Comparing Fly Ash Samples from Different Types of Incinerators for Their Potential as Storage Materials for Thermochemical Energy and CO2.

This study aims to investigate the physical and chemical characterization of six fly ash samples obtained from different municipal solid waste incinerators (MSWIs), namely grate furnaces, rotary kiln, and fluidized bed reactor, to determine their potential for CO2 and thermochemical energy storage (TCES). Representative samples were characterized via simultaneous thermal analysis (STA) in different atmospheres, i.e., N2, air, H2O, CO2, and H2O/CO2, to identify fly ash samples that can meet the minimum requirements, i.e., charging, discharging, and cycling stability, for its consideration as TCES and CO2-storage materials and to determine their energy contents. Furthermore, other techniques, such as inductively coupled plasma optical emission spectroscopy, X-ray fluorescence (XRF) spectrometry, X-ray diffraction (XRD), scanning electron microscopy, leachability tests, specific surface area measurement based on the Brunauer-Emmett-Teller method, and particle-size distribution measurement, were performed. XRF analysis showed that calcium oxide is one of the main components in fly ash, which is a potentially suitable component for TCES systems. XRD results revealed information regarding the crystal structure and phases of various elements, including that of Ca. The STA measurements showed that the samples can store thermal heat with energy contents of 50-394 kJ/kg (charging step). For one fly ash sample obtained from a grate furnace, the release of the stored thermal heat under the selected experimental conditions (discharging step) was demonstrated. The cycling stability tests were conducted thrice, and they were successful for the selected sample. One fly ash sample could store CO2 with a storage capacity of 27 kg CO2/ton based on results obtained under the selected experimental conditions in STA. Samples from rotary kiln and fluidized bed were heated up to 1150 °C in an N2 atmosphere, resulting in complete melting of samples in crucibles; however, other samples obtained from grate furnaces formed compacted powders after undergoing the same thermal treatment in STA. Samples from different grate furnaces showed similarities in their chemical and physical characterization. The leachability test according to the standard (EN 12457-4 (2002)) using water in a ratio of 10 L/S and showed that the leachate of heavy metals is below the maximum permissible values for nonhazardous materials (except for Pb), excluding the fly ash sample obtained using fluidized bed technology. The leachate contents of Cd and Mn in the fly ash samples obtained from the rotary kiln were higher than those in other samples. Characterization performed herein helped in determining the suitable fly ash samples that can be considered as potential CO2-storage and TCES materials.

Comparison of the Characteristics of Fly Ash Generated from Bio and Municipal Waste: Fluidized Bed Incinerators.

European solid waste incinerator plants still primarily use grate furnace technology, although circulating fluidized bed (CFB) technology is steadily expanding. Therefore, few investigations have reported on the environmental assessment of fly ash from fluidized incinerators. This research project aims to integrate information on fly ash derived from the combustion of municipal solid waste (FA1) and biomass (FA2) in fluidized bed incinerator facilities. Fly ash samples were comparatively analyzed by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM), and inductively coupled plasma optical emission spectroscopy (ICP-OES) to study the mineralogy, morphology, total heavy metal content, and leaching behavior, respectively. The analysis revealed that the two types of fly ash differ in their characteristics and leaching behavior. The concentration of most of the heavy metals in both is low compared to the literature values, but higher than the regulatory limits for use as a soil conditioner, whereas the high contents of Fe, Cu, and Al suggest good potential for metal recovery. The leaching ability of most elements is within the inert waste category, except for Hg, which is slightly above the non-hazardous waste limit.

Three new acid M+ arsenates and phosphates with multiply protonated As/PO4 groups.

