Bioleaching Of Chalcopyrite And Printed Circuit Boards Under The Assistance Of Microbial Fuel Cells

Simultaneous copper extraction and electricity generation are achieved in chalcopyrite bioleaching under the assistance of microbial fuel cells（MFCs）,but the Cu²⁺leaching efficiency is low and the leaching period is long.Silver ion（Ag₂SO₄）can promote the Cu²⁺leaching from chalcopyrite,but it is costly and difficult to recover from leachate.The silver content in silver-bearing ore is not low,and the price is lower than Ag₂SO₄,which can also be used to promote chalcopyrite bioleaching.Electronic wastes such as waste printed circuit boards（WPCBs）are called"urban mine"due to the richness of metal types and the metal content is much higher than that of primary ore.When using bioleaching technology to recover metals from WPCBs,it is necessary to supplement the needed energy substances（iron and sulfur）of the bioleaching microorganisms（iron-oxidizing microorganisms and sulfur-oxidizing microorganisms）.The low-grade sulfide ore has high content of sulfur and iron,which can provide the needed energy substances of the bioleaching microorganisms for the WPCBs bioleaching system.The present study was to explore the effect of silver ion and silver-bearing ore as additives based on chalcopyrite bioleaching under the assistance of MFCs.The feasibility of WPCBs/sulfide ores bioleaching under the assistance of MFCs was investigated by adding sulfide ore（chalcopyrite and pyrite）as the needed energy substances for the bioleaching microorganisms.The appropriate sulfide ore as additive to explore WPCBs pulp densities,sulfide ore pulp densities and initial p H of bioleaching on WPCBs/sulfide ore bioleaching under the assistance of MFCs.Under the optimal leaching conditions from the above studies on the WPCBs bioleaching,the mechanism model on WPCBs/sulfide ore bioleaching under the assistance of MFCs was initially established.It not only expands the research field of MFCs technology,but also proposes new idea and method for the comprehensive resource utilization of solid waste（electronic waste,low-grade ores and tailings,etc.）.The conclusions are as follows:（1）Adding Ag₂SO₄ or silver-bearing ores to chalcopyrite bioleaching under the assistance of MFCs could promote Cu²⁺leaching and electricity generation.Compared with the addition of Ag₂SO₄,the silver-bearing ore added to the chalcopyrite bioleaching under the assistance of MFCs could continuously and stably release Ag⁺,and also could keep Ag⁺of leachate at a suitable concentration,which was beneficial to the chalcopyrite bioleaching and the electricity production of MFCs system.After 260 days’leaching experiment,the Cu²⁺leaching efficiency of bioleaching columns which added sliver-bearing ore（C and C*）and bioleaching columns which added Ag₂SO₄（B and B*）were 10.03%,9.87%,6.63%and 6.55%,respectively.And higher than that of bioleaching columns（A and A*）without silver were 5.26%and 5.37%.Fe³⁺could be converted into jarosite which was difficult to dissolve and attached to the surface of carbon paper loaded of Pt/C（the cathode of the MFCs system）.The attachment of jarosite reduced the catalytic performance of Pt which loaded on the carbon paper surface,and thus the electricity production decreased.（2）WPCBs/sulfide ores bioleaching under the assistance of MFCs was feasible.Compared with the WPCBs/chalcopyrite hybrid system,WPCBs/pyrite hybrid system was more favorable for Cu²⁺leaching from WPCBs（64.64±1.64%vs.53.37±1.45%）and electricity production of MFCs.Compared with chalcopyrite,pyrite was less in alkaline substances but rich in iron and sulfur compared with chalcopyrite,which was the main reason for this phenomenon.（3）The higher the WPCBs pulp density was,the higher the Cu²⁺concentration of leachate was,but it was not conducive to the continuous leaching of Cu²⁺from WPCBs.The optimum pulp density of WPCB was 5.00 g/L,mainly due to the Cu²⁺concentration and p H value of leachate did not significantly inhibit bioleaching.Properly increasing the pyrite pulp density could promote Cu²⁺leaching and electricity production.When the WPCBs pulp density was 5.00g/L,the pulp density was 7.50g/L,the pyrite pulp concentration of 7.50 was favorable for the Cu²⁺leaching,and the highest Cu²⁺leaching efficiency was achieved under the above conditions,reaching 97%on the end of bioleaching.Under conditions where pre-acidification strengthened p H adjustment and bioleaching stopped p H adjustment,the low initial p H value of the bioleaching was beneficial to the Cu²⁺leaching and electricity production.When the initial p H value of bioleaching was 1.75,the leaching efficiency of Cu²⁺was the highest,reaching 90.37±1.95%.（4）There were three pathways of Cu²⁺leaching in the WPCBs/pyrite bioleaching system under the assistance of MFCs:chemical leaching,bioleaching and bioleaching with MFCs.The contribution percentages of the three pathways were:chemical leaching（28.22%）,bioleaching（42.93%）and bioleaching with MFCs（28.85%）.WPCBs/pyrite bioleaching under the assistance of MFCs could generate electricity,low content available sulfide of pyrite and high concentration dissolved oxygen near the anode（compared to the chalcopyrite column bioleaching under the assistance of MFCs in the conditions of high ore heap and high pulp density）were the main reasons for the low electricity production;the high concentration of heavy metal ions and harmful substances were the main reason for the rapid decline of electricity production.Microorganisms promote the oxidation of Fe²⁺and sulfides to generate Fe²⁺and acid,respectively,and the dissolution of copper in WPCBs mainly depended on the oxidation of these.MFCs system could alleviate the formation of sulfur passivation layer by improving the utilization of sulfur element and sulfide,which realized the continuous release of Cu²⁺and produced electricity.