Chalcopyrite is one of the most important copper minerals; however, the extracted efficiency of chalcopyrite is still not satisfactory in hydrometallurgy owing to its high lattice energy which leads to its low dissolution kinetics. To overcome the difficulties, many advanced technologies have been developed, including the selection of high effectively bacteria, the inhibition of the passivation film adhered onto the minerals surface, and the maintenance of solution redox potential under an optimum range. Up to date, considerable researches on the first two terms have been summarized, while the overview of the last term has been rarely reported. Based on corresponding works in recent years, key trends and roles of solution redox potential in copper hydrometallurgy, including its definition, effect and maintenance, have been introduced in this review.
Bioleaching is regarded as an essential technology to treat low grade minerals, with the distinctive superiorities of lower-cost and environment-friendly compared with traditional pyrometallurgy method. However, the bioleaching efficiency is unsatisfactory owing to the passivation film formed on the minerals surface. It is of particular interest to know the dissolution and passivation mechanism of sulfide minerals in the presence of microorganism. Although bioleaching can be useful in extracting metals, it is a double-edged sword. Metallurgical activities have caused serious environmental problems such as acid mine drainage (AMD). The understanding of some common sulfide minerals bioleaching processes and protection of Amd environment is reviewed in this article.
Bioleaching experiments combined with X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted to investigate three kinds of bornites from different regions leached by moderately thermophilic mixed bacteria of Leptospirillum ferriphilum YSK, Acidithiobacillus caldus D1 and Sulfobacillus thermosulfidooxidans ST. The results of bioleaching experiments showed that the leaching efficiency and the redox potential were significantly increased. The copper extraction efficiencies of three kinds of bornite maintained rapid growth until around the 12th day and no longer increased after the 18th reaching 83.7%, 96.5% and 86.6%, respectively. The XRD results of the leaching residue indicated that three kinds of bornites all produced jarosite in the late stage of leaching, and the leaching residues from of Daye Museum and Yunnan Geological Museum contained a mass of elemental sulfur. XPS analysis and scanning electron microscopy experiments showed that the surface of mineral particles was jarosite and the copper in the leaching residue was almost dissolved.
A mixed culture of bioleaching microorganisms was enriched. Then the mixed culture was preserved by liquid nitrogen cryopreservation for 6 months and 12 months, respectively, using PEG-2000 as the protective agent. The chalcopyrite leaching ability, activity and diversity of the mixed culture before and after preservation were compared. The results showed that the copper extraction rate was 95.7% in chalcopyrite bioleaching within 20 d by the original culture. After cryopreservation for 6 months and 12 months, the copper extraction rate of the mixed culture was 94.9% within 25 d and 93.6% within 35 d, respectively. The cell viability achieved 87% and 41% after being preserved for 6 months and 12 months, respectively. Furthermore, the ecology analysis identified Acidithiobacillus ferrooxidans, Acidithiobacillus caldus, Sulfobacillus thermotolerans and Pseudomonas aeruginosa in the original mixed culture. After cryopreservation for 12 months, the composition of community changed, but the predominant microorganisms still existed.
Silver ion can be useful in improving chalcopyrite bioleaching efficiency. In this work, leaching kinetics of this process was investigated using silver-bearing solid waste under different chalcopyrite/solid waste ratios. Bioleaching behavior indicates that silver-bearing solid waste can enhance the bioleaching process, and the redox potential is much higher than the proposed appropriate range (380-480 mV vs Ag/AgCl) with the solid waste added. There is a positive correlation between temperature and copper extraction rate. The kinetics data fit well with the shrinking-core model. Under these leaching conditions, the bioleaching of chalcopyrite is controlled by internal diffusion with calculated apparent activation energy (Ea) of 28.24 kJ/mol. This work is possible benificial to promote the industrial application of silver catalyst in leaching of chalcopyrite.
