AU2011318944B2 - Copper concentrate treatment method - Google Patents

Abstract

A copper concentrate treatment method characterized by comprising: a roasting step of roasting an enargite (Cu

Description

[DOCUMENT NAME] DESCRIPTION [TITLE OF THE INVENTION] COPPER CONCENTRATE TREATMENT METHOD [TECHNICAL FIELD] [0001] The present invention relates to a copper concentrate treatment method. More particularly, the present invention provides a method of recovering copper, by wet processing, from a roasted ore obtained by roasting enargite or a high-arsenic grade copper concentrate containing enargite as the principal component in an inert atmosphere. [BACKGROUND ART] [0002] Most copper ores produced in copper mines are sulfide ores. The sulfide ores are roughly classified into secondary copper sulfide ores of relatively high copper grades containing minerals such as chalcocite (Cu 2 S) and covellite (CuS) as the principal components, and primary sulfide ores of relatively low copper grades containing chalcopyrite (CuFeS 2 ) as the principal component. The sulfide ores are turned into copper concentrates by increasing the copper grades through fracturing, grinding, and ore dressing, and are subjected to dry copper smelting such as autogenous smelting. [0003] Meanwhile, copper oxide ores are produced in portions relatively close to the surface layers of copper mines. After sulfuric acid leaching, those copper oxide ores are normally treated in mine ancillary facilities by a wet smelting technique of solvent extraction and electrowinning (SX-EW) at relatively low costs. The production of copper oxide ores is very small among copper cores. Therefore, the facilities for treating oxide ores have been efficiently used to reduce the amount of capital investment, and wet smelting has been performed for mixed ores of oxide ores and secondary sulfide ores that can be relatively easily leached, or for secondary sulfide ores. [0004] Further, there is a movement to try wet smelting on primary sulfide ores. Due to high copper prices, there is an increasing demand for such applications in small-scale new mines with inadequate infrastructure such as roads for copper concentrate transportation, and in mines that are producing copper ores with decreasing grades and are suffering from higher production costs of copper concentrates for dry smelting and poorer copper and noble metal recovery rates. [0005] In recent years, the copper ores obtained from the copper mines in operation around the world contain primary sulfide ores as the principal components. In those copper ores, the impurities such as iron and sulfur are increasing, and the copper grade is dropping. This leads to increases in the production costs of copper concentrate for -I1dry copper smelting. The most controversial element among the impurities in the copper cores is arsenic. Arsenic is very harmful depending on existence forms thereof, and the use of arsenic in industrial fields is rare. Most of arsenic needs to be discarded or stored in a stable form. Therefore, in custom ore dry smelters, a certain restriction (normally smaller than about 0.3 mass percent) is put on the arsenic in copper concentrates to be purchased. If the amount of arsenic exceeds the value, the mine normally pays a penalty to the smelter in accordance with the excess amount. [0006] Therefore, the method of treating low-grade copper concentrates (primary sulfide ores) and the method of efficiently treating sulfide ores containing a large amount of arsenic to reduce costs and prolong the lives of mines are of great interest to the mines. Meanwhile, there is a high possibility that custom ore dry smelters need to cope with copper concentrates containing a large amount of arsenic in the future, due to depletion of high-quality mineral ores and the pressing demand and tight supply of copper concentrates. [0007] To solve those problems, there are wet treatment methods for the above described primary sulfide ores. A primary sulfide ore containing hardly-leachable chalcopyrite (CuFeS 2 ) as the principal component is subjected to ore dressing, and the copper in the primary sulfide ore is concentrated to an appropriate grade, to obtain a copper concentrate. This copper concentrate is subjected to sulfuric acid leaching in one of the following manners: 1) The copper concentrate is subjected to secondary grinding to 10 tm or smaller, and is subjected to sulfuric acid leaching in the presence of Fe (trivalent) while oxygen or air is blown thereinto as an oxidizer at 80 to 100'C. 2)The copper concentrate is pressurized, and is subjected to sulfuric acid leaching at 130 to 230*C. Those methods have been put into practical use in recent years. Also, there has been a suggested process to roast chalcopyrite in an inert atmosphere to obtain covellite (CuS) or chalcocite (CuzS), and then perform leaching. However, such a process has hardly been put into practice, due to a cost problem. [0008] As for a copper ore containing a large amount of arsenic, the arsenic is normally removed by ore dressing at high costs, to obtain a low-arsenic-grade copper concentrate, However, there is an attempt to treat the high-arsenic-grade copper concentrate as it is or the high-arsenic-content concentrate removed in the ore dressing stage. For example, there are the following methods: 1) Oxidizing roasting is performed to obtain a roasted ore (a copper oxide or a copper sulfate) that is easily leached, and the roasted ore is subjected to leaching. 2) Roasting is performed in an inert atmosphere, and the roasted ore obtained -2by removing arsenic as arsenic sulfide is subjected to a dry treatment. By the method 1), arsenic volatilizes as a highly-toxic arsenious acid. Therefore, the treatment has many problems, and has hardly been put into practice. The method 2) is regarded as the preprocessing for dry smelting, and does not have the effect of reducing the costs in copper concentrate transportation to remote places. Therefore, the method 2) has not been put into practice. [0009] The arsenic in copper ores is mainly in the form of enargite (Cu 3 AsS 4 ), which is a hardly-leachable mineral that has a dense modular structure and does not easily diffuse in a leaching solution. Although processes to attempt direct treatments have been suggested, there are cost problems with those processes, which have hardly been put into practice. [0010] United States Patent No. 5,993,635 (Patent Document 1) discloses a method of leaching out copper from a copper concentrate subjected to a flotation process in a solution containing 30 g/liter of Fe (trivalent) and 50 g/liter of H 2

