The development of visible-light-responsive photocatalysts with high efficiency, stability, and eco-friendly nature is beneficial to the large-scale application of solar hydrogen production. In this ...work, the production of biosynthetic ternary ZnCdS photocatalysts (Eg = 2.35-2.72 eV) by sulfate-reducing bacteria (SRB) under mild conditions was carried out for the first time. The huge amount of biogenic S
and inherent extracellular proteins (EPs) secreted by SRB are important components of rapid extracellular biosynthesis. The ternary ZnCdS QDs at different molar ratios of Zn
and Cd
from 15:1 to 1:1 were monodisperse spheres with good crystallinity and average crystallite size of 6.12 nm, independent of the molar ratio of Cd
to Zn
. All the ZnCdS QDs had remarkable photocatalytic activity and stability for hydrogen evolution under visible light, without noble metal cocatalysts. Especially, ZnCdS QDs at Zn/Cd = 3:1 showed the highest H
production activity of 3.752 mmol·h
·g
. This excellent performance was due to the high absorption of visible light, the high specific surface area, and the lower recombination rate between photoexcited electrons and holes. The adhered inherent EPs on the ZnCdS QDs slowed down the photocorrosion and improved the stability in photocatalytic hydrogen evolution. This study provides a new direction for solar hydrogen production.
Electroplating sludge contains amounts of valuable/toxic metals as a typical hazardous solid waste, but existing technology is hard to simultaneously gain the high recovery of valuable metals and its ...convert into general solid waste. In this study, indirect bioleaching process was optimized by using RSM for high recovery of four valuable metals (Ni, Cu, Zn and Cr) from electroplating sludge and its shift into general waste. The results showed that the maximum leaching rate respectively was 100% for Ni, 96.5% for Cu, 100% for Zn and 76.1% for Cr at the optimal conditions. In particular, bioleaching saw a much better performance than H2SO4 leaching in removal of highly toxic Cr (76.1% vs. 30.2%). The extraction efficiency of Cr by H2SO4 leaching sharply rose to 72.6% in the presence of 9.0 g/L Fe3+, suggesting that Fe3+ played an important role in the bioleaching of Cr. Based on bioleaching dynamics analysis, it was speculated that Fe3+ passes through the solid shell and enter inside the sludge to attack Cr assisting by extracellular polymeric substances (EPS), leading to high extraction and low residue of Cr. Meanwhile, due to high-efficient release and removal of valuable/toxic metals by bioleaching, the bioleached residues successfully degraded into general based on TCLP test and can be reused as construction material safely.
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•Active bioleachate leaching of electroplating sludge.•Rapid and efficient extraction of valuable metals by the active bioleachate.•The bioleaching process has some advantages over simple chemical leaching.•Determining the optimal process parameters by response surface method.•Detoxification of electroplating sludge was realized through bioleaching.
The pyrometallurgy coupling indirect bioleaching strategy is proposed for the recycling of WPCBs to avoid the disadvantages of time-consuming, low processing power, and relatively low efficiency of ...conventional bioleaching. The results show that under the pulp density of 2.5% (w/v), the low content (0.26 wt.%) of Ni in the raw WPCBs is completely extracted by indirect bioleaching, while the release rate of a high content (24.52 wt.%) of Cu is only 46.9%. However, the calcination pretreatment significantly improves Cu release by indirect bioleaching, and 100% Cu extraction is attained from the 600 °C-treated WPCBs at the high pulp density of 5.0% due to the formation of tractable CuO. Conversely, the release of Ni is inhibited by calcination evidently, and the indirect bioleaching efficiency of Ni declines from 34.9% to 10.1% when the pulp density lifts from 2.5% to 10.0% because of the formation of NiO with lower kinetics of acid-dissolution. On the other hand, due to the complete removal of Cu and the formation of insoluble NiO, the toxicity and environmental risk analysis indicates that the bioleaching residue of the 600 °C-treated WPCBs at the pulp density of 5.0% is completely detoxified and can be reused as non-hazardous materials safely, while the combination of the calcination and indirect bioleaching significantly reduces the environmental risk associated with the WPCBs. These findings provide the theoretical basis for a perfect combined process of pyrometallurgy and bioleaching for tackling the WPCBs from a technological perspective.
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•Siliceous tailings were mechanically activated using high-energy grinding.•Activated tailings T3 showed a superior pozzolanic activity.•Cements produced using T3 can meet the requirement of P•O 52.5 ...Portland cement.•Bulk and green disposal of siliceous tailings can be available by using this method.•This method can bring great environmental and economic benefits.