The crystal structures of caesium dihydrogen arsenate(V) bis[trihydrogen arsenate(V)], Cs(H2AsO4)(H3AsO4)2, ammonium dihydrogen arsenate(V) trihydrogen arsenate(V), NH4(H2AsO4)(H3AsO4), and dilithium bis(dihydrogen phosphate), Li2(H2PO4)2, were solved from single-crystal X-ray diffraction data. NH4(H2AsO4)(H3AsO4), which was hydrothermally synthesized (T = 493 K), is homeotypic with Rb(H2AsO4)(H3AsO4), while Cs(H2AsO4)(H3AsO4)2 crystallizes in a novel structure type and Li2(H2PO4)2 represents a new polymorph of this composition. The Cs and Li compounds grew at room temperature from highly acidic aqueous solutions. Li2(H2PO4)2 forms a three-dimensional (3D) framework of PO4 tetrahedra sharing corners with Li2O6 dimers built of edge-sharing LiO4 groups, which is reinforced by hydrogen bonds. The two arsenate compounds are characterized by a 3D network of AsO4 groups that are connected solely via multiple strong hydrogen bonds. A statistical evaluation of the As-O bond lengths in singly, doubly and triply protonated AsO4 groups gave average values of 1.70 (2) Šfor 199 As-OH bonds, 1.728 (19) Šfor As-OH bonds in HAsO4 groups, 1.714 (12) Šfor As-OH bonds in H2AsO4 groups and 1.694 (16) Šfor As-OH bonds in H3AsO4 groups, and a grand mean value of 1.667 (18) Šfor As-O bonds to nonprotonated O atoms.

CsGa(HAsO4)2, the first Ga representative of the RbAl(HAsO4)2 structure type.

The crystal structure of hydro-thermally synthesized (T = 493 K, 7 d) caesium gallium bis-[hydrogen arsenate(V)], CsGa(HAsO4)2, was solved by single-crystal X-ray diffraction. The compound crystallizes in the common RbAl(HAsO4)2 structure type (R32) and consists of a basic tetra-hedral-octa-hedral framework topology that houses Cs+ cations in its channels. The AsO4 tetra-hedron is disordered over two positions with site occupancy factors of 0.946 (1) and 0.054 (1). Strong hydrogen bonds strengthen the network. The structure was refined as inversion twin.

(NH4)Ga(HAsO4)2 and TlAl(HAsO4)2 - two new RbFe(HPO4)2-type M + M 3+ arsenates.

The crystal structures of hydro-thermally synthesized (T = 493 K, 7-9 d) ammonium gallium bis-[hydrogen arsenate(V)], (NH4)Ga(HAsO4)2, and thallium aluminium bis-[hydrogen arsenate(V)], TlAl(HAsO4)2, were solved by single-crystal X-ray diffraction. Both compounds crystallize in the common RbFe(HPO4)2 structure type (R c) and share the same tetra-hedral-octa-hedral framework topology that houses the M + cations in its channels. One of the two Tl sites is slightly offset from its ideal position. Strong O-H⋯O hydrogen bonds strengthen the network.

Two new Rb-Ga arsenates: RbGa(HAsO4)2 and RbGa2As(HAsO4)6.

The crystal structures of hydro-thermally synthesized (T = 493 K, 7-9 d) rubidium gallium bis-[hydrogenarsenate(V)], RbGa(HAsO4)2, and rubidium digallium arsenic(V) hexa-[hydrogenarsenate(V)], RbGa2As(HAsO4)6, were solved by single-crystal X-ray diffraction. Both compounds have tetra-hedral-octa-hedral framework topologies. The M+ cations are located in channels of the respective framework. RbGa(HAsO4)2 crystallizes in the RbFe(HPO4)2 structure type (Rc), while RbGa2As(HAsO4)6 adopts the structure type of RbAl2As(HAsO4)6 (Rc), which represents a modification of the RbFe(HPO4)2 structure type. In this modification, one third of the M3+O6 octa-hedra are replaced by AsO6 octa-hedra, and two thirds of the voids in the structure, which are usually filled by M+ cations, remain empty to achieve charge balance.

M+M3+2As(HAsO4)6 (M+M3+ = TlGa, CsGa, CsAl): three new metal arsenates containing AsO6 octa-hedra.