The effects of introducing M. sedula derivatives having different Cu2+-resistance on bioleaching capacity of a defined consortium (consisting of A. brierleyi DSM1651 and M. hakonensis HO1-1) were studied in column reactors at 70 °C. Introducing M. sedula copA mutant, a copper sensitive derivative, only had negligible effects on bioleaching. While introducing M. sedula ARS50-2, a Cu2+ resistant strain, substantially consolidated bioleaching process, with 27.77% more copper recovered after 58 d of bioleaching. Addition of M. sedula ARS50-2 likely enhanced the sulfur oxidation capacity of consortium after the 24th day under the Cu2+ stress. The majority of extreme thermoacidophiles were attached on minerals surface as indicated by quantitative PCR (qPCR) data. Successions of microbial community of extremely thermoacidophilic consortia that attached on surface of minerals were different from those in leachate. M. hakonensis HO1-1 was the dominant species attached on minerals surface in each column reactor throughout bioleaching process. The sessile M. sedula ARS50-2 remained as a major species till the 34th day. A. brierleyi DSM1651 was the most abundant planktonic species in leachate of each column reactor. These results highlight that higher Cu2+-resistance is a beneficial trait for extreme thermoacidophiles to process copper minerals.
For the high sulfur refractory gold concentrate with 41.82% sulfur and 15.12 g/t gold, of which 82.11% was wrapped in sulfide, a well-controlled stirring tank leaching was carried out to improve the bio-oxidation efficiency. Results show that bio-oxidation pretreatment can greatly improve the gold recovery rate of high-sulfur refractory gold concentrate, and at the optimum pH 1.3 in this study, compared with the process without pH control, the oxidation rate of sulfur increased from 79.31% to 83.29%, while the recovery rate of gold increased from 76.54% to 83.23%; under this condition the activity of mixed culture could be sustained and the formation of jarosite could diminish. The results also displayed that for the high sulfur refractory gold concentrate, the recovery of gold is positively correlated with the oxidation rate of sulfur, and the recovery rate of gold increases with the increase of sulfur oxidation rate within a certain range.
To design heap biooxidation process, it is necessary to understand its internal rules. The heap biooxidation of gold ore from Anhui province was researched in this study. The results showed that the main microorganisms in the heap were A. ferrooxidans, F. acidiphilum and L. ferrodiazotrophum. Under their combined action, gold leaching extent rose from 35.62% to 78.08% in 80 d. Boltzmann model matches the actual oxidation effect better and the model equations were obtained. The model predicted that the oxidation extents of arsenic and sulfur are 58.577% and 42.122% after one year, and the gold leaching extent was 80.40%. The arsenic and sulfur oxidation extents, and gold leaching extent were all linearly correlated. It is more reliable to predict gold leaching extent by sulfur oxidation extent. These results provided good guidance for practical application in the actual production.
Forced aeration is an effective way to accelerate the heap bioleaching process. To reveal the effects of different irrigation and aeration combinations on bioleaching performance of copper sulfides, numerical simulations with Comsol were carried out. Results showed the oxygen concentration is the highest at the bottom with forced aeration, the airflow transports spherically from the aeration pipeline to the slope, and the horizontal diffusion distance is further than vertical value. When the irrigation-to-aeration ratio is higher, the average heap temperatures are mainly decided by aeration rates; otherwise, temperature distributions are the equilibrium of mineral reaction heat, the livixiant driven heat and the airflow driven heat. When the aeration rate is higher than 0.90 m3/(m2·h), oxygen concentration is no longer a limiting factor for mineral dissolution. Additionally, on the premise of sufficient oxygen supply, Cu recovery rate is higher at the bottom with low irrigation rate; while it is higher at upper regions with high irrigation rate. The numerical analysis uncovered some insights into the dynamics and thermodynamics rules in bioleaching of copper sulfides with forced aeration.
Ferroplasma thermophilum, a sort of extreme acidophilic archaea, which can synthesize intracellular cobalt ferrite nanocrystals, is investigated in this study. The nanocrystals were analyzed with ultrathin sections and transmission electron microscope, with the size of 20–60 nm, the number of more than 30 in each cell at average, which indicated that F. thermophilum can synthesize intracellular nanocrystals and also belongs to high-yield nanocrystals-producing strain. Intriguingly, the nanocrystals contain ferrite and cobalt characterized by EDS X-ray analysis, suggesting that both cobalt and ferrite are potentially contributed to the formation of nanocrystals. Moreover, under the different energy source culture conditions of FeSO4 and CuFeS2, the size and the morphology of the nanocrystals are different. It was also found that the higher initial Fe availability leads to an induced synthesis of larger nanocrystals and the lower oxidation-reduction potential (ORP) leads to an induced effect on the synthesis of nanocrystals with abnormal unhomogeneous size, which suggested that the higher initial Fe availability and the lower oxidation-reduction potential lead to a higher uptake efficiency of iron ions of F. thermophilum by iron and ORP gradient culture.