Mineral processing tailings have increased dramatically, owing to the growing demands for minerals and metals over the past decades. These tailings pose significant hazards to local environments and human health. In this paper, the mechanical activation method was applied for improving the pozzolanic activity of siliceous tailings, and the activated siliceous tailings were used as admixtures in cement production. The geometrical characteristics, surface morphology, crystal structure, and pozzolanic activity of activated siliceous tailings were investigated systematically. Mechanical activation can reduce the particle size of tailings and increase the BET specific surface area up to 11.67 m2/g. The pozzolanic activity of activated tailings was enhanced to 81.15%. It is demonstrated that calcium silicate hydrate gels, ettringite (AFt), and hydrotalcite were the main hydrated products of activated tailings. The activated tailings were mixed in proportion with P•O 52.5 Portland cement to produce new cement. The new cement produced using 8% activated tailings can meet the requirement of P•O 52.5 Portland cement, exhibiting superior profits. This is a green method for bulk handling siliceous tailings and substituting Ordinary Portland Cement.
Harmful chemicals present in electric vehicle Li-ion batteries (EV LIBs) can limit the pulp density of bioleaching processes using Acidithiobacillus sp. to 1.0% (w/v) or lower. The strong enhancing ...mechanisms of extracellular polymeric substances (EPS) on the bioleaching of metals from spent EV LIBs at high pulp density (4% w/v) were studied using bio-chemical, spectroscopic, surface structure imaging and bioleaching kinetic methods. Results demonstrated that the added EPS significantly improved bioleaching efficiency of Ni, Co and Mn improved by 42%, 40% and 44%, respectively. EPS addition boosted the growth of cells under adverse conditions to produce more biogenic H+ while Fe3+ and Fe2+ were adsorbed by the biopolymer. This increased Li extraction by acid dissolution and concentrated the Fe3+/Fe2+ cycle via non-contact mechanisms for the subsequent contact bioleaching of Ni, CO and Mn at the EV LIB-bacteria interface. During the leaching process, added EPS improved adhesion of the bacterial cells to the EV LIBs, and the resultant strong interfacial reactions promoted bioleaching of the target metals. Hence, a combination of non-contact and contact mechanisms initiated by the addition of EPS enhanced the bioleaching of spent EV LIBs at high pulp density.
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•Added EPS greatly improve bioleaching yield of spent EV LIBs at pulp density of 4%.•Added EPS boost resistance of cell to toxic chemical to produce more H+ and Fe3+/Fe2+.•Added EPS enhance cell adhesion and oxidation.•EPS increased the interface reaction in favor of leaching.•There is a significant positive correlation between the dissolution efficiency of metals and the concentration of EPS.
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•Utilization of waste Zn-Mn batteries and SCR catalysts.•Novel ZMF@S10 magnetic photocatalysts.•High visible degradation performance of methylene blue.•The low recombination rate of ...photogenerated dots and holes.•Easy to recycle repeated degradation performance is stable.
The ZMF@S10 composite that was synthesized by using spent Zn-Mn batteries and abandon SCR catalyst as the starting materials for magnetic photocatalysts with high photocatalytic activity is successfully prepared in this study. The results showed that the core TiO2 crystal structure will transform from anatase to rutile, which was then covered in the ZMF. The efficient photocatalytic performance of the composites under visible light is due to the inhibition of the recombination rate of photogenerated dots and holes on the surface of ZMF by the presence of rutile TiO2. Besides, all composites show good stability, regeneration performance, and easy recycling.
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•Bioleaching is good at deep As removal from regenerated product of spent SCR catalyst.•Bioleaching results in a maximum As removal of 53.1% at a high pulp density of ...10%.•Corresponding As residue of 174 mg/kg below limiting value of 200 mg/kg is attained.•Strong activation of regenerated product occurs by bioleaching along with As removal.•Cells secrete an amount of cysteine accounting for As removal and product activation.
Selective catalytic reaction (SCR) is widely used in flue gas denitrification to convert NOx air pollutants into N2 and H2O in the presence of SCR catalyst, but arsenic poisoning causes serious deactivation of SCR catalyst and produces a huge amount of spent SCR catalyst worldwide. Therefore, the regeneration and recycling of spent SCR catalysts are of great necessity for the sustainable flue gas denitrification due to the very high cost of replacing commercial catalysts. Nowadays, a combination of alkali treatment and acid washing is usually used to regenerate spent SCR catalysts. However, high residue of As strongly inhibits the catalytic activity of the regenerated products. In this study, an active bioleaching liquor produced by Acidithiobacillus thiooxidans as indirect bioleaching was attempted to deeply remove As from the regenerated product for the first time. The results showed that bioleaching resulted in maximal As removal of 53.1% even at a high pulp density of 10% to harvest a minimum As residue of 174 mg/kg below the limiting value of 200 mg/kg; whereas H2SO4 leaching attained 6.7% As removal and as high as 345 mg/kg of As residue. A stronger activation of the regenerated products simultaneously occurred with the bioleaching. A great amount of cysteine in the bioleaching liquor secreted by the microbe accounts for both the enhancement of As removal and strong activation of the product. A novel mechanism is proposed to explain the excellent As removal by the indirect bioleaching based on nucleophilic attack of the sulfhydryl groups in cysteine.
