Thermal catalysis under dark ambient conditions in environmental remediation: fundamental principles, development, and challenges

Thermal catalytic degradation of organic pollutants conducted in the dark at room temperature under atmospheric pressure without the need of external chemicals and energy sources has attracted a lot of attention over the last two decades. It provides unparalleled advantages over other advanced oxidation processes (AOPs) in treating domestic and industrial contaminated wastewater from the viewpoint of energy/chemical conservation and ease of operation. Rich knowledge has been accumulated in terms of the synthesis and application of thermal catalysts though controversies remain regarding their underlying mechanisms. This review sheds light on the proposed thermo-catalysis mechanism for the first time and presents the development of thermal catalysts under dark ambient conditions with a focus on catalyst materials, catalytic activity, and mechanism. The present review aims to provide mechanistic insights into the rational design of novel and efficient catalysts, and their underlying mechanisms as well as the emerging challenges and perspectives in thermo-catalysis under dark ambient conditions used for the practical and efficient treatment of contaminated wastewater

Establishment of electrochemical methods to examine the adsorption of flotation surfactants onto a mineral surface

BACKGROUND Significant efforts have been devoted to examine the adsorption of flotation surfactants in both mechanistic studies and process implementations. However, quantitative electrochemical methods for flotation surfactant adsorption examination have not been well-established, despite of their low-cost, accurate, in-situ nature.RESULTS In this paper, voltametric measurement was proven to quantitatively examine the adsorption of activating copper and lead ions onto a pyrite surface. The activation was achieved by abrading minerals in a heavy-metal-bearing solution and the measurements were performed by transferring the minerals to a solution free of those heavy metals. This provided a simple but realistic simulation of the mineral grinding process and simplified the adsorption quantification by excluding any other irrelevant electrochemical reactions near the surface. Reliable electrochemical impedance spectroscopy (EIS) upon adsorption with convincing physical models for interpreting the interfacial structures also were obtained in this paper. The additional pseudocapacitive behaviour of the copper sulfide surface layer led to an increased capacitance of the measured EIS. A resistive but ion-permeable xanthate adsorption layer exhibited its own relaxation process. Voltammetry and impedance studies showed that cyanide competed with both copper and lead for their adsorption, whereas lead activation showed greater tolerance to cyanide than copper did.CONCLUSION Electrochemical methods have been established to examine the adsorption of copper, lead and xanthate onto pyrite surface, in relation to various flotation conditions, which exhibited significant implication to the flotation of pyritic gold ore using cyanide-bearing water. (c) 2020 Society of Chemical Industr

Preparation and properties of epoxy resin-coated micro-sized ferrosilicon powder

Ferrosilicon powder surface coated with a dense epoxy resin membrane was prepared via coating precipitation methods using silane coupling agents as the modifier and epoxy resin as the coating agent. FTIR, FESEM, MPMS-XL, and TG-DSC were used to analyze the morphology, surface composition, magnetic property and thermostability of ferrosilicon powder before and after the modification and coating. The experimental results indicate that epoxy resin membranes of a certain thickness were successfully coated onto the surface of ferrosilicon powder; coatings of epoxy resin contributed to the decreased the rate of weight loss via the reduced wear of the coatings and provided resistance to corrosion; the apparent viscosity of medium suspension with coated ferrosilicon was smaller than that of magnetite. Meanwhile, analysis reveals that room-temperature magnetic hysteresis loops of ferrosilicon powder remain basically unchanged before and after coating

Simulation and observation of magnetic mineral particles aggregating into chains in a uniform magnetic field

Based on the theory of magnetic dipoles, the 3D characteristics of the magnetic potential energy of magnetic particles in a magnetic field were analyzed, and the interaction force formula between the magnetic particles was derived. Additionally, the Velocity Verlet algorithm was adopted to simulate the interaction of soft magnetic particles, which were compared against the observed 2D dynamic processes of magnetite particles. The observational results are largely consistent with the simulation, which considers both the magnetic dipole force and the viscous resistance that occurs during the interaction of soft magnetic particles. Nevertheless, significant difference exists between the 2D dynamic observation and the simulation for the interaction of magnetite particles. Three series of experiments and simulation show that all the magnetic particles are arranged in chain structures and orientated along the direction of the external magnetic field. Furthermore, the results show that the time required for magnetic particles to form magnetic chains is negatively correlated with the intensity of the magnetic field, and positively correlated with the viscosity of the chosen medium

A method to evaluate the overall breakage degree of pre-weakening processing and its applications

The product fineness indicator t and the pre-weakening degree indicator percentage change of A * b value (C) were used to described the two aspects of the breakage result of processing with pre-weakening effect. However, there lacks a method to evaluate the ‘overall’ breakage degree with a single index. It was observed that when the high voltage pulse breakage (HVP breakage or HVPB) induced cracks inside pre-weakened particles were consumed during impact breakage, the breakage characteristics of the progeny particles are the same to raw ore particles. Based on this phenomenon, the concepts of equivalent size S and equivalent size reduction t are proposed. Raw ore particles of size S is ‘equivalent’ to pre-weakened particles of size S in terms of their impact breakage product size distribution. Therefore the value of S and the consequently derived t can be used to evaluate the overall breakage degree of pre-weakened particles. The calculation procedure of S and t is demonstrated in the context of HVP breakage. It is found that the impact breakage product of pre-weakened particles can be well predicted from S. In addition to the evaluation of overall breakage degree of pre-weakening processing, this method also has potential to apply in the simulation of comminution circuits with pre-weakening processing and the development of breakage model for processing with pre-weakening effect