The crystal structures of hydro-thermally synthesized (T = 493 K, 7 d) thallium(I) digallium arsenic(V) hexa-kis-[hydrogenarsenate(V)], TlGa2As(HAsO4)6, caes-ium digallium arsenic(V) hexa-kis-[hydrogenarsenate(V)], CsGa2As(HAsO4)6, and caesium dialuminium arsenic(V) hexa-kis-[hydrogenarsenate(V)], CsAl2As(HAsO4)6, were solved by single-crystal X-ray diffraction. The three compounds are isotypic and adopt the structure type of RbAl2As(HAsO4)6 (Rc), which itself represents a modification of the RbFe(HPO4)2 structure type and consists of a tetra-hedral-octa-hedral framework in which the slightly disordered M+ cations are located in channels. The three new compounds contain AsO6 octa-hedra assuming the topological role of M3+O6 octa-hedra. The As-O bond lengths are among the shortest As-O bond lengths known so far in AsO6 octa-hedra.

RbFe(HAsO4)2 and TlFe(HAsO4)2, two new hydrogenarsenates adopting two closely related structure types.

Rubidium iron bis-[hydrogen arsenate(V)], RbFe(HAsO4)2, and thallium iron bis-[hydrogen arsenate(V)], TlFe(HAsO4)2, were grown under mild hydro-thermal conditions (T = 493 K, 7 d). RbFe(HAsO4)2 adopts the RbFe(HPO4)2 structure type (space group Rc), while TlFe(HAsO4)2 crystallizes in the (NH4)Fe(HPO4)2 structure type (space group P ). Both compounds have tetra-hedral-octa-hedral framework topologies. The M+ cations are located in channels of the respective framework and are disordered in TlFe(HAsO4)2, which may suggest that the M+ cations can move in the channels.

M+M3+2As(HAsO4)6 and α- and ß-M+M3+(HAsO4)2 (M+M3+ = RbAl or CsFe): six new compounds crystallizing in three closely related structure types.

The crystal structures of hydrothermally synthesized (T = 493 K, 7-9 d) rubidium aluminium bis[hydrogen arsenate(V)], RbAl(HAsO4)2, caesium iron bis[hydrogen arsenate(V)], CsFe(HAsO4)2, rubidium dialuminium arsenic(V) hexakis[hydrogen arsenate(V)], RbAl2As(HAsO4)6, and caesium diiron arsenic(V) hexakis[hydrogen arsenate(V)], CsFe2As(HAsO4)6, were solved by single-crystal X-ray diffraction. The four compounds with the general formula M+M3+(HAsO4)2 adopt the RbFe(HPO4)2 structure type (R-3c) and a closely related new structure type, which is characterized by a different stacking order of the building units, leading to noncentrosymmetric space-group symmetry R32. The second new structure type, with the general formula M+M3+2As(HAsO4)6 (R-3c), is also a modification of the RbFe(HPO4)2 structure type, in which one third of the M3+O6 octahedra are replaced by AsO6 octahedra, and two thirds of the voids in the structure, which are usually filled by M+ cations, remain empty to achieve charge balance.

MIn(HAsO4)2 (M = K, Rb, Cs): three new hydrogen-arsenates adopting two different structure types.

Potassium indium bis-[hydrogen arsenate(V)], KIn(HAsO4)2, rubidium indium bis-[hydrogen arsenate(V)], RbIn(HAsO4)2, and caesium indium bis-[hydrogen arsenate(V)], CsIn(HAsO4)2, were grown under mild hydro-thermal conditions (T = 493 K, 7-8 d). KIn(HAsO4)2 adopts the KSc(HAsO4)2 structure type (space group C2/c), while RbIn(HAsO4)2 and CsIn(HAsO4)2 crystallize in the space group R-3c and are the first arsenate representatives of the RbFe(HPO4)2 structure type. All three compounds have tetra-hedral-octa-hedral framework topologies. The M+ cations, located in voids of the respective framework, are slightly disordered in RbIn(HAsO4)2. In KIn(HAsO4)2, there is a second K-atom position with a very low occupancy, which may suggest that the K atom can easily move in the channels extending along [101].