Leptospirillum ferriphilum YSK was added to a native consortium of bioleaching bacteria including Acidithiobacillus caldus, A. thiooxidans, A. ferrooxidans, Sulfobacillus thermosulfidooxidans, Acidiphilium spp., and Ferroplasma thermophilum cultured in modified 9K medium containing 0.5% (W/V) pyrite. The bioleaching efficiency markedly increased. Changes in community structure and gene expression were monitored with real-time PCR and functional gene arrays. Dynamic changes that varied in different populations in the consortium occurred after the addition of L. ferriphilum YSK, with growth of A. caldus S1, A. thiooxidans A01, Acidiphillum spp. DX1-1 promoted the growth of Ferroplasma L1, inhibited that of S. thermosulfidooxidans ST, and exerted little effect on that of A. ferrooxidans CMS. Genes encoding ADP heptose, phosphoheptose isomerase, glycosyltransferase, biotin carboxylase, and protoheme ferrolyase from L. ferriphilum, acetyl-CoA carboxylase from Acidiphillum spp., and doxD from A. caldus were up-regulated in 0–20 h. Genes encoding lipid A disaccharide synthase LpxB, glycosyl transferase, and ADP heptose synthase from A. ferrooxidans were up-regulated in 0–8 h and then down-regulated in 8–20 h. Genes encoding ferredoxin oxidoreductase from Ferroplasma sp. were up-regulated in 0–4 h, down-regulated in 4–16 h, and again up-regulated in 16–20 h. CbbS from A. ferrooxidans was down-regulated in 0–20 h.
In this paper, Sulfobacillus thermosulfidooxidans ST was selected for use in bioleaching of pyrite and chalcopyrite. The adsorption experiments revealed that more cells were adsorbed on the surface of pyrite than on the surface of chalcopyrite. The role of extracellular DNA (eDNA) in the bioleaching process was investigated by depletion of eDNA using DNase I. The number of cells attached on the chalcopyrite and pyrite surfaces decreased on a large scale, and the lag phase of cell growth increased, causing the leaching percentages of pyrite and chalcopyrite to decrease by approximately 11.6% and 20.5%, respectively. The formation and distribution of eDNA secreted during bioleaching was assessed by a fluorescent dye-based method and visualized by confocal laser scanning microscopy (CLSM). The content of eDNA increased with bioleaching time. Furthermore, ST showed a stronger capacity to produce eDNA on the surface of pyrite than on the surface of chalcopyrite. These results showed that the removal of eDNA has a more significant effect on the bioleaching of chalcopyrite than on pyrite.
Microorganisms, one of the key factors affecting the bioleaching process, change the components of extracellular polymeric substance (EPS) and community structure to survive in leaching environments. In this work, Fourier transform infrared (FTIR), X-ray powder diffraction (XRD) and 16S rDna high-throughput sequence analyses were used to reveal the microbial changes in planktonic and sessile phases during bioleaching. The results showed the occupation of sessile cells decreased from 66.2% to (10±3)%. After bioleaching, the planktonic and sessile cells have similar EPS, but they are different from the original cells. Pyrite dissolution mainly occurs at the early and late stages with the decreasing of particle diameter, by 50% and 40%, respectively. The 16S rDna gene based sequence analysis results in total of 1117420 Reads across the six samples, presented among 7 phyla, 9 classes, 17 orders, 23 families and 31 genera. Genera Leptospirillum and Sulfobacillus are the main bacteria at the early and middle stages, and Leptospirillum is the main genus at the end of bioleaching. Aquabacterium and Acidovorax are special genera in sessile cells and Weissella is special in planktonic ones.
The growing characteristics of metallic iron particles during reductive roasting of boron-bearing magnetite concentrate under different conditions were investigated. The size of the metallic iron particles was quantitatively measured via optical image analysis with consideration of size calibration and weighted ratio of image numbers in the core, middle and periphery zones of cross-section of pellets. In order to guarantee the measurement accuracy 54 images were captured in total for each specimen, with a weighted ratio of 1:7:19 with respect to the core, middle and periphery section of the cross-section of pellets. Increasing reduction temperature and time is favorable to the growth of metallic iron particles. Based on the modification of particle size measurement, in terms of time (t) and temperature (T) a predicting model of metallic iron particle size (D), was established as: D=125-0.112t-0.2352T-5.355×10-4t2+2.032× 10-4tT +1.134×10-4T2.
