Copper Sulphate from Metallic Scrap Copper
INTRODUCTION
The discovery of copper goes back to prehistoric times and has been mined for more than 6000 years. Gold was probably the first metal to attract man's attention because of its sparkling yellow color. Iron, in the form of meteorites, may, on the other hand, have been used before copper in some localities. Nonetheless, there is evidence that every ancient metal culture was actually introduced by the use of the red metal. The early age of copper, so the word goes, had its greatest development in Egypt. The most important copper-ore deposits of Antiquity were in Sinai, Syria, Afghanistan, Cyprus, Iberia and Central Europe. European copper mines of the Bronze Age are known in Austria, Germany, France, Spain, Portugal, Greece and Tyrol.
Today, annual consumption of copper is more than nine times as large. The annual usage of copper throughout the world has doubled since the 1970's to reach almost 20 million tons in 2005, of which 70% was produced by mining and 30% by recycling.
Up until recent years most of the discarded electrical and electronic equipment were generally crushed and land filled. Land filling with electronic waste (e-waste) can cause serious damage to the environment due to the hazardous products contained in waste electric and electronic equipment, WEEEs. This aims to prevent the generation of electrical and electronic waste and to promote re-use, recycling and other forms of recovery in order to reduce the quantity of the discarded waste. On the other hand the amount of precious metals, such as copper and gold that exist in the scrap could be a potential source for new raw material. However, the recycling of this type of scrap is still quite limited due to the heterogeneity of the materials present in the waste and the complexity in producing new equipment.
The methods applied in metal recovery from electronically waste are based on mechanical, pyrometallurgical or hydrometallurgical processes. The mechanical or physical processes have been utilized commercially in the recycling industry. The drawback with these processes is air pollution and high energy consumption.
According to Jin et. al hydrometallurgical methods are more exact, more predictable and more easily controlled than pyro metallurgical processing for metal recovery from computer main boards.
Hydrometallurgical processes are based on the dissolution of the metals in the raw material into, e.g. acidic or alkaline solutions. A hydrometallurgical process has a generally lower cost than a mechanical or a pyrometallurgical process and can be economically operated even on a small scale. Thus, this technique has been widely used to recover metals from other industrial wastes, due to its flexible, simple operation and energy-saving features.
Copper Recovery
Copper is one of the most widespread materials used in the production of electronic equipment and found in multiple appliances as, e.g. circuit boards. Copper recycling has lately become more important due to the depletion of the earth copper resources and thus the increased price for raw material. The development of recycling processes is an important issue to effectively utilize the copper resources, minimize the adverse effects of hazardous materials and protect our environment.
The processes used for copper recycling depend on the copper content in the raw material, its size distribution, and other constituents. Three general types can be defined:
- Type 1: Copper scrap, used for melting and refining or direct melting for products. This scrap accounts for about 95 % of all recycled copper. The value of the recycled copper is generally higher than its treatment costs.
- Type 2: Copper-containing special scrap such as cables, electronic components or printed circuit boards. Pre-treatment is necessary before melting the copper. The value of the recycled copper is generally in the range of the overall treatment cost.
- Type 3: Copper-containing residues, for example sludges from metal-plating industry. The copper content on these materials is low. The value of the recycled copper is generally lower than the treatment cost of the material.
Different methods have been studied for copper recovery. Some of the hydrometallurgical techniques use sulphuric acid solutions.
PROPERTIES
PHYSICAL AND CHEMICAL PROPERTIES
Anhydrous Copper (II) Sulphate
- Anhydrous Copper Sulphate is soluble in water, slightly soluble in methanol but insoluble in ethanol.
- It readily dissolves in aqueous ammonia and excess alkali metal cyanides, with the formation of complexes.
- The material is hygroscopic, with conversion into pent hydrate copper sulphate in moist air below 30 deg C.
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Appearance Form
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Powder
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Color
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Light Grey
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Melting Point/Freezing Point
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Melting Point/Range: 200°C.
