Relationships between galvanic interaction, copper extraction and community dynamics during bioleaching of chalcopyrite by a moderately thermophilic culture

Removal of antimonite and antimonate in aqueous solution by mugwort biochar modified by Acidithiobacillus ferrooxidans after pyrolysis

In the research, iron oxides-biochar composites (ALBC) were prepared from pristine biochar modified by Acidithiobacillus ferrooxidans (A. ferrooxidans) and pyrolyzed at 500 °C and 700 °C in order to remove antimonite (Sb(III)) and antimonate (Sb(V)) from water. The results indicated that biochar prepared at 500 °C and 700 °C (ALBC500 and ALBC700) were loaded with Fe₂O₃ and Fe₃O₄, respectively. In bacterial modification systems, ferrous iron and total iron concentrations decreased continuously. The pH values of bacterial modification systems including ALBC500 increased first and then decreased to a stable state, while the pH values of bacterial modification systems with ALBC700 continued to decrease. The bacterial modification systems can facilitate the formation of more jarosites by A. ferrooxidans. ALBC500 had optimal adsorbing capacities for Sb(III) (18.81 mg·g^-1) and Sb(V) (14.64 mg·g^-1). The main mechanisms of Sb(III) and Sb(V) adsorption by ALBC were electrostatic interaction and pore filling.

Enhanced effect of biochar on leaching vanadium and copper from stone coal tailings by Thiobacillus ferrooxidans

Among the many extraction technologies for recovering metal resources from tailings, bioleaching technology is gradually showing its momentum. In our research, the enhanced effect of biochar on the bioleaching of stone coal tailings by Thiobacillus ferrooxidans (T. ferrooxidans) has been explored. In the static bioleaching experiment for 10 days, the leaching rate of vanadium (V) and copper (Cu) increased by 26.8% and 21.0% respectively after adding 5 g/L biochar. The dynamic bioleaching experiment further verified that under the promotion of biochar, the 44 day cumulative leaching rate of V and Cu increased by 15.3% and 14.5%, respectively. The promoting effect of biochar on T. ferrooxidans was mainly reflected in two aspects. The unique porous structure of biochar created a microenvironment for free microorganisms for inhabitation, while storing abundant nutrients. Biochar can also act as an excellent electronic medium to promote electron transfer, improving the oxidation ability of T. ferrooxidans on Fe²⁺. Furthermore, the presence of biochar may effectively inhibit the formation of jarosite precipitation on tailings in bioleaching, thereby improving the dissolution of tailings and the release of metal elements. This study demonstrates that biochar-enhanced bioleaching may be an efficient and environmentally friendly method for recovering metal resources from tailings.

Recovery of valuable metals from spent mobile phone printed circuit boards using biochar in indirect bioleaching

Improving the bioleaching efficiency of metals from spent mobile phone printed circuit boards (PCBs) in a short time has been of major interest in recent years. In this paper, a novel cheap catalyst (oak wood biochar) was used to improve the copper and nickel bioleaching efficiency from spent mobile phone PCBs. The biochar was derived from oak wood through slow pyrolysis at a low temperature of 500 °C for 1h. The results of RSM optimization indicated that the optimum conditions to maximize copper and nickel recovery were 1.6 g/L biochar and 16 g/L pulp density. The findings indicated that compared to without the presence of biochar, the leach yields of copper and nickel were high. As much as 98% of copper and 82% of nickel were leached by indirect bioleaching under optimum conditions. The better performance in the presence of biochar is due to both galvanic interactions between biochar and solid waste. The biochemical characterization of bioleaching solution suggested that the high concentration of biochar (> 1.6 g/L) led to copper absorption by functional groups on the surface of biochar. Compared to chemical leaching, the bioleaching has better performance. Under optimum conditions, the copper and nickel recovery by indirect bioleaching was 36% and 64% more than that by chemical leaching. Also, it is found that biochar has a positive effect on the chemical leaching process. Therefore, in this paper, the function of biochar was elaborated not only in bio-hydrometallurgy but also in the hydrometallurgy process.

Intensified bioleaching of chalcopyrite concentrate using adapted mesophilic culture in continuous stirred tank reactors

The bioleaching of chalcopyrite concentrate, intensified by the adapted mesophilic culture in the continuous stirred tank reactors (CSTR) was investigated. The cumulative bioleaching efficiency of copper was found to be increased from 34.8% to 49.3% in CSTR-1, 40.3% to 71.2% in CSTR-2, and 44.3% to 73.8% in CSTR-3, while the temperature was elevated from 30 to 37 °C, respectively; whereas, the pulp density (10%, w/v), agitation speed (350 rpm), aeration (400 cc/min), and retention time (7 days across the three reactors) were also optimized to keep constant. Further, the activation energy calculated for copper dissolution under the continuous flow indicated that the surface-diffusion was the overall rate-limiting step for the bioleaching process. Instrumental analysis of solid samples could reveal the degradation pathways of chalcopyrite bioleaching as: CuFeS₂ → Cu₂S → Cu_0.3333Fe_0.6667S → H₉Fe₃O₁₈S₈. It follows a complex mechanism that includes the occurrence of polysulfide and cooperative mechanism along with the passivation onto mineral surfaces.

