Carl A. Francis

Heavy metal stabilization in municipal solid waste combustion bottom ash using soluble phosphate

Abstract Heavy metal chemical stabilization with soluble PO 4 3− was assessed for bottom ash from combustion of municipal solid waste. Bottom ash can contain heavy metals (e.g. Pb) that can leach. An experimental dose of 0.38 mols of soluble PO 4 3− per kg of residue was used without optimizing the formulation for any one heavy metal. The reduction in the fraction available for leaching according to the total availability leaching test was 52% for Ca, 14% for Cd, 98% for Cu, 99% for Pb, and 36% for Zn. pH-dependent leaching (pH 4, 6, 8) showed that the treatment was able to reduce equilibrium concentrations by 0.5 to 3 log units for these heavy metals. Bulk and surface spectroscopies showed that both crystalline and amorphous precipitates were present as insoluble metal phosphate reaction products. Dominant reaction products were calcium phosphates, tertiary metal phosphates, and apatite family minerals. Observed phases included, β-Ca 3 (PO 4 ) 2 (tertiary calcium phosphate); Ca 5 (PO 4 ) 3 OH (calcium hydroxyapatite); Pb 5 (PO 4 ) 3 Cl (lead chloropyromorphite); and Pb 5 (PO 4 ) 3 OH (lead hydroxypyromorphite). These are considered to be very geochemically stable mineral phases. The geochemical thermodynamic equilibrium model MINTEQA2 was modified to include both extensive phosphate minerals and simple ideal solid solutions in order to better model pH-dependent leaching. Both end members [e.g. Pb 5 (PO 4 ) 3 Cl, β-Ca 3 (PO 4 ) 2 ] and ideal solid solutions [e.g. (Pb 2 ,Ca)(PO 4 ) 2 ] were observed as controlling solids for Ca 2+ , Zn 2+ , Pb 2+ , and Cu 2+ . Controlling solids were not identified for Cd 2+ because pH dependent concentrations were generally below detection limits. The divalent metal cations in bottom ash were effectively stabilized by treatment with soluble PO 4 3− .

Characterization and phosphate stabilization of dusts from the vitrification of MSW combustion residues

Abstract The use of soluble PO 4 3− as a heavy metal chemical stabilization agent was evaluated for a dust generated from melting or vitrification of municipal solid waste combustion residues. Vitrification dusts contain high concentrations of volatile elements such as Cl, Na, K, S, Pb, and Zn. These elements are present in the dusts largely as simple salts (e.g. PbCl 2 , ZnSO 4 ) which are highly leachable. At an experimental dose of 0.4 moles of soluble PO 4 3− per kg of residue, the pH-dependent leaching (pH 5,7,9) showed that the treatment was able to reduce equilibrium concentrations by factors of 3 to 100 for many metals; particularly Cd, Cu, Pb and Zn. Bulk and surface spectroscopies showed that the insoluble reaction products are tertiary metal phosphate [e.g. Zn 3 (PO 4 ) 2 ] and apatite [e.g. Pb 5 (PO 4 ) 3 Cl] family minerals. Geochemical thermodynamic equilibrium modeling showed that apatite family and tertiary metal phosphate phases act as controlling solids for the equilibrium concentrations of Ca 2+ , Zn 2+ , Pb 2+ , Cu 2+ , and Cd 2+ in the leachates during pH-dependent leaching. Both end members and ideal solid solutions were seen to be controlling solids. Soluble phosphate effectively converted soluble metal salts into insoluble metal phosphate phases despite the relatively low doses and dry mixing conditions that were used. Soluble phosphate is an effective stabilization agent for divalent heavy metals in melting dusts where leachable metals are present in high concentrations.

Tetrahedrally coordinated boron in Al-rich tourmaline and its relationship to the pressure–temperature conditions of formation

An Al-rich tourmaline from the Sahatany Pegmatite Field at Manjaka, Sahatany Valley, Madagascar, was structurally and chemically characterized. The combination of chemical and structural data yields an optimized formula of X (Na0.53Ca0.09□0.38) Y (Al2.00Li0.90Mn2+0.09Fe2+ 0.01) Z Al6 (BO3)3 T [Si5.61B0.39]O18 V (OH)3 W [(OH)0.6O0.4], with a = 15.777(1), c = 7.086(1) A ( R 1 = 0.017 for 3241 reflections). The 〈 T –O〉 distance of ~ 1.611 A is one of the smallest distances observed in natural tourmalines. The very short 〈 Y –O〉 distance of ~ 1.976 A reflects the relatively high amount of Al at the Y site. Together with other natural and synthetic Al-rich tourmalines, a very good inverse correlation ( r 2 = 0.996) between [4]B and the unit-cell volume was found. [4]B increases with the Al content at the Y site approximately as a power function with a linear term up until [4]B ≈ Si ≈ 3 apfu and Y Al ≈ 3 apfu, respectively, in natural and synthetic Al-rich tourmalines. Short-range order considerations would not allow for [4]B in solid solution between schorl and elbaite, but would in solid solutions between schorl, “oxy-schorl”, elbaite, liddicoatite, or rossmanite and hypothetical [4]B-rich tourmaline end-members with only Al3+ at the Y site. By plotting the [4]B content of synthetic and natural Al-rich tourmalines, which crystallized at elevated PT conditions, it is obvious that there are pronounced correlations between PT conditions and the [4]B content. Towards lower temperatures higher [4]B contents are found in tourmaline, which is consistent with previous investigations on the coordination of B in melts. Above a pressure of ~ 1000–1500 MPa (depending on the temperature) the highest observed [4]B content does not change significantly at a given temperature. The PT conditions of the formation of [4]B-rich olenite from Koralpe, Eastern Alps, Austria, can be estimated as 500–700 MPa/630 °C.

