Bioleaching of copper from a low-grade chalcopyrite ore

Experiments conducted in this study provide good evidence that the rate of oxidation of chalcopyrite can be increased many fold by the action of the iron-oxidising, chemoautotrophic bacteria, Thiobacillus ferrooxidans. Studies were made between the range 28–48°C and between pH 2.0 and 3.5. The optimum temperature and pH were found to be 35°C and 2.7, respectively. Particle sizes of chalcopyrite ore used in the study were between 60 and 190 μm in diameter. The rate of leaching was found to be directly proportional to the decrease in particle size. Supply of air to the system had a pronounced effect on the leaching of chalcopyrite by T. ferrooxidans. During the same period of 48 days, the conversion of copper obtained was 17.8, 58 and 54.4% in stationary, a shake flask and a percolator system, respectively.     

N-heterocyclic carbene gold(I) and copper(I) complexes in C-H bond activation

Environmental concerns have and will continue to have a significant role in determining how chemistry is carried out. Chemists will be challenged to develop new, efficient synthetic processes that have the fewest possible steps leading to a target molecule, the goal being to decrease the amount of waste generated and reduce energy use. Along this path, chemists will need to develop highly selective reactions with atom-economical pathways producing nontoxic byproduct. In this context, C-H bond activation and functionalization is an extremely attractive method. Indeed, for most organic transformations, the presence of a reactive functionality is required. In Total Synthesis, the "protection and deprotection" approach with such reactive groups limits the overall yield of the synthesis, involves the generation of significant chemical waste, costs energy, and in the end is not as green as one would hope. In turn, if a C-H bond functionalization were possible, instead of the use of a prefunctionalized version of the said C-H bond, the number of steps in a synthesis would obviously be reduced. In this case, the C-H bond can be viewed as a dormant functional group that can be activated when necessary during the synthetic strategy. One issue increasing the challenge of such a desired reaction is selectivity. The cleavage of a C-H bond (bond dissociation requires between 85 and 105 kcal/mol) necessitates a high-energy species, which could quickly become a drawback for the control of chemo-, regio-, and stereoselectivity. Transition metal catalysts are useful reagents for surmounting this problem; they can decrease the kinetic barrier of the reaction yet retain control over selectivity. Transition metal complexes also offer important versatility in having distinct pathways that can lead to activation of the C-H bond. An oxidative addition of the metal in the C-H bond, and a base-assisted metal-carbon bond formation in which the base can be coordinated (or not) to the metal complexes are possible. These different C-H bond activation modes provide chemists with several synthetic options. In this Account, we discuss recent discoveries involving the versatile NHC-gold(I) and NHC-copper(I) hydroxide complexes (where NHC is N-heterocyclic carbene) showing interesting Br?nsted basic properties for C-H bond activation or C-H bond functionalization purposes. The simple and easy synthesis of these two complexes involves their halide-bearing relatives reacting with simple alkali metal hydroxides. These complexes can react cleanly with organic compounds bearing protons with compatible pK(a) values, producing only water as byproduct. It is a very simple protocol indeed and may be sold as a C-H bond activation, although the less flashy "metalation reaction" also accurately describes the process. The synthesis of these complexes has led us to develop new organometallic chemistry and catalysis involving C-H bond activation (metalation) and subsequent C-H bond functionalization. We further highlight applications with these reactions, in areas such as photoluminescence and biological activities of NHC-gold(I) and NHC-copper(I) complexes.     

Synthesis and crystal structures of copper(I) iodide complexes chelating with bis(ethylamidophosphine)

Two copper(I) iodide complexes with polydentate bis(ethylamidophosphine) ligands were synthesized, characterized with crystal structures. They include a dimeric complex [Cu(μ-I)(CH₂NHCOC₂H₄PPh₂)₂]₂ 1 containing a planar Cu₂I₂ rhombohedron with two doubly bridged ligands and a tetrameric complex {Cu₄(μ-I)₄[(CH₂NHCOC₂H₄PPh₂)₂]₂} 3 with all the coppers and iodines forming a highly distorted cubane geometry.     

Electrochemically protected copper(I)-catalyzed azide-alkyne cycloaddition

The copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction has found broad application in myriad fields. For the most demanding applications that require high yields at low substrate concentrations, highly active but air-sensitive copper complexes must be used. We describe here the use of an electrochemical potential to maintain catalysts in the active Cu(I) oxidation state in the presence of air. This simple procedure efficiently achieves excellent yields of CuAAC products from both small-molecule and protein substrates without the use of potentially damaging chemical reducing agents. A new water-soluble carboxylated version of the popular tris(benzyltriazolylmethyl)amine (TBTA) ligand is also described. Cyclic voltammetry revealed reversible or quasi-reversible electrochemical redox behavior of copper complexes of the TBTA derivative (2; E(1/2)=60 mV vs. Ag/AgCl), sulfonated bathophenanthroline (3; E(1/2)=-60 mV), and sulfonated tris(benzimidazoylmethyl)amine (4; E(1/2) approximately -70 mV), and showed catalytic turnover to be rapid relative to the voltammetry time scale. Under the influence of a -200 mV potential that was established by using a reticulated vitreous carbon working electrode, CuSO4 and 3 formed a superior catalyst. Electrochemically protected bioconjugations in air were performed by using bacteriophage Qbeta that was derivatized with azide moieties at surface lysine residues. Complete derivatization of more than 600 reactive sites per particle was demonstrated within 12 h of electrolysis with substoichiometric quantities of Cu3.     

