A Review on Novel Techniques for Chalcopyrite Ore Processing

Chalcopyrite ores are usually processed by means of hydrometallurg ical or pyrometallurgical processes, but due to environmental aspects and the possibility of increased exp loitation of mixed and lower grade ores and relat ively small isolated deposits, there has been a worldwide upsurge of interest in the hydrometallurg ical processes of this ore as compared to pyrometallurgy. The different concentrates obtained through differential flotation in pyrometallu rgy are usually of poor quality with low metal recovery. This further makes pyrometallurgical processing of chalcopyrite very difficult and costly and rendered them difficult to commercialize. As a result, the metal value is preferab ly extracted directly from low grade ores through hydrometallurg ical process. A detailed review of chalcopyrite deposits, production and consumption, min ing, ore processing, steps involved in the pyrometallurgical and hydrometallurgical processing of copper as well as the dissolution kinetics and microbial studies of chalcopyrite ore were discussed.


Introduction
Chalcopyrite is derived fro m the Greek words "chalkos", copper and "pyrites" strike fire and it is also known as copper pyrite (Szy manowski, 1996). It is a brassy to golden yello w colo r mineral and was first discovered in Po lk Country in 1847. The first mine opened in 1850 and first smelter was opened in 1885 and was operated until 1987 wh en it was closed du e to u n fav ou rab le econ o mics (Rotuska and Chimjeleniki, 2008). Chalcopyrite (CuFeS 2 ) is the most common copper bearing mineral on earth (Nesse, 2000). Chalcopyrite is of primary importance and occurs in igneous and metamorphic rock and in metalliferous veins (McGraw-Hill, 1998). It contains many minerals including copper, zinc, sulfur and iron. A ll were produced at different times. At first, copper was the most important product and sulfur was a poisonous waste product. By the 1980's, 70% of production value came fro m the production of sulfuric acid (Hyvarinen et al. 2003). It is not on ly the most abundant of copper su lfid es, but also the most stab le minerals because of its structural configuration (face-centered tetragonal lattice). It is also the most refractory to hydrometallurg ical processing (Haver and Wang, 1971). Chalcopyrite is the p rimary mineral wh ich by alteration and successive enrich with copper produces the series, starting with chalcopyrite and going through bornites (Cu 5 FeS), covellite (CuS), chalcocite (Cu 2 S) and ending rarely as native copper (Brantley, 2003).
At present, there are basically two main methods emp loyed worldwide in order to process chalcopyrite for metal production. The most important one is the conventional -pyrometallurgy method: comprised numerous types of shaft and flash technologies, which consists of crushing, grinding, flotation, smelting, refining and electro-refining. This method is applied to sulphide flotation concentrates rather than ores and is economically feasible for copper rich feed for large scale operations. A second method is hydrometallurgy and this method is applied to the rest of the world's primary copper production. Hydrometallu rgy consists of crushing, leaching (non-oxidation leaching, at mospheric leaching and pressure leaching), solvent extraction and electrowinning. Hydrometallu rgical processing can be effectively applied to oxidized ores containing CuO, Cu 2 O, carbonates and some silicates, as well as sulfide ores with chalcopyrite as a predominant copper mineral. Hydro metallurgical methods are used in countries having readily availab le deposits with low copper content with sulphur of oxidized form at the same time (USA, Chile, Australia and Peru) (Majima et al. 1985). Hydro metallurg ical processing of chalcopyrite concentrates has received considerable attention over the last three decades (Haver and Wang, 1971).
Approximately 70% o f the world's copper reserves are contained in the mineral chalcopyrite (Tho mas, 2009). Thus, chalcopyrite, the most common ore of copper, occurs and widely distributed in metallic veins associated with pyrite (FeS 2 ), phyrrhotite (Fe 7 S 8 ), bornites (Cu 5 FeS), chalcocite (Cu 2 S), sphalerite (ZnS), galena (PbS), calcite (CaCO 3 ), siderite (FeCO 3 ), dolo mite (CaCO 3 •MgCO 3 ) etc. Many carry gold or silver and became an ore of those metals. Often in subordinate amount with large bodies of pyrite (FeS 2 ), making them serve as low-grade copper ores. Usually massive often making up golden sulfide mixtu re crystals over sphalerite surface (Szy manowski, 1996). Natural chalcopyrite has no solid solution series with any other sulfide minerals. There is limited substitution of Zn with Cu despite chalcopyrite having the same crystal structure as sphalerite (ZnS). However, it is often contaminated by a variety of other trace elements such as Co, Ni, Mn, Zn and Sn substituting for copper and Fe, Se and As substitute for sulfur, and trace amount of Ag, Au, Pt, Pd, V, Cr, In, Al and Sb are reported. It is most likely that many of these elements are present in finely inter-g rown mineral within the chalcopyrite (Hershel, 2011). A large portion of the copper produced in the world is obtained by the smelting of chalcopyrite and ores associated with it (Yin et al. 1995).