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Vapor Pressure
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9,7 h Pa at 25°C
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Relative Density
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3,603 g/mL at 25°C
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Bulk Density
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1 kg/m3
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Copper (II) Sulphate Pent-hydrate
- Copper(II) sulfate penta-hydrate decomposes before melting at 150°C (302°F), losing two water molecules at 63°C (145 °F), followed by two more at 109°C (228°F) and the final water molecule at 200°C (392°F).
Dehydration proceeds by decomposition of the tetra aqua copper (2+) moiety, two opposing aqua groups are lost to give a di-aqua copper (2+) moiety. The second dehydration step occurs with the final two aqua groups are lost. Complete dehydration occurs when the only unbound water molecule is lost.
- At 650°C (1,202°F), copper (II) sulfate decomposes into copper (II) oxide (CuO) and sulfur trioxide (SO3).
- Its blue color is due to water of hydration. When heated in an open flame the crystals are dehydrated and turn grayish-white.
- Copper sulfate reacts with concentrated hydrochloric acid very strongly. In the reaction the blue solution of copper (II) turns green, due to the formation of tetra chloro-cuprate (II):
Cu2+ + 4 Cl- → CuCl2-4
It also reacts with more reactive metals than copper (e.g. Mg, Fe, Zn, Al, Sn, Pb, etc.):
CuSO4 + Zn → ZnSO4 +Cu
CuSO4 + Fe → FeSO4 + Cu
CuSO4 + Mg → MgSO4 + Cu
CuSO4 + Sn → SnSO4 + Cu
3 CuSO4 + 2 Al → Al2(SO4)3 + 3 Cu
Some metals more reactive than others like magnesium and aluminium will cause a secondary reaction. They will form hydroxides with the water while releasing some hydrogen gas. The copper formed is deposited on the surface of the other metal. The reaction stops when no free surface of the metal is present anymore.
USES & APPLICATIONS
Uses of Copper Compounds
Copper sulphate, blue stone, blue vitriol are all common names for pent hydrated cupric sulphate, Cu S04 5 H20, which is the best known and the most widely used of the copper salts. Indeed it is often the starting raw material for the production of many of the other copper salts. Today in the world there are more than 100 manufacturers and the world's consumption is around 200,000 tons per annum of which it is estimated that approximately three-quarters are used in agriculture, principally as a fungicide.
Manufacture In the production of copper sulphate virgin copper is seldom, if ever, used as the starting raw material. Copper ores are used in countries where these are mined. For the bulk of the world's production nonferrous scrap is the general source. The scrap is refined and the molten metal poured into water to produce roughly spherical porous pieces about the size of marbles which are termed "shot". This shot is dissolved in dilute sulphuric acid in the presence of air to produce a hot saturated liquor which, if the traditional large crystals of copper sulphate are required, is allowed to cool slowly in large cooling vats into which strips of lead are hung to provide a surface for the crystals to grow on. If the granulated (snow) crystal grades are desired, the cooling process is accelerated by agitating the liquor in water cooled vessels.
PROCESS TECHNOLOGY
The polymeric coat on the copper scraps was initially removed using some quantity of industrial grade of sulphuric acid, which can later be washed off to obtain the pure copper metal scraps. The copper metal scraps were digested at elevated temperature with constant stirring using concentrated sulphuric acid.
After digestion, the copper sulphate was extracted with a lot of distilled water and later filtered to remove all unwanted and undigested wastes in the mixture. The filtered blue solution of copper sulphate was later concentrated to allow the formation of hydrated copper sulphate. The crystals were later re-crystallized in distilled water to obtain a purer form of the salt. The crystals were later dried and packaged.
METHODS OF OPERATION
This process relates to a method and apparatus for the recycling of scrap metal, such as the recycling of copper scrap material.
In certain operations where useful byproducts are formed, these byproducts are subjected to pressure leaching in order to produce saleable products. For example, in a lead smelting operation for the recovery of lead, copper matter is obtained as a byproduct. In order to increase the commercial viability of the process, the copper matte is further treated in a pressure leaching stage in an autoclave to convert the copper matte to copper sulphate, which, for example, is useful as an animal feed supplement.
