This study investigates the leaching kinetics of vanadium (V) and molybdenum (Mo) from calcification-roasted waste hydrogenation catalysts in sulfuric acid. XRD analysis confirms V and Mo exist as CaV2O6 and CaMoO4, respectively. Kinetic analysis shows that both metals follow the shrinking core model with product layer diffusion control (R2 > 0.98). For V, the activation energy is 10.2 kJ mol−1 with a reaction order of 0.64, indicating physical diffusion control through a loose product layer. For Mo, the activation energy is 43.8 kJ mol−1 with a reaction order of 0.81. Although exceeding the classical diffusion control range, this value is attributed to diffusion through a dense CaSO4 product layer formed during leaching, which significantly increases mass transfer resistance. The macroscopic kinetic equations were established for both metals. This study elucidates the differential kinetic behaviors of V and Mo and provides theoretical guidance for optimizing waste hydrogenation catalysts recycling.
The sustainable recovery of vanadium from low-grade V–Ti–magnetite concentrate faces challenges in conventional processes, including high reagent costs, generation of sodium-rich wastewater, and energy-intensive evaporation steps. Aiming at the problems of high cost of pure sulfuric acid leaching and difficult disposal of titanium dioxide waste acid or titanium white waste acid (TWWA) in traditional vanadium extraction processes, this study introduces an integrated calcification roasting–titanium dioxide waste acid leaching route. This waste acid is produced in the sulfuric acid process for the TiO₂ white pigment production abbreviated as TWWA. The new route enables simultaneous vanadium extraction and reutilization of TWWA, establishing an industrial symbiosis model. The novelty of this work lies in achieving the collaborative disposal of TWWA and vanadium extraction from V–Ti–magnetite concentrate, and revealing the phase transformation and kinetics of chemical reactions of vanadium during roasting and leaching. Under optimized conditions- CaCO₃ dosage of 6 wt%, roasting temperature of 1373 K, roasting time of 2 h, leaching temperature of 333 K, and leaching time of 3 h—vanadium leaching efficiency reached 95.7%, with residual vanadium content in the leach residue reduced to 0.03 wt%. Mechanistic analysis indicates that vanadium is released from spinel structures and converted into acid-soluble Ca₃V₂O₈, facilitating selective leaching. Reaction kinetics prove that the leaching process is controlled by interfacial chemical reaction with an apparent activation energy of 98.9 kJ/mol. Compared with conventional sodium roasting methods, the proposed approach offers advantages in reagent substitution, waste reduction, and closed-loop resource utilization. This work presents a low-carbon circular pathway that integrates vanadium extraction with effective use of Titanium dioxide waste acid (TDWA).
Phosphorus (P) recovery from basic oxygen furnace (BOF) slag is of great importance for the sustainable resource utilization, but its efficient recovery is hindered. To achieve efficient recovery of P and utilization of all components, a novel process involving high-temperature modification treatment, selective leaching, and precipitation was proposed. In this study, BOF slag was remelted with red mud (RM) rich in Fe2O3 to investigate the mineralogical reconstruction and then the P-bearing phase was leached selectively. The results showed that RM addition achieved phase reconstruction, promoted the formation of Fe-bearing phases, and facilitated P enrichment in the C2S-C3P solid solution. Acid leaching results showed that RM modification significantly enhanced P extraction. The slag modified with 30 wt% RM achieved the highest leaching efficiency of P, reaching about 80% at pH = 2, while Fe, Al, and Mn remained largely insoluble, achieving selective leaching. The C2S-C3P solid solution was preferentially dissolved, whereas the Fe-bearing phases remained in the residue, which can be reused inside steelmaking process. Subsequent pH-controlled precipitation of the leachate with Ca(OH)2 achieved a P precipitation efficiency of about 98% at pH 8 and an overall P recovery (%) of about 78.4% from BOF slag. The precipitation was identified as hydroxyapatite with 17.4 wt% P2O5, indicating its potential application as a fertilizer. This study provided a novel strategy for coprocessing of BOF slag and RM, achieving efficient recovery of P and reutilization of Fe sources from both BOF slag and RM.
The rapid growth of end-of-life photovoltaic modules has raised increasing concerns regarding lead contamination and the loss of valuable resources, particularly silicon and silver. Conventional nitric acid leaching can effectively recover silver but is associated with nitrogen oxide emissions and the co-dissolution of impurities, which complicate subsequent separation and purification. In this study, an ultrasound-assisted acetic acid–hydrogen peroxide leaching process was developed for the green and efficient recovery of silver from end-of-life crystalline silicon photovoltaic cell powder. The leaching parameters were optimised using single-factor experiments and response surface methodology. Under the optimal conditions, the silver leaching efficiency reached 98.1%. Moreover, the results indicate that increasing ultrasonic power intensified the heating effect during leaching, with the effect becoming more pronounced as the irradiation time increased. Therefore, the enhancement of Ag leaching under ultrasonic irradiation may be associated not only with intensified cavitation and mass transfer but also with the increase in slurry temperature. A screening-level sustainability comparison further demonstrated that the proposed process offers a clear environmental advantage by reducing the risk of nitrogen oxide emissions and nitrate/total nitrogen loading in the leachate. However, its advantages in terms of leachate volume and energy consumption were found to be scenario-dependent. Therefore, further evaluation should consider downstream silver separation, wastewater treatment, chemical oxygen demand management, and acid recycling.
To address the wastewater treatment challenge involving di-(2-ethylhexyl) phosphoric acid (P204), this study employed membrane separation techniques to investigate the separation of the P204/Na2SO4 system. Using 1,2-bis(triethoxysilyl) ethane (BTESE) as the precursor, an organic-inorganic hybrid SiO2 membrane was prepared with the sol-gel method. The resultant pure BTESE membrane exhibited a pure water permeation coefficient of 42.3 L m−2 h−1 bar−1. The rejection for P204 and Na2SO4 were 91.0% and 87.7%, respectively, indicating an inability to achieve effective separation of the two substances. To reduce the rejection of Na2SO4, a BTESE/PEI composite membrane was constructed by coating polyethyleneimine (PEI) on the surface of the BTESE membrane. The introduced PEI endowed the membrane with positive surface charges, achieving a synergistic separation effect combining size sieving and electrostatic repulsion. The results showed that the pure water permeation coefficient of the BTESE/PEI-0.1 wt% (BP-0.1 wt%) composite membrane was 36.4 L m−2 h−1 bar−1, with the rejection for P204 remaining at 85.9%, while the rejection for Na2SO4 decreased to 19.0%, successfully achieving the selective separation of the two substances. Nevertheless, when applied to real high-salt wastewater, the rejection of P204 and Na2SO4 drop sharply to 20.7% and 14.6%, respectively. Such performance degradation is mainly attributed to the salting-out effect under high-salt conditions. It distorts the solvation layer and aggregation state of P204 molecules, allowing P204 to pass through membrane pores and deteriorating the membrane's selective separation ability.