KInAs2O7, a new diarsenate with the TlInAs2O7 structure type.

Potassium indium diarsenate(V) was grown under mild hydro-thermal conditions (T = 493 K, 7 d) at a pH value of about 1. It adopts the TlInAs2O7 structure type (P-1, Z = 4) and is closely related to the KAlP2O7 (P21/c) and RbAlAs2O7 (P-1) structure types. The framework topology of KInAs2O7 is built of two symmetrically non-equivalent As2O7 groups which share corners with InO6 octa-hedra. The K atoms are located in channels extending along [010].

M3+(H2AsO4)(H2As2O7) (M3+ = Al, Ga) and In2(H2AsO4)2(H2As2O7)2: a new layer structure type and a new framework structure type containing the rare H2As2O72- group.

The crystal structures of hydrothermally synthesized aluminium dihydrogen arsenate(V) dihydrogen diarsenate(V), Al(H2AsO4)(H2As2O7), gallium dihydrogen arsenate(V) dihydrogen diarsenate(V), Ga(H2AsO4)(H2As2O7), and diindium bis[dihydrogen arsenate(V)] bis[dihydrogen diarsenate(V)], In2(H2AsO4)2(H2As2O7)2, were determined from single-crystal X-ray diffraction data collected at room temperature. The first two compounds are representatives of a novel sheet structure type, whereas the third compound crystallizes in a novel framework structure. In all three structures, the basic building units are M3+O6 octahedra (M = Al, Ga, In) that are connected via one H2AsO4- and two H2As2O72- groups into chains, and further via H2As2O72- groups into layers. In Al/Ga(H2AsO4)(H2As2O7), these layers are interconnected by weak-to-medium-strong hydrogen bonds. In In2(H2AsO4)2(H2As2O7)2, the H2As2O72- groups link the chains in three dimensions, thus creating a framework topology, which is reinforced by weak-to-medium-strong hydrogen bonds. The three title arsenates represent the first compounds containing both H2AsO4- and H2As2O72- groups.

New M+, M3+-arsenates - the framework structures of AgM3+(HAsO4)2 (M3+ = Al, Ga) and M+GaAs2O7 (M+ = Na, Ag).

The crystal structures of hydro-thermally synthesized silver(I) aluminium bis-[hydrogen arsenate(V)], AgAl(HAsO4)2, silver(I) gallium bis-[hydrogen arsenate(V)], AgGa(HAsO4)2, silver gallium diarsenate(V), AgGaAs2O7, and sodium gallium diarsenate(V), NaGaAs2O7, were determined from single-crystal X-ray diffraction data collected at room temperature. The first two compounds are representatives of the MCV-3 structure type known for KSc(HAsO4)2, which is characterized by a three-dimensional anionic framework of corner-sharing alternating M3+O6 octa-hedra (M = Al, Ga) and singly protonated AsO4 tetra-hedra. Inter-secting channels parallel to [101] and [110] host the Ag+ cations, which are positionally disordered in the Ga compound, but not in the Al compound. The hydrogen bonds are relatively strong, with O⋯O donor-acceptor distances of 2.6262 (17) and 2.6240 (19) Šfor the Al and Ga compounds, respectively. The two diarsenate compounds are representatives of the NaAlAs2O7 structure type, characterized by an anionic framework topology built of M3+O6 octa-hedra (M = Al, Ga) sharing corners with diarsenate groups, and M+ cations (M = Ag) hosted in the voids of the framework. Both structures are characterized by a staggered conformation of the As2O7 groups.

CsAl(H(2)AsO(4))(2)(HAsO(4)): a new monoclinic protonated arsenate with decorated kröhnkite-like chains.

