5.2.4Copper extraction and initial processing -
Like for zinc, quantitative descriptions of mercury mass balances over copper extraction operations - corresponding input and output distribution estimates - seem not to be easily available. Therefore, the quantitative aspects of the description in this section have been put together piece by piece from different sources.
-
Large scale industrial mining and metal extraction operations are few in number in any country where they operate, their feed materials and production configurations vary significantly, and they may be significant mercury release sources. Given these factors, it is highly recommended to use a point source approach in the inventory, and compile point source specific data from the operating companies themselves, if feasible, as well as from other relevant data sources with knowledge of the specific production facilities.
5.2.4.1Sub-category description -
Ore for extraction of copper (mainly sulphide ore) can contain trace amounts of mercury. In the extraction of the copper from the ore, processes are used which release this mercury from the rock material. This mercury may evaporate and follow the gaseous streams in the extraction processes (in most cases) or follow wet (liquid) process streams, depending on the extraction technology used. Unless the mercury is captured by process steps dedicated to this purpose, major parts of it may likely be released to the atmosphere, land and aquatic environments. Retained mercury may be sold in the form of "calomel" (Hg2Cl2), normally sold for off site extraction of metal mercury) or on-site processed metal mercury, or it may be stored or deposited as solid or sludgy residues (Environment Canada, 2002). Marketing of recovered by-product mercury from extraction of non-ferrous metals represent a substantial part of the current global mercury supply. Besides these output pathways, parts of the mercury input follows co-produced sulphuric acid (European Commission, 2001; Zhang et al., 2012; Outotec, 2012).
Processes involved -
The principal steps in copper extraction include production of copper-rich concentrate from raw ore, roasting of the concentrate (to produce “calcine”), and smelting in a furnace, which both occur at high temperatures. The overall process includes numerous steps, including a final step called “converting”, with the purpose of eliminating the remaining iron and sulphur present in the process material, leaving molten “blister” copper (US EPA 1997a). Facilities that conduct this overall process of producing copper from ore are commonly called “primary copper smelters”. For a thorough description of the process, see US EPA (1997a) or European Commission (2001). Further refining of the blister copper is not expected to cause significant mercury releases (at least as regards mercury originating from the copper ore).
Mining of ore and production of concentrates -
Ore is mined principally from open pit mines, and copper-rich fractions are separated from the waste rock after grinding and milling to reduce particle sizes by mechanical separation processes; usually floatation or other processes employing suspension in water are employed.
-
Different copper ore types exist, but the most economically important are the sulphidic minerals chalcopyrite, bornite and chalcocite (Ullmann, 2001). In some cases copper is mined from mineral deposits also containing other metals, for example copper-and-nickel deposits and copper-zinc-pyrite deposits (Krivtsov and Klimenko, 1997).
-
The produced concentrate is transported to the extraction plants, which may be receiving concentrate from mines nearby, but also from the global market.
-
Waste rock with no or low metal content and the parts of the reject ore material which has been separated from the copper-rich concentrate (parts of the so-called tailings), is usually stored on site in tailings ponds, tailings piles/heaps or back-filled into the mines.
-
The waste rock and tailings may - just like the generated concentrates contain trace amounts of mercury. This material is much more susceptible to weathering than the original deposits, due to the reduced particle sizes and higher accessibility for air and precipitation. For sulphidic ores, which are important ore types for production of several base metals, this weathering liberates and oxidizes the contained sulphur and produce sulphuric acid. The acid renders the constituents more soluble and thus increases leaching of the metal to the environment many fold as compared to the untouched mineral deposit. This process is called "acid rock drainage" (or ARD) and is considered a serious environment risk (European Commission, 2003).
-
Few data has been identified on mercury concentrations in crude ore and reject material, where as more data have recently been published on mercury concentrations in copper concentrates. Quantitative data on release of mercury from waste rock and mining tailings to air, water and land has not been identified. But this release source should not be neglected, because even moderate mercury concentrations in the material may possibly render substantial mercury amounts mobile because of the enormous amounts of materials handled in mining operations.
