Kinetics of chemical leaching of chalcopyrite from low grade copper ore: behavior of different size fractions

The kinetics of the chemical leaching of copper from low grade ore in ferric sulfate media was investigated using the constrained least square optimization technique. The experiments were carried out for different particle sizes in both the reactor and column at constant oxidation-reduction potential （Eh）, pH values, and temperature. The main copper mineral was chalcopyrite. About 40% of Cu recovery is obtained after 7 d of reactor leaching at 85℃ using -0.5 mm size fraction, while the same recovery is obtained at 75℃ after 24 d. Also, about 23% of Cu recovery is obtained after 60 d of column leaching for ＋4--8 mm size fraction whereas the Cu recovery is as low as about 15% for ＋8--12.7 and ＋12.7--25 mm size fractions. A 4-stage model for chalcopyrite dissolution was used to explain the observed dissolution behaviors. The results show that thick over-layers of sulphur components cause the parabolic behavior of chalcopyrite dissolution and the precipitation of Fe3＋ plays the main role in chalcopyrite passivation. In the case of coarse particles, transformation from one stage to another takes a longer time, thus only two stages including the initial reaction on fresh surfaces and S0 deposition are observed.

Bioleaching of copper oxide ore by P seudomonas aeruginosa

Bioleaching is an environmentally friendly method for extraction of metal from ores. In this study, bioleaching of copper oxide ore by Pseudomonas aeruginosa was investigated. Pseudomonas aeruginosa is a heterotrophic bactermm that can produce various organic acids in an appropriate culture medium, and these acids can operate as leaching agents. The parameters, such as particle size, glucose percentage in the culture medium, bioleaching time, and solid/liquid ratio were optimized. Optimum bioleaching conditions were found as follows： particle size of 150-177 μm, glucose percentage of 6%, bioleaching time of 8 d, and solid/liquid ratio of 1：80. Under these conditions, 53% of copper was extracted.

Inhibition of acid mine drainage and immobilization of heavy metals from copper flotation tailings using a marble cutting waste

Acid mine drainage （AMD） with high concentrations of sulfates and metals is generated by the oxidation of sulfide beating wastes. CaCO3-rich marble cutting waste is a residual material produced by the cutting and polishing of marble stone. In this study, the feasibility of using the marble cutting waste as an acid-neutralizing agent to inhibit AMD and immobilize heavy metals from copper flotation tailings （sul- fide-beating wastes） was investigated. Continuous-stirring shake-flask tests were conducted for 40 d, and the pH value, sulfate content, and dissolved metal content of the leachate were analyzed every 10 d to determine the effectiveness of the marble cutting waste as an acid neu- tralizer. For comparison, CaCO3 was also used as a neutralizing agent. The average pH value of the leachate was 2.1 at the beginning of the experiment （t = 0）. In the experiment employing the marble cutting waste, the pH value of the leachate changed from 6.5 to 7.8, and the sul- fate and iron concentrations decreased from 4558 to 838 mg/L and from 536 to 0.01 mg/L, respectively, after 40 d. The marble cutting waste also removed more than 80wt% of heavy metals （Cd, Cr, Cu, Ni, Pb, and Zn） from AMD generated by copper flotation tailings.

Comparative study on the passivation layers of copper sulphide minerals during bioleaching

The bioleaching of copper sulphide minerals was investigated by using A. ferrooxidans ATF6. The result shows the preferential order of the minerals bioleaching as djurleite〉bomite〉pyritic chalcopyrite〉covellite〉porphyry chalcopyfite. The residues were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. It is indicated that jarosite may not be responsible for hindered disso- lution. The elemental sulfur layer on the surface of pyritic chalcopyrite residues is cracked. The compact surface layer of porphyry chalcopy- rite may strongly hinder copper extraction. X-ray photoelectron spectroscopy （XPS） further confirms that the passivation layers of covellite, pyritic chalcopyrite, and porphyry chalcopyrite are copper-depleted sulphide Cu4S11, S8, and copper-rich iron-deficient polysulphide CtuFe2S9, resoectivelv. The ability of these oassivation layers was found as Cu4Fe2S9〉Cu4S11〉S8〉iarosite.

Investigation on leaching of malachite by citric acid

Leaching of an oxidized copper ore containing malachite, as a new approach, was investigated by an organic reagent, citric acid. Sulfuric acid is the most common reagent in the leaching of oxide copper ores, but it has several side effects such as severe adverse impact on the environment. In this investigation, the effects of particle size, acid concentration, leaching time, solid/liquid ratio, temperature, and stirring speed were optimized. According to the experimental results, malachite leaching by citric acid was technically feasible. Optimum leaching conditions were found as follows： the range of particle size, 105-150 μm; acid concentration, 0.2 M; leaching time, 30 min; solid/liquid ratio, 1：20 g/mL; temperature, 40℃; and stirring speed, 200 r/min. Under the optimum conditions, 91.61% of copper was extracted.