Presence Of Chalcopyrite Research Articles

Effect of lead nitrate on cyanidation of gold ores: progress on the study of the mechanisms

This paper discusses some of the latest efforts to improve the understanding of the use of lead nitrate in cyanidation. The study is based on an electrochemical approach to establish the nature of the mechanisms related to gold, a surface analysis study, using X-ray photoelectron spectroscopy (XPS), to determine the modifications on gold and sulphide minerals (pyrite, pyrrhotite and chalcopyrite) and an investigation that focus on the improvements of cyanidation. In a cyanide solution, lead nitrate, lead sulphide and lead sulphite react with gold to form AuPb 2, AuPb 3 and metallic lead, which clearly accelerate the gold dissolution. The nature of the sulphide minerals affects the formation of lead or lead alloys on the gold surface. XPS did not find any lead on the surface of gold in the presence of pyrite or pyrrhotite but found a very thin layer (...50 A) in presence of chalcopyrite. Further investigation is required to study the effect of the presence of other sulphides. It is proposed that in presence of sulphide minerals, sometimes lead does not report on gold because of its high affinity for sulphide minerals (competing reactions). Pyrite, chalcopyrite and pyrrhotite showed different reaction mechanisms with lead nitrate. Lead nitrate forms a hydroxide layer on pyrite particles, which reduces the reaction rate with cyanide. The disolution of pyrite generates a sulphur layer on gold. This layer is less important in presence of lead. The effect of lead nitrate is subtler for chalcopyrite and pyrrhotite because it was less effective to retard the reaction of sulphides with cyanide and the reaction of iron with oxygen. For gold, the addition of lead nitrate has the same effect with pyrrhotite than with pyrite; inhibiting partially the formation of a sulphur layer. This was not observed for the gold in the chalcopyrite system. The results indicate that the strategy of lead nitrate addition, to be optimal, should be a function of the mineralogical composition of the ore. The formation of a passive layer on gold particles has a significant influence in the initial stages of leaching. The addition of lead nitrate notably decreased its inhibiting effect. In one case study, the lead nitrate treatment increased the overall gold extraction and decreased the cyanide consumption for an additional gross revenue of $ CND2.2 millions.

Interaction of chalcopyrite and sphalerite with pyrite during leaching by Thiobacillus ferrooxidans and Thiobacillus thiooxidans

The interaction of chalcopyrite and sphalerite with pyrite during leaching by Thiobacillus ferrooxidans and Thiobacillus thiooxidans was studied in shake-flask leaching experiments and in respirometer experiments with resting cells. Two samples of pyrite (Nos. 1 and 2) were used. In shake-flask experiments in the absence of bacteria, the copper and zinc extraction rates increased in the presence of No. 1 pyrite from 1.6 to 10.2 and 13%, respectively, and in the presence of No. 2 pyrite from 1.6 to 3.5 and 5.8%, respectively. Thus the effect of pyrite was greater with sphalerite than with chalcopyrite and the No. 1 pyrite was more effective than the No. 2 pyrite. Thiobacillus ferrooxidans increased the leaching rates of Cu from chalcopyrite (from 1.6 to 11.1%), of Zn from sphalerite (from 1.6 to 36%), and of Fe from pyrite (from 7.3 to 29.9% (No. 1) and from 5.1 to 49.3% (No. 2)), although a period of adaptation was required for sphalerite leaching. Thiobacillus thiooxidans did not leach Cu form chalcopyrite, but increased leaching of Zn from sphalerite (from 1.6 to 8.3%) and some Fe from pyrite (from 7.3 to 9.5% (No. 1) and from 5.1 to 13.1% (No. 2)). In the chalcopyrite–pyrite mixture, Cu leaching was further stimulated by T. ferrooxidans (from 10.2 to 14.5% (No. 1) and from 3.5 to 12.2% (No. 2)) and by T. thiooxidans (from 3.5 to 5.8% (No. 2)). The Zn leaching from the sphalerite–pyrite combination increased further with T. ferrooxidans (from 13.0 to 61.7% (No. 1) and from 5.8 to 65.8% (No. 2)) and T. thiooxidans (from 13.0 to 22.4% (No. 1) and from 5.8 to 14.7% (No. 2)). The Fe solubilization from pyrite was inhibited by the presence of chalcopyrite or sphalerite with or without bacteria. Short-term respirometer studies generally supported the leaching results. Oxygen consumption was faster for chalcopyrite or sphalerite in the presence of pyrite. The effect was stronger for sphalerite, although the rapid pyrite oxidation by T. ferrooxidans was inhibited by the interaction. Chalcopyrite alone was oxidized by T. ferrooxidans but not by T. thiooxidans, while sphalerite alone was oxidized only by the latter. It is concluded that shake-flask leaching and Warburg respirometer experiments complement each other in elucidating the complex processes involved in bacterial metal leaching of sulfide ores. Key words: Thiobacillus, sulfide ores, oxidation, mineral leaching.

