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[Display omitted] • A new strategy based on ion complexation for the regeneration of gas-phase mercury removal adsorbents was proposed. • The KCl solution had excellent elution effect on HgO on MnTi adsorbent. • The MnTi adsorbent could be well reused. MnTi adsorbent prepared by precipitation method was used to remove elemental mercury in pure nitrogen atmosphere, and TPD method was employed to investigate the mechanism of mercury elution from mercury-loaded MnTi adsorbent in KCl solution. In the gas-phase mercury adsorption process, the MnTi adsorbent removed mercury with a high efficiency of 50% under pure nitrogen atmosphere. The effects of stirring time, eluent concentration, and pH on Hg elution efficiency were evaluated in the liquid-phase Hg elution process. Mercury elution was assisted by adequate stirring time and eluent concentration. The pH value of the environment influenced mercury elution, with an acidic environment being more effective for mercury oxide elution. According to the experimental results, the highest mercury elution efficiency of 0.5 M KCl solution was 79%. The active chlorine produced during the elution process was valuable for reuse. The mercury removal performance of the reused MnTi adsorbent was not significantly different from that of the fresh adsorbent. The elution mechanism of HgO was also proposed, with the key link being the reaction of HgO(red) in solution with excess Cl− to form [HgCl 4 ]2− complexes, which then entered the liquid phase. It was possible to conclude that KCl solution had a high potential for mercury elution from mercury-carrying adsorbents and waste adsorbent reuse. [ABSTRACT FROM AUTHOR]

• The dissolution difficulty in metal chlorine solution followed the order of HgSO 4 < HgO < HgS. • NaCl, KCl, CeCl 3 , MnCl 2 , AlCl 3 , CaCl 2 , FeCl 3 , and CuCl 2 solutions could react with HgSO 4 to generate HgCl 2. • MnCl 2 , AlCl 3 , CaCl 2 , FeCl 3 , and CuCl 2 solutions could react with HgO to produce HgCl 2. • Only CuCl 2 could react with HgS to produce HgCl 2. • CuCl 2 solution could protect active site of metal oxide adsorbents and avoid the reduction of HgCl 2 to Hg 2 Cl 2. Washing regeneration of Hg adsorbent not only has good economic benefits, but also effectively avoids the secondary pollution of Hg caused by the accumulation or landfill of used Hg adsorbents. The common Hg-containing substances on used Hg adsorbent are HgS, HgO, HgSO 4 , and HgCl 2 , which requires the solution to be able to react with insoluble HgS, HgO, and HgSO 4 to produce easy-soluble HgCl 2. Considering the characteristics of containing Cl ion and oxidation capacity, metal chloride solution was chosen for washing regeneration of Hg adsorbent. In this study, the reaction between HgS, HgO, HgSO 4 and metal chlorine solutions including NaCl, KCl, CeCl 3 , MnCl 2 , AlCl 3 , CaCl 2 , FeCl 3 , and CuCl 2 were separately studied using thermodynamic calculation software (FactSage 5.2). The subsequent supporting experiments were also conducted for verifying the correctness of thermodynamic calculation. The results showed that without the input of external energy, all the NaCl, KCl, CeCl 3 , MnCl 2 , AlCl 3 , CaCl 2 , FeCl 3 , and CuCl 2 solutions could react with HgSO 4 to generate HgCl 2. While only MnCl 2 , AlCl 3 , CaCl 2 , FeCl 3 , and CuCl 2 solutions could react with HgO to produce HgCl 2 , and only CuCl 2 solution could react with HgS to produce HgCl 2. The leaching and dissolution difficulty in metal chlorine solution followed the increasing order of HgSO 4 < HgO < HgS. Finally, the feasibility of the precipitation method using NaOH solution for separating Hg2+ was verified by combining the thermodynamic calculation results, characterization and tests (ICP-OES and Hg-XPS) results. Considering CuCl 2 was the only solution that could react HgS, HgO, and HgSO 4 to produce HgCl 2 , and could protect active site of common metal oxide for Hg removal, as well as had a good oxidation ability for avoiding the reduction of HgCl 2 to insoluble Hg 2 Cl 2 , CuCl 2 solution was finally determined as the suitable solution for washing regeneration of Hg adsorbent. [ABSTRACT FROM AUTHOR]