-
-
As mentioned, copper extraction involves a complex network of processes, which will not be described in details here. With regard to mercury flow and release pathways, copper extraction normally roughly resembles the "pyrometallurgical" process path described for zinc, see section 5.2.3 for the description. One major difference is that some copper smelters do not employ roasting/sintering before the concentrate is fed to the furnace, but only drying. As a consequence, more of the sulphur - and possibly also mercury - in the feed stays in the molten material lead to the next process step, the so-called converting in such facilities, where it is vented by a blow-through of air/oxygen. Another difference from zinc production is the so-called fire-refining step, which takes place after the converting. Hydrocarbons (gas) or sometimes "green" timber logs are added to the molten copper containing material to reduce metal oxides to elemental metal and other constituents (European Commission, 2001). These carbon sources are additional sources to mercury inputs to the extraction processes; no data are, however, available to quantify their contributions to mercury releases.
-
Recycled copper scrap may be added to the feed material to the smelting steps, but is not considered a major input source of mercury to the process. Copper and zinc, or copper and nickel, (and other metals) are sometimes produced in parallel, semi-integrated process lines in the same smelters (Environment Canada, 2002).
-
The primary releases of mercury from the feed materials happen during the drying/roasting step (if present) and from the smelting furnace. In addition, converters and refining furnaces may emit any residual mercury left in the material flow through the copper extraction process (US EPA, 1997a). If no mercury removal step is included in the off gas treatment before the acid plant, most of these releases will be lost to the atmosphere. If exhaust gases from the drying/roasting, furnace and/or converter steps are lead through highly efficient particle filters (ESPs and/or fabric filters) and in some cases mercury-specific filters, part of the mercury in the gas may be retained with the particles or in mercury by-products.
5.2.4.2Main factors determining mercury releases and mercury outputs
Table 5 76 Main releases and receiving media during the life-cycle of copper extraction and initial processing
Phase of life cycle
|
Air
|
Water
|
Land
|
Products
*2
|
General waste
|
Sector specific treatment/
disposal
|
Wastes from mining and production of concentrates
|
x
|
X
|
X
|
|
|
X
|
Extraction of primary copper from concentrate
|
X
|
X
|
X
|
X
|
|
X
|
Manufacture of refined copper and products *1
|
|
|
|
|
|
|
Use of copper
|
|
|
|
|
|
|
Disposal of copper
|
|
|
|
|
|
|
Notes: *1: Mercury releases could in principle happen due to fossil fuel usage, but the copper metal is not
expected to be a mercury input source to the refining and manufacturing steps;
*2: In sulphuric acid, mercury by-products, and perhaps other process-derived by-products;
X - Release pathway expected to be predominant for the sub-category;
x - Additional release pathways to be considered, depending on specific source and national situation.
-
The concentration of mercury in the ore/concentrate, and the amount of ore/concentrates used are important factors determining mercury releases.
-
The presence of a dedicated mercury removal step will influence the distribution between output pathways considerably. With mercury removal, releases to the atmosphere will be converted to by-product outputs and releases to land, waste deposition and water. In case sulphuric acid is produced, releases to sulphuric acid (a marketed by-product) will also be converted in the mercury removal step to the same output pathways.
-
Since part of the mercury input may be retained with particles in exhaust gas particle filters, the presence of high efficiency ESP's and fabric filters may also reduce atmospheric mercury releases significantly - if filter dust is not recycled back into the process - and convert the retained mercury to solid, suspended and/or liquid residues.
-
Waste water from different process steps can contain mercury and must be treated carefully to avoid or minimise releases to aquatic environments.
-
The extent of releases to the environment from waste material deposition, including waste rock, tailings from concentration steps, extraction process residues, exhaust gas cleaning residues and waste water treatment residues, is very dependent on how carefully the waste deposits are managed. Poorly managed deposits may result in substantial releases to air, water and land.