The vital functions of extracellular polymeric substances (EPS) have been well recognized in bioleaching of sulfide ores. However, no report is available about the role of EPS in bioleaching of spent ...catalyst. To completely and deeply understand the functions of EPS in bioleaching of spent catalyst, the generation behavior of EPS at various pulp densities during bioleaching was characterized by three-dimensional excitation-emission matrix (3DEEM), and its relevance with bioleaching performance and process parameters were analyzed using mathematical means. The results showed that the EPS contain humus-like substances as main component (>70%) and protein-like substances as minor component (<30%). Both total EPS and humus-like substances mainly keep growing over the whole duration of bioleaching at low pulp density of 5.0% or lower; whereas total EPS and humus-like fraction keep declining at high pulp density of 7.5% or higher. Among the total EPS and its components, humus-like substances only have a positive significant correlation with bioleaching efficiencies of both Co and Mo and affect bioleaching process more greatly due to greater correlation coefficient. Biofilm appears at the spent catalyst surface under 2.5% of pulp density mediated by EPS while no biofilm occurs at 10% of pulp density due to shortage of EPS, accounting for the great difference in bioleaching efficiencies between high and low pulp densities which are 48.3% for Mo and 50.0% for Co at 10% of pulp density as well as 75.9% for Mo and 78.8% for Co at 2.5% of pulp density, respectively.
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•The EPS contains above 70% humus-like substances and below 30% protein-like substances.•Total EPS and humus-like part kept rising over bioleaching period at low pulp density.•Total EPS and humus-like part kept falling over leaching period at high pulp density.•Biofilm appears at spent catalyst surface at low pulp density of 2.5% mediated by the EPS.•Humus-like substances have positive significant link with bioleaching yield of both Co and Mo.
A large amount of sulfur-bearing hazardous wastes, including sulfur sludge, are generated in the production and processing of oil/natural gas/coal gas/biomass gas, which are difficult to dispose of ...with traditional processes, such as incineration or landfills. In the present work, a homemade membrane bioreactor (MBR) with an efficient volume of 10 m3 was utilized to continuously and efficiently remove sulfur (S0) from sulfur sludge and produce sulfuric acid (H2SO4) by using chemoautotrophic acidophilic cells on an industrial scale for the first time. The bio-oxidation process was also modelled and optimized by using response surface methodology. The quadratic models describe the causal relationships between the production rate of H2SO4 at pH 1.0 or the time required for the pH to decrease to 1.0 and three important control parameters (temperature, aeration rate and stirring velocity). The MBR maintained high-density growth of cells (≈2.1 × 109/mL) throughout the entire operational period due to the excellent interception performance, establishing a basis for efficient sulfur removal and H2SO4 production. Under the optimized process controls of 33.6 °C for the temperature, 3.1 m3/min for the aeration rate and 83 rpm for the stirring velocity, a high production efficiency of H2SO4 at pH 1.0 (≈850 L/h) is obtained. Accordingly, the sulfur removal efficiency and sulfur residual concentrations reached 93% and 4.1% after 20 days of contact, respectively. The current study demonstrates that the MBR is suitable for industrial scale operations, for continuous and efficient sulfur removal and for production of H2SO4 from sulfur-bearing hazardous wastes. The green microbial means not only save very expensive disposal expense of sulfur-bearing hazardous wastes but also gain benefits through the manufacture of valuable H2SO4, displaying great business value and wide application prospect.
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•Membrane bioreactor keeps much high density of acidophilic cells for efficient oxidation of S0.•A maximum H2SO4 production of ≈850 L/h with pH 1.0 is obtained under optimizing conditions.•The sulfur removal efficiency in sulfur sludge reaches 93% after 20 days due to oxidation of S0.•The sulfur residual content in sulfur sludge drops to 4.1% after 20 days due to sulfur removal.•Membrane bioreactor is qualified for sulfur removal and production of H2SO4 from sulfur sludge.
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