• The influence of gasification medium on Hg0 release and oxidation were elucidated. • The inhibition and promotion of gasification products on Hg0 oxidation were explained. • The advantages and disadvantages of common OC on Hg0 oxidation were summarized. • The effects of reaction temperature and reactor configuration on Hg0 release and oxidation were introduced. • Appropriate H 2 O(g) content, OC with weak adsorption and strong oxidation capacity, and suitable AR temperature were suggested. Chemical looping combustion (CLC) of coal can effective achieve the capture and storage of CO 2 , reduce the emission of NO x , and realize the energy cascade utilization. During the process of CLC, mercury (Hg) will release from coal and enrich in gas. If Hg has not been effectively treated, it will not only cause the serious harm to human body and environment, but also affect the purification and storage of CO 2 by mixing with CO 2 , as well as lead to the corrosion of equipment, which highlights the importance of Hg removal in CLC. This review summarized the influence and mechanism of gasification medium (signal CO 2 , signal H 2 O vapor, as well as mixture of CO 2 and H 2 O vapor), gasification products (CO, H 2 , NH 3 , HCl, and H 2 S), oxygen carrier (single metal oxides of Fe 2 O 3 , MnO 2 , Co 3 O 4 , CuO, and CeO 2 , CaSO 4 , mixed OC, and natural-ores OC), reaction temperature, as well as reactor configuration in fuel reactor and air reactor on the release, oxidation, and transfer of Hg in CLC of coal. Based on these above, several suggestions about the selection of appropriate H 2 O(g) content to minimize the release of Hg and promote the oxidation of Hg0, the selection of OC with weak adsorption capacity and strong oxidation performance, the preparation and application of Cu, Mn, Co spinel structured oxides for promoting the catalytic oxidation of Hg0 in CLC high-temperature furnace, and the choice of an appropriate air reactor temperature to maximize the oxidation of Hg0 in the AR and reduce the escape of Hg from the AR outlet were provided for promoting the removal of Hg for CLC in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hg0 adsorption with C and S on the FeS surface has been studied via DFT-D2 method. • DOS and ICOHP demonstrated the interaction between the adsorbates and the surfaces. • Carbon can promote mercury physisorption on the pristine FeS(0 0 1)-S surface. • The HgS generation process occurs through Langmuir-Hinshelwood Mechanism. Elemental mercury (Hg0) adsorption behaviors and mechanisms on the low-Miller index mackinawite surface (FeS(0 0 1)-S surface), with the engagement of carbon or sulfur, were investigated via DFT-D2 theoretical calculations. The simulation results show that the most favorable adsorption site for the C and Hg atoms was the lower-S site on the pristine surface, while S atom preferred the upper-S site. C atom could cause charge transfer and inter-atomic charge redistribution during adsorption. The carbon atom performs as a linker to connect the substrate and the Hg atom in the most stable mercury adsorption geometry onto the carbon-doped surface. Hg0 is physically adsorbed over the sulfur-doped surface. The HgS molecule chemically attached to the surface at the upper-S site via the Hg atom to form a S-Hg-S structure, and its generation process follows Langmuir-Hinshelwood Mechanism. Firstly, the Hg and S atoms were pre-adsorbed on the FeS(0 0 1)-S surface. Then the system needed to overcome an activation energy barrier (E b) of 89.82 kJ·mol−1. It was an endothermic process in which two separate atoms generated HgS*. However, C atom will impede the reaction as occupying the adsorption sites of mercury and sulfur. [ABSTRACT FROM AUTHOR]

