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As can be retained by Fe components in coal during high-temperature combustion, which is beneficial for reducing As emissions. In this study, high-temperature As adsorption experiments were carried out in a fixed-bed experimental system with As model compound and minerals. The adsorption amount of As was much higher when Fe 2 O 3 , SiO 2 , and Al 2 O 3 acted together than when they acted alone. As was mainly distributed in the Fe-Si-Al minerals generated by the reaction of the three oxides, for which the Fe 2 O 3 :SiO 2 :Al 2 O 3 mass ratio of 1:1:1 was the most favorable, and the maximum adsorption amount of As was 18.2 mg·g−1. Density functional theory calculations were carried out for the adsorption of As 2 O 3 by Fe 2 O 3 , SiO 2 , Al 2 O 3, and Fe 2 Al 4 Si 5 O 18. Fe 2 Al 4 Si 5 O 18 had the highest adsorption energy for As 2 O 3 , indicating the most stable adsorption. As 2 O 3 was adsorbed on the Fe and Si sites. The adsorption ability of the Fe site was strengthened in Fe 2 Al 4 Si 5 O 18 relative to that in Fe 2 O 3. The formation of Fe-O-Si and Fe-O-Al in the mineral promoted electron transfer from the adsorbent to As 2 O 3 molecule, thereby strengthening adsorption. These results can guide the optimization of coal blending methods and the modification of adsorbents to control As emissions in coal-fired systems. [ABSTRACT FROM AUTHOR]

The retention of arsenic (As) during coal combustion facilitates As emission control. A fixed-bed experimental system was used to conduct devolatilization and char combustion experiments at 1100–1300 °C using three types of coal. Both processes contributed to the As release. As in coal was bound to carbonate, oxide, sulfide, and aluminosilicate (Als-As). During devolatilization, carbonate- and oxide-bound As and Als-As remained stable, while sulfide-bound As was completely decomposed. The gaseous As was partially retained as Char-As. During char combustion, Char-As was oxidized to As 2 O 3 , which was partially retained by minerals. Carbonate- and oxide-bound As reacted with silicon (Si) and aluminum (Al) to produce Als-As, which was the main As form in ash. As retention was significantly inhibited by the destruction of the lattice structure. As retention by char during devolatilization and minerals during char combustion promoted As enrichment in solid products and its removal. [Display omitted] [ABSTRACT FROM AUTHOR]

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 K 2 CO 3 , 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, K 2 CO 3 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. [Display omitted] • The effect of biomass-coal blending combustion on lead (Pb) transformation was studied. • The release of Pb in coal was promoted during blending combustion. • K compounds in biomass promoted the release of Pb, while Cl had little effect. • K 2 CO 3 and KCl could both react with aluminosilicate and release residual Pb. • K 2 CO 3 had a stronger promoting effect on Pb release than KCl. [ABSTRACT FROM AUTHOR]

Arsenic (As) pollutants are highly toxic and using Ca-based minerals to adsorb As 2 O 3 is effective for emission control. In this study, a fixed-bed experimental system was used to study the adsorption of As 2 O 3 by the mixture of CaO, SiO 2 , and Al 2 O 3 at 1200 °C. The amount of As adsorbed by multiple minerals was higher than that by single minerals, indicating enhanced adsorption of As 2 O 3 under the coupling effects of Ca, Si, and Al. The adsorption amount of As first increased and then decreased with an increase in the CaO:(SiO 2 +Al 2 O 3) and SiO 2 :Al 2 O 3 ratios. Adsorbed As was mainly enriched in Ca-Si-Al mineral, including Ca 2 Al 2 SiO 7. Density Functional Theory calculation was conducted to study the As 2 O 3 adsorption on the Ca 2 Al 2 SiO 7 (0 0 1) surface. The analysis of Mulliken charge and density of states showed that As 2 O 3 molecules formed Al-O, O-As, and Ca-O bonds with the Al, O, and Ca sites. Si and Al in Ca 2 Al 2 SiO 7 enhanced the adsorption ability of Ca sites by promoting electron transfer. Si/Al ratio close to 1:1 is conducive to the formation of Si-O-Al structures, thus further enhancing the adsorption. The results can help optimize coal blending strategies and modify adsorbents to further reduce As emissions during coal combustion. [Display omitted] • As 2 O 3 adsorption by Ca-Si-Al mineral was studied experimentally and theoretically. • As 2 O 3 adsorbed by mix of CaO, SiO 2 and Al 2 O 3 is mainly enriched in Ca-Si-Al mineral. • Ca, O, and Al sites on the Ca 2 Al 2 SiO 7 surface are active for As 2 O 3 adsorption. • Si and Al can increase the activity of Ca site and thus enhance adsorption. • The adsorption is strongest when Si:Al= 1:1 due to the formation of Si-O-Al structure. [ABSTRACT FROM AUTHOR]

