Copper Extraction TechniquesBelow is a copy of an article from Wikipedia that says sulphuric acid extraction of copper is a closed circuit process where the sulphuric acid is recycled back to the heap leach pad after removal of the copper sulphate. This is already a proven safe process that is in use in numerious locations. Here is the link followed by the article:
https://en.wikipedia.org/wiki/Copper_extraction_techniques
Copper extraction techniques
From Wikipedia, the free encyclopedia
This article is about historical production methods. For modern methods, see
Flash smelting .
Copper extraction from its ores involves a series of processes. First the oremust usually be concentrated. Then it must be roasted to convertsulfides to oxides, which are smelted to produce matte. Finally, itundergoes various refining processes, the final one being electrolytic.The main ore in use today is chalcopyrite (CuFeS2), which accounts for about 50% of copper production.
For economic and environmental reasons, many of the byproducts of extraction are reclaimed. Sulfur dioxide gas, for example, is captured and turned into sulfuric acid — which is then used in the extraction process.
[edit]Concentration
Most copper ores contain only a small percentage of copper metal bound up within valuable ore minerals, with the remainder of the ore being unwanted rock or gangue minerals, typically silicate mineralsor oxide minerals for which there is often no value. The average gradeof copper ores in the 21st century is below 0.6% Cu, with a proportionof ore minerals being less than 2% of the total volume of the ore rock. Akey objective in the metallurgical treatment of any ore is theseparation of ore minerals from gangue minerals within the rock.
The first stage of any process within a metallurgical treatment circuit is comminution,where the rock particles are reduced in size such that ore particlescan be efficiently separated from gangue particles, thereafter followedby a process of physical liberation of the ore minerals from the rock.The process of liberation of copper ores depends upon whether they areoxide or sulfide ores.
For oxide ores, a hydrometallurgical liberation process is normallyundertaken, which uses the soluble nature of the ore minerals to theadvantage of the metallurgical treatment plant. For sulfide ores, bothsecondary (supergene) and primary (unweathered), froth flotation isutilised to physically separate ore from gangue. For special nativecopper bearing ore bodies or sections of ore bodies rich in supergennative copper, this mineral can be recovered by a simple gravitycircuit.
[edit]Oxide ores
Oxidised copper ore bodies may be treated via several processes, withhydrometallurgical processes used to treat oxide ores dominated bycopper carbonate minerals such as azurite and malachite, and other soluble minerals such as silicates like chrysocolla, or sulfates such as atacamite and so on.
Such oxide ores are usually leached by sulfuric acid, usually using a heap leach or dump leach process to liberate the copper minerals into a solution of sulfuric acid laden with copper sulfate in solution. The copper sulfate solution (the pregnant leach solution) is then stripped of copper via a solvent extraction and electrowinning (SX-EW)plant, with the barred sulfuric acid recycled back on to the heaps. Alternatively, the copper can be precipitated out of the pregnantsolution by contacting it with scrap iron; a process called cementation.Cement copper is normally less pure than SX_EW copper. Commonlysulfuric acid is used as a leachant for copper oxide, although it ispossible to use water, particularly for ores rich in ultra-solublesulfate minerals.[citation needed]
In general froth flotationis not used to concentrate copper oxide ores, as oxide minerals are notresponsive to the froth flotation chemicals or process (i.e.; they donot bind to the kerosene-based chemicals). Copper oxide ores haveoccasionally been treated via froth floatation via sulfidationof the oxide minerals with certain chemicals which react with the oxidemineral particles to produce a thin rime of sulfide (usuallychalcocite), which can then be activated by the froth flotation plant.
[edit]Secondary ores
Secondary sulfides – those formed by supergene secondary enrichment – are resistant (refractory)to sulfuric leaching. These ores are a mixture of copper carbonate,sulfate, phosphate, and oxide minerals and secondary sulfide minerals,dominantly chalcocite but other minerals such as digenite can be important in some deposits..
Supergene ores rich in sulfides may be concentrated using frothflotation. A typical concentrate of chalcocite can grade between 37% Cuto 40% Cu in sulfide, making them relatively cheap to smelt compared tochalcopyrite concentrates.