The crystal structure of hydrothermally synthesized caesium aluminium bis[dihydrogen arsenate(V)] hydrogen arsenate(V), CsAl(H(2)AsO(4))(2)(HAsO(4)), was determined from single-crystal X-ray diffraction data collected at room temperature. The compound represents a new structure type that is characterized by decorated kröhnkite-like [100] chains of corner-sharing AlO(6) octahedra and AsO(4) tetrahedra. Ten-coordinated Cs atoms are situated between the chains, which are interconnected by five different hydrogen bonds [O...O = 2.569 (4)-2.978 (4) A]. All atoms are in general positions. CsAl(H(2)AsO(4))(2)(HAsO(4)) is very closely related to CsGa(H(1.5)AsO(4))(2)(H(2)AsO(4)) and isotypic CsCr(H(1.5)AsO(4))(2)(H(2)AsO(4)).

Octahedral As in M+ arsenates--architecture and seven new members.

Arsenates with arsenic in octahedral coordination are very rare. The present paper provides an overview of all known M(+) arsenates(V) containing octahedrally coordinated arsenic (M(+) = Li, Na, K, Rb, Cs, Ag) and the crystal structures (determined from single-crystal X-ray diffraction data) of the following seven new hydrothermally synthesized members belonging to six different structure types, four of which are novel: LiH(2)As(3)O(9), LiH(3)As(2)O(7), NaHAs(2)O(6)-type KHAs(2)O(6), KH(3)As(4)O(12) and isotypic RbH(3)As(4)O(12), CsAs(3)O(8) and NaH(2)As(3)O(9)-type AgH(2)As(3)O(9). The main building unit of these compounds is usually an As(4)O(14) cluster of two edge-sharing AsO(6) octahedra sharing two apical corners each with two AsO(4) tetrahedra. The different connectivity between these clusters defines the different structure types. The novel CsAs(3)O(8) structure, based on a derivative of the As(4)O(14) cluster, is the most condensed of all these M(+) arsenates, with an O/As ratio of only 2.67 compared with values of 2.75-3.5 for the remaining members. This is achieved through polymerization of the cluster derivatives to infinite chains of edge-sharing AsO(6) octahedra. The ([4])As/([6])As ratio drops to only 0.5. All but two of the protonated title compounds show protonated AsO(6) octahedra. Hydrogen bonds range from very strong to weak. An analysis of bond-length distribution and average bond lengths in AsO(6) octahedra in inorganic compounds leads to an overall mean As-O distance for all known AsO(6) octahedra (with R factors < 0.072) of 1.830 (2) A.

Octahedral-tetrahedral framework structures of InAsO4.H2O and PbIn(AsO4)(AsO3OH).

Indium arsenate(V) monohydrate, InAsO4.H2O, (I), crystallizes in the structure type of MnMoO4.H2O. The structure is built of In2O8(H2O)2 dimers (mean In-O=2.150 A) corner-linked to slightly distorted AsO4 tetrahedra (mean As-O=1.686 A). The linkage results in a three-dimensional framework, with small voids into which the apical water ligand of the InO5(H2O) octahedron points. The hydrogen bonds in (I) are of medium strength. Lead(II) indium arsenate(V) hydrogen arsenate(V), PbIn(AsO4)(AsO3OH), (II), represents the first reported lead indium arsenate. It is characterized by a framework structure of InO6 octahedra corner-linked to AsO4 and AsO3OH tetrahedra. The resulting voids are occupied by Pb2O10(OH)2 dimers built of two edge-sharing highly distorted PbO6(OH) polyhedra (mean Pb-O=2.623 A). The compound is isotypic with PbFe(III)(AsO4)(AsO3OH). The average In-O bond length in (II) is 2.157 A. In both arsenates, all atoms are in general positions.

CsGa(H1.5AsO4)2(H2AsO4) and isotypic CsCr(H1.5AsO4)2(H2AsO4): decorated kröhnkite-like chains in two unusual hydrogen arsenates.

