FI60239B - SAETT ATT RAFFINERA METALLISKT KOPPAR PAO EN PYROMETALLURGISK VAEG - Google Patents

Description

0αΜ *** \ mi i ANNOUNCEMENT PUBLICATION _ Λ _ „Ä ® ^ UTLÄGGNINCSSKIIIFT 602 39 5¾¾ C <45> 10 K 17: 1 ^ (51) K» .ik? /Int.a.3 C 22 B 15/14 ENGLISH - FINLAND (21) P * t * nttJh * lc # mi * -PMvnttnrfkrfn, 3181 + / 72 (22) Hakemitptlvl - Amöfcnlnpdtj 1 ^ +. 11.72 * * (23) AlkupUvi — Gittlghvtadig lU.11.72 (41) Tullut Julkl olfcntllg 16.03 73

National Board of Patents and Registration ... ________, '(44) Date of issue. -

Patents and registration AmMcan utltfd och utUkrlfwn publlccrad 31.08.8l (32) (33) (31) * η * · «Χ amolkma — Baglrd prkxitat 15. H. 71 usa (us) 198981+ (71) The International Nickel Company of Canada, Limited, Copper Cliff, Ontario, Canada (CA) (72) Malcolm Charles Evert Bell, Port Colborne, Ontario, Canada (CA)

John Kenneth Pargeter, Varvick, New York, USA (7I +) Oy Kolster Ab (5I +) A way to purify metallic copper pyrometallurgically - Sätt att raffinera metalliskt koppar p & en pyrometallurgisk väg

The invention relates to a process for the pyrometallurgical purification of metallic copper containing not more than 5% of iron, not more than 10% of oxygen and not more than 1% of sulfur and at least one volatile impurity which is arsenic, bismuth, lead, selenium, tellurium, tin or zinc.

Cement copper, i.e. copper precipitated with metallic iron from acidic treatment solutions, is separated from the solution and can be treated by magnetic separation and / or a screening method to produce better quality cement copper. Cement copper, whether refined or not, has been considered as an intermediate that is either recycled back to smelting or added in small amounts to copper electrolytes during electrical cleaning. The use of cement copper as an intermediate imposes a burden on the smelting or electrical cleaning capacity and does not provide any similar advantages.

Precipitates of metal-copper can also be obtained by reducing the hydrogenation of copper-containing treatment solutions at an elevated pressure of 25 kp / cm 4 and a temperature of 290 ° C. Such powders are generally finely divided and contain up to about 0.1% sulfur and 0.01% iron.

It has been proposed that cement copper be treated by screening and magnetic separation techniques to obtain a cement copper of at least anode grade. The definition of this product alone indicates that further treatments for electronic cleaning are required. After electrical cleaning, the material must be further processed to produce copper in a usable form. After enrichment of semen copper by magnetic separation and screening, it must be melted to form anodes, which are electrically purified to cathodes, which may be melted to produce commercial grades of copper.

It has now been found that cement copper can be purified pyrometallurgically by means of a special two-stage treatment under reduced pressure, after which oxygen and casting can be removed from the copper.

The invention is characterized in that metallic copper is melted without forming a separate copper oxide phase in a free oxygen-containing atmosphere to form iron as slag and to form a copper bath containing impurities, the oxygen content exceeding at least sulfur content. at a reduced pressure of less than 0.01 atmospheres until the sulfur content is less than 0.001%, the purge gas is stopped and the pressure above the copper bath is reduced to less than 0.002 atmospheres to evaporate volatile impurities, the copper bath is depleted of oxygen and then the copper is cast.

After desulfurization, the single-phase copper bath contains at least about 1% oxygen. The purge gas stream is stopped after the copper bath has a sulfur content of less than about 0.001% and the bath is evacuated to at least about 0.002 atmospheres to further purify it by evaporating from the bath at least one impurity selected from the group consisting of arsenic, bismuth, lead, selenium, tellurium , tin and zinc. Oxygen is then removed from the copper bath. Prior to casting, the copper bath may optionally be treated with phosphorus to provide oxygen-free copper.

As mentioned above, cement copper is prepared by doping copper from acidic treatment solutions with metallic iron. If the iron used as a precipitant is coarse or massive, the precipitated copper may cover the entire surface of the iron and the precipitation reaction will stop completely. As the particle size of the metallic iron used to precipitate copper decreases, the iron content of cement copper also decreases. When using coarse metallic iron particles in copper deposition, cement copper can be treated by magnetic separation and / or screening to improve the quality of the copper to less than about 3% iron and more than about 90% copper. Thus, according to a preferred embodiment of the invention, the cement copper is initially treated by magnetic separation and / or screening to produce a higher quality cement copper.

