Experimental and DFT studies on the characteristics of PbO/PbCl2 adsorption by Si/Al- based sorbents in the simulated flue gas

Effects of active silicon amendment on Pb(II)/Cd(II) adsorption: Performance evaluation and mechanism

In this study, a high-Si (Si) adsorbent (APR@Sam) was prepared by acid leaching slag (APR) from lead-zinc (Pb-Zn) tailings based on high-temperature alkali melting technology. The synthesized Si-based materials were applied to aqueous solutions contaminated with Pb and cadmium (Cd) to investigate the crucial role of active Si in sequestering heavy metals. The adsorption capacities of APR@Sam and the Si-depleted material (APR@Sam-NSi) were studied under different pH and temperature conditions. The results showed that as the pH increased from 3 to 7, the adsorption capacity increased, the active Si content in the solution increased by 63 %, and the maximum pH of the solution after adsorption was 7.12. After the removal of active Si, the Pb (II) and Cd (II) adsorption capacities of APR@Sam decreased by 45 % and 11.96 %, respectively. OH- promoted the release of Si into the solution, enhancing the material's adsorption efficiency. The reaction mechanism is mainly attributed to surface complexation guided by Si-O and Si-O-Si bonds, metal cation exchange, and bidentate coordination. The results indicated that the Si component is critical for the removal of Pb (II) and Cd (II) by APR@Sam and provide valuable insights into resource recovery strategies from leaching residues.

Migration and transformation of Pb, Cu, and Zn during co-combustion of high-chlorine-alkaline coal and Si/Al dominated coal

Shaerhu (SEH) coal is abundant in Xinjiang, China. The utilization of SEH suffers from severe ash deposition, slagging, and fouling problems due to its high-chlorine-alkaline characteristics. The co-combustion of high-alkaline coal and other type coals containing high Si/Al oxides has been proven to be a simple and effective method that will alleviate ash-related problems, but the risk of heavy metals (HMs) contamination in this process is nonnegligible. Hence, the volatilization rates and chemical speciation of Pb, Cu, and Zn in co-combusting SEH and a high Si/Al oxides coal, i.e., Yuanbaoshan (YBS) coal were investigated in this study. The results showed that the addition of SEH increased the volatilization rates of Pb, Cu, and Zn during the co-combustion at 800°C from 23.70%, 23.97%, and 34.98% to 82.31%, 30.01%, and 44.03%, respectively, and promoted the extractable state of Cu and Zn. In addition, the interaction between SEH and YBS inhibited the formation of the Pb residue state. SEM-EDS mapping results showed that compared to Zn and Cu, the signal intensity of Pb was extremely weak in regions where some of the Si and Al signal distributions overlap. The DFT results indicated that the O atoms of the metakaolin (Al2O3⋅2SiO2) (001) surface were better bound to the Zn and Cu than Pb atoms after adsorption of the chlorinated HMs. These results contribute to a better understanding of the effects of high-alkaline coal blending combustion on Pb, Cu, and Zn migration and transformation.

Effect of biomass-coal blending combustion on Pb transformation

Biomass-coal blending combustion is an effective method for utilizing biomass; however, its pollutant emission requires attention. Herein, the effect of biomass-coal blending combustion on lead (Pb) transformation was explored. Combustion experiments were conducted in a fixed-bed reactor, using coal, corn stalk, rice stalk, bamboo flour and their mixtures as fuels, at 1000, 1100, 1200 and 1300 °C. The Pb release ratios were determined by measuring its content in the fuels and solid-phase combustion products. The distribution of Pb forms was analyzed using sequential chemical extraction. The results indicate that blending combustion significantly enhanced the release of Pb. At blending ratio 1:1, the release ratios increased by 1.54-27.2%, 5.30-15.6%, and 2.31-7.76% at 1000, 1100, and 1200 °C, respectively. The potassium (K) components in biomass, mainly KCl and K2CO3, had a significant promoting effect on Pb release. K compounds facilitated the release of residual Pb through reactions with aluminosilicates. The promotion effect weakened as the temperature increased due to the faster evaporation rate of K. When the mass fractions of K in the fuels were equal, K2CO3 exhibited a stronger promoting effect. HCl had minimal impact on the transformation of Pb. The results are helpful for optimizing the combination of biomass and coal to control Pb emission from the blending combustion source.