The gold dissolution in anoxic cyanide solution in the presence of chalcopyrite was studied with a rotating disc electrode. It was found that the presence of chalcopyrite reduced and enhanced the dissolution activity of pure gold in the low and high potential regions, respectively. The dissolution of gold was diffusion-controlled at low potentials (≤177 mV) and low cyanide concentrations (≤980 mg/L); however, above the cyanide concentration of 980 mg/L, the current density of gold decreased and the dissolution of gold changed from diffusion-control to electrochemical reaction-control. At high potentials (>177 mV), gold dissolution was always controlled by diffusion. In cyanide solution containing chalcopyrite, appropriate increase of pH value and temperature could accelerate the dissolution of gold, but high pH value would promote the generation of passivation, which was harmful for the dissolution of gold in cyanide solution.
A hydroxyl-functionalized magnetic fungus nanocomposite (MFH@GO) was prepared by a simple one-pot method for the removal of Cr(VI) from wastewater. The adsorption behavior of MFH@GO to Cr(VI) in wastewater was discussed in detail. At pH of 5.0 and temperature of 323.15 K, MFH@GO had higher adsorption capacity to Cr(VI) (58.4 mg/g) than the unmodified fungus and GO. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetry and differential thermal analysis (TG-DTA), scanning electron microscopy and energy dispersive X-Ray spectroscopy (SEM-EDX) were employed to determine the characteristics of MFH@GO. Results showed that magnetic graphene oxide nanoparticles significantly enhanced the physiochemical properties of the fungi. In addition, the adsorption mechanisms analyses show that Cr(VI) could be reduced and mineralized into ferric chromate in residues. These results suggested that MFH@GO could be used as an promising and alternative biosorbent for removal of Cr(VI) from industrial wastewater.
This study investigates tribological performance of MoS2 coating on slipper pair in axial piston pump. Firstly, the MoS2 coating on the surface of slipper pair was prepared by atmospheric plasma spraying treatment technology. Secondly, the tribological characteristics of slipper pair under various working conditions were evaluated on ring-on-block tester in oil lubrication. The original and worn surfaces of the specimens were analyzed with scanning electron microscope and energy dispersive spectrometer, and then the wear morphologies of the MoS2 coatings were imaged by X-ray photoelectron spectroscopy. The experimental results showed that the friction coefficients of Cu-based materials with MoS2 coating decreased by about 0.05 at 800 N. Especially, when the external load was set to 800 N, the wear rate of the ZY331608 decreased by about 16.4% after the substrates were treated by the MoS2 coating, which exhibited excellent anti-friction and wear resistance. The formation of the MoS2 lubricating film could be classified into four stages, including the initial friction stage, anchoring stage of MoS2 on friction surface, covering stage of the sliding surface by MoS2 and the formation stage of MoS2 film. The dominating wear mechanisms of Cu-based materials with MoS2 coating were adhesive wear and abrasive wear accompanied with oxidative wear.
To study the flexural behavior and calculation model, 8 coral aggregate concrete (CAC) beams with different types of steel were designed. The flexural behavior of CAC beam was tested. The failure mode, bearing capacity, the maximum crack width (ws) and average crack spacing (lm) were studied. A calculation model for the bearing capacity of CAC beam was proposed. The results indicated that with the steel strength increased, the cracking moment (Mcr) and ultimate moment (Mu) of CAC beam increased, and the development of the ws gradually slowed, which effectively inhibited the formation of cracks and improved the flexural behavior of CAC beam. For CAC structures in the ocean engineering, it is recommended to use organic new coated steel to extend its effective service life. In addition, considering the influence of steel corrosion, a calculation model for the Mcr, Mu, lm and ws of CAC beam was established.
To investigate the effect of alternating magnetic field on austenite transformation process in the case of rapid heating, the austenite kinetics model of AISI 1045 steel was built for spot continual induction hardening (SCIH) process. The results shows that the effect of alternating magnetic field on austenite transformation fraction reaches the maximum (about 3%) when heating rate is the lowest. Relatively low magnetic flux density still has a certain effect on the austenite transformation process during the SCIH process. Concave surface structure can reduce the influence scope of alternating magnetic field on surface in all cases and the minimum influence scope appears when the feed path of inductor is longitudinal. Convex surface structure can minimize the influence scope of alternating magnetic field in depth when the feed path of inductor is longitudinal. The austenite distribution of transitional region on surface for horizontal movement is more uniform than that for longitudinal movement. The austenite distribution of transitional region in depth for longitudinal movement is more uniform than that for horizontal movement. The simulated results are consistent with the experimental results and the austenite transformation kinetics model developed for SCIH process is valid.