Each metal copper precipitate containing not more than about 5% of iron, not more than about 1% of sulfur, not more than about 10% of oxygen, not more than about 0.1% of arsenic, not more than about 0.1% of bismuth, not more than about 0.1% of lead, not more than about 0 .01% selenium, up to about 0.01% tellurium, up to about 0.1% tin and up to about 0.1% zinc can be treated by the process of the invention. As mentioned above, a pair of cement sticks can be easily improved by magnetic separation and screening. Such refined cement copper may contain up to about 3% iron, up to about 1% sulfur, up to about 10% oxygen, up to about 0.1% arsenic, up to about 0.1% bismuth, up to about 0.1% lead, up to about 0 .01% selenium, not more than about 0,01% tellurium, not more than about 0,1% tin and not more than about 0,1% zinc. Copper powder prepared by precipitation with water from treatment solutions containing up to 0.5% sulfur, 0.01% iron and arsenic, bismuth, lead, selenium, tellurium, 60239 tin and zinc in the above areas can also be treated by the process of the invention. It should be noted that, unless otherwise indicated, the liquid mixtures shown are by weight and the gaseous mixtures by volume.

If the metal-copper reactor contains more than about 2% oxygen, the cement copper is treated with a reducing agent during smelting to reduce the oxygen content and prevent the formation of an immiscible cuprous oxide phase, which is highly corrosive to the furnace, and copper losses from ferrous slag. The copper precipitate, whether refined or not, is preferably mixed with a carbonaceous reducing agent, the amount of which is adjusted for the iron and sulfur contents of the copper precipitate so that the final oxygen content of the copper bath after smelting exceeds at least the sulfur content and is less than that of a separate immiscible copper oxide phase. The carbonaceous reducing agent can be either a liquid or a solid. The amount of carbonaceous reducing agent added to the metal-copper precipitate depends on the oxygen contents of the copper precipitate. The amounts of carbonaceous reducing agent added are adjusted so that the carbonaceous reducing agent, sulfur and iron, effectively produces molten copper with an oxygen content of less than about 1.5% - In most cases, the amount of carbonaceous reducing agent added to the copper precipitate is between about 0.5 and 5% by weight of cement copper. to ensure that the oxygen content of the molten copper is less than about 1.5% · The oxygen content can, of course, be adjusted by melting in a gas atmosphere that reduces to copper oxide.

Copper deposits usually contain a considerable number of particles that are finer than 0.0U3 mm and that, when heated, can cause dusting, which also results in metal losses. Fine copper precipitates can also cause material handling problems and can make smelting treatment less efficient when using induction furnaces. As a result, it is preferable to form a mixture of copper pellets and a carbonaceous reducing agent in an agglomerate and conventional manner. The mixture of copper pellets and carbonaceous reducing agent is formed into spheres in a conventional manner or into briquettes using conventional compression treatments. Regardless of the way in which the mixture of cement copper and carbonaceous reducing agent is agglomerated, the particle size of the agglomerates should be at least about 0.1 mm and preferably at least about 20 mm in order to reduce the difficulties associated with dusting, material handling and less efficient smelting.

5,60239

The copper precipitate, whether agglomerated or not, is melted to form a copper bath and floating slag containing iron oxide. In order to allow rapid removal of iron oxide slag and to promote subsequent removal of impurities, the mixture of cement copper and carbonaceous reducing agent is heated to a temperature of at least about 1200 ° C and preferably to a temperature between about 1250 and 100 ° C. At the temperatures in the above range, the molten copper is sufficiently liquid to allow the iron oxide formed in the copper to rise rapidly to the surface of the bath, from which the iron oxide is removed as solid slag. Efficient and substantially complete removal of iron oxide slag from the bath is a preferred embodiment of the invention, as removal of iron oxide slag promotes subsequent desulfurization and purification treatment under reduced pressure. High temperatures are also effective in increasing the rate of subsequent desulfurization and other purification reactions.

After the iron content of the copper bath has been reduced to less than about 0.01% and the iron oxide slag has been removed from the bath, a vacuum of less than about 0.01 ik Hg and preferably between about 0.001-0.0002 ik Hg is applied to the bath, while the purge gas may contain free oxygen, is passed through the bath to reduce its sulfur content to less than about 0.001 #, preferably to less than about 0.0005%. It is believed, although the invention is not limited to this assumption, that inert gas bubbles passing through the melt give up the energy required to produce sulfur dioxide-gas bubble embryos, there is a large difference in chemical potential between to reduce it. The purge gas is a group of gases formed by nitrogen, argon, air, carbon dioxide and oxygen. In most cases, gas flow rates between about 0 »3 and 6.1 cubic meters per hour per square meter of bath surface are used, with the intention of providing all the benefits of gas flushing and mixing while reducing the need for equipment.