It is also an object of the present method to provide a process and apparatus for the recycling of a scrap material for the production of a useful product.
FIG. 1 is a flow diagram illustrating the method according to the method; and
FIG. 2 is a schematically side view of an apparatus for use in the method.
Fig. 1
Fig. 2
Referring to FIG. 1, copper matte from a lead smelter is treated in a continuous pressure leaching process in a pressure vessel or autoclave 10 to convert the copper sulphide in the matte to soluble copper sulphate.
The pressure leaching stage is in effect a pressure oxidation and it is carried out in the presence of oxygen using sulphuric acid.
The matter contains several minerals, such as copper sulphide (Cu2 S), copper arsenide (Cu3 As), lead sulphide (PbS) and elemental lead as bullion.
The following reactions take place in the autoclave 10:
Cu2 S+H2 SO4 +5/2O2 ➝2CuSO4 +H2 O PAC PbS+2O2 ➝PSO4
The matter is screened as it is fed to a ball mill 12 for grinding, first at one inch and then 6 mesh. The oversize materials are crushed and then returned for rescreening. Eventually the lead bullion particles greater than 6 mesh are returned to the lead smelter for processing.
The ball mill 12 grinds the matte to 80%-200 mesh.
The matter is stored in a stock tank 14 in the form of slurry at 75% solids, from where it is fed to the autoclave 10.
In addition to the copper matte slurry, scrap copper wire is introduced into the autoclave 10 to be leached with the copper matte. An aspect which renders the process feasible is the introduction of the scrap material to the autoclave separately from the metal concentrate.
The copper wire is fed to the autoclave 10 using a feeding apparatus 16, which is shown in more detail in FIG. 2. The feeding apparatus 16 overcomes the pressure difference between the autoclave pressure and atmospheric pressure, so that the copper wire can be fed to the autoclave 10 without interrupting the leaching operation.
The feeding apparatus 16 comprises a hopper 18 leading into a pressurization chamber 20 which in turn leads into the autoclave 10 via a safety valve, in the form of a ball valve 22.
A first rotating disc valve 24 is operative between the hopper 18 and the chamber 20 and a second rotating disc valve 26 is operative between the chamber 20 and the autoclave 10. The valves 24 and 26 have self cleaning faces.
A feeder in the form of a conveyor belt 28 is provided for feeding scrap copper wire to the hopper 18.
In operation, copper wire is introduced into the chamber 20 by opening the valve 24 while the valve 26 is closed. Once the chamber 20 is charged with copper wire, the valve 24 is closed and the chamber 20 is pressurized by the introduction of gas under pressure, as indicated by the arrow 30, in order to increase pressure in the chamber 20 to above that of the autoclave 10.
The autoclave 10 is then charged with copper wire by opening the valve 26 while the valve 24 remains closed. The cycle is then repeated for a next batch of copper wire.
In this way the autoclave 10 is charged without interrupting the pressure leach in the autoclave 10.
A solution flush, as indicated by the arrow 32, is used at one or more locations to sweep the system clean when required.
Prior to opening the valve 24 for the next charge, the chamber 20 is depressurized, as indicated by the arrow 34 and the gas content of the chamber 20 is passed to a scrubber.
During the pressure leach in the autoclave 10, the matter and the copper wire react with the acid at 160° C. under 1380 kPa gauge pressure of oxygen. The copper is leached into solution and the lead remains in the residue as lead sulphate. Additional acid is introduced into the autoclave 10 to ensure the complete dissolution of the copper wire according to the equation:
Cu°+2H+ +1/2O2 ➝Cu+2 +H2 O
The slurry discharged from the autoclave 10 is fed to a letdown and filter feed tank 35. Sulphuric acid for effecting the leaching operation is fed to the autoclave 10 from a recycle tank 36, which also contains water and mother liquor which is recycled from a crystallizer in which the copper sulphate is crystallized. The sulphuric acid, water and mother liquor are mixed in the recycle tank 36 in suitable proportions for optimum leaching of copper in the autoclave 10.
