Fundamentals On The Coupled Bio-leaching Of Ocean Polymetallic Nodules And Low-grade Nickel Sulfide Ore

The utilization of low-grade complex polymetallic ore has always been a focus and technical problem in the field of mineral processing.Based on the oxidation-reduction property of manganese-oxide and nickel-sulfide ore,a coupled bio-leaching of oceanic ocean polymetallic nodules and low-grade nickel sulfide ore using Acidithiobacillus ferrooxidans as leaching bacteria was investigated in the paper.This leaching process simultaneously extracted nickel,manganese,copper,and cobalt from both ores.The synergistically dissolving characteristic of the main minerals was interpreted by thermodynamic analysis.Acorrding to the reductive dissolution of oceanic polymetallic nodules cathode and oxidative dissolution of low-grade nickel sulfide ore anode,the biological corrosion effects was expounded.The influences of bacteria on redox between electrodes during the process were performed on the specific responses of electrochemical kinetics.In an acidic leaching system,polymetallic nodules and low-grade nickel sulfide ore could form a corrosion cell by contact,which leads to reduction-oxidation dissolution of the main minerals of both ores,due to the reductive leaching potential of manganese-iron oxide of the former was much higher than the oxidative dissolution potential of sulfide minerals of the latter.In this process,the Ni,Cu,Co elements of the polymetallic nodules could be leached with the reductive dissolution of the minerals inclusions of Mn(IV)-oxide by the sulfide of nickel ore.Simultaneously,the Ni,Cu,Co elements of the low-grade nickel sulfide could be oxidation decomposed by the Mn(IV)-oxide minerals of nodules.The optimum conditions of coupled A.ferrooxidans bio-leaching is measured by series tests.The optimized parameters are as follows:temperature 30 ?,pH 1.8,ore size of-0.038 mm 80%,mass ratio of Mn/S of 1/1.3,liquid-solid ratio of 12.5:1,140 r min-1 vibration rate,1.0 g·L-1 initial Fe3+ concentration,1.5×108/mL initial amount of bacteria.Under this conditions for leaching 96 h,the extraction ratios of Ni,Mn,Cu,Co reach 95.3%,97.3%,92.2%,97.8%,respectively,with 17,13,14.3,12.5 percentage points higher than that of the bacteria-and-Fe(III)free aicd system.According to the extraction ratios of corresponding metals increasing linearly in the incipient 48 h,the average leaching rates of Ni,Mn,Cu,Co are 16 mg L h-1,120.3 mg·L h-1,6.4 mg·L·h-1,1.01 mg·L·h-1 under the optimal bio-leaching conditions,respectively,representing growths of 91%,70%,47%,34%over that of the bacteria-and-Fe(?)free faintly acid system.The main elements of both ores could be synergistically extracted by the coupled A.ferrooxidans bio-leaching.The results of electrochemical testing show that the coupled bio-leaching of ocean polymetallic nodules cathode and low-grade nickel sulfide ore anode is controlled by the electrochemical reaction happened at the interface.The reduction of the cathode performs a strong dependency on the conversion of Mn(IV)mineral to Mn(?)substances and a controlling trait of the preceding chemical reaction.The dissolution of the anode presents dynamic current characteristic of potential impetus and it is determined by the oxidative dissolution of sulfide minerals mainly related to the oxidizing reaction of Fe3+/Fe2+ and sulfur-containing species.A.ferrooxidans accelerates mobile and conversion of electron and proton to the surface of the cathode and facilitates the transport and cycle of electron pairs of MnO2/Mn2+ and Fe3+/Fe2+ for the cathode.A.ferrooxidans affects the anode by improving transfer rate of active species on the surface and promoting the conversions of Fe3+/Fe2+ couple and sulfur-containing matters.Those influences cause a decrease in charge transfer impedance of the electrodes,the positive polarization of the cathode and the negative polarization of the anode,an increment in the potential difference between the cathode and anode,and an enhancement on the galvanic interaction,leading to an increase in synergistic leaching rates of the main elements.The extractions of valuable metals,by means of coupled bio-leaching of oceanic polymetallic nodules cathode and low-grade nickel-sulfide ore anode,are the movement of holes of substances on the interface of ore electrode and lixivium.The leaching of cathode performs the movement of O2-vacancy of high-valence manganese-oxide and hole of its corrosive intermediate products of Mn3+.The dissolution of anode shows the movement of hole of Fe2+ formed in Fe(?)-containing sulfide minerals.The beneficial effects of A.ferrooxidans on metals leaching are the improvement in movement of proton and hole between electrodes and electrolytes.Results of this paper expand the theory and practice research of polymetallic manganese-oxide and sulfide minerals processing.It provides a new process for the use of low-grade and refractory ore.