If the copper bath does not contain enough oxygen to eliminate sulfur to provide a sulfur dioxide and oxygen content between about 0.1 and 1.5% after desulfurization, additional oxygen must be added to the bath. This can be accomplished by introducing air or oxygen into the bath or by adding oxidized copper powder to it.

6 60239

The desulfurization is preferably performed at a vacuum of less than about 0.01 atmospheres and preferably between about 0.001 and 0.0002 atmospheres. In this area, desulphurisation takes place without imposing excessive requirements on vacuum equipment. At high pressures, a desulfurization rate with a sulfur content of less than about 0.001% is not commercially advantageous because the use of lower pressures results in more efficient, complex, and expensive equipment to maintain such low pressures, especially when using inert gas purge.

When the sulfur content is reduced to a certain level, e.g. less than about 0.001% or even less than about 0.0005%, the gas flow is stopped and final purification is started to reduce the amount of at least one impurity selected from the group consisting of arsenic, bismuth, lead, selenium, tellurium, tin and zinc. The bath oxygen content is adjusted to a value between about 0.1 and 1.5% t and the copper bath is subjected to a vacuum of less than about 0.0002 atmospheres, preferably less than about 0.0001 atmospheres, to further purify the bath by evaporating at least one impurity selected from the group consisting of arsenic, bismuth, lead, selenium, tellurium, tin and zinc. The copper melt is kept mechanically or inductively at this stage in the swirling accounts to promote the evaporation of any of the above impurities. Although vigorous agitation can be achieved by passing an inert cake through the melt, it has been found that the lower pressures provided without an inert gas are more effective in eliminating said impurities than those provided by an inert gas passing through the melt. This purification treatment is effective in reducing the concentrations of arsenic, bismuth, lead, tin and zinc to less than about 0.001% while at least halving the concentrations of selenium and tellurium.

After purification, the copper bath contains about 0.1-1.5% oxygen and is preferably deoxidized before casting. At least partial deoxidation can be accomplished by passing a reducing gas, such as hydrogen, carbon monoxide, natural gas, or propane, through a copper bath. Conducting a reducing gas through a copper bath works relatively well, but it has surprisingly been found that when the oxygen content is about 0.05%, a solid reducing agent, such as solid carbon or coke, is kinetically more effective in lowering the oxygen content.

As a result, a solid reducing agent is added to the copper bath either during the entire deox binder treatment or during its final stages, i. when the oxygen content of the bath 7 60239 has decreased to about 0.05% or less, to reduce the oxygen content to about 0.01%, preferably about 0.005%. · If oxygen-free copper is desired, the copper melt can preferably be completely deoxidized by adding phosphorus. The deoxidation treatment using solid carbon is preferably performed under reduced pressure below about 0.01 atmospheres, e.g. between about 0.005 and 0.0005 atmospheres. During deoxidation, the bath is kept in a swirling state by purging it with a non-oxidizing gas, i. with an inert or reducing gas. Inert gases such as nitrogen or argon are preferably used as the purge gas to reduce the difficulties associated with dissolved hydrogen at low oxygen concentrations. When performing deoxidation under reduced pressure, gas flow rates between about 0.3 and 6.1 cubic meters per hour per 1 square meter are used to provide the required vortex without still applying excessive stresses to the vacuum equipment. Very different purge gas flow rates can be used to perform deoxidation at ambient pressure if the copper bath is sufficiently stirred. After deoxidation, the copper alloy is cast into conventional pieces.

The copper bath is desulfurized, purified and deoxidized at a temperature of at least about 1200 ° C, and preferably at a temperature between about 1250 ° and 11 ° C to ensure rapid and substantially complete desulfurization, purification and deoxidation. Various treatments can be performed in any type of furnace, but it has been found advantageous to use induction furnaces, in which case the mixing effect of these furnaces can be exploited. Induction furnaces also have the added advantage of completely eliminating the possibility of copper fouling due to the combustion products of the fuel. An additional advantage of induction furnaces is that they can be easily equipped with a suitable vacuum device.

The following examples illustrate the results that can be obtained by carrying out the invention.