SO

4 at a pulp density of 10% at 90*C. The leaching time is 10 hours in a case where an oxygen gas is blown thereinto, and the leaching time is 14 hours in a case where air is blown thereinto. This method is characterized by pulverizing a hardly-leachable mineral to a particle size of 5 pim or smaller prior to leaching. [0011] As embodiments in the patent document, there are two example methods of leaching an enargite-containing copper concentrate. In the first example, a copper concentrate (formed with 20.9 mass percent of enargite, 11.9 mass percent of chalcocite, and 50 mass percent of pyrite) containing 19.5 mass percent of Cu, 4.0 mass percent of As, and 23 mass percent of Fe is pulverized to a 80% pass particle size of 3.5 im, and is treated by the above described leaching method. As a result, a copper leaching rate of 92% is achieved. In the second example, a copper concentrate (formed with 1.3 mass percent of enargite, 9.4 mass percent of chalcocite, 29.6 mass percent of pyrite, and the remaining mass percent of gangue components such as silica) containing 8.1 mass percent of Cu, 0.2 mass percent of As, and 13 mass percent of Fe is pulverized to a 80% pass particle size of 5 im, and is treated by the above described leaching method. As a result, a copper leaching rate of 95% is achieved. [0012] In the two examples, the copper leaching rates are both 90% or higher. As can be seen from a comparison between those two examples, the copper leaching rate becomes lower, as the proportion of enargite increases. Also, to compensate for that, the copper concentrate particles are made smaller than 5 im by pulverization. That is, by this method, pulverization to obtain fine particles is costly, and the leaching rate in a copper concentrate containing enargite as the principal component becomes lower. -3 - PRIOR ART DOCUMENT PATENT DOCUMENT [0013] PATENT DOCUMENT 1: United States Patent No. 5,993,635 [0013a] The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. [0013b] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof. SUMMARY OF THE INVENTION [0014] The present invention was made to address the above issues, and an aspect thereof is to provide a method of recovering copper efficiently and economically from enargite or a copper concentrate containing enargite as the principal component. [0015] In order to achieve the above aspect, a copper concentrate treatment method according to the present invention is characterized by including: a roasting step of roasting enargite (Cu 3 AsS 4 ) or a copper concentrate containing enargite as the principal component thereof in an inert atmosphere at 550 to 700'C; and a leaching step of leaching out copper by using a chloridizing leaching technique by which an oxidizer containing Cu (divalent) and Fe (trivalent) is added to the roasted ore obtained in the roasting step, the roasted ore containing pyrite as the principal component thereof. By the copper concentrate treatment method according to the present invention, it is possible to recover copper efficiently and economically from enargite or a copper concentrate containing enargite as the principal component. [0016] In the roasting step, a sulfur source may be added. In the leaching step, an oxidation treatment using an oxygen gas or air may be performed. In the leaching step, the leaching solution temperature may be adjusted to 70 to 90'C. In the leaching step, the Cl density in the leaching solution may be adjusted to 80 