Electronic interactions in copper(I) and silver(I) complexes between the ligands and metals as evidenced with cyclic voltammetry

The electronic interaction between datively bonded phosphanes, 2,2′-bipyridine and 1,10-phenanthroline ligands, and copper(I) and silver(I) ions has been studied with cyclic voltammetry. Based on the shifts of reduction potentials of the metals, various degrees of interactions have been identified. They are correlated with the type and molecular structure of the bridging ligand.     

Identification of copper(II) and copper(I) and their interconversion in Cu/ZSM-5 De-NOx catalysts

A combined Fourier transform IR (FT-IR) and electron paramagnetic resonance (EPR) study shows that copper in ‘excessively exchanged’ Cu/ZSM-5 is initially present as OH bridged Cu²⁺ dimers, besides isolated Cu²⁺ ions. Upon heating, the dimers lose water and become oxygen bridged [Cu---O---Cu]²⁺ complexes. These are ‘EPR-silent’, presumably as a consequence of antiferromagnetic coupling of the unpaired electrons in each Cu²⁺; they are, however, detectable by their perturbation of the lattice vibrations, detected by a FT-IR band at 918–923 cm⁻¹. Reduction by hydrogen or carbon monoxide converts the [Cu---O---Cu]²⁺ complexes to pairs of Cu⁺ ions, while the color changes from green to grey. Reductive adsorption of nitrogen monoxide on Cu²⁺ results in the formation of Cu⁺---NO⁺. Destructive thermal desorption of nitrogen monoxide at 100°C not only restores the Cu²⁺ ions, but also appears to regenerate the [Cu---O---Cu]²⁺ complex. The results suggest that pairs of copper ions are instrumental in the catalytic decomposition of nitrogen monoxide.     

Bioleaching of copper via iron oxidation from chalcopyrite at elevated temperatures

The effect of elevated temperature on the bioleaching of copper from chalcopyrite (CuFeS₂) via iron oxidation using Acidithiobacillus ferrooxidans under mesophilic conditions was studied. It was shown that temperature tolerant and ore adapted strains of At. ferrooxidans could extract copper significantly better than non-adapted cultures at elevated temperatures. The presence of soluble iron and its oxidative state, as a determining factor in copper leaching were found to be closely related to pH and temperature.     

Homogeneous catalysis of the reduction of nitrobenzene by bromotris(triphenylphosphine) copper (I)

Homogeneous reduction of nitrobenzene by hydrogen in presence of complex [Cu^IBr(PPh₃)₃] as catalyst has been investigated. From a study of various operational parameters, it has been observed that maximum reduction occurred at 2.5 × 10³ kPa pressure and at 473–513 K and resulted in 75% aniline, 10% azobenzene, 2% nitrosobenzene in ethanol, and 70% aniline, 5% azobenzene, 7% nitrosobenzene in dimethylformamide, calculated on the basis of input nitrobenzene. In an attempt to elucidate the reduction mechanism two new intermediates, [CuHPPh₃Br]₂ (I) and [(C₆H₅N=NC₆H₅)Cu₂(PPh₃)₄Br₂] (II), have been isolated and characterised by elemental analysis, spectral, thermal, magnetic and p.m.r. studies.     

A bithiazole-containing calix[4]arene podand as versatile ligand for copper(I) and copper(II)

A new calix[4]arene-based bithiazole podand designed to complex copper(I) or copper(II), and the corresponding complexes, have been synthesised and characterised. Structural information was notably obtained for the copper(I) complex by a ¹H¹⁵N HMBC NMR experiment.     

Synthesis of macrocyclic phenanthrolines with exotopic binding sites. Probing their complexation behavior with copper(I) and iron(II)

Starting from 4,7-dichlorophenanthroline ( 1 ) a synthetic approach is developed to novel macrocyclic mono- and bisphenanthrolines ( 5a – d , 6a – d ) with exotopic binding sites. As these coordinating compounds are characterized by a flexible spacer unit, their utility as ligand for the construction of oligomeric, dendritic and box-like structures in the presence of copper(I) and iron(II) is evaluated. Spectroscopic data suggest that with copper(I) the [1+1] adduct [Cu₂( 6c )( 7 )]²⁺ is formed.     