Hydrothermally synthesized caesium gallium(III) hydrogen arsenate(V), CsGa(H1.5AsO4)2(H2AsO4), (I), and isotypic caesium chromium(III) hydrogen arsenate(V), CsCr(H1.5AsO4)2(H2AsO4), (II), represent a new structure type and stoichiometry among MI-MIII hydrogen arsenates. The crystal structure, determined from single-crystal X-ray diffraction data, is based on an infinite octahedral-tetrahedral chain and can be described as a decorated kröhnkite-like chain. The chains extend parallel to [100] and are separated by ten-coordinated Cs atoms. The hydrogen-bonding scheme comprises one very short symmetry-restricted hydrogen bond, with O...O distances of 2.519 (4) and 2.508 (4) A in (I) and (II), respectively, and two further medium-strong hydrogen bonds, all of which reinforce the connections between adjacent chains. The average Ga-O and Cr-O bond lengths are 1.973 (15) and 1.980 (13) A, respectively, and the average As-O bond lengths in the two protonated arsenate groups lie within a very narrow range [1.690 (18)-1.69 (3) A]. The Cs atom is located on a centre of inversion, while the MIII and As2 atoms lie on twofold axes. Relationships to CaBa2(HPO4)2(H2PO4)2 and other compounds containing decorated kröhnkite-type or kröhnkite-like chains are discussed.

Alkali scandium arsenates. I. The framework structures of KSc(HAsO4)2 and RbScAs2O7.

The crystal structures of hydrothermally synthesized potassium scandium hydrogen arsenate(V), KSc(HAsO4)2, (I), and rubidium scandium diarsenate(V), RbScAs2O7, (II), were determined from single-crystal X-ray diffraction data collected at room temperature. Compound (I) represents a new microporous structure type, designated MCV-3, which is characterized by a three-dimensional framework of corner-sharing alternating ScO6 octahedra and HAsO4 tetrahedra. Intersecting tunnels parallel to [101] and [110] host eight-coordinate K atoms. There is one hydrogen bond of medium strength [O...O = 2.7153 (18) A]. Compound (II) is the first reported diarsenate with a KAlP2O7-type structure and is isotypic with at least 27 A(I)M(III) diphosphates. The average Sc-O bond lengths in (I) and (II) are 2.09 (2) and 2.09 (3) A, respectively. The K and Sc atoms in (I) lie on an inversion centre and a twofold axis, respectively. All atoms in (II) are in general positions.

Alkali scandium arsenates. II. The framework structures of alpha- and beta-CsSc(HAsO4)2.

The crystal structures of hydrothermally synthesized alpha-, (I), and beta-caesium scandium bis[hydrogen arsenate(V)], (II), both CsSc(HAsO4)2, have been determined from single-crystal X-ray diffraction data collected at room temperature. The dimorphs are both characterized by a three-dimensional negatively charged framework of corner-sharing alternating ScO6 octahedra and HAsO4 tetrahedra. The charge-balancing Cs+ cations are located in a system of three intersecting tunnels in (I) and in tunnels parallel to the a axis in (II). Strong to weak hydrogen bonds reinforce both frameworks. The average Sc-O bond lengths are 2.098 and 2.094 A, respectively. Compound (I) is triclinic and isotypic with (NH4)Fe(III)(HPO4)2, alpha-A(I)V(III)(HPO4)2 (A is NH4 or Rb) and alpha-(NH4)(Al(0.64)Ga(0.36))(HPO4)2. Compound (II) is monoclinic and isotypic with (H3O)Fe(III)(HPO4)2, beta-A(I)V(III)(HPO4)2 (A is NH4 or Rb), CsIn(HPO4)2 and RbSc(HPO4)2. Both (I) and (II) represent the first arsenate examples of their structure types. The Cs and Sc atoms in (I) lie on inversion centres. In (II), all atoms are in general positions. A brief overview is presented of the six structure types shown by A(I)M(III)(HXO4)2 compounds (X is P or As).