When feeding the autoclave 10, the matte and mother liquor are sampled regularly to determine the Pb, Cu, H2 SO4 and as content. These assays are used to calculate the acid flow to and the total flow from the recycle tank 36. Normal target levels for solution discharging from the autoclave 10 are 180 g/l Cu and 15 g/l H2 SO4.
The autoclave discharge slurry is kept hot to prevent crystallization of the copper sulphate in the filter feed tank 35. The slurry is then filtered through a filter press 40 to separate the copper sulphate solution from the lead sulphate cake. The cake is washed and discharged from the filter 40 into a lugger box for return to the smelter to recover the lead and silver values. The filtrate is passed to a feed tank 42. From the feed tank 42, the copper sulphate solution is fed continuously to a crystallizer section for the production of copper sulphate.
PROCESS FLOW DIAGRAM
Raw Material (Scrap)
Shredder
Cyclone Light Fraction
Screening
Heavy Fraction
Magnetic Separator
Autoclave
Filter Press
Cuso4 Recycling Plant
Crystallizer
Tray Dryer
Cuso4 (Pure)
PLANT ECONOMICS
Rated Plant capacity = 33.33 MT/day
= 9999.00 MT/annum
COPPER SULPHATE FROM METALLIC SCRAP
Basis
No. of working days = 25 days/month
= 300 days/annum
No. of shifts = 3 per day
One shift = 8 hours
LAND & BUILDING COST TOTAL Rs. 6,22,50,000.00
PLANT & MACHINERY
1. Hammer Mill
2. Cyclone
3. Magnetic Conveyor Belt
4. Screen
5. Ball Mill
6. Autoclave Cap. 20 Ton
7. Filter Press
8. Recycling Plant
9. Crystallizer
10. Tray Dryer
11. Storage Tanks for Sulphuric Acid
12. Soft Water Plant
13. Boiler
14. Recirculation Pump
15. Automatic Packing Unit
16. Weighing Unit
17. Elevators & Escalators
18. Instrumentation & Process Control Equipment
19. Exhaust System
20. Miscellaneous Machine like valves, motors, pipeline & fittings etc.
21. Erection & Installation
TOTAL Rs. 1,18,71,000.00
FIXED CAPITAL
1. LAND & BUILDING Rs. 6,22,50,000.00
2. PLANT & MACHINERY Rs. 1,18,71,000.00
3. OTHER FIXED ASSETS Rs. 1,14,30,000.00
TOTAL Rs. 8,55,51,000.00
WORKING CAPITAL REQUIREMENT/MONTH
RAW MATERIALS
1. Copper Scrap
2. Sulphuric Acid
3. Printed Packing Bags
4. Laboratory, ETP & Other Chemicals
5. Consumable Store
TOTAL Rs. 18,97,67,970.00
TOTAL WORKING CAPITAL/MONTH
1. RAW MATERIAL Rs. 18,97,67,970.00
2. SALARY & WAGES Rs. 53,13,600.00
3. UTILITIES & OVERHEADS Rs. 13,44,000.00
TOTAL Rs. 19,64,25,570.00
COST OF PROJECT
TOTAL FIXED CAPITAL Rs. 8,55,51,000.00
MARGIN MONEY Rs. 14,73,19,177.80
TOTAL Rs. 23,28,70,177.80
TOTAL CAPITAL INVESTMENT
TOTAL FIXED CAPITAL Rs. 8,55,51,000.00
TOTAL WORKING CAPITAL FOR 3 MONTHS Rs. 58,92,76,710.00
TOTAL Rs. 67,48,27,710.00
TURN OVER/ANNUM = Rs. 2,82,00,00,000.00
PROFIT SALES RATIO = 13.34 %
RATE OF RETURN = 55.74 %
BREAK EVEN POINT (B.E.P) = 23.98 %