Reducing CO/NO and absorbing heavy metals in self-sustained smouldering of high-moisture sludge by regulating inert media with low-cost natural zeolite

Smouldering is a low-energy, low-cost, effective treatment technology for sludge with high moisture. However, combustible gas and pollution in the flue gas limit the low-cost operation. This work proposes a novel method to in-situ reduce gas emissions (CO, NO, VOCs) and absorb heavy metals by regulating inert media with low-cost natural zeolite in self-sustained smouldering of sludge, and the effect of natural zeolite blending ratio on the performance is deeply investigated by fixed-bed and smouldering experiments. Fixed-bed experiments show that adding natural zeolite contributes to the sludge reaction owning to the confined catalysis with porous structure, as observed by the more rapid oxygen consumption, lower CO/NO concentrations. Moreover, smouldering experiments demonstrate that the endothermic dehydroxylation and dehydroxylation processes of the pure natural zeolite decreases the smouldering temperature and the propagation velocity, reduces the pyrolysis layer, but adding natural zeolite significantly reduces the concentrations of CO/NO/VOCs in the flue gas. Furthermore, higher heavy element content in the post-reaction natural zeolite is observed, indicating that the inorganic minerals in natural zeolite can effectively absorb the heavy elements. Taking reaction intensity, CO/NO/VOCs reduction and heavy element absorption into account, adding a small amount of natural zeolite (Sand: Natural-zeolite = 2.90:0.10) may be reasonable with obtaining good performance. Finally, the organic components in condensable liquids of the smouldering flue gas are deeply analyzed, and the main components is 36.7% for amides and 23.41% for nitrogen-containing heterocyclic compounds. This work can provide a possible pathway and useful information for the low-cost application of the sludge smouldring technology.

Conversion mechanism of selenium on activated carbon surface: Experimental and density functional theory study

The mechanism of SeO2 capture by activated carbon (AC) was explored via combining experiments with density functional theory (DFT). Adsorption experiments confirmed that after mass loss coefficient correction of AC, the selenium capture capacity of AC reached 7.76 mg/g at 350 °C. AC reached a saturated selenium removal capacity of 9.93 mg/g at 50 min. The weight loss curve recorded the temperature window of selenium desorption on AC surface at about 305 °C. The XPS spectrum revealed that the decomposition and reduction behavior of SeO2 on the AC surface promoted the existence of selenium in the form of Se0. DFT calculations showed that SeO2 was chemically adsorbed on the typical Armchair and Zigzag surfaces of AC, and the adsorption energies of the most stable structures were - 89.77 and - 235.12 kcal/mol, respectively. The effect of temperature on selenium capture via AC was studied by thermodynamic and kinetic analysis. Temperature increase promoted the decomposition and reduction of SeO2 on the AC surface. Kinetic analysis further confirmed that the transformation of Se4+→Se0 was more dominated by decomposition behavior. A part of SeO2 in the gas phase was reduced to Se0 by CO and enriched on AC as elemental selenium.

Equilibria of semi-volatile isothiazolinones between air and glass surfaces measured by gas chromatography and Raman spectroscopy

Trace amounts of semi-volatile organic compounds (SVOCs) of the two isothiazolinones of 2-methylisothiazol-3(2H)-one (MIT) and 2-octyl-4-isothiazolin-3-one (OIT) were detected both in the air and on glass surfaces. Equilibria of SVOCs between air and glass were examined by solid phase microextraction-gas chromatography/mass spectrometry (SPME-GC/MS). Surface to air distribution ratios of K_sa for MIT and OIT were determined to be 5.10 m and 281.74 m, respectively, suggesting more abundant MIT in the gas phase by a factor of ∼55. In addition, a facile method of silver nanocube (AgNC)-assisted surface-enhanced Raman scattering (SERS) has been developed for the rapid and sensitive detection of MIT and OIT on glass surfaces. According to MIT and OIT concentration-correlated SERS intensities of Raman peaks at ∼1585 cm^-1 and ∼1125 cm^-1, respectively. Their calibration curves have been obtained in the concentration ranges between 10^-3 to 10^-10 M and 10^-3 to 10^-11 M with their linearity of 0.9986 and 0.9989 for MIT and OIT, respectively. The limits of detection (LODs) of the two isothiazolinones were estimated at 10^-10 M, and 10^-11 M for MIT and OIT, respectively. Our results indicate that AgNC-assisted SERS spectra are a rapid and high-ultrasensitive method for the quantification of MIT and OIT in practical applications. The development of analytical methods and determination of the Ksa value obtained in this study can be applied to the prediction of the exposure to MIT and OIT from various chemical products and dynamic behaviors to assess human health risks in indoor environments.