5.2.4.3Discussion of mercury inputs
Table 5 77 Overview of activity rate data and mercury input factor types needed to estimate releases from copper extraction and initial processing
Life-cycle phase
|
Activity rate data needed
|
Mercury input factor
|
Wastes from mining and production of concentrates
|
Metric tons of reject material
produced per year
|
g mercury/metric ton in reject material produced *1
|
Input to extraction of primary copper from concentrate
|
Metric tons of concentrate used per year
|
g mercury/metric ton
concentrate
|
Notes: *1 Such wastes may include lower grade material (lower lead concentrations), and the mercury concentrations may be similar to concentration in the input ore material. If no concentration data for reject materials are available, concentration data for the ore used may be applied for forming a rough estimate.
-
Hylander and Herbert (2008) collected data for mercury concentrations in concentrates for zinc, copper and lead production for all mines globally, for which data were available through market studies published by BrookHunt and Associates Ltd. (2005, 2006a; 2006b). The individual data are proprietary, but data were aggregated in charts showing the distribution of mercury concentration in relevant concentrates; see Figure 5 -12 for data on cupper concentrates. The authors note that no data from Chinese mines were available.
Figure 5 12 Distribution of mercury concentrations in cupper concentrates globally (reprinted with permission from Hylander and Herbert, 2008. Copyright 2008 American Chemical Society).
-
UNEP/AMAP (2012) proposed the following default mercury input factors for copper extraction based on (Hylander and Herbert, 2008; Outotec, 2012) as well as other information: Minimum: 1; medium: 30, and maximum: 100 g mercury/metric ton of concentrate used. Converted to a basis of copper produced, the corresponding factors were respectively 2.1, 107.5 and 716.8 g mercury/metric ton copper produced, when using a concentrate used/Cu produced ratio of 2.11-7.17 (intermediate value 3.58).
Table 5 78 Examples of mercury concentration in copper concentrates, as well as in ore and rejects
Country
|
Location
|
Type
|
Average Hg
concentration,
g Hg/metric ton
|
Range of Hg concentration in samples,
g/metric ton
|
Data source
|
In ore
|
Canada
|
Brunswik Works
|
|
2.1
|
|
Klimenko and Kiazimov (1987)
|
Russian Federation
|
Ural
|
|
10-25
|
|
Kutliakhmetov (2002)
|
|
South Ural, 4 locations
|
Copper and pyrite, massive
|
9.8-13 *1
|
|
Fursov (1983)
|
Kazakhstan
|
Kusmurun
|
Copper and pyrite, massive
|
9.2
|
4.3-16.70
(11 samples)
|
Fursov (1983)
|
|
Dzhezgaz-gan
|
Cuprous limestone, massive (chalcopyrite)
|
3.2
|
2.8-3.68
(15 samples)
|
Fursov (1983)
|
|
Dzhezgaz-gan
|
Cuprous limestone, disseminated (bornite)
|
1.5
|
1.23-1.87
(11 samples)
|
Fursov (1983)
|
|
Counrad
|
Copper and porphyry, disseminated (primary)
|
0.9
|
0.76-1.02
(8 samples)
|
Fursov (1983)
|
In reject material from production of concentrates
|
Canada
|
Brunswik Works
|
From production of zinc, copper, lead and compound concentrates
|
0.69
(at ore Hg conc. 2.1)
|
|
Klimenko and Kiazimov (1987)
|
Russian Federation
|
Ural
|
From production of zinc, copper and compound concentrates
|
|
1-9
(at ore Hg conc. 10-25)
|
Kutliakhmetov (2002)
|
In concentrates
|
Canada
|
Brunswik Works
|
|
2.3
|
|
Klimenko and Kiazimov (1987)
|
Russian Federation
|
Ural
|
From copper pyrite type ore
|
|
28-41
|
Kutliakhmetov (2002)
|
|
Unknown
|
From pyrite and polymetal type
|
|
0.22 - 65
|
Bobrova et al., (1990); Ozerova (1986)
|
|
Unknown
|
From stratiformic lead-and-zinc type
|
|
2 - 290
|
Bobrova et al., (1990); Ozerova (1986)
|
|
Unknown
|
From copper pyrite type
|
|