• A novel Hg0 removal adsorbent OMC-Cl was synthesized. • The presence of C-Cl functional groups exerts inhibitory effects on the formation of HgO and HgS. • DFT reveals the effect mechanism of C-Cl functional groups. • OMC-Cl exhibits excellent capacity in adsorption–desorption cycles. Wet desorption presents an environmentally sustainable approach for the disposal of deactivated elemental mercury (Hg0) removal adsorbents. However, the prevalence of insoluble Hg compounds in the adsorption products poses a significant impediment to the wet desorption process. In this work, an ordered mesoporous carbon modified with C-Cl functional groups (OMC-Cl) was synthesized via the evaporation-induced self-assembly (EISA) method. It has a high specific surface area (∼630 m2/g), large pore volume (∼0.64 cm3/g), and uniform pore size (∼22.0 nm). The presence of C-Cl functional groups provides a remarkable adsorption capacity to the adsorbent, exhibiting high adsorption efficiency in various adsorption atmospheres (96.8 % in pure N 2 ; 91.7 % in N 2 + H 2 S) and promoting the prevalence of soluble HgCl 2 in the adsorption product. Density functional theory analysis has elucidated that the C-Cl functional groups exerted inhibitory effects on the formation of HgO and HgS mainly by weakening the adsorption process of Hg0 on C = O and C-S. The desorption efficiencies of adsorption products in the above atmospheres in HCl solution (0.5 mol/L) achieved 95.4 % and 81.3 %, respectively. The high concentration of H+ ions serves to prevent the re-adsorption of Hg2+ by the -SH generated during the adsorption process. Furthermore, the adsorbent desorbed in HCl solution manifests substantial potential for recyclability. This study introduces a novel approach for efficient wet desorption in terms of designing active sites to modulate the adsorption products and pore structures to facilitate mass transfer. [ABSTRACT FROM AUTHOR]

• The novel washing regeneration methods for AC using CuCl 2 solution was proposed and verified. • CuCl 2 solution showed excellent performance on eluting Hg-containing compounds on spent AC. • Elution process restored the well-developed pore structure and reactive functional groups of AC. • CuCl 2 -AC showed a higher (above 99%) and more stable Hg removal performance than raw AC. • Hg-containing compounds on spent CuCl 2 -AC were mainly easy-soluble HgCl 2. Mercury pollution in syngas has received increasing attention. Regeneration of AC can reduce the cost and avoid Hg secondary release effectively. The performance of CuCl 2 solution on AC regeneration was studied combining fixed-bed reactor, Hg-TPD, and characterization tests (BET, SEM-EDS, XPS, and FT-IR). Hg adsorption on AC in N 2 mainly followed physisorption. There was a synergistic contribution of HCl and H 2 S on Hg removal, in which HCl promotion was stronger than H 2 S. The main Hg-containing compounds on AC in HCl were HgCl 2 and HgO, in H 2 S were HgO and HgS. The well-developed pore structure of AC enhanced Hg adsorption while inhibited the elution of Hg-containing compounds. CuCl 2 solution exhibited an excellent synergy in the elution of Hg-containing compounds and the impregnation modification of AC, which not only eluted the Hg-containing compounds, restored the well-developed pore structure, and recovered the reactive oxygen-containing functional groups effectively, but also brought in Cu and Cl for promoting Hg removal by generating Hg-Cu and HgCl 2 respectively. The best impregnation content of CuCl 2 was 10% that exhibited higher (above 99%) and more stable Hg removal efficiency than raw AC, and the dominant Hg-containing compound was easy-soluble HgCl 2 , proving the practicability of CuCl 2 solution on AC regeneration. [ABSTRACT FROM AUTHOR]

• The effects and mechanisms of CO, H 2 , NH 3 and HCl on HgS and HgO generation in H 2 S atmosphere were respectively clarified. • The species and stability of Hg-containing products in H 2 S + CO, H 2 S + H 2 , and H 2 S + NH 3 , and H 2 S + HCl were respectively determined. • The feasibility of adjusting the syngas components and modifying by CuCl 2 impregnation for promoting the solution washing regeneration were respectively evaluated. • The effect and promotional mechanism about the impregnation modification of CuCl 2 were respectively determined. Inhibiting the generation of insoluble HgO and HgS, as well as promoting the generation of HgCl 2 can significantly contribute to the solution washing regeneration of adsorbent for Hg removal in syngas. In this study, CeO 2 -MnO 2 /TiO 2 (Ce-Mn/Ti) was chosen as the Hg adsorbent, the fixed-bed test, Hg-TPD, and characterization test (including BET, SEM-EDS, and XPS) were conducted. Firstly, the effects of different concentrations