Global Chalcopyrite Deposit
Chalcopyrite deposits across the globe are as represented in Fig. 1. It is a fairly co mmon mineral and therefore, only the finest of localities will be mentioned.
Large, well shaped crystals occur in nu merous places in Cornwell (England) as well as Akita, Ugo and Tochigi prefectures, Japan. Many fine crystals occur in the northern section of Mexico. Certain occurrences are La Bufa, Chihuahua, Charcas, San Lu is Potosi and the Noche Buena mine, near Mazapil, Zacatecas Mexico (Hershel, 2011). The French Greek mine in Chester Co. Pennyslvania has produced huge crystal, many distorted and highly tarn ished. Large amount of chalcopyrite occurs with sphalerite (ZnS), galena (PbS) and marcasite in the Joplin District of Missouri Okhlaho ma and Kansas, USA.
Chalcopyrite is widely distributed in the United States but usually in connection with other copper minerals in equal or greater amount found at Butte, Montana, Bingham, Utah, various districts in california, colorado, Arizona (Nevada, 2011). Many fine crystals occur in the northern section; certain occurrences are La Bufa, Ch ihuahua, Charcas -San Luis Potosi, and the Noche Buena mine near Mazapil, Zacatecas the sudburdy Canada. Chalcopyrite is also found in content metamorphic deposit in limestone (Bisbee, Arizona). Giant deposit crystals were found in Freirina, Northern Chile and also vast deposits are found in Northern Mexico (Hershel, 2011).
Chalcopyrite is the copper ore deposit of Falu m, Sweden of Namagaland in South Africa. However, vast crystals or deposits occur in Ishiagu, Ebonyi State; South Eastern region of Nigeria (West Africa). High great chalcopyrite deposit can also be found in Baluba, East of Lusaka (Zambia).
A well shaped chalcopyrite crystal occurs in many places such as Akita, Ugo and Tochigi prefectures Japan (Chuck and Virg inia, 2011). Large, well shaped crystals of chalcopyrite also occur in numerous places in Falu m (Sweden), Rio Tinto (Spain), Mansfeld (Germany), Lu kku laisvaara Ultrabasic Massif, Olanga (Ou lanka) River, Ounlanka Plutonic comp lex and Karelia Republic (Northern Region, Russia).

Chalcopyri te Ore Producti on
The sulfide ore minerals including chalcopyrite (CuFeS 2 ), sphalerite (ZnS), galena (PbS) prov ide the major sources of the world's base metals (Cu, Zn, Pb, respectively), whereas pyrite is virtually ubiquitous as a metalliferous mineral in sulfide ore deposits (Crang and Vanghan, 1994). The first step in recovering metal fro m their mineral is that of finding ore-bodies in which metal sulfides are present in a sufficient quantity and as a result of o xidation of the sulfide mineral in nature weathering underground. The induced polarization e xploration technique involves applying a series of current pulses to two electrodes inserted into ground and analyzing the induced voltage at two different electrodes also inserted into the ground (Jones, 1999). Valuable minerals are thus extracted fro m the ore by means of flotation separation, extractive metallurgy or leaching.

Flotation Separat ion
Valuable mineral in an ore such as chalcopyrite ore can be separated from each other and fro m wo rthless gauge minerals by the froth flotation process. The process was developed in Australia at the start of the 20 th Century to treat the primary sulfidic silver/lead/zinc ore at Broken Hill (Woods and Doyle, 2000). Many approaches were pursued to solve the sulfide problem at Broken Hill before selective flotation was developed. The successful technology involve first crushing the ore, typically to a part icle size o f about 5 to 50 micro meter to liberate separate grains of the various valuable mineral and worth less gauge components. Then the particle is pulped with water and the surface of the mineral of the interest selectively made hydrophobic through the addition of organic specie which is term collector. Following this procedure, a stream of air bubbles is passed through the pulp; the bubbles attach to levitate the hydrophobic particles and are collected in a froth layer that disengages from the flotation cell by flowing over the weir of the cell. A frother such as a long chain alky l alcohol is added to create a stable froth layer in the cell. The collector used at Broken Hill in the early days was eucalyptus oil derived fro m the leaves of the ubiquitous Australia "gu m" tree. Following the success at Broken Hill, mining companies throughout the world rapidly adopted the flotation process (Young et al. 2003). Flotation also used to split copper and nickel sulfides and separate them fro m iron sulfides and gangue minerals. Cobalt appears in the nickel concentration and the cobalt is subsequetly recovered. Flotation has developed from the treatment of simple ores to the ever more co mplex ones that are being fund today. Thus, for examp le, the three metals in copper/lead/zinc o re are floated into three concentrates, each containing one of the metals (Pletcher et al. 1993).

Extract ive Metallurgy
Metal sulfide flotation concentrates occur in a number of ways. These include using pyrometallurgy or smelting at high temperature. In this process, the sulfur in the metal sulfide is o xidized with air or o xygen to sulfur dio xide and mo lten matte is produced.
Flotation concentrates can also be processed using hydrometallu rgy in which the metal sulfide is dissolved (leached) into an aqueous solution (Bergy and Yianatos, 2001). Most oxide of copper minerals dissolves readily in sulfuric acid so that leaching is reasonably straight forward. A concentrated, pure copper sulfate solution suitable for electrowinning is produced fro m the initial leach solution by selectively transferring the copper ion to an organic phase by a process known as solvent extract ion and returning them again to an aqueous phase (Young et al. 2003). Co mplexing agents are dissolved in an organic solvent at low vapour pressure kerosene and this phase is intimately dispersed within the aqueous leach solution in a mixer-settler. The copper selectively co mplexes with the reagent and is transferred into the organic phase. The copper replace hydrogen ion in the co mp lex and hydrogen ions are subsequently transferred to the aqueous phase. The two phases are allowed to separate in the settler section and then the aqueous acid solution termed the "raffinate" is recycled to ore leach ing. The loaded organic phase is sent to a second mixer-settler where it is reacted with a strong aqueous sulfuric acid solution. Here, the copper is exchanged for hydrogen ions and transferred into the second aqueous phase from wh ich the metal is efficiently recovered by electrolysis. The overall process of dissolution, solvent extraction and electrowinning is known as SX-EW. Fig. 3 shows a typical flo w diagram of LX/SX/ EW.
The commercial interest in the solvent extraction of copper from chalcopyrite began in the North American and was in itially the result of leach ing studies of low grade oxide minerals that were not available for upgrade and concentration by flotation technique. Their loss to waste dump represented poor management of natural resources and importantly a loss of potential revenue that the mining companies in the USA could not afford because of their labour cost and overall low mineralogical grades relat ive to other copper producing countries. With copper being an international traded co mmod ity, the concept of p roducing the metal at lowest possible cost was important, otherwise, the copper industry in the US would be at significant disadvantages relative to other nations (Seward, 2001).

