Catalytic regeneration of mercury sorbents

Eco-friendly treatment of copper smelting flue dust for recovering multiple heavy metals with economic and environmental benefits

Handling flue dust in an environmentally friendly manner has become an urgent task for pollution prevention in the copper industry. Here, driven by the low-carbon notion, we report a process that enables the selective retrieval of multiple metals (As, Cu, Pb, Zn, and Bi) from copper smelting flue dust (CSFD). This process employed low-temperature roasting to separate arsenic from heavy metals, thereby eliminating the tedious separation steps required by existing processes. Subsequently, Zn and Cu were dissolved in water, while Pb and Bi were left as a solid residue. We achieved 98.23% extraction of Cu via Zn cementation at a micro-voltage of 0.50 V. Utilizing the difference in solubility, Bi was selectively dissolved from the residue using a NaCl-HCl medium, which enabled the subsequent production of metallic Bi through electrowinning. Finally, more than 99% of Pb in the solid was reduced to elemental Pb by mechanochemical reduction. Through optimized process conditions, high-purity As2O3 (99.04%), lead ingot (99.95%), metallic copper (94.16%), and bismuth (99.20%) were obtained. Our economic assessment revealed significant advantages, demonstrating the industrial feasibility of this process. Consequently, this study presents an effective and cost-efficient system for CSFD disposal while minimizing the environmental impact and fostering a circular economy.

Unveiling Hg-binding protein within black deposit formed on Golgi-Cox-stained brain neuron

BACKGROUND

Golgi-Cox staining has been conventionally used for investigating neuronal development. After the brain tissue is subject to Golgi-Cox staining, black deposits are formed on the surface of the stained neurons because of mercuric sulfide, which does not show a fluorescence response under two-photon excitation. However, we unexpectedly observed fluorescence emitted by these black deposits during two-photon fluorescence measurements. Further, the in-depth of physical and chemical methods analysis revealed that the black deposits on the stained neurons are composed of Hg-binding proteins.

METHODS

We studied black deposits present in the Golgi-Cox-stained mouse brain neurons using techniques such as multiple-photon microscopy, scan electron microscopy, micro-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.

RESULTS

The emitted fluorescence was because of the fluorescence groups of Hg-binding protein present within the Golgi-Cox deposits on the neuronal surface.

CONCLUSIONS

The presence of Hg-binding proteins within black deposits on the surface of Golgi-Cox-stained neurons was proven for the first time. The novel interaction between the neurons and Hg²⁺ ions during Golgi-Cox staining help to understand the mechanism of Golgi-Cox staining.

Elemental mercury removal by a novel advanced oxidation process of ultraviolet/chlorite-ammonia: Mechanism and kinetics

A novel advanced oxidation process (AOP) of ultraviolet/chlorite-ammonia (UV/NaClO₂-NH₄OH) was developed to remove Hg⁰ from flue gas. The distribution of mercury concentration in three solutions of NaClO₂-NH₄OH, KCl, and H₂SO₄-KMnO₄ was determined by cold atom fluorescence spectrometry (AFS). The role of NH₄OH was to help NaClO₂ preserving and/or stabilizing Hg²⁺ meanwhile inhibiting the photo-production of ClO₂. In the absence of UV, decreasing pH promoted the release of Hg²⁺ from NaClO₂-NH₄OH; introducing NO, SO₂, O₂, Br^-, Cl^-, and HCO₃^- suppressed Hg⁰ oxidation. In the presence of UV, rising temperature accelerated the release of Hg²⁺ from NaClO₂-NH₄OH; while SO₂, Br^- and HCO₃^- facilitated Hg⁰ oxidation. In the absence and presence of UV, Hg⁰ oxidation was controlled by ClO₂^- and by ClO/Cl₂O₂/HO/ClO₂, respectively. The formations of ClO/HO/ClO₂ were confirmed by electron spin resonance (ESR). X-ray photoelectron spectroscopy (XPS) revealed that the products of Hg⁰ and ClO₂^- were HgCl₂, and ClO₂, Cl-, ClO₃-, Cl₂, and ClO₄-, respectively. Analysis of kinetics showed that the Hatta numbers were 23-133 and 69-305 without and with UV, respectively, thus, the gas-film mass transfer was the rate-determining step. This paper gives a new insight in radical behavior in Hg⁰ oxidation.

Catalytic removal of mercury from waste carbonaceous catalyst by microwave heating

Waste carbonaceous catalyst (WCC) from vinyl chloride monomer (VCM) production is a potential environmental threat due to the mercury toxicity. Microwave heating (MWH) was used to decontaminate WCC. Treatment temperature had a stronger influence on mercury removal than that of treatment time while mercury removal was highly depended on treatment time at lower temperature. When WCC was treated at 350 °C for 60 min, 400 °C for 30 min and 450 °C or more for 10 min, leaching toxicity of mercury conformed to the US EPA standard. 99.98% of total mercury was removed and residual mercury concentration was only 4.5 mg kg^-1 when treated at 500 °C for 30 min. Soluble and exchangeable Hg and Hg combined with labile organics were more easily to be removed than that of Hg bound to crystalline Fe/Al oxides, Hg combined with non-labile organics and HgS. The removal limit for different mercury species may be achieved at 500 °C. Evaporation removal of mercury followed exponential decay model. Activation energy for mercury removal was reduced due to the catalytic effect of MWH. Removal mechanisms of mercury included thermal evaporation, breakdown of molecular bonds, selective stripping of carbonaceous impurities.

Study on non-isothermal kinetics of the thermal desorption of mercury from spent mercuric chloride catalyst

Kinetics of the thermal desorption of mercury from spent mercury chloride catalysts were investigated using non-isothermal thermal analysis technique. Complex mercury species absorbed on waste catalysts were revealed by sequential extraction procedure. A scheme of six reactions was applied to elucidate mercury desorption kinetics. Activation energy estimated by model-free isoconversional methods is a slightly increasing function of conversion, implying a variation in the mechanism controlling mercury desorption. Average value of apparent activation energy (116.32kJ/mol) calculated by isoconversional Starink method was used to determine reaction mechanism using model-fitting and z(α) master method. One dimensional diffusion appears to govern mercury desorption process in the conversion range of 10%-40%, and then the reaction kinetic is controlled by two and three dimensional diffusion at greater conversion.

Multifunctional polymers built on copper–thioether coordination

Copper–thioether coordinated block polymers were successfully constructed to form mechanically tough materials with a color response towards hydrochloric acid and hydrogen peroxide.

Ag-modified AgI–TiO2 as an excellent and durable catalyst for catalytic oxidation of elemental mercury

Iodine acted as an accelerant for Hg⁰ oxidation, and chlorine further converted the intermediate to the HgCl₂ final product.