to 180 g/liter. In the leaching step, the Fe (trivalent) may be adjusted to 1 to 3 g/liter, and the Cu (divalent) may be adjusted to 10 to 25 g/liter. EFFECTS OF THE INVENTION [0017] According to the present invention, it is possible to recover copper efficiently and economically from enargite or a copper concentrate containing enargite as the -4principal component. BRIEF DESCRIPTION OF THE DRAWINGS [0018] FIG. 1 is an operation flow according to an embodiment of the present invention; FIG. 2 shows the results of a copper concentrate XRD analysis prior to roasting according to an embodiment of the present invention; FIG. 3 shows the results of a copper concentrate XRD analysis after roasting at 550'C according to an embodiment of the present invention; FIG. 4 shows the results of a copper concentrate XRD analysis after roasting - 4a at 600*C according to an embodiment of the present invention; FIG. 5 shows copper leaching rates in a case where chloridizing leaching is performed on a copper concentrate after roasting according to an embodiment of the present invention; and FIG. 6 shows copper leaching rates in a case where chloridizing leaching is performed on a copper concentrate prior to roasting according to a comparative example of the present invention. MODES FOR CARRYING OUT TI-IE INVENTION [0019] In the following, this study will be described in greater detail by way of examples. [0020] The present invention aims to provide a method of recovering copper efficiently and economically from enargite (Cu 3 AsS 4 ) or a copper concentrate containing enargite as the principal component thereof by roasting and dividing the enargite or the copper concentrate in an inert atmosphere into a volatile containing arsenic sulfide as the principal component thereof and a roasted ore containing chalcopyrite as the principal component thereof, and subjecting the roasted ore to a wet treatment. [0021] The object to be treated in the present invention is a copper concentrate. Particularly, the object is a copper concentrate containing a large amount of arsenic, with enargite being the principal component. The grade of the copper concentrate containing enargite as the principal component includes 15 to 35 mass percent of copper and 5 to 15 mass percent of arsenic, depending on the amounts of the coexisting pyrite (FeS 2 ) and the gangue component. In the present invention, the copper concentrate is pre-dried at such a temperature that the mineral species and grades do not change in the copper concentrate. When drying is performed with hot air, the temperature of the copper concentrate at the outlet of the drying machine is normally about 90*C, and the moisture percentage in the copper concentrate is 0.5% or lower. [0022] The dried copper concentrate is heated in an inert atmosphere at 550 to 700*C for 10 to 60 minutes (the roasting process). The inert gas is mainly a nitrogen gas. The temperature and the atmosphere are necessary conditions for transforming the copper concentrate mainly containing enargite into arsenic sulfide and pyrite and the like, and the reaction time is the necessary time for not leaving unreacted enargite. As for the balance between arsenic and sulfur, if the original concentrate contains a large amount of pyrite or the like, S in the formula (1) is covered by S generated from degradation of the pyrite in a treatment temperature region, and therefore, becomes unnecessary as shown in the reaction formula (2).