Leach ing
Leaching is a heterogeneous reaction that takes place at the interface between a solid and liquid phase and sometimes a gaseous phase. At the boundary between the two phases, a diffusion layer is formed. The d issolution of mineral ore takes place through the following stages: (1) diffusion of reactant through the diffusion layer, (2) adsorption of the reactant on the solid, (3) chemical reaction between the reactant and the solid, (4) desorption of the product from the solid and (5) diffusion of the product through the diffusion layer. Any of these stages (1) -(5) may be the rate controlling step depending on its relative speed to the others as represented in Fig. 4.  (Crest, 2000) These processes are normally dominated by stage 1 and 5, both of which involved diffusion. The rate of chemical reaction at the interface is much faster than the rate of diffusion of reactant to the interface. The following equations describe the relationship between dissolution and leaching time (t), K is the rate constant. (1 ) (1 ) Kt Chemically controlled process is the opposite of the above mechanism type since the rate of chemical reaction is much slower than the rate of diffusion given by equation (2).
These processes strongly depend on temperature since the rate of chemical reaction increases with temperature, but independent of the agitation speed since diffusion plays an insignificant ro le in the process.
Mixed kinetic process is a hybrid of the two types as the chemical and diffusion rate will be of the same magnitude. Equation (3) summarizes this mechanism where "b" is a direct function of surface reaction.
For pract ical purposes, b is always equal to 1 and α is the fraction of the ore d issolved at a given leaching t ime (Crest, 2000).

Chalcopyri te Ore Consumption
Approximately 70% o f the world's copper reserves are contained in the mineral chalcopyrite. Currently, copper is extracted fro m high-grade chalcopyrite through smelting a high temperature process with undesirable environ mental side effects (Thomas, 2009) The world's production (supply) and consumption (demand) of chalcopyrite (copper) have increased dramat ically in the past 25 years. As large developing countries have entered the global market, demand for mineral co mmodities has increased. In the last 20 years, the Andean region of South America has emerged as the world most productive copper region. In 2007, about 45% of the world 's copper was produced fro m the Andes Mountain (USA ). The United State produced 8%, virtually all copper produced in the United State comes from Arizona, Utah, Mexico, Nevada or Montana in decreasing order of production.
The risk of d istribution to the global copper supply is considered to be low because copper production is globally dispersed and is not limited to a single country or region due to its importance in construction and power transmission. However, the impact of any copper supply distribution would be high.
(2) economy in China contributed to a tripling of its annual refined copper consumption during the 8 years fro m 1999 to 2007. The global consumption of copper fro m 1980 to 2008 is shown in Fig. 5.
Copper is one of the most widely recycled of all metals and approximately one-third o f all copper consumed world wide is recycled. Recycle copper and its alloy can be re-melted and used directly or further reprocessed to refined copper without losing any of the metals' chemical and physical properties (Dixon and Dreisinger, 2003).

Market Potentials and Industrial Applicati ons of Copper
Copper was one of the first metals ever ext racted and used by humans and it has made vital contributions to sustaining and improving society since the dawn of civilizat ion. As man learned to fashion his weapon from iron and steel, copper began to assume another roles. Being a durable metal and possession of great beauty, it is used extensively for household utensils, water p ipe, marine uses and other purposes that required resistance to corrosion. Copper is easily stretched, molded and shaped. It is resistance to corrosion and conducts heat and electric ity efficiently. The unusual ability of this mineral to conduct electric current account for its greatest use today (McGraw-Hill, 1998). As a result, copper was important to early human and continue to be a material of choice for a variety of domestic, industrial and high-technology applications today (USGS, 2009).
Copper producers all around the world are facing continuously increase demands, both economically and environmentally. During the last decade, the production chain of copper fro m chalcopyrite has shifted mo re and more into direction where copper is smelted by custom smelters far away fro m copper mines (Jukka and Likka, 2005).
The first commercial plant for chalcopyrite treat ment started at the Rancher's Bagdad Mine in 1968 with a production capacity of 6,000 tons per annum. The first large plants was bought into operation in Zambia to produce 100,000 tons per annum in 1973 and by 1980 new plants were on stream in the USA, Mexico and Chile to produce a total production capacity of appro ximately 180,000 tons per annum. Today, there is a total world market potential of 20.4 million tons which costs at 110 US dollar per ton (Seward, 2001).

Mining of Chalcopyrite
Chalcopyrite is a co mmon mineral and is found in almost all sulfide deposit and is often disseminated through igneous rock (Haver and Wang, 1971). For lo wer grade deposit located near the surface, the open -pit method is the most practical for the mining of large tonnages of material. Large t rack mounted drill of ore is prepared for b lasting and the broken ore is hauled to the ore d ressing plant by truck (at up to 150 tons per load) o r conveyor. In underground mining, vertical shaft are sunk well over 1,000 met re (3,300 ft) below the surface and channels are extended to the ore body. The ore, broken by drilling and blasting is hoisted through the shaft and conveyed to the processing plant. In some cases, primary crushing takes place underground and in others, a ramp and trucks carry ore to the surface (McGraw-Hill, 1998).

