Activated Carbons Derived FromOrganic Sewage Sludge For The RemovalOf Mercury From Aqueous Solution (original) (raw)
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Using activated carbons for elimination the health threatening mercury from the aqueous solutions
Mercury is one of the priority pollutant listed by USEPA as it can easily pass the blood-brain barrier and affect the fetal brain. In this review paper, the efforts which have been done for controlling the mercury emissions from aqueous solutions were evaluated. Mercury (Hg) is one of the heavy metals of concern and has been found in the waste waters coming from manufacturing industry, and natural sources. Among several types of technology for removing of Hg in water (chemical precipitation, reverse osmosis, ion-exchange, etc.), adsorption is one of most frequently used. It is a complex process involving physical, chemical, and electrical interactions at sorbent surfaces. Therefore, in this study will investigate effective parameters such as pH, initial concentration and surface characteristic.
Role of activated carbon structural properties and surface chemistry in mercury adsorption
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In this work the performance of activated carbons prepared from raw and demineralised lignite for gas-phase Hg° removal was evaluated. A two-stage activation procedure was used for the production of the activated samples. In order to study the effect of mineral matter on pore structure development and surface functionality of the activated carbons, a demineralisation procedure involving a three-stage acid treatment of coals, was used, prior to activation. Hg° adsorption tests were realized in laboratory-scale unit consisted of a fixed-bed reactor charged with the tested activated samples. The examined adsorbent properties that may affect removal capacity were the pore structure, the surface chemistry and the presence of sulphur on the surface of activated carbons. The obtained results revealed that activated carbons produced from demineralised lignite posses a high-developed micropore structure with increased total pore volume and BET surface area. These samples exhibit enhanced Hg° adsorptive capacity. In all cases, mercury removal efficiency increased by sulphur addition. Finally, the starting material properties and activation conditions affect the concentration and the type of the oxygen groups on activated carbon surface, that have been determined with TPD-MS experiments.
Role of Activated Carbon Precursor in Mercury Removal
Industrial & Engineering Chemistry Research, 2020
Adsorption studies of contaminants using activated carbon do not always take into consideration the raw material used in its production. Mercury adsorption mechanisms governed by carbene sites are more significant when graphitic-like activated carbons are employed versus lignocellulosic-based activated carbons, whose carbon rings are less aromatic. In this laboratory, fixed-bed study, bituminous coal-based activated carbon was compared to coconut-and wood-based activated carbons (both less aromatic) for elemental mercury removal in nitrogen at 25°C. Activated carbon produced from bituminous coal performed far better for mercury adsorption compared to the more aliphaticderived activated carbons from coconut shells and wood. The results showed no correlation between mercury removal and the activated carbon physical properties including Brunauer−Emmett−Teller surface area, pore size, or pore volume. When the bituminous coal-based activated carbon was hydrogen-treated at 850°C to stabilize its carbene sites, the resulting mercury breakthrough curve became very similar to that of the wood-and coconut-based carbons. It is hypothesized this phenomenon is a result of stabilization of carbene sites which are more available in aromatic carbons. By the direct impact of carbene stabilization on mercury adsorption, it can be concluded that carbene sites and their abundance are an essential part of mercury adsorption.
Removal of gas-phase elemental mercury by iodine- and chlorine-impregnated activated carbons
Atmospheric Environment, 2004
Gas-phase Hg 0 adsorption experiments were carried out using iodine (I)-and chorine (Cl)-impregnated granular activated carbons in a laboratory-scale fixed-bed reactor. To verify the effect of chemical loading contents on removal of mercury, different concentrations of chemicals such as KI and HCl were applied. In addition, two types of impregnated activated carbons (ACs) were tested at different temperature conditions. The characteristics of impregnated ACs were analyzed using scanning electron microscopy/energy-dispersive spectroscopy for surface morphology and chemical contents. BET analysis for surface area and X-ray spectroscopy for identification of mercury compounds on the carbon surface were conducted.
Removal of mercury ion from aqueous solution by activated carbons obtained from biomass and coals
Fuel Processing Technology, 2002
The adsorption of Hg(II) from aqueous solution at 293 K by activated carbons obtained from apricot stones, furfural and coals was studied. Adsorption studies were performed under the varying conditions of time of treatment, metal ion concentration and pH. The process of adsorption followed Langmuir isotherm. The removal of Hg(II) increased with the increase of pH of the solution from 2 to 5 and remained constant up to pH 10. Desorption studies were preformed.