Catalysed air oxidation of thiosulfate and tetrathionate for pollution abatement

Thiosulfate and tetrathionate are oxidized to sulfate by air at atmospheric pressure in the presence of CuS, Cu 2S or chalcopyrite (CuFeS 2) concentrate under mild temperature conditions (30–60°C). In the presence of CuS and Cu 2S, sulfate is produced from thiosulfate by series-parallel reaction paths involving tetrathionate as an intermediate product. However, in the presence of chalcopyrite which contains ferric iron, thiosulfate is rapidly and quantitatively oxidized to tetrathionate which then undergoes slow oxidation to sulfate. Of the three chalcopyrite concentrates used in this work; viz., Opemiska, Bethlehem and Lornex, best results were obtained with the Opemiska concentrate. In the presence of this material used as a 15% slurry in water, 450 ppm thiosulfate (S 2O 3 2−) is completely oxidized to sulfate by air in 24 hours at 30°C and in 9 hours at 40°C. Use in slurry reactors in continuous operation over several weeks shows that the catalytic activity of the chalcopyrite concentrate remains constant, obviating the need for any regeneration treatment. The rate data obtained with CuS, Cu 2S and chalcopyrite concentrates agree well with a pseudo-homogeneous first order kinetic scheme, yielding values of rate constants for series-parallel reaction paths which have been used in modelling, successfully, the catalyzed air oxidation of thiosulfate.

Metamorphic features in Appalachian massive sulphides

AbstractMassive stratiform and stratabound sulphide bodies in the central Appalachians exhibit a wide variety of metamorphic features which are typical of similar deposits world-wide. The ores occur as lens- to plate-like bodies which are concordant with the enclosing meta-sediments and volcanics and are interpreted as products of Late Precambrian to Early Palaeozoic submarine volcanism. Sulphide mineralization ranges from pyritic to pyrrhotinic bodies with variable, but Zn- and Cu-dominant, base-metal contents. The deposits have been subjected to metamorphism ranging from greenschist to amphibolite grade. The metamorphism has been pervasive and has resulted in thorough recrystallization of most ores and intense deformation of pyrrhotinic ores, but does not appear to have significantly altered original sulphide assemblages. Recrystallization has homogenized most sulphide minerals including pyrite and sphalerite, so that any original compositional zoning is no longer seen. The presence of chalcopyrite has apparently promoted an increase in grain size and has facilitated post-metamorphic retrograde re-equilibration. Consequently, sphalerite geobarometry is not reliable in Cu-bearing assemblages. Pyrrhotines, mostly hexagonal, have re-equilibrated to low temperatures but commonly display pressure twins and kink-banding, apparently due to the late stages of deformation. Characteristic mineralogical changes in the host rocks include changes in the abundance of minerals, changes in the Fe: Mg ratios, and the presence of gahnite.

Sphalerite geobarometry in the Cu-Fe-Zn-S system

Phase relations have been determined among sphalerite, pyrite, pyrrhotite, and intermediate solid solution (iss) from 439 degrees to 725 degrees C at 1 bar and 353 degrees to 760 degrees C at 5 kb. The extents of solid solution in the four-phase assemblage are described as functions of temperature (in Kelvins) by the following equations: log mole % ZnS in iss (1 bar) = 2.795 - 1,632 T (super -1) , log mole % ZnS in iss (5 kb) = 2,659 - 1,608 T (super -1) , log mole % CuS in pyrrhotite (1 bar) = 2,546 - 1,866 T (super -1) , log mole % CuS in sphalerite (1 bar) = 4.202 - 3,755 T (super -1) , and log mole % CuS in sphalerite (5 kb) = 4.084 - 3,791 T (super -1) . The pressure dependence (in kb) of the composition of sphalerite in equilibrium with pyrite and pyrrhotite with or without iss can be expressed for the temperature-independent portion of the sphalerite geobarometer as P = 42.30 - 32.10 log mole % FeS.Because of the low solubility of copper in sphalerite in the four-phase assemblage below 650 degrees C, the presence of chalcopyrite in natural ores should be of no consequence to sphalerite geobarometry over its temperature-independent portion. Nevertheless, sphalerites which are inhomogeneous in FeS and which contain abundant blebs of chalcopyrite in excess of the amount that can be reasonably accounted for by an equilibrium process of solubility and subsequent exsolution are a common feature of many sulfide ores. Such sphalerite grains should be avoided in applying the geobarometer. The chalcopyrite blebs may be a product of a premetamorphic sphalerite-chalcopyrite intergrowth or represent true exsolution from sphalerite in any one of (1) a former sphalerite + pyrrhotite + iss equilibrium, (2) a stable four-phase assemblage at temperatures above the temperature-independent portion of the geobarometer, or (3) a metastable four-phase assemblage in which pyrite was inert. Use of the sphalerite geobarometer requires a thorough understanding of the textural relationships and discrimination of equilibrium from disequilibrium or low-temperature reequilibrated assemblages.

Growth of Iron-Oxidizing Thiobacilli in the Presence of Chalcopyrite and Galena

Iron-oxidizing thiobacilli were adapted to grow on a chalcopyrite and a galena ore concentrate. When grown on the chalcopyrite concentrate, the bacteria exhibited a doubling time of 38.4 +/- 2.9 h, with a final cellular protein concentration of 185 mug/ml and solubilization of 10.3 g of copper per liter. When grown on the galena ore concentrate, the generation time was 39.6 +/- 2.7 h, with a final cellular protein concentration of 120 mug/ml. Galena was converted to lead salts soluble in 1 M ammonium acetate to a concentration of 20.2 g of lead per liter. X-ray diffraction and refractive-image analysis indicated that the smaller-sized particles were favored in this process. Galena was converted to anglesite, and soluble copper was liberated from chalcopyrite with the concurrent formation of jarosite.