Effect of pyrite on the electrochemical behavior of chalcopyrite at different potentials in pH 1.8 H2SO4

Chalcopyrite is the most abundant, but also one of the most refractory, copper sources. One way to enhance chalcopyrite’s electrochemical dissolution is by mixing it with pyrite. To understand how and to what extent pyrite affects chalcopyrite’s electrochemical dissolution at different potentials, the electrochemical behaviors of chalcopyrite, pyrite, and chalcopyrite–pyrite couples in pH 1.8 H2SO4 were studied by potentiodynamic and electrochemical impedance spectroscopy. Potentiodynamic curves showed their different electrochemical reaction states and electrode surface characteristics. From open-circuit potential to 470 mV (vs saturated calomel electrode), chalcopyrite–pyrite was passivated with Cu1− xFe1− yS2 [Formula: see text]; from 470 to 580 mV, trans-passive dissolution occurred, and in the passive region, Cu1− xFe1− yS2 transformed into Cu1− x− zS2; from 580 to 700 mV was an active region; and a pseudo-passive region was formed with CuS when the potential was above 700 mV. The smaller charge transfer resistance and passive resistance, as well as the smaller inductive relaxation, revealed how and to what extent the coupled pyrite accelerated the electrochemical dissolution of chalcopyrite.

Enhanced "contact mechanism" for interaction of extracellular polymeric substances with low-grade copper-bearing sulfide ore in bioleaching by moderately thermophilic Acidithiobacillus caldus

In order to enhance the "contact mechanism" governing the interaction of extracellular polymeric substances (EPS) with low-grade copper-bearing sulfide ore for the bioleaching of copper, moderately thermophilic Acidithiobacillus caldus was subjected to exogenous intervention with iron and sulfur. The enhancement of the contact mechanism was systematically investigated by evaluating the attached cells/EPS dynamics, intracellular adenosine triphosphate (ATP), cell functional groups, gene transcriptional level, and ore characteristics. Confocal laser scanning microscopy (CLSM) revealed that exogenous intervention with iron and sulfur led to the production of a denser EPS layer and faster adsorption of the attached cells to the ore based on differential fluorescence staining, which indicated enhancement of the "contact mechanism". The increased intracellular ATP content of the attached cells in the exogenous substrate system provided the required energy for the adsorption processes associated with the "contact mechanism". Fourier-transform infrared spectroscopic (FTIR) analysis of the attached cells and the ore showed a dramatic shift of the NH and COS peaks (associated with EPS formation), whereas the FTIR peaks of SO and SO₄^2- associated with sulfur metabolism were also significantly influenced. Moreover, reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that the expression of genes related to cellular energy metabolism (nuoB, nuoC, atpE, atpF), sulfur metabolism (sor, sqr, sdo, soxA), biofilm formation (pgaA, pgaB), and cell colonization (acfA, acfB, acfC, acfD) was up-regulated after exogenous intervention, verifying enhancement of the "contact mechanism" at the transcriptional level. In addition, scanning electron microscopy (SEM) indicated more obvious adsorption traces on the ore surface. X-ray diffraction (XRD) indicated the presence of more complex derivatives, such as Fe₃(SO₄)₄, FeSO₄, Fe₂(SO₄)₃, and Cu₂S, which is suggestive of more active iron/sulfur metabolism with addition of the exogenous iron and sulfur. Overall, a model for bioleaching of low-grade copper-bearing sulfide ore by moderately thermophilic A. caldus was constructed. The results of this investigation should provide a guide for similar industrial bioleaching processes.

Metal biorecovery and bioremediation: Whether or not thermophilic are better than mesophilic microorganisms

Metal mobilization and immobilization catalyzed by microbial action are key processes in environmental biotechnology. Metal mobilization from ores, mining wastes, or solid residues can be used for recovering metals and/or remediating polluted environments; furthermore, immobilization reduces the migration of metals; cleans up effluents plus ground- and surface water; and, moreover, can help to concentrate and recover metals. Usually these processes provide certain advantages over traditional technologies such as more efficient economical and environmentally sustainable results. Since elevated temperatures typically increase chemical kinetics, it could be expected that bioprocesses should also be enhanced by replacing mesophiles with thermophiles or hyperthermophiles. Nevertheless, other issues like process stability, flexibility, and thermophile-versus-mesophile resistance to acidity and/or metal toxicity should be carefully considered. This review critically analyzes and compares thermophilic and mesophilic microbial performances in recent and selected representative examples of metal bioremediation and biorecovery.