0.3 - 150
|
Bobrova et al., (1990); Ozerova (1986)
|
|
Unknown
|
From cupriferous sandstone
|
|
4
|
Bobrova et al., (1990); Ozerova (1986)
|
|
Unknown
|
From vanadium-iron-copper type
|
|
70
|
Bobrova et al., (1990); Ozerova (1986)
|
|
Unknown
|
From copper-molybdenum type
|
|
0.02
|
Bobrova et al., (1990); Ozerova (1986)
|
|
Unknown
|
From copper-nickel type
|
|
0.14 – 0.4
|
Bobrova et al., (1990); Ozerova (1986)
|
General, coverage unknown
|
Unknown geography
|
|
0.5 - 8
|
|
Confidential European data source
|
Global
|
|
Global average
|
62
(median 4)
|
(see Figure 5 -12)
|
Hylander and Herbert (2008)
|
China
|
|
2 copper smelters
|
|
1.48 and 4.23
|
Zhang et al. (2012)
|
|
|
Typical medium value
|
30
|
|
Outotec (2012)
|
Notes: *1: Range between averages in several locations, 38 samples in all.
5.2.4.4Examples of mercury in releases and wastes/residues Examples of outputs from production of concentrates -
Two examples of mercury distribution in the outputs from production of non-ferrous metal concentrates (including copper concentrates) are given under the same heading in the zinc extraction section (see Table 5 -70 and Table 5 -70in section 5.2.3). The two examples are quite different and may not necessarily be representative; they serve only as indications here.
Examples of outputs from production of copper metal -
As mentioned above, quantitative descriptions of mercury mass balances over copper extraction works - corresponding inputs and output distribution estimates - are scarce in the literature.
-
Zhang et al. (2012) have reported detailed mass balances for six non-ferrous smelters (zinc, lead and copper) with relatively low atmospheric emissions in China. UNEP (2011) reported on the output distribution of mercury from a combined zinc/copper smelter. These data are described in the section on zinc extraction above. The few data available do not indicate major differences in the mercury output distribution pattern between different base metals production.
-
An attempt of developing a complete output distribution overview was, however, made by Yanin (in Lassen et al., 2004) for Russian crude copper smelters; the estimated output distribution is shown in Table 5 -79. The estimates are based on theoretical considerations and should be regarded as indicative only.
-
For comparison with the air emission factors described below, an example can be calculated using Yanins estimates above. At a mercury concentration of 13.8 g/metric ton in the concentrate used, a copper concentration of 15% in the same concentrate, and an extraction rate of 93% of the copper input, the calculated air emission factor would be 13.8 g Hg/metric ton conc. / 0.15 metric ton Cu/metric ton conc. * 0.93 = 11.7 g Hg/metric ton of copper produced. This is comparable to the atmospheric emission factor for the Hudson Bay smelter in Canada, shown in Table 5 -80 below.
Table 5 79 Indicative estimates of the output distribution (in relative terms) of mercury from copper smelters under Russian conditions (Yanin, in Lassen et al., 2004).
Release pathway
|
Atmosphere
|
Waste water
|
Slag dumped
|
Sludge dumped
|
"Arsenate cake" dumped
|
"Lead cake" sold to Pb extraction
|
Liquid sulphur *2
|
Washing acid *2
|
Sum
|
Share of Hg inputs *1
|
0.12
|
0.02
|
0.04
|
0.38
|
0.06
|
0.11
|
0.14
|
0.14
|
1.00
|
Outputs in g Hg/ metric ton produced copper, for an example with input of 13.8 g Hg/metric ton concentrate
|
0.12
|
0.02
|
0.04
|
0.38
|
0.06
|
0.11
|
0.14
|
0.14
|
1.00
|
Notes: *1 Corrected here for internal recycling of filter dust to the furnace (steady state assumed);
*2 Liquid sulphur - a by-product - and washing acid is most likely sold; this is, however, not mentioned
in the reference.