There is a relatively complex flow state inside the high speed on-off valve, which often produces low pressure area and oil reflux in the high-speed opening and closing process of the spool, causing cavitation and vortex and other phenomena. These phenomena will affect the stability of the internal flow field of the plate valve and the flow characteristics of the high speed on-off valve. Aiming at the problems of small flow rate and instability of internal flow field, a new spool structure was designed. The flow field models of two-hole and three-hole plate spools with different openings were established, and software Ansys Workbench was chosen to mesh the model. The standard k-ε turbulence model was selected for numerical simulation using Fluent software. The pressure distribution and velocity distribution under the same pressure and different opening degree were obtained. The structure and parameters of the optimization model were also obtained. The stability analysis of flow field under different pressure was carried out. The results demonstrate that the three-hole spool has a similar flow field change with the two-hole spool, but it does not create a low pressure zone, and the three-hole spool can work stably at 2 MPa or less. This method improves the appearance of low pressure area and oil backflow in the process of high speed opening and closing of spool. The stability of flow field and the flow rate of high speed switch valve are improved. Finally, the products designed in this paper are compared with existing hydraulic valve products. The results show that the three-hole plate type high speed on-off valve designed in this paper maintains the stability of the internal flow field under the condition of 200 Hz and large opening degree, and realizes the increase of flow rate.
The evolution of temperature field of the continual motion induction cladding and the depth of heat affected zone are studied in this study. A three-dimensional finite element model for the point type continual induction cladding is established to investigate temperature distributions of fixed and motion induction cladding modes. The novel inductor is designed for cladding of curved surfaces. The modeling reliability is verified by the temperature measurements. The influence of process parameters on the maximum temperature and the generation and transfer of heat are studied. Quantitative calculation is performed to its melting rate to verify the temperature distribution and microstructures. The results show that a good metallurgical bond can be formed between the cladding layer and substrate. The melting rate gradually falls from the top of the cladding layer to the substrate, and the grain size in the substrate gradually rises. The heat affected zone is relatively small compared to integral heating.
This paper presents a risk evaluation model of water and mud inrush for tunnel excavation in karst areas. The factors affecting the probabilities of water and mud inrush in karst tunnels are investigated to define the dangerousness of this geological disaster. The losses that are caused by water and mud inrush are taken into consideration to account for its harmfulness. Then a risk evaluation model based on the dangerousness-harmfulness evaluation indicator system is constructed, which is more convincing in comparison with the traditional methods. The catastrophe theory is used to evaluate the risk level of water and mud inrush and it has great advantage in handling problems involving discontinuous catastrophe processes. To validate the proposed approach, the Qiyueshan tunnel of Yichang-Wanzhou Railway is taken as an example in which four target segments are evaluated using the risk evaluation model. Finally, the evaluation results are compared with the excavation data, which shows that the risk levels predicted by the proposed approach are in good agreements with that observed in engineering. In conclusion, the catastrophe theory-based risk evaluation model is an efficient and effective approach for water and mud inrush in karst tunnels.
Anchor bolts are commonly used throughout underground mining and tunnelling operations to improve roof stability. However, premature failures of anchor bolts are significant safety risks in underground excavations around the world due to susceptible bolt materials, a moist and corrosive environment and tensile stress. In this paper, laboratory experiments and hydrogeochemical models were combined to investigate anchor bolt corrosion and failure associated with aqueous environments in underground coal mines. Experimental data and collated mine water chemistry data were used to simulate bolt corrosion reactions with groundwater and rock materials with the PHREEQC code. A series of models quantified reactions involving iron and carbon under aerobic and anaerobic conditions in comparison with ion, pH and pE trends in experimental data. The models showed that corrosion processes are inhibited by some natural environmental factors, because dissolved oxygen would cause more iron from the bolts to oxidize into solution. These interdisciplinary insights into corrosion failure of underground anchor bolts confirm that environmental factors are important contributors to stress corrosion cracking.