of CO, H 2 , NH 3 , and HCl on the generation of HgS, HgO, and HgCl 2 on adsorbent was investigated. Although the increase of CO, H 2 , and NH 3 concentration can inhibit the generation of HgS and HgO to different extents, and the increase of HCl concentration can promote the production of HgCl 2 , but they will also lead to the increase in Hg concentration to varying degrees, indicating the adjustment on syngas components and concentrations is not a feasible method. Subsequently, the effects of different concentrations of modification reagent with CuCl 2 were studied. The optimal impregnation ratio of CuCl 2 was determined as 10%, in which the Hg removal efficiency in H 2 S atmosphere could reach over 97%, and almost of the Hg-containing product was easy-soluble HgCl 2. The great advantage of impregnation modification of CuCl 2 is attributed to the uniform and dense distribution of CuCl 2 , as well as the strong activity of CuCl 2 itself towards Hg0 oxidation to HgCl 2. The impregnation modification of CuCl 2 can significantly improve the Hg removal efficiency, inhibit the generation of HgS and HgO, and promote the generation of HgCl 2 , which is verified as a feasible method to improve the solution washing regeneration of Hg adsorbent. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Hg0 removal adsorbent CeO x -amTiO 2 was synthesized via the evaporation-induced self-assembly method. • Ordered mesostructures significantly facilitated the adsorption and desorption process. • Oxygen vacancies on carriers can reduce the adsorption energy of Hg compounds. • The desorption of Hg from adsorbents exhibited biphasic kinetics. Improper disposal of deactivated mercury (Hg) adsorbents will cause secondary contamination which is still hazardous to human beings. Wet desorption is a green and environmentally friendly method, but there is a lack of sufficient study. In this work, a cerium oxide loaded ordered mesoporous amorphous titanium dioxide (CeO x -amTiO 2) composite is obtained based on the evaporation-induced self-assembly (EISA) process. It possesses a high specific surface area (∼198 m2/g), uniform pore diameters (∼14.7 nm), and large pore volume (∼0.49 cm3/g). The CeO x -amTiO 2 demonstrates high adsorption capacity in various atmospheres (63.3 % in pure N 2 , 95.0 % in N 2 + 400 ppm H 2 S), and achieves a desorption efficiency of 93.2 % in 0.2 mol/L sodium thiosulfate (Na 2 S 2 O 3) solution. The large specific surface area and ordered mesostructure significantly facilitate the mass transfer process, reasonably explaining the strong adsorption capacity and fast desorption kinetics. X-ray photoelectron spectroscopy (XPS) characterization and thermodynamic calculations reveal that the reduction of Ce3+ plays a key role in the desorption of Hg. In addition, the amorphous carrier structure reduces the binding strength between the adsorption product and the adsorbent, further accelerating the desorption process. This study provides a pathway for the efficient desorption of Hg0 removal adsorbents. [ABSTRACT FROM AUTHOR]

• The proportion and elution difficulty of Hg-containing substances followed HgS(black) > HgS(red) > HgO(red). • The elution was basically completed within 2 min with efficiency of 98.38 %. • Higher concentration, higher temperature and lower pH were conducive to the elution. • The elution followed the first-order two-domain model in which HgO and HgS belonged to the rapid and slow part. Mercury (Hg) pollution in syngas has received increasing attention. The adsorbent can effectively remove Hg from syngas, and the removal of Hg-containing substances before the landfill of spent adsorbent can avoid Hg secondary pollution effectively. H 2 S was the main resource for the generation of stable and insoluble HgS in syngas. In this work, the elution of Hg-containing substances from the spent CeO 2 -MnO 2 /TiO 2 (Ce-Mn/Ti) adsorbent in H 2 S atmosphere by CuCl 2 solution was studied. The optimum temperature for Ce-Mn/Ti to remove Hg0 in H 2 S atmosphere was 160 °C. The Hg-containing substances were HgS (black), HgS (red), and HgO (yellow), in which both the proportion and elution difficulty followed the descending order of HgS(black) > HgS(red) > HgO(yellow). The elution