are smelted in a furnace to produce purified copper. The flue gases may be exhausted from either or both of a smelting furnace and a converting furnace, and gypsum may preferably be introduced into the converting furnace. In this process, the gas discharged from the furnace is treated to produce sulphuric acid. Gypsum is produced from the waste liquid treatment produced at the acid plant. Gypsum is recirculated to the converting furnace where it decomposes according to the

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