-
A few examples of emission factors are available, but only for atmospheric emissions of mercury, and with no links to corresponding mercury inputs with concentrates or ore.
-
Examples of emission factors for direct atmospheric emissions from copper production are given in Table 5 -80 below. Low atmospheric emission factors would generally indicate that a large part of the mercury inputs are transferred to marketed by-product mercury (metal or compounds), and/or to on-site waste deposits with a potential for future releases to all media. Some minor parts of the mercury inputs may be transferred to releases to aquatic environments as a consequence of wet processes in the emission reduction systems. For the nickel/copper smelter mentioned, produced slag is used for road and railroad construction.
-
Based on self reported emissions data from 7 primary copper smelters in the USA for year 1993, US EPA estimated total atmospheric mercury releases at 57 kg per year in 1994, from smelters with a metal production capacity of approximately 1.4 million metric tons (1995/96 capacity)(US EPA, 1997b). Corresponding atmospheric release rates per product output can be calculated to approximately 0.04g Hg/metric ton of metal production "capacity".
Table 5 80 Examples of emission factors for direct atmospheric releases from copper production
Country/
Region
|
Facility/
location
|
Reported mercury releases to the atmosphere per product output
|
Indications of emission reduction technology level
(atmospheric releases)
|
Remarks
|
Data
reference
|
USA
|
National average
|
0.04g Hg/metric ton of metal production "capacity"
|
|
Self-reported atmospheric Hg releases. Unclear if "capacity" mirrors actual production.
|
US EPA (1997a)
|
Canada
|
Hudson Bay M&S, Manitoba
|
8.2 g Hg/metric tons of product (zinc, copper etc.)
|
Appears to be moderate: ESP's, but no Hg removal or acid plant
|
|
Environment
Canada (2002)
|
Noranda Horn
|
1.8 g Hg/metric tons of product (copper etc.)
|
Furnace and new converter line equipped with ESPs, Hg removal and acid plant; old converters processing parts of the feed is only equipped with ESPs
|
Also processes recycled copper.
|
Environment
Canada (2002)
|
Inco Copper Cliff
|
0.01 g Hg/metric tons of product (Copper, nickel etc.)
|
Furnace off gas line with wet PM filter and acid plant, but no Hg removal; Drying + converting steps off gas with ESPs only
|
Combined nickel/copper smelter. Part of slag from furnace is used for railway and road construction. Apparently feed may have lower Hg concentrations than for other Canadian smelters mentioned here (Toolkit authors remark)
|
Environment
Canada (2002)
| -
According to the European Commission (2001), output of by-product mercury in the production of non-ferrous metals (other than dedicated mercury mining) amounted to an estimated 350 metric tons mercury in Europe in 1997. These processes generally produce mercury or calomel in the range of 0.02-0.8 kg mercury per metric ton of (other) metals produced; depending of the mercury content of the input concentrates.
5.2.4.5Input factors and output distribution factors -
Based on the information compiled above on inputs and outputs and major factors determining releases, the following default input and distribution factors are suggested for use in cases where source specific data are not available. It is emphasized that the default factors suggested in this Toolkit are based on a limited data base, and as such, they should be considered subject to revisions as the data base grows. Also, the presented default factors are expert judgments based on summarized data only.
-
The primary purpose of using these default factors is to get a first impression of whether the sub-category is a significant mercury release source in the country. Usually release estimates would have to be refined further (after calculation with default factors) before any far reaching action is taken based on the release estimates.
-
Due to lack of data, no default factors can be set for the mining and concentrating processes. Note that this implies that the mercury release estimates calculated from default factors may likely tend to underestimate the total releases from the sector.
a) Default mercury input factors -
Actual data on mercury levels in the particular concentrate composition used will lead to the best estimates of releases.
