Secondary Phosphate Research Articles

Seasonal variations of rare earths and yttrium distribution in the lowland Havel River, Germany, by agricultural fertilization and effluents of sewage treatment plants

REE and Y (REY) distribution in the lowland Havel River passing the Federal State of Berlin, Germany, depends on contributions of point sources such pharmaceutical and high-tech industries, acid water from the open pit lignite mining, and medical application of very stable organic Gd chelates. Another omnipresent dispersed source of REY are water-soluble Ca-phosphates containing micro-amounts of Eu(II)-bearing barite as components of common agricultural fertilizers. After distribution in the field during the cold season (October through March) these Ca-phosphates dissolve and secondary phosphates and calcite precipitate both being enriched in light REE. Heavy REE are preferably exported by runoff together with part of the micro-contaminant barite leading to high Yb/Nd ratios in the Havel water and REY distribution patterns with only small Eu deficits. During the warm season (April through September) light REE together with phosphate are leached from secondary soil minerals by runoff. The micro-component barite is retained in vegetation-covered soil. Thus, REY patterns of Havel water show significant Eu deficits. The high Gd anomalies result from medical applications of Gd-chelates which after urination pass the sewage treatment plants. The seasonal variations of total Gd in the Havel River are artifacts based on seasonal locally varied discharge of effluents from sewage treatment plants. The natural Gd concentration of 8pmol/l in the northern Havel is enhanced to 3300pmol/l, when the Havel River leaves Berlin territory. The elimination of phosphate from Lake Tegel water affects the fractionation of REE but not the concentration of total Gd. Although enhanced in total phosphorus (TP), the REE concentrations in the water from the Spree River and the Teltow Canal are less than in the Havel water before their confluence. Only Yb and Lu do not decrease. The contributors of the Havel River are high in total organic carbon (TOC) and dissolved organic carbon (DOC) compared to the Havel water before their indicating that REY are preferentially sorbed by settling organic matter. Applying PHREEQC and assuming that only 10% of TP is present as ortho-phosphate yields that only carbonate complexes are essential.

Natural fumarolic alteration of fluorapatite, olivine, and basaltic glass, and implications for habitable environments on Mars.

Fumaroles represent a very important potential habitat on Mars because they contain water and nutrients. Global deposition of volcanic sulfate aerosols may also have been an important soil-forming process affecting large areas of Mars. Here we identify alteration from the Senator fumarole, northwest Nevada, USA, and in low-temperature environments near the fumarole to help interpret fumarolic and acid vapor alteration of rocks and soils on Mars. We analyzed soil samples and fluorapatite, olivine, and basaltic glass placed at and near the fumarole in in situ mineral alteration experiments designed to measure weathering under natural field conditions. Using synchrotron X-ray diffraction, we clearly observe hydroxyl-carbonate-bearing fluorapatite as a fumarolic alteration product of the original material, fluorapatite. The composition of apatites as well as secondary phosphates has been previously used to infer magmatic conditions as well as fumarolic conditions on Mars. To our knowledge, the observations reported here represent the first documented instance of formation of hydroxyl-carbonate-bearing apatite from fluorapatite in a field experiment. Retreat of olivine surfaces, as well as abundant NH4-containing minerals, was also characteristic of fumarolic alteration. In contrast, alteration in the nearby low-temperature environment resulted in formation of large pits on olivine surfaces, which were clearly distinguishable from the fumarolic alteration. Raman signatures of some fumarolically impacted surfaces are consistent with detection of the biological molecules chlorophyll and scytenomin, potentially useful biosignatures. Observations of altered minerals on Mars may therefore help identify the environment of formation and understand the aqueous history and potential habitability of that planet.