Factors Affecting the Mining of Chalcopyrite
Factors which may contribute to the decision to mine or not to mine chalcopyrite mineral resources include the following: (a) The availability of the rock or o re is obviously necessary: When min ing begins, the richest sources of ore are mined first and lower grade ore is mined later. So, as time passes, the cost of mining tend to goes up and this was the case with iron mining and phosphate in Tennessee.
(b) The availability of alternative sources of materials also affects decision to mine: The discovery of vast amount of bird guano in South America in the late 19 th Century destroyed the Saltpeter industry in Tennessee.
(c) Change of technology affects mining decisions: The ma king of tools fro m chart stopped when iron tools were introduced. The quarrying of dimension limestone practically stopped when techniques of making and using cement improved.
(d) Govern mental policy also affects decision of mining: Saltpeter min ing flourished Tennessee in early 19 th Century as a result of large-scale US govern ment purchase of saltpeter to make gunpowder for the war of 1812.
(e) Pollution either in the min ing or fro m the use of the fin ished product can affect min ing decisions, either by increasing the cost of production or by increasing the demand for the product (Rotuska and Chimjelen iki, 2008).

Chalcopyri te Ore Processing
The first step in the chalcopyrite processing is to liberate the copper minerals and remove waste constituents such as alu mina, limestone, pyrite and silica so that the copper and non-ferrous mineral values are concentrated into a product containing between 20 to 30 percent copper. The second step involves either smelting or leaching to remove a large proportion of impurity particularly iron and in the case of sulfides ore, sulphur. The final step, refining, removes the last traces of the impurity elements and produces a copper product of 99.99 percent purity (McGraw-Hill Encyclopedia, 1998).
Once the chalcopyrite concentrate containing copper and other metals of value (such as gold, silver) has been produced, the next step is to remove impurity element. In older processes, the concentrate containing between 56 -10 percent water, is first roasted in a cylindrical, refractory lined furnace of either the hearth or fluid ized bed type. As concentrate is fed into the roaster, it is heated by a stream of hot air to about 590℃. Vo latile impu rit ies such as arsenic, mercury and some of the sulphur are driven off, the sulphur being removed as sulphur dioxide (SO 2 ). What remains is an oxidized product containing a percentage of sulphur that is sufficiently low fo r s melt ing. Th is is t raditionally done in a reverberatory o r electric furnace into wh ich concentrate is fed along with a suitable amount of flu x. These are heated by combusted fuel or electrical current to a temperature of 1230℃ -1300℃, producing an artificial copper iron sulfide that settles in a mo lten pool at the bottom of the furnace (McGraw-Hill, 1998).
In the roaster, the copper concentrate (chalcopyrite) is partially o xid ized to produce alkaline (Cu 2 S) and sulphur dio xide (SO 2 ) gas. The chalcopyrite ore is heated strongly with silicon -d io xide (silica) and air or o xygen in the furnace or series of furnaces. The copper (II) ion in the chalcopyrite is reduced to copper (I) sulfide wh ich is reduced further to copper metal in the final stages. The iron in the chalcopyrite ends up converted into an iron (II) silicate slag which is removed. Most of the sulfur in the chalcopyrite turns to sulfur dio xide gas. Th is is used to make sulfuric acid via the contact process (copper extraction and purificat ion). Overall equations for these series of steps are: The copper (I) sulfide is converted to copper with a final blast of air.
As of 2005, roasting is no longer common in chalcopyrite concentrate treatment. Thus, direct smelting using the following smelting technologies: flash smelting, Noronda, USA s melt ing, Mitsubishi or EL Temento furnace are in use till date.

Smelting Process (Pyrometallurgy)
Pyro metallurgical practice typically involves smelt ing converting, anode casting and electro-refin ing of the anodes to high purity copper metal. The s melt ing and refining processes used well established technologies are energy efficient and have high metal recoveries including those of gold and silver (Yin et al. 1995). Th is begin with a dry concentrate containing less than one percent water, which along with flu x is contacted in a furnace by a blast of oxygen or oxygen enriched air (McGraw-Hill Encyclopedia, 1998). Pyro metallurgical extraction involves heating the mineral cake in a blast furnace; o xygen pressure and temperature are carefully controlled. The first stage involve the separation of copper and iron ore (Equation 7), followed by the addition of silica (SiO 2 ) to the blast furnace to convert iron (II) o xide to a less dense liquid layer of slag, iron (III) silicate which is poured off.
2 CuFeS 2 + 4O 2 Cu 2 S + 2FeO + 2SO 2 (g) FeO (l) + SiO 2 (s) FeSiO 3 The calcine is then mixed with silica and limestone and smelted at 1200 o C (in an exothermic reaction) to fo rm a liquid called copper matte. This temperature allows reactions to proceed rapidly, and allow the matte and slag to melt, so that they can be tapped out of the furnace. During smelt ing, several reactions occur. For examp le, iron o xide and sulphide are converted to slag which is floated off the copper matte: In a parallel react ion, the iron sulphide is converted to slag: The slag is discarded or reprocessed to recover any remain ing copper. In the 3 rd stage of ext raction, copper (I) sulphide is reduced to copper metal upon reaction with oxygen air: Depending on the co mposition of the concentrate, it is possible to carry out smelting autogenously. That is, without the use of auxiliary fuel as is required in reverberatory or electric arc s melt ing. In addition to reducing the consumption of fuel, the new processes produce relatively low volu mes of gas which being high in sulfur dio xide is usually carried out in separate furnace to ensure that the final smelter product reaches the level of 99.5 percent copper that is required for electrolytic refin ing. At this point, the copper is cast into anode, the shape and weight of which are dictated by the particular electrolyt ic refining (McGraw-Hill, 1998).