4Cu3AsS 4 + 12FeS 2 + 2S -+ 12CuFeS 2 + As 4

S

6 (1) FeS 2 -+ FeS + S (2) If the above copper concentrate is short of sulfur compared with arsenic. however, the shortfall needs to be compensated by adding a sulfur source. In this manner, preferable arsenic removal can be performed in advance. A preferred arsenic grade in the concentrate after the roasting is 1.0 mass percent or lower, or more preferably, 0.5 mass percent or lower. [0023] The above roasting process is performed by using a rotary kiln or the like. As a result of the above described reaction treatment, a roasted ore mainly containing pyrite, and arsenic sulfide and elemental sulfur to be volatilized and recovered are obtained. [0024] Efficient leaching cannot be performed on enargite even by a chloridizing leaching technique, a high-temperature pressure sulfuric acid leaching technique, or the like. After the above described treatment, however, the recovered roasted ore can be immediately used in a wet process such as the above technique capable of leaching a copper concentrate containing pyrite as the principal component. [0025] The inventors conducted leaching on a copper concentrate containing enargite as the principal component prior to roasting by a chloridizing leaching technique using the oxidation power of Fe (trivalent) and Cu (divalent). As a result, the copper leaching rate was 51%. However, after performing leaching on the copper concentrate after the roasting, the copper leaching rate dramatically increased to 90%. At this point, the density of Fe (trivalent) is adjusted I to 3 g/liter, and the density of Cu (divalent) is adjusted to 10 to 25 g/liter. To do so, 67 to 135 g/liter of CuC 2 .2H 2 0 and 7 to 20 g/liter of FeCl 3 are added, but the amounts of the additions vary with the amounts of copper and iron (pyrite) in the copper concentrate being treated. Also, an oxygen-containing gas is blown thereinto, so as to oxidize the iron. The oxygen containing gas may be an oxygen gas, air, or an oxygen-enriched gas, for example. If the oxygen-containing gas is air, I to 4 liter/minute is blown thereinto. The roasted ore after the roasting is adjusted to 50 to 200 g/liter, and an oxidizing leaching process is performed. As for the chloridizing leaching solution, the Cl density is adjusted to 80 to 180 g/liter, and the Cl is used in the above described leaching. Chlorine is added through NaCl or the like, to adjust the Cl density. The leaching temperature is preferably 70 to 90*C, so that preferred leaching is performed. [0026] In the above described roasting process, the volatilized arsenic sulfide and elemental S are isolated from the exhaust gas, and are turned into a more stable form. The volatilized arsenic sulfide and elemental S are then discarded or stored where necessary. To recover volatile matter, a capacitor, an electrical dust collector, a -6wash-column, or the like is used. However, to isolate and recover arsenic sulfide, arsenious acid, and elemental sulfur, as well as the accompanying roasted ore, those apparatuses are combined, and a diluted air is introduced, or adiabatic cooling is performed by humidifying. Also, part of the sulfur is turned into a sulfurous acid gas by a small amount of oxygen in the nitrogen gas or a small amount of air that has entered the apparatus. Therefore, a desulfurization facility is provided where necessary. Examples [0027] (Example 1) FIG. I shows a flowchart of an operation to treat a copper concentrate containing enargite as the principal component. After a copper concentrate containing enargite as the principal component (Cu grade:= 24 mass percent, Fe grade = 23 mass percent, As grade:= 9 mass percent, and S grade = 39 mass percent) was dried at 90*C for 10 hours, the copper concentrate was subjected to a heat treatment in an inert atmosphere at 550*C for 60 minutes, to obtain a roasted ore containing pyrite as the principal component. Table I shows the grades of Cu, Fe, As, and S in the copper concentrate before and after the treatment, and the weight percent after the transformation, with 100 being the weight percent prior to the transformation. The particle size of the copper concentrate was 40 to 100 ptm, since pulverization was not performed. FIG. 2 shows the results of an XRD analysis on the (original) copper concentrate prior to roasting. FIG. 3 shows the results of an XRD analysis on the copper concentrate after roasting at 550*C. [Table 1] GRADE OF EACH ELEMENT IN COPPER CONCENTRATE BEFORE AND AFTER ROASTING AT 550" C Cu Fe As S wt% CONCENTRATE BEFORE 24 20 9.1 39 100 ROASTING CONCENTRATE AFTER 27 24 0.7 36 89 ROASTING [0028] According to Table I and FIG. 2, the concentrate prior to the roasting is substantially made of enargite and pyrite, and the molar ratio between the enargite and the pyrite is 1:3.5. [0029] According to Table 1 and FIG. 3, most of the concentrate after the roasting was chalcopyrite, and part of the concentrate was turned into tennantite (CuuZAs 4 SO) generated in the course of degradation of enargite, and unreacted pyrite. This reaction is basically expressed by the reaction formula (1): 4Cu 3 AsS 4 + l2FeS 2 + 2S -+ 12CuFeS 2 + As 4

S

6 (1) If the original concentrate contains a large amount of pyrite, S in the formula (1) is covered by the S generated by degradation of the pyrite in a test temperature region as shown in the reaction formula (2), and therefore, becomes unnecessary: FeS 2 -> FeS + S (2) In Example 1, there is a shortage of sulfur, since sulfur is not added prior to the roasting. The reaction in that case is expressed by the following formula (3): 4Cu 3 AsS4, -* 6Cu 2 S + As 4