Some supergene sulfide deposits can be leached using a bacterial oxidationheap leach process to oxidize the sulfides to sulfuric acid, which alsoallows for simultaneous leaching with sulfuric acid to produce a copper sulfate solution. As with oxide ores, solvent extraction and electrowinning technologies are used to recover the copper from the pregnant leach solution.
Supergene sulfide ores rich in native copper minerals are refractoryto treatment with sulfuric acid leaching on all practicable time scales,and the dense metal particles do not react with froth flotation media.Typically, if native copper is a minor part of a supergene profile itwill not be recovered and will report to the tailings. When rich enough,native copper ore bodies may be treated to recover the contained coppervia a gravity separation circuit where the density of the metal is usedto liberate it from the lighter silicate minerals. Often, the nature ofthe gangue is important, as clay-rich native copper ores provedifficult to liberate.
[edit]Froth flotation
Froth flotation cells to concentrate copper and nickel sulfide minerals, Falconbridge, Ontario.
The modern frothflotation process was independently invented the early 1900s inAustralia by C.V Potter and around the same time by G. D. Delprat.[2]
At the current level of technology all primary sulfide ores of coppersulfides, and most concentrates of secondary copper sulfides (beingchalcocite), require smeltingto produce copper from the sulfide minerals. Some experimentalhydrometallurgical techniques to process chalcopyrite are beinginvestigated but as of 2009 are unproven outside of laboratories.[citation needed]Some vat leach or pressure leach processes exist to solubilisechalcocite concentrates and produce copper cathode from the resultingleachate solution, but this is a minor part of the market.
Carbonate concentrates are a relatively minor product produced fromcopper cementation plants, typically as the end-stage of a heap-leachoperation. Such carbonate concentrates can be treated by a SX-EW plantor smelted.
The copper ore is crushed and ground to a size such that anacceptably high degree of liberation has occurred between the coppersulfide ore minerals and the gangue minerals. The ore is then wet,suspended in a slurry, and mixed with xanthatereagents (or other reagents of the thiol class), which react with the copper sulfide mineral particle to make it hydrophobic on its surface. (Besides xanthates, dithiophosphates and thionocarbamates are commonly used).
The treated ore is introduced to a water-filled aeration tank containing surfactant such as methylisobutyl carbinol(MIBC) which is an alcohol. Air is constantly forced through the slurryand the air bubbles attach to the hydrophobic copper sulfide particles,which are conducted to the surface, where they form a froth and areskimmed off. These skimmings are generally subjected to acleaner-scavenger cell to remove excess silicates and to remove othersulfide minerals which can deleteriously impact the concentrate quality(typically, galena), and the final concentrate sent for smelting.
The rock which has not floated off in the floatation cell is either discarded as tailings, or processed to extract other elements or other ore minerals such as galena, sphalerite if they exist.
To improve the process efficiency, lime is used to raise the pH of the water bath, causing the collector to ionize more and to preferentially bond to chalcopyrite (CuFeS2) and avoid the pyrite (FeS2). Iron exists in both primary zone minerals.
Copper ores containing chalcopyrite can be concentrated to produce aconcentrate with between 20% and 30% copper-in-concentrate (usually27–29% Cu); the remainder of the concentrate is iron and sulfur in thechalcopyrite, and unwanted impurities such as silicate gangue mineralsor other sulfide minerals, typically minor amounts of pyrite, sphalerite or galena.
Chalcocite concentrates typically grade between 37% and 40% copper-in-concentrate, as chalcocite has no iron within the mineral.
[edit]Roasting
In the roaster, the copper concentrate is partially oxidised to produce calcine and sulfur dioxide gas. The stoichiometry of the reaction which takes place is:
2CuFeS2(s) + 3O2(g) ? 2FeO(s) + 2CuS(s) + 2SO2(g)
As of 2005, roasting is no longer common in copper concentratetreatment. Direct smelting using the following smelting technologies; flash smelting, Noranda, ISASmelt, Mitsubishi or El Teniente furnace are now used.
[edit]Smelting
The calcine is then mixed with silica and coke and smelted at 1200 °C (in an exothermic reaction) to form a liquid called copper matte.This temperature allows reactions to proceed rapidly, and allow thematte and slag to melt, so they can be tapped out of the furnace. Incopper recycling, this is the point where scrap copper is introduced.