Massive chromite in the Brenham pallasite and the fractionation of Cr during the crystallization of asteroidal cores

Abstract Large (≥2 mm) chromite grains are present in IIIAB iron meteorites and in the main-group pallasites ( pmg ), closely related to high-Au IIIAB irons. Pallasites seem to have formed by the intrusion of a highly evolved metallic magma from a IIIAB-like core into fragmented olivine of the overlying dunite mantle. High Cr contents are commonly encountered during the analyses of metallic samples of high-Au IIIAB irons and main-group pallasites, an indication that Cr contents were high in the intruding liquid and that Cr behaved as an incompatible element during the crystallization of the IIIAB magma, contrary to expectations based on the negative IIIAB Cr-Ni and Cr-Au trends among low-Au IIIAB irons. In a region about 10 cm across in the Brenham main-group pallasite massive chromite fills the interstices between olivine grains, the site normally occupied by metal in Brenham and other pallasites. The massive chromite may have formed as a late cumulus phase; because Fe-Ni was also crystallizing, its absence in the chromite-rich region suggests a separation associated with differences in liquid buoyancy. The coexisting chromite and olivine are zoned; in the olivine FeO is highest in pallasitic (olivine-metal) regions, lowest in rims adjacent to chromite, and intermediate in the cores of these olivines. Chromite shows the opposite zoning, with the highest FeO contents at grain edges adjacent to olivine. The observed gradients are those expected to form by Fe-Mg exchange between olivine and chromite during slow cooling at subsolidus temperatures. Compared to normal Brenham, contents of phosphoran olivine and phosphates are higher in the chromitic pallasitic region. We also report data for large-to-massive chromites present in pmg Molong and in high-Au IIIAB Bear Creek that, like Brenham, formed from a highly evolved magma. The Bear Creek chromite has a much lower Mg content than that in the pallasites, implying that, in the pmg , the Mg was extracted from the olivine during high-temperature reaction with the precipitating chromite. There are other circumstantial arguments indicating that Cr was incompatible in the metal during the crystallization of the IIIAB magma, with the concentration in the residual magma rising from an initial value of about 300 μg/g to a value around 700 μg/g when Bear Creek and Brenham were formed. We consider possible explanations for these negative Cr-Au and Cr-Ni trends and find the most probable one to be that they reflect sampling artefacts resulting from analysts avoiding visible chromite (and the commonly associated phase FeS) when choosing metal samples.

Petrographic and spectroscopic characterization of phosphate-stabilized mine tailings from Leadville, Colorado.

The use of soluble PO4(3-) and lime as a heavy metal chemical stabilization agent was evaluated for mine tailings from Leadville, Colorado. The tailings are from piles associated with the Wolftone and Maid of Erin mines; ore material that was originally mined around 1900, reprocessed in the 1940s, and now requires stabilization. The dominant minerals in the tailings are galena (PbS), cerrusite (PbCO3), pyromorphite (Pb5(PO4)3Cl), plumbojarosite (Pb0.5Fe3(SO4)2(OH)6), and chalcophanites ((Pb,Fe,Zn,Mn)Mn2O5 x 2H2O). The tailings were treated with soluble PO4(3-) and lime to convert soluble heavy metals (principally Pb, Zn, Cu, Cd) into insoluble metal phosphate precipitates. The treatment process caused bulk mineralogical transformations as well as the formation of a reaction rind around the particles dominated by Ca and P. Within the mineral grains, Fe-Pb phosphosulfates, Fe-Pb sulfates (plumbojarosite), and galena convert to Fe-Ca-Pb hydroxides. The Mn-Pb hydroxides and Mn-(+/-Fe)-Pb hydroxides (chalcophanites) undergo chemical alteration throughout the grains during treatment. Bulk and surface spectroscopies showed that the insoluble reaction products in the rind are tertiary metal phosphate (e.g. (Cu,Ca2)(PO4)2) and apatite (e.g. Pb5(PO4)3Cl) family minerals. pH-dependent leaching (pH 4,6,8) showed that the treatment was able to reduce equilibrium concentrations by factors of 3 to 150 for many metals; particularly Pb2+, Zn2+, Cd2+, and Cu2+. Geochemical thermodynamic equilibrium modeling showed that apatite family and tertiary metal phosphate phases act as controlling solids for the equilibrium concentrations of Ca2+, PO4(3-) Pb2+, Zn2+, Cd2+, and Cu2+ in the leachates during pH-dependent leaching. Both end members and ideal solid solutions were seen to be controlling solids.

