Enhancement of elemental mercury adsorption by silver supported material

Mercury, generally found in natural gas, is extremely hazardous. Although average mercury levels are relatively low, they are further reduced to comply with future mercury regulations, which are stringent in order to avoid releasing to the environment. Herein, vapor mercury adsorption was therefore investigated using two kinds of supports, granular activated carbon (GAC) and titanium dioxide (TiO₂). Both supports were impregnated by silver (5 and 15 wt.%), before testing against a commercial adsorbent (sulfur-impregnated activated carbon, SAC). The adsorption isotherm, kinetics, and its thermodynamics of mercury adsorption were reported. The results revealed that Langmuir isotherm provided a better fit to the experimental data. Pseudo second-order was applicable to describe adsorption kinetics. The higher uniform Ag dispersion was a key factor for the higher mercury uptake. TiO₂ supported silver adsorbent showed higher mercury adsorption than the commercial one by approximately 2 times. Chemisorption of mercury onto silver active sites was confirmed by an amalgam formation found in the spent adsorbents.     

Impact of selected solution factors on arsenate and arsenite removal by nanoiron particles

Introduction  

The nano-scale zero-valent iron (NZVI) was used for the removal of arsenite (As(III)) and arsenate (As(V)) in aqueous solution. Batch experiments were conducted to investigate the effects of initial pH, initial arsenic concentration, dissolved oxygen (DO), and ratio of As(III)/As(V) on arsenic removal.     

Photocatalytic degradation of paraquat using nano-sized Cu-TiO2/SBA-15 under UV and visible light

Photocatalytic degradation of paraquat using mesoporous-assembled Cu-TiO₂/SBA15 under UV and visible light was investigated. The catalyst was synthesized by impregnation of Cu-TiO₂ colloids onto SBA-15. The colloids of Cu-TiO₂ were prepared via sol-gel method while the mesoporous support was prepared using hydrothermal technique. The catalyst was characterized using X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, UV diffuse reflectance spectroscopy, Zeta potential and X-ray adsorption spectroscopy. Results from characterizations showed that Cu doped TiO₂ had a small crystalline size and was well-dispersed on SBA-15. The inclusion of SBA-15 significantly enhanced the photocatalytic activity of the catalyst. Among the three types of undoped catalyst in this study (P25, TiO₂, TiO₂/SBA-15), TiO₂/SBA-15 yielded the highest degradation of paraquat for all pH under UV illumination. Meanwhile 2 wt.% Cu-TiO₂/SBA-15 yielded the highest activity under visible light.     

Synthesis and characterization of Fe-MCM-41 from rice husk silica by hydrothermal technique for arsenate adsorption

Rice husk (RH) agro-waste was used as a raw material for synthesizing mesoporous molecular sieves, MCM-41. The Fe-MCM-41 was prepared by the hydrothermal technique (HT), resulting in a higher surface area and crystallinity than when prepared under ambient conditions. In addition, a hexagonal structure was clearly seen with hydrothermal technique (HT) preparation. The adsorption of arsenate by HT-Fe-MCM-41 was investigated. The factors studied affecting arsenate adsorption capacity were ferric content in MCM-41, contact time, pH of solution, and initial arsenate concentration. It was found that HT-Fe-MCM-41 at the Si/Fe mole ratio of 10 gave the highest adsorption capacity. Arsenate adsorption reached equilibrium within 4 h. The adsorption capacity of HT-Fe-MCM-41 (Si/Fe = 10) was affected by the initial pH value and the initial arsenate concentration. The adsorption capacity was highest at pH 3 and decreased thereafter with increases in the pH of solution value. The Langmuir model fit the arsenate adsorption isotherm well. The maximum adsorption capacity for arsenate was 1,111 μg g⁻¹.     

Enhancement of elemental mercury adsorption by silver supported material

Mercury, generally found in natural gas, is extremely hazardous. Although average mercury levels are relatively low, they are further reduced to comply with future mercury regulations, which are stringent in order to avoid releasing to the environment. Herein, vapor mercury adsorption was therefore investigated using two kinds of supports, granular activated carbon (GAC) and titanium dioxide (TiO₂). Both supports were impregnated by silver (5 and 15 wt.%), before testing against a commercial adsorbent (sulfur-impregnated activated carbon, SAC). The adsorption isotherm, kinetics, and its thermodynamics of mercury adsorption were reported. The results revealed that Langmuir isotherm provided a better fit to the experimental data. Pseudo second-order was applicable to describe adsorption kinetics. The higher uniform Ag dispersion was a key factor for the higher mercury uptake. TiO₂ supported silver adsorbent showed higher mercury adsorption than the commercial one by approximately 2 times. Chemisorption of mercury onto silver active sites was confirmed by an amalgam formation found in the spent adsorbents.