Example I

Cement copper obtained by alloying copper from sulphate extraction solutions using torn, tin-free cans containing 0.7% sulfur, 6% oxygen, 1.2% iron, 0.029% arsenic, 0.038% lead, 0.0023% selenium, 0.0007 % tellurium and minor amounts of calcium oxide, silica and alumina were melted in air in an induction furnace equipped with a vacuum unit to form iron, calcium oxide, silica and alumina as slag and to form a copper bath containing 0.01% iron, 0.30% r, 1 * 9% oxygen. The slag was removed from the bath surface and the pressure of 8 60239 was then reduced to 0.0003 atmospheres by means of a vacuum device while nitrogen was passed through the bath at a rate of * + »57 cubic meters per hour per 1 square meter of bath surface to reduce the sulfur content to 0.0005 1 the pressure was reduced to 0.0001 atmospheres to further clean the bath. At this stage of the purification treatment, the amounts of arsenic, lead, selenium and tellurium had decreased to 0.01 #, less than 0.002% t 0.001% and 0.0003%, respectively. Carbon was then added to the bath and the bath was again purged with nitrogen at a rate of 3.66 cubic meters per square meter of melt surface per hour to reduce the oxygen content of the bath to 0.02%. The bath was then cast.

Example II

This example confirms that molten copper can be more easily liberated from sulfur by using simultaneous purge with inert gas and vacuum treatment compared to vacuum treatment alone, even if pressures of 1/10 or less of those used with inert gas are used. Two copper baths were formed, one containing 1.2 λ of oxygen and 120 parts per million (mo) of sulfur, and the other containing 0.95% of oxygen and 100 mo of sulfur, by heating the cement copper to 1260 ° C. It contained 120 mol of sulfur and was simultaneously subjected to vacuum and purge with nitrogen, which was passed at a rate of about 1.6 cubic meters per 1 square meter of melt surface per hour. An equilibrium pressure of between about 200 and 250 microns was rapidly applied to the surface of the bath, and the sulfur content decreased to less than 1 mo in about 1 hour. The sulfur content and bath pressure at different times are shown in Table IA. The copper bath containing 100 mol of sulfur was subjected to such pressures between about 15 and 32 microns, and the sulfur content of the bath was measured at various times and the results obtained are shown in Table IB. When nitrogen was introduced, it took almost 2 hours to reduce the sulfur content to 1 mo even though the pressures were less than 1/10 of the pressures used for nitrogen purging.

Table IA

Time min. Pressure mmHg S concentration mo 0 300 120 12 0.2U 9 22 0.25 b 33 0.2U 1 U6 0.20 1 63 0.21 <a 9 60239

Table IB

Time min. Pressure mm ^ g S content mo 0 300 100 20 0.032 20

50 0.025 U

80 0.018 3 110 0.016 1 IUO 0.015 1

Comparing the results obtained in Tables IA and IB, it is obvious that the simultaneous use of purging and vacuum significantly improves the removal of sulfur under vacuum.

Example III

Although the conduction of inert gas greatly improves the desulfurization under reduced pressure, this example confirms that the use of inert gas also affects other purification reactions without the need to apply too low pressures and that two-stage vacuum treatment is advantageous to obtain a good purification result. Two copper baths were formed, one containing 19 mo selenium and 13 mo tellurium and the other containing 29 mo selenium and 11.5 mo tellurium, by heating the cement copper to 1260 ° C. Both baths were oxidized in the presence of more than 1% oxygen. The bath containing 19 mol of selenium was simultaneously purged with nitrogen at a rate of U, 57 cubic meters per 1 square meter of bath area per hour and vacuumed between 200 and 250 microns, sampled at various time points and analyzed for selenium and tellurium concentrations to give the table. 2A. The bath, which initially contained 29 mol of selenium, was reduced to a vacuum of between 15 and 32 microns, and in this case samples were taken after specified periods of time and analyzed for selenium and tellurium content, and the results are shown in Table 2B.

Table 2A

Time min Pressure mmHg Se, mo Te, mo 12 0.2U 21 23 22 0.25 23 15 33 0.2U 18 2b b6 0.20 19 23 63 0.21 23 2b 10 60239

Table 2B

Time min. Pressure mmHg Se, mo Te, mo.

20 0.032 29 11.1 50 0.025 28 7.6 80 0.018 21 7.3 110 0.016 17 5.8 lfcO 0.015 12 8.7

The results shown in Tables 2A and 2B show that lower vacuum pressures are more effective in purifying copper from selenium and tellurium, and especially from tellurium.