S

6 (3) The reaction expressed by the formula (3) requires a higher temperature to progress. Therefore, it can be said that, in Example 1, a complete transformation into chalcopyrite cannot be achieved even after a 60-minute reaction time. [0030] The roasted ore obtained after the roasting was treated at 80*C by using a chloridizing leaching technique. In this leaching test, a chloridizing leaching solution containing 180 g/liter of Cl was used, and 18 g/liter of Cu (divalent) and 2 g/liter of Fe (trivalent) were added as the copper oxidizer to the chloridizing leaching solution. In a 3-liter beaker, 2.5 liters of the above solution was prepared, and the roasted ore was added to the solution, so that the pulp density became 90 g/liter. The solution was then stirred while air is blown into the solution at 2.5 liter/minute, and the copper leaching rate was checked. The leaching operation was performed in four stages. The leaching time in each of the first stage and the second stage was 3 hours, and the leaching time in each of the third stage and the fourth stage was 5 hours. In the first stage, the roasted ore was leached. In each of the second stage and thereafter, the residues obtained through the filtration performed in the previous leaching stage were treated by using a new leaching solution having the above described composition. [0031] FIG. 5 shows the copper leaching rate in a case where the roasted ore after roasting at 550*C was leached by the above described chloridizing leaching technique. A copper leaching rate of 72% was achieved at last. Also, the arsenic could be removed, and the copper could be leached out, without pulverization of the copper concentrate as in Patent Document 1. [0032] (Example 2) Table 2 shows the analytical values of the roasted ore obtained by treating the enargite-based copper concentrate used in Example I under the same roasting conditions as above, except for a temperature of 600'C. FIG. 4 shows the results of an XRD analysis on the copper concentrate after the roasting at 600*C. [Table 2] GRADE OF EACH ELEMENT IN COPPER CONCENTRATE BEFORE AND AFTER ROASTING AT 600' C Cu Fe As S wt% CONCENTRATE AFTER ROASTING 29 24 0.4 34 83 [0033] According to Table 2 and FIG 4, the arsenic removal and mineral transformation from enargite further progress, and most of the enargite turns into a copper iron sulfide of chalcopyrite or cubanite (CuFe2S 3 ). It is considered that part of the copper has turned into chalcocite. Since no pyrite peaks are observed, it can be determined that the reaction has almost finished. [0034] FIG 5 shows the copper leaching rate in a case where the roasted ore subjected to the roasting at 600'C was leached by the above described chloridizing leaching technique, as well as the result of the leaching of the roasted ore subjected to the roasting at 550*C. The copper leaching rate became 91% at last, and a higher leaching rate than the result of the roasting at 550*C was achieved. Also, 96% of the arsenic was released to the exhaust gas system, and the copper leaching process was efficiently conducted. Further, the arsenic could be removed in advance, and the copper could be leached out, without pulverization of the cooper concentrate as in Patent Document 1. [0035] (Comparative Example) For comparisons with the copper leaching rates in Example 1 and Example 2, FIG 6 shows copper leaching rates achieved in a case where an original concentrate containing enargite as the principal component was not subjected to a roasting treatment and was leached as it is in the same manner as above. The leaching rate was low, and reached only 52% at last. That is, it was confirmed that enargite, which is a hardly-leachable material, could be treated by roasting without any problems as to conditions such as the leaching time and temperature in practice. -9-

Claims (8)

1. A copper concentrate treatment method comprising: a roasting step of roasting enargite (Cu 3 AsS 4 ) or a copper concentrate containing enargite as a principal component thereof in an inert atmosphere at 550 to 700'C; and a leaching step of leaching out copper by using a chloridizing leaching technique by which an oxidizer containing Cu (divalent) and Fe (trivalent) is added to a roasted ore obtained in the roasting step, the roasted ore containing pyrite as a principal component thereof.

2. The copper concentrate treatment method according to claim 1, wherein in the roasting step, a sulfur source is added.

3. The copper concentrate treatment method according to claim 1 or 2, wherein in the leaching step, an oxidation treatment using an oxygen gas or air is performed.

4. The copper concentrate treatment method according to any one of claims 1 to 3, wherein in the leaching step, a leaching solution temperature is adjusted to 70 to 90'C.

5. The copper concentrate treatment method according to any one of claims 1 to 4, wherein in the leaching step, a Cl density in a leaching solution is adjusted to 80 to 180 g/liter.

6. The copper concentrate treatment method according to any one of claims 1 to 5, wherein in the leaching step, the Fe (trivalent) is adjusted to 1 to 3 g/liter, and the Cu (divalent) is adjusted to 10 to 25 g/liter.

7. A copper concentrate treated by the method according to any one of claims 1 to 6.

8. A copper concentrate treatment method according to claim 1, substantially as hereinbefore described with reference to any one of the Examples and/or Figures. - 10 -