Sorption of mercury onto waste material derived low-cost activated carbon
Applied Water Science, 2014
The present study was performed to develop the low-cost activated carbon (AC) from some waste materials as potential mercury (Hg) sorbent to remove high amount of Hg from aqueous phase. The ACs were prepared from banana peel, orange peel, cotton fiber and paper wastes by pyrolysis and characterized by analyzing physico-chemical properties and Hg sorption capacity. The Brunauer Emmett and Teller surface areas (cotton 138 m 2 /g; paper 119 m 2 /g), micropore surface areas (cotton 65 m 2 /g; paper 54 m 2 /g) and major constituent carbon contents (cotton 95.04 %; paper 94.4 %) were higher in ACs of cotton fiber and paper wastes than the rest two ACs. The Hg sorption capacities and removal percentages were greater in cotton and paper wastes-derived ACs compared to those of the banana and orange peels. The results revealed that elevated Hg removal ability of cotton and paper wastes-derived ACs is largely regulated by their surface area, porosity and carbon content properties. Therefore, ACs of cotton and paper wastes were identified as potential sorbent among four developed ACs to remove high amount of Hg from aqueous phase. Furthermore, easily accessible precursor material, simple preparation process, favorable physico-chemical properties and high Hg sorption capacity indicated that cotton and paper wastes-derived ACs could be used as potential and lowcost sorbents of Hg for applying in practical field to control the severe effect of Hg contamination in the aquatic environment to avoid its human and environmental health risks.
Adsorption Science & Technology, 2014
The effects of treatment of an activated carbon with sulphur precursors on its textural properties and on the ability of the complex synthesized for mercury removal in aqueous solutions are studied. To this end, a commercial activated carbon has been modified by treatments with aqueous solutions of Na 2 S and H 2 SO 4 at two temperatures (25 and 140 °C) to introduce sulphur species on its surface. The prepared adsorbents have been characterized by N 2 (-196 °C) and CO 2 (0 °C) adsorption, thermogravimetric analysis, temperature-programmed decomposition and X-ray photoelectron spectroscopy, and their adsorption capacities to remove Hg(II) ions in aqueous solutions have been determined. It has been shown that the impregnation treatments slightly modified the textural properties of the samples, with a small increase in the textural parameters (BET surface area and mesopore volumes). By contrast, surface oxygen content was increased when impregnation was carried out with Na 2 S, but it decreased when H 2 SO 4 was used. However, the main effect of the impregnation treatments was the formation of surface sulphur complexes of thiol type, which was only achieved when the impregnation treatments were carried out at low temperature (25 °C). The presence of surface sulphur enhances the adsorption behaviour of these samples in the removal of Hg(II) cations in aqueous solutions at pH 2. In fact, complete Hg(II) removal is only obtained with the sulphur-containing activated carbons.
Sorption of Elemental Mercury by Activated Carbons
Environmental Science & Technology, 1994
The mechanisms and rate of elemental mercury (HgO) capture by activated carbons have been studied using a bench-scale apparatus. Three types of activated carbons, two of which are thermally activated (PC-100 and FGD) and one with elemental sulfur (S) impregnated in it (HGR), were chosen to study the effects of surface area (approximately 550-1000 m2/g), sorption temperature (23-140 "C), and HgO concentration (30 and 60 ppb of Hgo in nitrogen). Investigations revealed that sorption occurs in active sites in PC-100 and FGD which are either depleted or deactivated upon heat treatment at 140 "C. For HGR, sorption at 23 "C occurred in non-S sites residing in the external surface, and sorption of 140 "C primarily occurred through the reaction of HgO and S. Desorption studies for PC-100 and HGR revealed the sorption mechanism to be a combination of physisorption and chemisorption at 23 "C, whereas chemisorption is the primary route at 140 "C.
Treated activated carbons, prepared by heat treatment of activated carbon sorbents under the protection of argon (Ar), were subjected to synthetic flue gases to investigate its elemental mercury (Hg 0) capture and the specific role of HCl and O 2. To elucidate the adsorption mechanisms & binding properties, subsequent sorbents were characterized by X-ray photoelectron spectroscopy and X-ray absorption fine structure spectroscopy. The results suggest that Hg 0 capture on the heat treated activated carbon (TAC) under HCl atmosphere mainly follows Eley-Rideal reaction mechanism, where, HCl reacts with the basic active carbon sites on the TAC leading to the formation of Cl-containing active sites, subsequently gaseous Hg 0 heterogeneously reacts with these Cl-containing active sites through electron-transfer and forms HgCl x compounds. Both the 2.42 Å and 2.39 Å bonding distance of Hg-Cl shows that only one of the two valence electrons on mercury bond with Cl, while the other electron bonds with the basic active carbon site covalently. In presence of HCl and O 2 , the synergistic effect of O 2 on Hg 0 adsorp-tion might attribute to the O 2 adsorption and the subsequent formation of oxygen-containing functional groups (OFGs) on TAC, which increase the amount of effective activated sites for Hg 0 adsorption and at the same time enhance the adsorbing kinetics of adjacent Cl-containing sites.