If no information is available on the mercury concentration in the concentrates used in the extraction step, a first estimate can be formed by using the default input factors selected in Table 5 -81 below (based on the data sets presented in this section). Because concentrations vary so much, it is recommended to calculate and report intervals for the mercury inputs to this source category. The low end default factors has been set to indicate a low end estimate for the mercury input to the source category (but not the absolute minimum), and the high end factor will result in a high end estimate (but not the absolute maximum). The medium estimate is used in the default calculations in Inventory level 1 of the Toolkit. If it is chosen not to calculate as intervals, the use of the maximum value will give the safest indication of the possible importance of the source category for further investigation. Using a high end estimate does not automatically imply that actual releases are this high, only that it should perhaps be investigated further.
Table 5 81 Default input factors for mercury in concentrates for crude copper production
Material
|
Default input factors;
g mercury per metric ton of concentrate;
(low end - high end (intermediate)
|
Copper concentrate
|
1 - 100 (30)
|
Note: *1: The asymmetric medium value is due to the uneven distribution of mercury concentartions in concentrates on the global market; see the description of (Hylander and Herbert, 2008) above.
-
If desired, these default factors can be converted to a basis of mercury inputs per copper produced, by the use of a concentrate used/copper produced ratio of 2.11-7.17 (intermediate value 3.58 ton concentrate used per ton copper produced) as derived by UNEP/AMAP (2012). The corresponding factors are low end: 2.1, medium 107.5 and high end 716.8 g mercury/metric ton copper produced. Note that the default Toolkit spreadsheet calculations are based on mercury per concentrate.
b) Default mercury output distribution factors -
Based on the data on mercury output distribution presented in this section, as well as in the section above on zinc, the following default factors are suggested.
Table 5 82 Default output distribution factors for mercury from extraction of copper from concentrates.
Phase of life cycle
|
Air
|
Water
|
Land
*1
|
Product
*1, *2
|
General waste
|
Sector specific treatment/
disposal *1
|
Mining and concentrating
|
?
|
?
|
?
|
?
|
x
|
x
|
Production of copper from concentrate:
|
|
|
|
|
|
|
Smelter with no filters or only coarse, dry PM retention
|
0.90
|
|
?
|
|
|
0.10
|
Smelters with wet gas cleaning
|
0.49
|
0.02
|
?
|
|
|
0.49
|
Smelters with wet gas cleaning and acid plant
|
0.10
|
0.02
|
?
|
0.42
|
|
0.46
|
Smelters with wet gas cleaning, acid plant and Hg specific filter
|
0.02
|
0.02
|
?
|
0.48
|
|
0.48
|
Notes: *1 Deposition of residues will likely vary much between countries and perhaps even between individual facilities, and may be on land, in the mine, in impoundments, often on-site.
*2: Marketed by-products with mercury content include, calomel, elemental mercury, sludge for off-site mercury recovery, low grade washing acids, sulphuric acid, liquid sulphur and filter cake or other residues sold or transferred to other metal production activities or other sectors.
c) Links to other mercury sources estimation -
In case of combined smelters producing several non-ferrous metals from the same concentrate, it is suggested to assign the mercury releases to the metal produced in the largest amounts. In case of parallel processing of different concentrates in parallel production lines, assign the mercury releases separately to the major metal produced in each line.
5.2.4.6Source specific main data -
The most important source specific data would in this case be:
-
Measured data or literature data on the mercury concentrations in the ores and concentrates extracted and processed at the source;
-
Amount of ore/concentrates extracted and processed, and
-
Measured data on the distribution of mercury outputs with (preferably all) output streams, including mercury percentages retained by emission reduction equipment applied on the source (or similar sources with very similar equipment and operating conditions).
-
The presence of a mercury removal unit at a specific extraction plant may indicate that a major share of the mercury outputs is not released to the atmosphere, but is instead marketed and sold as a by-product or stored on-site.
Dostları ilə paylaş: |