The slag is discarded or reprocessed to recover any remaining copper.
[edit]Conversion to blister
The matte, which is produced in the smelter, contains around 70%copper primarily as copper sulfide as well as iron sulfide. The sulfuris removed at high temperature as sulfur dioxide by blowing air throughmolten matte:
In a parallel reaction the iron sulfide is converted to slag:
The end product is (about) 98% pure copper known as blisterbecause of the broken surface created by the escape of sulfur dioxidegas as the copper ingots are cast. By-products generated in the processare sulfur dioxide and slag.
[edit]Reduction
The blistered copper is put into an anode furnace (a furnace that uses the blister copper as anode) to get rid of most of the remaining oxygen. This is done by blowing natural gasthrough the molten copper oxide. When this flame burns green,indicating the copper oxidation spectrum, the oxygen has mostly beenburned off. This creates copper at about 99% pure. The anodes producedfrom this are fed to the electrorefinery.
[edit]Electrorefining
Apparatus for electrolytic refining of copper
The copper is refined by electrolysis. The anodes cast from processed blister copper are placed into an aqueous solution of 3–4% copper sulfate and 10–16% sulfuric acid.Cathodes are thin rolled sheets of highly pure copper. A potential ofonly 0.2–0.4 volts is required for the process to commence. At theanode, copper and less noble metals dissolve. More noble metals such assilver and gold as well as selenium and telluriumsettle to the bottom of the cell as anode slime, which forms a saleablebyproduct. Copper(II) ions migrate through the electrolyte to thecathode. At the cathode, copper metal plates out but less nobleconstituents such as arsenic and zinc remain in solution.[1] The reactions are:
At the anode: Cu(s) ? Cu2+(aq) + 2e–
At the cathode: Cu2+(aq) + 2e– ? Cu(s)
[edit]Concentrate and copper marketing
Copper concentrates produced by mines are sold to smelters andrefiners who treat the ore and refine the copper and charge for thisservice via treatment charges (TC's) and refining charges (RC's). TheTC's are charged in US$ per tonne of concentrate treated and RC's arecharged in cents per pound treated, denominated in US dollars, withbenchmark prices set annually by major Japanese smelters. The customerin this case can be a smelter, who on-sells blister copper ingots to arefiner, or a smelter-refiner which is vertically integrated.
The typical contract for a miner is denominated against the LondonMetal Exchange price, minus the TC-RCs and any applicable penalties orcredits. Penalties may be assessed against copper concentrates accordingto the level of deleterious elements such as arsenic, bismuth, lead or tungsten. Because a large portion of copper sulfide ore bodies contain silver or gold in appreciable amounts, a credit can be paid to the miner for these metals if their concentration within the concentrateis above a certain amount. Usually the refiner or smelter charges theminer a fee based on the concentration; a typical contract will say acredit is due for every ounce of the metal in concentrate above acertain concentration; below that if it is recovered the smelter willkeep the metal and sell it to defray costs.
Copper concentrate is traded either via spot contracts or under longterm contracts as an intermediate product in its own right. Often thesmelter sells the copper metal itself on behalf of the miner. The mineris paid the price at the time that the smelter-refiner makes the sale,not at the price on the date of delivery of the concentrate. Under aQuotational Pricing system, the price is agreed to be at a fixed date inthe future, typically 90 days from time of delivery to the smelter.
A-grade copper cathodeis of 99.999% copper in sheets that are 1 cm thick, and approximately 1meter square weighing approximately 200 pounds. It is a true commodity, deliverable to and tradeable upon the metal exchanges in New York (COMEX), London (London Metals Exchange) and Shanghai(Shanghai Futures Exchange). Often copper cathode is traded upon theexchanges indirectly via warrants, options, or swap contracts such thatthe majority of copper is traded upon the LME/COMEX/SFE but delivery isachieved indirectly and at remove from the physical warehousesthemselves.
The chemical specification for electrolytic grade copper is ASTM B 115-00 (a standard that specifies the purity and maximum electrical resistivity of the product).
[edit]See also
[edit]External links