Leach ing Process (Hydrometallurgy)
Hydrometallu rgy is applied to the rest of the world's primary copper production, objected main ly on o xide and/or low grade copper ore due to significantly lower operating cost (Dresher, 2001). Treat ment chain in hydrometallurgy processes are usually consisted of crushing, leaching (non-oxidative leaching, solvent ext raction and electrowinning). Hydro metallurgical processing can be effectively applied to o xidized ores containing CuO, Cu 2 O, carbonate and some silicates and rarely for sulphide ore with chalcocite and covellite as predominant copper mineral (King, 2007;Stevanovic et al. 2009).
Beginning of solvent extraction process development objected on metal extraction fro m leach solutions, date from the 60s of last century. Beforehand, solvent extraction processes were used in analytical chemical assaying (Habashi, 2007). Hydrometallurg ical methods are used in countries having readily available deposit with low copper content and with surplus of o xid ized forms at the same time (USA, Ch ile, Australia and Peru). The most important development in copper hydrometallurgy with respect to the growing number of its application as well as for its future potential has been solvent extraction process. It becomes the achievement which revolutionized copper production all over the world and enabled to introduce hydrometallurgy for industrial scale (Stevanovic et al. 2009). Occasionally, it is adopted in preference to smelting or pyrometallurgy and is carried out at lower temperatures and thus eliminates the generation of sulfur dio xide. There are, however, effluents and residues that must be treated in o rder to p rotect environment. In the hydrometallurgical processes, the ore or concentrate (chalcopyrite) is brought into close contact with a leach solution (frequently sulfuric acid) that dissolves the copper and leaves a residue of gangue (and frequently precious metals). Various system, some quite comp lex are used to bring copper minerals into contact with the leach solution, wash and filter the residue and finally purify the solution to remove dissolved iron and other impurities (McGraw-Hill, 1998). So me experimental hydrometallu rgic al techniques to process chalcopyrite are being investigated, but as of 2009 are unproven outside the laboratories. So me rod leach or pressure leach process exist to solubilise chalcocite concentrate and produce copper cathode fro m the resulting leach solution, but this is a minor part of the ma rket.

Ch loride Leach ing
Only ch loride of metal in a high valence state such as ferric or cupric will leach metal fro m their sulfides because oxidation is necessary. Of the nu merous chloride routes, ferric chloride (FeCl 3 ) leach ing of chalcopyrite concentrates which was init iated by the U.S. Bureau of M ines, Reno Metallurgy Research Center in 1969 received significant attention (Philips, 1976).

Intec Copper Process
The intec copper process is a proven, patented hydrometallu rgical process for the extraction of pure copper and precious metal fro m sulphide concentrates. The process is based on the electrolytic deposition at the cathode of LM E (London Metal Exchange). Grade A purity copper fro m a purified sodium chloride, sodium bro mide electrolyte during electrowinning; the mixed halide species BrCl 2 is generated, characterized when it is re-circu lated to treat incoming concentrate feed (Crest, 2000).

Description of Intec Copper Process
The patented intec copper process was developed for the recovery at LME Grade A purity fro m sulfide concentrates. Essentially, the intec copper process consists of the three sequential circuits: leach ing, purification and electrowinning. A simp le flow diagram for the intec copper process is shown in Fig. 6.

The Cuprex Process
The cuprex process leaches chalcopyrite concentrate at atmospheric pressure with ferric chloride solution in two stages. The pregnant liquor containing copper, iron and minor amount of impurities mainly zinc, lead and silver is sent to the extraction stage of the SX circuit where it is contacted at ambient temperature with a kerosene solution DS5443. The copper, selectively transferred to the o rganic phase is ext racted in three stages. The aqueous solution of copper chloride is then sent to the electrolysis section as catholyte, which is fed to the cathode compartment of an electrowinning cell to produce granular copper. Electrowinning of copper fro m chloride solution take place in a diaphragm cell where the cathode and anode compart ment are separated by a rein forced cation-selective ion-exchange memb rane. Ch lorides generated at the anode is recovered and used to deoxid ize the cuprous chloride generated in the catholyte during electrowinning.

Pressure Sulfate Leaching
Thermodynamically favorable at an elevated pressure, the use of high pressure in chalcopyrite concentrate leaching has led to a reliab le and cost co mpetitive p rocess option. A strong resurgence of interest in the pressure sulfate leaching of chalcopyrite concentrates occurred after developments in construction of materials, more efficient mills for fine o r ult rafine grind ing of sulfides and successful implementation of autoclave technology for zinc and refractory metals (Jones, 1999). Based on the literature data for sulfide leaching especially chalcopyrite in an o xid izing acidic mediu m and the characterization of the leach liquor and residues obtained, the following chemical reactions were chosen to study CuFeS 2 , H 2 SO 4 , NaNO 3  The CESL process is a divergent approach to low pressure oxidation in which a high proportion of sulfide (sulphur) remain in the elemental form in leach residue (McCunn et al. 2004). This process also employ a chloride enhanced oxidative pressure leach in a controlled amount of acid designed to convert the copper to a basic copper sulfate salt, the iron to haematite and sulfur to elemental sulfur. The flo w diagram of a CESL process is shown in Fig. 7.

Dynatec Process
The dynatec process involves oxidative leaching of chalcopyrite concentrate at 150 o C using coal at a modest dosage (25 kg/t of concentrate) as an effective anti-agglomerant (Co llins and Kofluk, 1998). Su lfide oxidation chemistry is similar to the CESL p rocess. A high extraction of copper (98%) is achieved by either recycling the unleached sulfide to the leach after the floating and removal of elemental sulfur (melt ing and filtration) or pre-treating the concentrate with a fine grinding (+90 -25µm).