Luminescent staircase copper(I) coordination polymer based on planar Cu3I3

Copper(I) coordination polymer [Cu₃I₃L]_n (1) has been synthesized by the reaction of CuI and 1,4-bis((cyclohexylthio)acetyl)piperazine (L). Structural and photophysical studies of 1 in solid state are reported. The bonding of Cu₃I₃ produces staircase polymers interconnected by the sulfur atoms of L.     

Bio-hydrometallurgical processing of low grade chalcopyrite for the recovery of copper metal

A process flowsheet was developed to recover copper metal from the lean sulfide ore of copper available at Malanjkhand, Hindustan Copper Limited (HCL), India. Copper pregnant leach solution (PLS) obtained from bio-heap leaching of chalcopyrite containing 0.3% copper was purified through solvent extraction (SX) and the copper recovered by electrowinning (EW). The copper-free raffinate obtained from SX stripping unit was returned back to the bioleaching circuit. The purity of the electrolytic copper produced at pilot scale was found to be 99.96%. During electrowinning, the effect of flow rate of electrolyte on current efficiency and energy consumption was also studied.     

Separation of chalcopyrite and pyrite from a copper tailing by ammonium humate

Copper tailings constitute a large proportion of mine wastes. Some of the copper tailings can be recycled to recover valuable minerals. In this paper, a copper tailing was studied through the chemical analysis method, X-ray diffraction and scanning electron microscope-energy dispersive spectrum. It turned out that chalcopyrite (Cu) and pyrite (S) were the main recoverable minerals in the tailing. In order to separate chalcopyrite from pyrite in low pulp pH, ammonium humate (AH) was singled out as the effective regulator. The depression mechanism of AH on the flotation of pyrite was proved by FTIR spectrum and XPS spectrum, demonstrating that there was a chemical adsorption between AH and pyrite. By Response Surface Methodology (RSM), the interaction between AH, pulp pH and iso-butyl ethionine (Z200) was discussed. It was illustrated that the optimal dosage of AH was 1678 g·t^-1 involving both the recovery of Cu and S. The point prediction by RSM and the closed-circuit flotation displayed that the qualified Cu concentrate and S concentrate could be obtained from the copper tailing. The study indicated that AH was a promising pyrite depressor in the low pulp pH from copper tailings.     

Polarographic studies of copper(II) in aqueous dimethylsulphoxide and aqueous acetone and free energy of transfer of copper(I) and copper(II) from water to dimethyl-sulphoxide-water mixtures

Polarographic studies of Cu(ClO₄)₂ in aqueous dimethylsulphoxide (DMSO) mixtures have identified compositions in which Cu(I) is stable. The half-wave potentials E_1/2, of Cu(II)/Cu(I) and Cu(I)/Cu(Hg) decrease in DMSO-water mixtures and values of free energies of transfer, ΔG_tr, of Cu(II) and Cu(I) from water to aqueous DMSO are reported. Similar measurement in aqueous acetone mixtures show that ΔG_tr Cu(II) increases upon addition of acetone.     

Copper(I) and copper(II) complexes in solution and the crystalline state

Model studies on the copper-protein interaction that may catalyze lipid oxidation have been made by studying the copper complexes of glycyl-L-histidyl-glycine and ε-aminocaproic acid. The compositions of the complexes in solution were measured by emf methods. The structures of solid complexes were determined by x-ray diffraction techniques. The results indicate that all the solid complexes have their counterparts by species formed in solution. One of 28 papers presented at the Symposium, “Metal-Catalyzed Lipid Oxidation,” ISF-AOCS World Congress, Chicago, September 1970.     

Control of debromination in solution polymerisation of copper(I) 4-bromobenzenethiolate

Fresh poly(phenylene sulfide) (PPS) fibers have pleated surface morphology and banded texture. These structural features are similar to those of poly(phenylene terephthalamide) fiber (Kevlar), whereas some unique morphologies were observed for the long-term stored PPS fibers, which have not been found with liquid crystalline polymer fibers including Kevlar. The long-term stored PPS fibers show a decreased T_g and a decreased onset temperature of melting, compared with their fresh counterparts, which is attributed to stress relaxation and resulting disorientation in the amorphous region of the fibers. Combination of the observed typical morphologies with polarized optical microscopy and X-ray diffraction analysis suggests that PPS possesses liquid crystalline nature.     

Silsesquioxane Chemistry, 5. Retention of the Cu4O4 core upon formation of the first copper(I) silsesquioxane from tetrameric copper(I)-t-butoxide

The first copper(I) silsesquioxane derivative, Cu₄O₄[Cy₇Si₇O₉(OSiMe₃)]₂ (4) was prepared by reacting tetrameric copper(I)-t-butoxide, (CuOtBu)₄ (3), with the monosilylated silsesquioxane precursor Cy₇Si₇O₉(OH)₂(OSiMe₃) (2) in a 1:2 molar ratio. An X-ray diffraction study revealed the presence of a centrosymmetric dimer. A slightly puckered Cu₄O₄ ring forms the central part of a complex structure comprising nine eight-membered inorganic ring systems.