Example IV

This example confirms that molten copper can be deoxidized more efficiently by means of carbon under reduced pressure, at the same time conducting an inert gas, as compared with hydrogen bubbles passed through molten copper. A copper bath containing 0.26% oxygen was formed, and a mixture of hydrogen and nitrogen gas containing 75% hydrogen was bubbled through this bath at a rate of 0.20 cubic meters per hour, corresponding to 30 cubic meters per 1 square meter of melt area per hour, which the flow rate ensured rapid mixing of the bath. The oxygen content of the bath was determined after specified time periods and the results obtained are shown in Table 3A. A second copper bath containing 0.27% oxygen was also formed, and granular graphite having an equivalent amount of 1% of the bath was made to float on the surface of the bath. The bath was subjected to a vacuum of 1 + 00-500 microns while purging with nitrogen at a rate of 0.023 cubic meters per hour, corresponding to 3.35 cubic meters per square meter of bath area. The oxygen content of the bath was determined after specified time periods and the results are shown in Table 3B.

Table 3A

Time min. Oxygen content by weight- $ 0 0.26

13 0, lU

22 0.066 30 0.0 * 5 1 * 0 0.021 50 0.017 60 0.0105 11 60239

Table 3B

Time min. Oxygen content by weight- $ 0 0.27 10 0.13 20 0.0H

30 0.0lU

1 + 0 0.0068 50 0.0025

The results obtained in Tables 3A and 3B confirm that deoxidation of copper when carbon is used under reduced pressure, although it involves kinetically slower liquid-solid reactions, actually occurs faster than deoxidation with hydrogen, which is thought to be more kinetically reactive.

For comparison purposes, a separate deoxidation test was performed at atmospheric pressure using granular graphite and purging with an inert gas.

After 50 minutes, the oxygen content of the bath was 0.01% t, which was four times the oxygen content of a gas deoxidized for 50 minutes with carbon and conducting an inert gas under reduced pressure. Within 65 minutes, the oxygen content had been reduced to 0.0032% t, indicating that deoxidation using granular carbon and purging with inert gas could also be accomplished without reduced pressure.

It can be seen that the present invention provides a pyrometallurgical process for purifying copper metal precipitated from aqueous solutions. Although the invention has been described in connection with the treatment of cement copper, it will be apparent to one skilled in the art that the method can also be used to purify electrically refined or electrically purified copper containing impurities of sulfur during melt treatment or containing harmful amounts of arsenic, bismuth, lead, selenium, tellurium , tin and zinc.

Although the invention has been described above in description of preferred embodiments thereof, it is to be understood that various changes may be made therein without departing from the scope of the invention, as will be apparent to those skilled in the art. For example, copper slurries containing amounts of oxygen that are high relative to the sulfur content can be simultaneously treated at a later stage of desulfurization to desulfurize and partially deoxidize while continuing to purge with a non-oxidizing gas and using a second stage treatment to eliminate other impurities. Such modifications are also within the scope of the invention.

Claims (11)

1. Methods of Refining Pit A Pyrometallurgical Path Metallic Copper Containing Not More Than 5% Iron, No More Than 10% Oxygen And No More Than 1% Sulfur of the metallic copper being melted, without forming a separate cuprous oxide phase, in a gas atmosphere containing free oxygen for slagging iron and forming a copper bath containing impurities, the oxygen content exceeding at least the sulfur content, the slag being separated from the copper bath, a cleaning gas free oxygen is passed through the copper bath while the bath is poured at a vacuum below 0.01 atmospheres until the sulfur content is less than 0.001%, the onset of the purge gas is terminated and the pressure above the copper bath is reduced to a value below 0.002 atmospheres to evaporate the volatile pollutants, the copper bath is then deoxidized . 2. A method according to claim 1, characterized in that the metallic copper is made up of cement cups which have been refined before melting either by sieving or magnetic separation or by these beds. 3. A method according to claim 1 or 2, characterized in that the copper bath is kept at a temperature of 125 ° -1000 ° C during the desulphurisation and evaporation of the impurities. in +. Process according to any one of claims 1-3, characterized in that the purification gas consists of nitrogen, argon, air or oxygen. 5- A method according to any of the preceding claims, characterized in that purification gas is passed through the bath 0.3 - 6 m 2 Vn for 2 hours per m of the surface of the bath. 6. A process according to any of the preceding claims, characterized in that the copper bath after desulfurization contains 0.1 - 1.5% oxygen. 7. A method according to any of the preceding claims, characterized in that the bath is added to the bath after desulfurization to adjust the bath's oxygen content to a value of 0.1 - 1.5% · 8. A process according to any one of the preceding claims, characterized in that the copper bath is deoxidized by the addition of granular koi and purification with a non-oxidizing gas.