Total Pressure Oxidation
The total pressure oxidation uses water as the leach med iu m and converts most of the sulfide sulfur to copper sulfate and sulfuric acid (King et al. 1994). Reground concentrates is slurried in acid ic recycle solution and pumped into the first compart ment of an autoclave operated at 210 -220 o C, with sparked o xygen to maintain 700 kPa of over pressure. Basic iron sulfate (hydroniumjarosite) is a significant co-product which will collect silver and other monovalent cation.   (Dresher, 2004). This was constructed in a stirred reactor containing dilute sulfuric acid into which air is blo wn, hydrothermophilic microorganis m which operate at a temperature between 60 o C and 90 o C are used. Leaching of chalcopyrite concentrate is complete within 10 days (Dresher, 2004 Conducted in a series of counter current reactors, the thermophilic microorganisms are used at temperature of 25 -55 o C, p H 0.5 -2.5 is maintained within the reactors. Carbon dio xide is obtained from ambient air, nutrients are added to the leach liquor and retention time is about 30 days. The plant employs moderate thermophilic to o xid ize the sulfides followed by conventional SX-EW to recover the contained copper, which achieved recovery rate of 96.4 % and a residency period of six days (Dresher, 2004)

Dissolution Kinetic Studies on Chalcopyrite Ores
Various reported works on the dissolution kinetics and solvent extraction of copper fro m chalcopyrite o res are discussed thus. It is important to note that limited data in this area of research fro m Nigeria o rig in has been documented (Olubamb i et al. 2006). These authors did not address some kinetic parameters such as activation energy (Ea), reaction order, Arrhenius constant etc. for the better prediction of the dissolution mechanism that could be used in the selective and purification of copper fro m the ores by solvent extraction technique.
A study reported by Lu (1982) studied the effect of chloride ions on the dissolution of the mineral in oxygenated acid solution and they concluded that the presence of sodium ch loride (NaCl) in the leaching solution promoted the formation of porous sulphur layer, favouring the diffusion of the leaching reagents through the film product of the reaction continuation in the surface of the mineral. Winand (1991) also studied the addition of sodium chloride (NaCl) in the copper sulphide leaching that attributed to the formation o f copper ch loride co mplex ion as being a decisive factor for increasing the leaching rate for increasing the copper solubility in the system Cl -/Cu (II) and/ or Cu (I). He suggested that NaCl act on the elemental sulphur layer and also on the solubility of copper comp lexes in the reaction system with aim to imp roving the copper extraction fro m the sulfide mineral in a relatively short time with low operation cost, taking into consideration the influence of a cationic surfactant.
Vania-Mori et al. (2009) studied the advantages of copper sulphide CTA B (Cetyl-three-ethyl ammoniu m bromide) on the electro-leaching of copper sulfide (chalcopyrite) flotation concentrate. The result of the electro-leach ing process shared that extraction of copper in the presence of surfactant cation CTAB had an increased extraction co mpared to the results of the one without CTAB. The test shows evidence that the electro-leaching p rocess makes possible the production of chlo rate ion that dissolves the copper sulphides releasing copper ion to solution, which are simultaneously reduced in the cathode surface.
The first stage of the proposed reaction mechanism wh ich is the sulfuric acid leaching is very slow and was enhanced by the addition of hydrogen peroxide. When the very reactive sulfide radical fro m H 2 O 2 co mes in contact with the highly reactive sulfide mineral, elemental sulfur is formed.
and then the elemental sulphur is later o xid ized to sulphate ions.
When copper or zinc react with sulfate, copper sulfate and zinc sulfate are formed, wh ich are very soluble and dissociated in aqueous solutions: The slow copper dissolution rate fro m chalcopyrite has been attributed to the format ion of a passivating layer on the mineral surface (Co rdoba et al. 2009). Based on this, several works in terms of theories and hypothesis have been proposed. Burkin (1969) suggested that the leaching of chalcopyrite with Fe 3+ favours the formation of a diffusion film over its surface made of a semi-conductor bimetallic sulfide with chemical and structural properties different fro m chalcopyrite. Those intermediate products that proceed fro m the solid state transformat ion favour the solubilization of cations fro m the crystal lattice at d ifferent rates. The models assume that the chemical reaction does not take place on the interface but across the thickness of the reaction phase. The proposal by Ammou-Chokrou m et al. (1977) showed that the copper dissolution rate is controlled by the formation and evolution of a compact diffusion layer of a copper polysulfide (less reactive) and with less iron content than the original chalcopyrite. The th ickness of that layer would be the result of two opposite reactions viz; the formation of a copper passive layer because of the slower diffusion of copper than iron in solid state obeying a parabolic law and the d issolution of the passivating layer according to a linear law in which a porous film of elemental sulfur is formed. According to Abraitis et al. (2004) on acid leaching and dissolution of major sulfides ore mineral process and galvanic effect on comp lex system, it was concluded that the rate of acid dissolution of metal sulphide in mixedmineral system can be dramat ically affected by galvanic effects with rates increasing by factor as great as 30 times in some cases and that the combination of conventional bulk leaching experiment with surface analysis techniques can lead to new insight into the mechanis m of the dissolution through an understanding of reaction stoichiometry.