Engineering SrCuxO composition to tailor the degradation activity toward organic pollutant under dark ambient conditions

The composition of SrCu O mixed metal oxides (MMOs) was engineered via varying the amount of copper relative to strontium. As-synthesized SrCu O were highly active for degrading methyl orange (MO) pollutant at dark ambient conditions without the aid of other reagents. The catalytic activity of SrCu O demonstrated a reverse-volcano relationship with copper content. Copper-rich MMOs (SrCu O) exhibited the highest degradation activity for MO by far and degraded ca. 96% MO within 25\ua0min. MO degradation over SrCu O was a surface-catalytic reaction and fitted pseudo-first-order reaction kinetics. The contact between MO molecules and catalyst surface initiated the reaction via the catalytic-active phase (Cu /Cu redox pair), which serves as an electron-transfer shuttle (⋯ Cu → + e Cu → − e Cu ⋯) from MO to dissolved O , inducing the consecutive generation of reactive oxygen species, which resulted in MO degradation as evidenced by radical trapping experiment. XPS and XRD analysis revealed that active phases in SrCu O materials underwent irreversible transformation after reaction, contributing to the observed deactivation in the cycling experiment. The observations in this study demonstrate the significance of chemical composition tailoring in catalyst synthesis for environmental remediation under dark ambient conditions. [Figure not available: see fulltext.]

Inductive effect between atomically dispersed iridium and transition-metal hydroxide nanosheets enables highly efficient oxygen evolution reaction

Oxygen evolution reaction (OER) remains the bottleneck of many energy transformation and storage technologies due to the sluggish kinetics. Transition-metal (TM) hydroxide nanosheets with high-valent TM ions possess high intrinsic catalytic activity toward OER. Herein, by taking advantage of the inductive effect, this work presents a facile and universal strategy to fabricate atomic iridium (Ir) incorporated TM hydroxide nanosheets as highly active OER electrocatalysts. As a representative, the fabricated Ir-Ni(OH) (4 wt% Ir) exhibits remarkable OER performance with a low overpotential (235 mV at 10 mA cm), a small Tafel slope (58.4 mV dec), and excellent durability (60 h) in alkaline solution, significantly outperforming the benchmark IrO and Ni(OH). Mechanism studies unveil that the inductive effect between Ni and Ir endows Ni(OH) with high-valent Ni species, which facilitate the adsorption of nucleophilic intermediates and boost the OER activity and long-term stability of Ir-Ni(OH). More importantly, the reported strategy could be extended to synthesize other monometallic/bimetallic TM hydroxide nanosheets (Co, CoMn) as highly efficient OER electrocatalysts. This work should pave a universal and promising avenue to rationally design and controllably synthesize efficient yet robust OER electrocatalysts in energy-related fields

Growth behavior of iron grains during deep reduction of copper slag

The change in granularity of iron grains in copper slag during coal-based deep reduction was identified using optical microscopy and the Image J analysis software. The growth behavior of iron grains was investigated based on the Hillert dynamic model. The results indicate that the granularity and sphericity of iron grains are strongly affected by the reduction time and temperature during the deep reduction process. It is found that in isothermal condition, the growth rate of iron granularity increases with time exhibiting an S-shape characteristic. Meanwhile, in non-isothermal condition, the growth rate of iron granularity increases exponentially with temperature. When the reduction temperature is in the range of ~1423–1573 K and the reduction time was in the range of ~30–180 min, the grain growth kinetic parameters are calculated as follows: growth index n = 1.424 ± 0.07855, apparent activation energy Q = 116.17 kJ∙mol, and pre-exponential factor as 20,839.38

Effect of feed quantity on breakage degree of ore particles subjected to high voltage pulses

The effect of spatial arrangement of feed sample on the breakage degree of high voltage pulse breakage (HVPB) product was investigated by varying the number of feed particles discharged simultaneously inside a processing vessel. Two kinds of hard porphyry copper ores were treated using the commercial HVPB tester SELFRAG Lab and a custom-made unit respectively. The results indicate that, at given electrode gap and specific energy, the fineness (t10) of HVPB product increases with feed quantity, while the pre-weakening degree (CAb) of HVPB product decreases with feed quantity. A new index of equivalent product fineness (t10e), which reflects the combined effect of\ua0t10\ua0and\ua0CAb, is employed to represent the overall breakage degree of HVPB product. It is found that the value of\ua0t10e\ua0has a positive relation with the feed quantity of HVPB tests. The effect of feed quantity on ore behaviour in HVPB is attributed to the influence of particles bed volume on breakdown strength and the negative effect of water gap between ore particles and top electrode. Finally, it is recommended to take feed quantity into consideration in HVPB studies to obtain comparative testing results, and to select the most appropriate breakage degree indexes from\ua0t10,\ua0CAb\ua0and\ua0t10e\ua0according to research aim. Particularly, electrode gap just filled by feed particles is preferred to optimize the over breakage degree of ore particles