Limitations of Fe2+ and Mn2+ site occupancy in tourmaline: Evidence from Fe2+- and Mn2+-rich tourmaline

Abstract Fe2+- and Mn2+-rich tourmalines were used to test whether Fe2+ and Mn2+ substitute on the Z site of tourmaline to a detectable degree. Fe-rich tourmaline from a pegmatite from Lower Austria was characterized by crystal-structure refinement, chemical analyses, and Mössbauer and optical spectroscopy. The sample has large amounts of Fe2+ (~2.3 apfu), and substantial amounts of Fe3+ (~1.0 apfu). On basis of the collected data, the structural refinement and the spectroscopic data, an initial formula was determined by assigning the entire amount of Fe3+ (no delocalized electrons) and Ti4+ to the Z site and the amount of Fe2+ and Fe3+ from delocalized electrons to the Y-Z ED doublet (delocalized electrons between Y-Z and Y-Y): X (Na0.9Ca0.1) Y(Fe2+2.0Al0.4Mn2+0.3Fe3+0.2) Z(Al4.8Fe3+0.8Fe2+0.2Ti4+0.1) T(Si5.9Al0.1)O18 (BO3)3V(OH)3W[O0.5F0.3(OH)0.2] with a = 16.039(1) and c = 7.254(1) Å. This formula is consistent with lack of Fe2+ at the Z site, apart from that occupancy connected with delocalization of a hopping electron. The formula was further modified by considering two ED doublets to yield: X(Na0.9Ca0.1) Y(Fe2+1.8Al0.5Mn2+0.3Fe3+0.3) Z(Al4.8Fe3+0.7Fe2+0.4Ti4+0.1) T(Si5.9Al0.1)O18 (BO3)3V(OH)3W[O0.5F0.3(OH)0.2]. This formula requires some Fe2+ (~0.3 apfu) at the Z site, apart from that connected with delocalization of a hopping electron. Optical spectra were recorded from this sample as well as from two other Fe2+-rich tourmalines to determine if there is any evidence for Fe2+ at Y and Z sites. If Fe2+ were to occupy two different 6-coordinated sites in significant amounts and if these polyhedra have different geometries or metal-oxygen distances, bands from each site should be observed. However, even in high-quality spectra we see no evidence for such a doubling of the bands. We conclude that there is no ultimate proof for Fe2+ at the Z site, apart from that occupancy connected with delocalization of hopping electrons involving Fe cations at the Y and Z sites. A very Mn-rich tourmaline from a pegmatite on Elba Island, Italy, was characterized by crystal-structure determination, chemical analyses, and optical spectroscopy. The optimized structural formula is X(Na0.6□0.4) Y(Mn2+1.3Al1.2Li0.5) ZAl6TSi6O18 (BO3)3V(OH)3 W[F0.5O0.5], with a = 15.951(2) and c = 7.138(1) Å. Within a 3σ error there is no evidence for Mn occupancy at the Z site by refinement of Al ↔ Mn, and, thus, no final proof for Mn2+ at the Z site, either. Oxidation of these tourmalines at 700-750 °C and 1 bar for 10-72 h converted Fe2+ to Fe3+ and Mn2+ to Mn3+ with concomitant exchange with Al of the Z site. The refined ZFe content in the Fe-rich tourmaline increased by ~40% relative to its initial occupancy. The refined YFe content was smaller and the distance was significantly reduced relative to the unoxidized sample. A similar effect was observed for the oxidized Mn2+-rich tourmaline. Simultaneously, H and F were expelled from both samples as indicated by structural refinements, and H expulsion was indicated by infrared spectroscopy. The final species after oxidizing the Fe2+-rich tourmaline is buergerite. Its color had changed from blackish to brown-red. After oxidizing the Mn2+-rich tourmaline, the previously dark yellow sample was very dark brown-red, as expected for the oxidation of Mn2+ to Mn3+. The unit-cell parameter a decreased during oxidation whereas the c parameter showed a slight increase.