Previous US Bu reau of mines (USBM) research on the leaching of chalcopyrite with ferric sulfate[Fe 2 (SO 4 ) 3 ] demonstrated that surfactant addition enhance chalcopyrite (CuFeS 2 ) leaching and that surfactant selection has a significant impact on the init ial leaching rate (Schultz et al., 1995).
Dutrizac and MacDonald (1971) studied chalcopyrite leaching using 0.1 M Fe 2 (SO 4 ) 3 -0.1 M H 2 SO 4 (sulfuric acid). They reported a rap idly decreasing leaching rate in the absence of chloride. When 6 g/L chlo ride is added, leaching becomes linear. Such behaviour suggests a change in leaching mechanism. They also reported that there is no leaching enhancement for chloride additions when the temperature is less than 50 o C. Muniz -Ribadeneira and Go mberg (2001) also reported that 0.05 -1.0 N NaCl (sodium chloride), 0.29 to 58 g/ L imp roves copper leaching at 23 to 25 o C in 1 N H 2 SO 4 .
Murr et al. (2006) reported that both NaCl and KCl (potassium ch loride) improve chalcopyrite leaching at pH 2.0 and 28 o C. It was agreed that KCl enhances chalcopyrite leaching, but attributed the effect to potassium rather than chloride. This study also reported that the over potential (a measure of resistance to oxidation) developed during oxidation of sulfides in a sulfate system is not observed in chloride system. The reason for this could be attributed to chloride functioning as an electron transfer agent. Such behaviour was concluded to enhance leaching in an oxidation -reduction reaction by facilitating transfer of the electron fro m the species being oxidized.
Mujina et al. (2008) leached chalcopyrite in acidic Fe 2 (SO 4 ) 3 and FeCl 3 solution and found that S 0 formed on chalcopyrite grain surfaces in both experiments, but the S 0 formed in Fe 2 (SO 4 ) 3 was denser than that formed in FeCl 3 . This could be contributed the slower o xidation rate determined for Fe 2 (SO 4 ) 3 leach ing compared to that for FeCl 3 leaching. Hundstrom et al. (2005) examined an investigation of chalcopyrite (Cu FeS 2 ) dissolution in cupric chloride solutions. The results obtained determined that the dissolution of a stationary chalcopyrite sample was controlled by diffusion in the react ion product layer at pH 3 and changing to chemical rate control at pH 1. The FeOOH formation in addit ion to the elemental sulphur favours chalcopyrite dissolution. Al-Harahsheh (2008) used ferric chloride leaching of copper fro m chalcopyrite. The effect of stirring speed and temperature on chalcopyrite leaching were investigated. Agitation was found to have a negative effect on cupric ion, the fact that cupric comp lexes are formed during the leaching process where the cupric ion is considered as a string oxidant. Jiang et al. (2002) studied the dissolution kinetic of manganese silver associate ores and found that hydrogen peroxide greatly increase sulfuric acid recovery of silver. The reaction order of H 2 SO 4 and H 2 O 2 was determined as 0.80 and 0.68, respectively. Silver leaching was found to be diffusion -controlled by the following kinetic model: (22) where α = the mo le fraction o f the ore dissolved, t = time in minutes, k = mass transfer coefficient. Antonijevic et al. (2004) on the other hand, studied the dissolution kinetics of chalcopyrite by hydrogen peroxide in sulfuric acid. Copper recoveries were found to be significantly increased as the concentration of sulfuric acid and hydrogen peroxide increased. Nevertheless, all these research studies have been centered on high grade ore and none on low-grade comp lex as in the case of Nigerian ore.
The anodic dissolution of chalcopyrite was studied by Jordan and Vargas (2009) with an electrochemical technique that allows direct measurement of anodic dissolution current in small chalcopyrite particles. Their approach enabled to analyze chalcopyrite d issolution kinetic according to the shrinking core model and to propose a mechanis m for the control of the dissolution rate.
More recently, several researchers have pointed out that high redox potentials promote passivation of chalcopyrite during leaching. Hiroyoshi et al. (2001) proposed a reaction mode which involves the intermediate reduction of chalcopyrite to Cu 2 S and oxidation of ferrous ion, followed by the oxidation of Cu 2 S by ferric ion to cupric ion and elemental sulfur. Also, Nicol and Lazaro (2003) proposed that chalcopyrite reduction can be achieved by protonic attack at potential value lower than 0.4 V releasing Cu 2+ , Fe 2+ and H 2 S. Then hydrogen sulfide is o xid ized by ferric ion to cupric ions and elemental sulfur. According to this model, the rate o f H 2 S decreases with increasing chalcopyrite surface potential fro m 0.5 V to 0.7 V. Previous to this works, other authors had also found better chalcopyrite dissolution rates at relatively low potential (Kametani and Aoki, 1985;Barr et al., 1992;Third et al., 2000;Third et al., 2003 andOkamoto et al., 2003 Cordoba et al. (2008) have shown that the passivation of chalcopyrite is related to high potential value (e.g. high Fe 3+ /Fe 2+ ratio). It was concluded that the leaching solution of ferric/ferrous sulfate reach rap idly an equilibriu m at which the activ ities of both ions are equal and related to a critical potential of appro ximately 0.65 V vs SHE. Thus, when the redo x potential is in itially very h igh, there is the tendency to equilibriu m that favours the fast precipitation of ferric ion as jarosite and then the passivation of chalcopyrite.