Exploring arsenic (As) transformation during coal combustion is beneficial for reducing its pollution. Herein, combustion experiments were developed at 1100–1300 °C in a fixed-bed experimental system with 25 types of coal samples. The occurrences of As in coal and combustion products were characterized. All the original forms of As in coal were found to be unstable during combustion. As retained in ash existed as water-soluble and ion-exchangeable and residual forms, but only as residual form at combustion temperature above 1200 °C. The distribution of As in gaseous and solid combustion products varied widely by coal types, which resulted from the coupling effects of multi-minerals in coal. Co-combustion experiments were conducted using As model compounds and pure minerals, by which the interaction of Ca, Fe, Si and Al minerals to retain As was elucidated. The As transformation during coal combustion was primarily attributed to the coupling action of Ca, Fe, Si and Al minerals in coal. As a result, As was retained as Ca–Si–Al–As and Fe–Si–Al–As composite salts in the ash, which have little environmental hazard. Utilizing the coupling effects of multi-minerals during combustion help reduce As pollution from coal-fired plants. [Display omitted] • Arsenic (As) transformation during combustion of 25 coal samples was studied. • The release ratios of As during combustion vary in a wide range of 18–100%. • As is only retained as residual form in the ash at combustion temperatures ≥1200 °C. • Multi-minerals retain As as Ca–Si–Al–As and Fe–Si–Al–As composite salts. • Coupling of Ca/Fe, Si and Al strengthens As retention and its mechanism is proposed. [ABSTRACT FROM AUTHOR]

Study on selenium (Se) transformation during coal combustion will facilitate the development of emission–control technologies. A fixed–bed reactor was used to conduct pyrolysis and combustion experiments involving three types of coal at 600–1000 °C. In an inert atmosphere, the release ratios of Se increased slowly as temperature increased, varying between 56% and 74% for different coals at 1000 °C. All forms of Se in coal were thermally unstable and the conversion of Se in other forms into residual and organic–bound Se occurred. In an oxidizing atmosphere, the release ratios of Se differed significantly for different coals at low temperatures, but approached 100% at 1000 °C. Each form of Se in coal was released in different ratios. The water–soluble and ion–exchangeable Se, and carbonate– and oxide–bound Se were produced in the solid products. The oxidizing atmosphere was more conducive to the release of Se because the sulfide– and organic–bound Se was fully oxidized. Se could be converted into water–soluble and ion–exchangeable form and released less in Ca–rich coal. Sulfur (S) prohibited Ca from adsorbing Se by forming CaSO 4 , promoting the release of Se in S–rich coal. Unlabelled Image • Se transformations during pyrolysis and combustion of coals were investigated. • An oxidizing atmosphere facilitated the release of Se from the coal. • Se forms differ in stability and may convert to other form during thermal process. • The effect of inorganic contents in the coal on Se transformation was discussed. [ABSTRACT FROM AUTHOR]