Experimental and theoretical studies on the adsorption characteristics of Si/Al-based adsorbents for lead and cadmium in incineration flue gas

Si/Al-based adsorbents are effective adsorbents for capturing heavy metals in incineration flue gases at high temperatures in the furnace. In this work, the adsorption characteristics and adsorption mechanisms of Si/Al-based adsorbents for lead and cadmium vapors were studied using a combination of experimental and density functional theory (DFT) calculations. The trapping performance of a series of Si/Al-based adsorbents for Pb and Cd vapors was investigated using a self-designed gas-solid two-phase rapid adsorption experimental system. The results showed that kaolinite and montmorillonite exhibited better heavy metal adsorption capacity than SiO₂ and Al₂O₃, and were significantly stronger for Pb than for Cd. Chemisorption dominated the capture of Pb/Cd by Si/Al-based adsorbents at high temperatures. The results of DFT calculations indicated that the chemisorption mechanisms dominated the adsorption of Pb and Cd species on the metakaolinite (001) surface, and the adsorption energy of Pb species on the metakaolinite surface was greater than that of Cd species. The exposed O atoms and unsaturated Al atoms of metakaolinite (001) surface were effective adsorption active sites for heavy metals and their chlorides. In the adsorption reaction, the binding of Pb/Cd atoms and surface exposed O sites, as well as the strong interaction between Cl and unsaturated Al atoms, were responsible for the capture of Pb and Cd chlorides by metakaolinite.

On the adsorption and reactivity of element 114, flerovium

Flerovium (Fl, element 114) is the heaviest element chemically studied so far. To date, its interaction with gold was investigated in two gas-solid chromatography experiments, which reported two different types of interaction, however, each based on the level of a few registered atoms only. Whereas noble-gas-like properties were suggested from the first experiment, the second one pointed at a volatile-metal-like character. Here, we present further experimental data on adsorption studies of Fl on silicon oxide and gold surfaces, accounting for the inhomogeneous nature of the surface, as it was used in the experiment and analyzed as part of the reported studies. We confirm that Fl is highly volatile and the least reactive member of group 14. Our experimental observations suggest that Fl exhibits lower reactivity towards Au than the volatile metal Hg, but higher reactivity than the noble gas Rn.

Molecular Dynamics Simulation of Ion Adsorption and Ligand Exchange on an Orthoclase Surface

Orthoclase (K-feldspar) is one of the natural inorganic materials, which shows remarkable potential toward removing heavy metal ions from aqueous solutions. Understanding the interactions of the orthoclase and metal ions is important in the treatment of saline wastewater. In this paper, molecular dynamics simulations were used to prove the adsorption of different ions onto orthoclase. The adsorption isotherms show that orthoclase has remarkable efficiency in the removal of cations at low ion concentrations. Aluminol groups are the preferential adsorption sites of cations due to higher negative charges. The adsorption types and adsorption sites are influenced by the valence, radius, and hydration stability of ions. Monovalent cations can be adsorbed in the cavities, whereas divalent cations cannot. The hydrated cation may form an outer-sphere complex or an inner-sphere complex in association with the loss of hydration water. Na+, K+, and Ca2+ ions mainly undergo inner-sphere adsorption and Mg2+ ions prefer outer-sphere adsorption. On the basis of simulation results, the mechanism of ion removal in the presence of orthoclase is demonstrated at a molecular level.