PT Unknown
AU Krok, B
TI Microcalorimetric Investigations on Copper Sulfide Bioleaching
PD 03
PY 2016
LA en
AB The aim of this work is the establishment of a microcalorimetric determination method to assign the chemical and biological degradation of copper sulfides (chalcopyrite, chalcocite and covellite). This study included the screening for microorganisms for copper sulfide bioleaching, the verification of microcalorimetric determination with different ore types and various temperatures and the thermodynamic calculation of the reaction energy ΔrU by means of the measured heat output and the determined iron, copper and sulfate ions in the leachate. During this work microscopic observation of the microbial attachment towards chalcopyrite and the cuprous copper stability within the leachate were made.
After the adaptation of the leaching set-up during mesophilic bioleaching up to 9 % iron and 8 % copper could be recovered, during moderate thermophilic bioleaching up to 25 % iron and 12 % copper could be leached from chalcopyrite and during the bioleaching with thermophilic archaea up to 7.4 % iron and 24 % copper could be recovered.  In general for every condition sterile controls leached only 25-50 % of the total iron and copper recovered by bioleaching. 
Chalcocite leaching showed in the mesophilic temperature range up to 17 % copper recovery by chemical leaching and bioleaching. In contrast, with moderate thermophilic leaching only 17 % copper were leached chemically, but up to 41 % was due to bioleaching. Copper recovery during bioleaching of covellite was similar for the mesophilic and moderate thermophilic temperature ranges, i.e. 2 -15 %. During the experiments high pH values (pH > 2.5) and copper concentrations (Cu > 100 mM) were reached.
Up to 82 %, 90 % or 85 % of the recovery rates of the standard reaction energy calculated for the dissolution of chalcopyrite were calculated via microcalorimetry for mesophiles, moderate thermophiles and thermophiles, respectively. If the recovery rate of the standard reaction energy is underestimated, not all bonds within the chalcopyrite are broken and not all energy is released. Precipitation of ions (especially iron ions) could lead to an overestimation of the recovery rate. 
For mesophilic chalcocite leaching 5-12 % and for moderate thermophilic leaching 32-38 % of the standard reaction energy could be detected via microcalorimetry. However, for covellite leaching 10-15 % of the standard reaction energy could be detected regardless of the temperature.
Though microcalorimetry is suitable for the assessment of bioleaching activity with chalcopyrite ores, in this study it is rather not a suitable technique for chalcocite or covellite bioleaching. However, this might be exclusively due to the used minerals themselves. 
The biofilm formation on chalcopyrite was followed by the Confocal Laser microscopy. The images of microbially colonized chalcopyrite showed that the population density differed with the conditions under which the microorganisms were pre-grown. Iron sulfate and pyrite pre cultivated microorganisms showed higher attachment to chalcopyrite than chalcopyrite pre-cultivated ones. Sulfur pregrown cells were easily detachable from the mineral during the staining procedure. A high coverage of chalcopyrite by attached microorganisms does not correlate with an enhanced extraction of copper.
During the leaching experiments considerable amounts of cuprous copper could be determined within the leachate of chalcopyrite. Based on colorimetric determination of the copper speciation in solution significant amounts (up to 80 % of the total concentration) of copper were found to be present as cuprous copper.
ER