The crystal structure of stichtite, re-examination of barbertonite, and the nature of polytypism in MgCr hydrotalcites

Abstract Stichtite, ideally Mg6Cr2CO3(OH)16∙4H2O, from Stichtite Hill, Tasmania, Australia, and barbertonite, also ideally Mg6Cr2CO3(OH)16∙4H2O, from the Kaapsehoop asbestos mine, South Africa, have been studied by powder X-ray diffraction and their structures have been refined using the Rietveld method. Stichtite from Stichtite Hill crystallizes in the rhombohedral space group R3̄m, with unitcell parameters a = 3.09575(3) and c = 23.5069(6) Å, V = 195.099(6) Å3, with Z = 3/8. Barbertonite from the Kaapsehoop asbestos mine crystallizes in the hexagonal space group P63/mmc. The co-type specimens of barbertonite were found to be intergrown mixtures consisting of barbertonite and stichtite. Unit-cell parameters of barbertonite from the co-type specimens were a = 3.09689(6), c = 15.6193(8) Å, and V = 129.731(8) Å3 and a = 3.09646(6), c = 15.627(1) Å V = 129.76(1) Å3, and Z = ¼. Rietveld refinements of both stichtite and barbertonite show that they are polytypes rather than polymorphs and do not represent distinct mineral species. Several possible nomenclature systems are discussed for the naming of hydrotalcite minerals and groups. Raman band assignments are also presented for stichtite from Stichtite Hill. Stichtite and hydrotalcite minerals make up a large proportion of the ore at the Mount Keith nickel mine in Western Australia. Bulk powder diffraction shows the ore contains 6.1 wt% stichtite and 5.6 wt% iowaite. Hydrotalcite group minerals provide an important potential reservoir of CO2. At Mount Keith, the amount of CO2 mined as stichtite could exceed 45 000 metric tons per year, while exchange of Cl for CO3 could fix in excess of 40 000 metric tons CO2 per year if end-member iowaite is reacted to form pyaroaurite.

Fettelite, [Ag6As2S7][Ag10HgAs2S8] from Chañarcillo, Chile: Crystal structure, pseudosymmetry, twinning, and revised chemical formula

Abstract The crystal structure of the rare mineral fettelite was solved using intensity data collected from a twinned crystal from Chañarcillo, Copiapó Province, Chile. This study revealed that, in spite of the strong hexagonal pseudosymmetry, the structure is monoclinic (space group C2) with a = 26.0388(10), b = 15.0651(8), c = 15.5361(8) Å, β = 90.48(1)°, and V = 6094.2(5) Å3. The refinement of an anisotropic model led to an R index of 0.0656 for 7143 observed reflections [I > 2σ(I)] and 0.0759 for all 17 447 independent reflections. Fettelite is intimately twinned with six twin domains. The structure consists of the stacking of two module layers along [001]: an A module layer with composition [Ag6As2S7]2- and a B module layer with composition [Ag10HgAs2S8]2+. The As atoms form isolated AsS3 pyramids typical of sulfosalts, Hg links two sulfur atoms in linear coordination, and Ag occupies sites with coordination ranging from quasi linear to almost tetrahedral. The A module layer found for fettelite is identical to that described for the minerals belonging to the pearceite-polybasite group. On the basis of information gained from this characterization the crystal chemical formula was revised according to the structural results, yielding [Ag6As2S7][Ag10HgAs2S8] (Z = 8).

Chlorapatite (Ca5(PO4)3Cl) Characterization by XPS: An Environmentally Important Secondary Mineral

Chlorapatite (Ca5(PO4)3Cl) is an environmentally important secondary phosphate mineral, one of the apatite family of minerals. It is of significance geochemically in ore, soil, sedimentary, and waste systems. We have used XPS to study the binding energy of primary photoelectrons from the powder of a well-fractured massive block sample. The sample is from Telemark, Norway and is part of the Harvard University Mineralogical Museum’s collection. General survey and high-resolution spectra were collected using a Perkin Elmer Physical Electronics 5200C spectrometer. Adventitious carbon was used for energy referencing. Charge corrected binding energies for the photoelectrons of chlorapatite (Ca 2p3/2, Ca 2p1/2, P 2p3/2, P 2p1/2, P 2s, O 1s, Cl 2p3/2, and Cl 2p1/2) are reported. The charge corrected binding energy for Si 2p photoelectrons of either isomorphically substituted silicate (e.g., Ca5(PO4,SiO4)3Cl) or host quartz present in the natural sample is also reported. The observed binding energies are useful in...

Gold Crystals A Primer

C ularity, or symmetry, makes crystals particularly fascinating. Gold crystallizes with the highest symmetry allowed in crystals, making its forms elegant and easy to visualize. However, most specimens of crystallized gold consist of threads, wires, arborescent forms, and leaves. More or less ideal single crystals of gold are rare and never large-usually 2 cm or less. They are ideal for the micromounter and thumbnail collector. This article reviews the ideal forms because understanding