Microbi al Leaching Studies on Chalcopyrite
Biohydrometallurgy treat ments have been practiced extensively for metal recovery fro m lo w-grade sulfidebearing materials (Maouf, 1971). The thiobacillus ferrooxidans which is responsible for metal dissolution derives the necessary energy for its life process from oxidation of ferrous iron (Silverman, 1967) and reduced valence inorganic sulfur co mpounds (Silver and Torma, 1974) and thus utilizes carbon dio xide fo r gro wth when cultured on metal plates.
Most studies to date, Biswas and Davenport (1980) and Torma et al. (1972) have been concentrated on improving both the kinetic of copper dissolution by using a large number of bio leaching species (mesophilic and moderately or extremely thermophilic microorganisms, and the knowledge of how certain physical factor (part icle size, temperature, p H, cataly zing ions) affect the process. The results thus far obtained have made possible to establish the most suitable conditions for carrying out the bioleaching process, but have not revealed the cause which bring about a decrease in the ext raction rate after certain t ime.
Go mez et al. (1995) used culture which is principally formed for Thiobacillus ferroxidans, Thiobacillus thioxidans and leptosipinillum ferooxidans. The result of their investigation showed that the reactivity of the chalcopyrite gradually increase with the bacterial treat ment. Karanam et al. (2007) carried out bioleaching studies on periolatin colu mns using low-grade copper containing rock (granite). The experiment made use of lixiv iant consisted of acidified ferric sulfate containing acidophilic microorganis m. Leaching parameters studied were lixiv iants flow rate, particle size, and bed height. The results showed that the leaching efficiency increases with decrease in particle size and lixiv iant flow rate.
According to Nowaczyk et al. (1998) Fro m this study, the process can be described as a first order react ion inhib ited by the product according to the following equations: x o and x are the init ial and current concentration of the substrate, respectively. Therefore, Fro m the latter equation, the kinetic parameters of the reaction were calcu lated: the rate constant of leaching (k 1 ), the inhibit ion rate constant (k 2 ) and the induction period (t o ) (Nowaczyk et al., 1998). The results obtained in this study allo w a conclusion that the proposed kinetic model can be used for optimizat ion of the process parameter using thiobacillus ferrooxidans bacteria.
Many researchers (Konishi et al., 1999;Torress et al., 1995, and Ho ward and Gu indwell 1999) reported that thermophile macroorganism such as sulfolobus acidiamus and metallosphaera have been shown to leach chalcopyrite to high extraction at temperature range 65 -75 o C, both in shakes flask and stirred tanks. The success of thermophile over mesophiles has not yet been clearly explained, but it has been observed that thermophile leaching takes place in a fairly low potential environ ment (380 -500 mV Ag/AgCl) in wh ich chalcopyrite passivation is not observed ( The experiments verify the enhancement due to chloride and surfactant addition in the leaching system of chalcopyrite and H2SO4.

ND = Not Det ermined
The future of bio mining is challenging, as it offers advantages of operational simplicity, low capital and operational cost and shorter construction which no other alternative process can provide. In addition, minimu m environmental impact and the use of this technology in the mining industry are set to increase. Once commercial scale, high -temperature processes have been designed, the variety of mineral that will become acquiescent to bio-mining will increase. Although, the viability of microbes that flourish at temperature 55 o C is not yet well-p roven commercially, it appears that one can isolate iron and/or sulfur-o xidizing organisms for whatever temperature is required (Mohd et al., 2009).
In summary, some other reported works fro m the literature on the hydrometallurg ical processing of chalcopyrite ores fro m various parts of the globe is presented in Table 1.
Fro m Table 1, it is important to note that no reported works of chalcopyrite ore processing from Nigerian orig in has been made.

Conclusions
Hydrometallu rgical treat ment of chalcopyrite (CuFeS 2 ) is a growing technology (Hyvarinen and Hamalainen 1999). In recent times, attention has been drawn to low-grade complex sulfide ores due to the decline in the world deposits of high -grade ores. Comp lex sulfide ores are in many cases difficu lt to treat with conventional mineral processing method and the concentrate produced is often not clean enough. This seriously limits their commercial value (Fan et al. 2005). Differential flotation does not release all the constituent phases and so the different concentrates obtained are of poor quality with low metal recovery. This makes further pyro metallurg ical p rocessing of these ores very difficult and costly (Hyvarinen et al. 2003) and rendered them d ifficu lt to co mmercialize. Consequently, the metal value is preferably extracted directly fro m the low grade ores through hydrometallurgical process (Hiroyoshi et al. 2001). The basis of hydrometallu rgy is justified not only by economical, but also ecological reasons. Increasing demand of industry for metals leads to a quick exhaustion of the best or the easiest accessible resources which stimulate the search for new environmental -friendly solutions such as bio-hydrometallurgy to enable exploitation of poor deposit or recovery of metal fro m industrial wastes.
In general, experiences have been shared based on various researches on hydrometallurgical process and now we find that many deposit around the world that have previously not been regarded as suitable for economic exploitation are being re-considered and this will hopefully lead to the valuable economic regeneration of other mineralogical areas.
In conclusion, it is pert inent to note that there are two main methods employed worldwide for p rocessing chalcopyrite for metal production. The most impo rtant one is the conventional -pyro metallurgy method comprised numerous types of shaft and flash technologies, which consists of crushing, grinding, flotation, smelting refining and electro-refining. Th is method is applied to sulfide flotation concentrates rather than ores and is economically feasible for copper rich feed for large scale operations. A second method, hydrometallurgy is applied to the rest of the world 's primary copper production. Hydro metallurgy consists of crushing, leaching (non-o xidation leaching, atmospheric leaching and pressure leaching), solvent extraction and electrowinning and can be effect ively applied for o xid ized ores as well as for sulfide ores with chalcopyrite as a predominant copper mineral. In general, due to interests that include environmental aspects and the possibility o f increased explo itation of mixed and lower grade ores and relatively small isolated deposits, there has been a worldwide upsurge of interest in hydrometallu rgical process for the production of copper.