was basically completed within 2 min with excellent efficiency of 98.38 %. Higher concentration, higher temperature, and lower pH were conducive to the elution, and the optimum concentration and temperature were 1.0 mol/L and 45 °C respectively. The elution followed the first-order two-domain model, in which HgO and HgS were the rapid and slow part respectively. The elution not only retained the favorable mesoporous structure, but also enabled the eluted Ce-Mn/Ti adsorbent to have a higher efficiency and a better stability on Hg removal by loading the active component of CuCl 2. This study demonstrated that CuCl 2 could be a good eluent for the elution of Hg-containing species and the reutilization of metal oxide-based adsorbent. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effects and mechanisms of adsorbent composition, syngas component and reaction temperature on Hg0 removal by MOBA were individually elucidated. • The mechanisms, advantages and disadvantages of three regeneration methods for MOBA were systematically summarized. • The prospects of spine AB 2 O 4 adsorbent on Hg0 removal and the elution regeneration method on used MOBA were highlighted. • Further works about the synergistic removal of Hg0 and H 2 S by MOBA in syngas, and Hg0 removal by MOBA in syngas at a higher temperature range were suggested. The injection of adsorbent can effectively remove Hg from syngas, in which metal oxide based adsorbent (MOBA) is a promising adsorbent as their simultaneous adsorption and oxidation properties. This review summarized the influences and mechanisms of adsorbent composition, syngas component, and reaction temperature on Hg0 removal by MOBA in syngas. The adsorption of Hg0 by CeO 2 -based, Fe 2 O 3 -based, CuO-based, and V 2 O 5 -based MOBA belong to physisorption, the adsorption of Hg0 by MnO 2 and Co 3 O 4 belong to chemisorption. The oxidation of Hg0 by MOBA follows Mars-Maessen mechanism. The Hg0 removal capacity of MOBA with different composition follows the descending sequence of V 2 O 5 > MnO 2 > Co 3 O 4 > Fe 2 O 3 > CuO(CeO 2). H 2 S and HCl are beneficial to Hg0 removal by MOBA, but CO, H 2 , and H 2 O are harmful to Hg0 removal by MOBA. The influence of H 2 S, HCl, and CO are affected by their concentration. Both HCl and H 2 S can mitigate the inhibition of CO and H 2 on Hg0 removal by MOBA. The increase of temperature can both promote and inhibit Hg0 removal by MOBA. In addition, the advantages and disadvantages of three main regeneration methods of thermal regeneration, non-thermal plasma regeneration, and elution regeneration were respectively summarized, especially the prominent advantages of elution regeneration method were emphasized. Finally, further works about the development of spine MOBA, the synergistic removal of Hg0 and H 2 S by MOBA, study at higher temperature range, and the application of elution regeneration method were summarized to provide some references for the application of MOBA on Hg0 removal in syngas. [ABSTRACT FROM AUTHOR]

• The effect of industrial solid waste coal ash on biomass pyrolysis was explored. • Different experimental parameters were concerned to investigate the influence. • The effect of coal ash was more significant with high heating rate. • Coal ash increased the yield of pyrolysis gas at 800 °C, while inhibited gas formation at lower temperature. To discern influence of inorganic substances in coal on the co-utilization of coal and biomass, coal ash (CA) was added to biomass for pyrolysis. TG–FTIR and fixed bed reactor were used for pyrolysis of corn straw (CS) with CA. XRF and XRD were used to detect the reactants and products components, respectively. At constant heating rate. CA slightly promoted char and gaseous products formation. In the fixed bed reactor, the effect varied with temperature and CA addition ratio. The char and gas yields were changed due to the Si, Al, and other inorganic substances in CA. CS/CA = 1 had the greatest influence on char. Gas yield were reduced at 500–700 °C, but increased at 800 °C with a small proportion of CA. When CA was 1/10 of CS at 800 °C, the gas yield increased by 9.3%, and CH 4 , CO, and H 2 increased by 26.1%, 8.4%, and 37.7%, respectively. [ABSTRACT FROM AUTHOR]