Clay Mineralogy of Gelic Soils from the Fildes Peninsula, Maritime Antarctica

The general physical and chemical properties of Antarctic soils have been long studied, although detailed soil mineralogy remains comparatively little explored. The aim of this study was to characterize the clay mineralogy of soils from Fildes Peninsula, King George Island, Maritime Antarctica. The clay fraction of four soil profiles was studied by x-ray diffraction (XRD). Poorly crystalline mineral phases were sequentially treated with 0.1 mol L−1 sodium pyrophosphate, 0.2 mol L−1 ammonium oxalate, and 0.5 mol L−1 NaOH. After each extraction, differential XRD patterns were obtained. The presence of primary minerals in the clay fraction, such as K-feldspar, plagioclase, pyroxene, and mica, indicates the low degree of chemical weathering. However, ornithogenic influence leads to the phosphatization of the mineral substrate and neoformation of secondary phosphates containing Fe and Al, such as leucophosphite, metavariscite, and minyulite. Overall, what makes these Antarctic soils unique is (i) the widespread occurrence of poorly crystalline minerals in the clay fraction with concentrations ranging from 20.9 to 65.6%, (ii) their association with organic matter forming organo-metallic complexes, and (iii) Al- and Si-rich oxides (allophane and imogolite) and poorly crystalline Fe oxides. Such high amounts of poorly crystalline mineral phases can compensate for the generally low clay content, favoring the retention of ionic and polar chemical compounds, including pollutants.

Raman and infrared spectroscopic characterization of the phosphate mineral paravauxite Fe2+Al2(PO4)2(OH)2⋅8H2O

We have undertaken a vibrational spectroscopic study of paravauxite the Siglo XX mine, Bustillo Province, northern of Potosí department, Bolivia. This mine is important source for rare and unusual secondary phosphate minerals and is the type locality for a number of rare phosphates such as vauxite, sigloite, metavauxite and for jeanbandyite. The chemical formula of the studied sample was determined asFe0.952+,(Al0.07)Σ1.02(Al)2.09(PO4)1.97(OH)1.98·7.90(H2O).The Raman spectrum is dominated by an intense Raman band at 1020cm−1 assigned to the PO43-ν1 symmetric stretching mode. Low intensity Raman bands found at 1058, 1115 and 1148cm−1 are assigned to the PO43-ν3 antisymmetric stretching vibrations. Raman bands of paravauxite at 537, 570, 609 and 643cm−1 are assigned to the ν4PO43- bending modes whilst the Raman bands at 393 and 420cm−1 are due to the ν2PO43- bending modes. The Raman spectral profile of paravauxite in the hydroxyl stretching region is broad with component bands resolved at 3086, 3215, 3315, 3421, 3505 and 3648cm−1. Vibrational spectroscopy enables the assessment of the molecular structure of paravauxite to be undertaken.

SEM–EDX, Raman and infrared spectroscopic characterization of the phosphate mineral frondelite (Mn2+)(Fe3+)4(PO4)3(OH)5

We have analyzed a frondelite mineral sample from the Cigana mine, located in the municipality of Conselheiro Pena, a well-known pegmatite in Brazil. In the Cigana pegmatite, secondary phosphates, namely eosphorite, fairfieldite, fluorapatite, frondelite, gormanite, hureaulite, lithiophilite, reddingite and vivianite are common minerals in miarolitic cavities and in massive blocks after triphylite. The chemical formula was determined as (Mn0.68, Fe0.32)(Fe3+)3,72(PO4)3.17(OH)4.99.The structure of the mineral was assessed using vibrational spectroscopy. Bands attributed to the stretching and bending modes of PO43- and HOPO33- units were identified. The observation of multiple bands supports the concept of symmetry reduction of the phosphate anion in the frondelite structure. Sharp Raman and infrared bands at 3581cm−1 is assigned to the OH stretching vibration. Broad Raman bands at 3063, 3529 and 3365cm−1 are attributed to water stretching vibrational modes.

Rare Earth Elements Geochemistry of Sheikh‐Marut Laterite Deposit, NW Mahabad, West‐Azarbaidjan Province, Iran

AbstractLaterite deposit at Sheikh‐Marut (NW Mahabad, West‐Azarbaidjan province, Iran) occurred within middle–upper Permian carbonate rocks. It consists of seven stratiform and/or discontinuous lenticular layers extending over 4.2 km in length and having thicknesses ranging from 3 to 14 m. Mineralogical data show that the ores contain kaolinite and hematite as major and boehmite, diaspore, halloysite, amesite, anatase, and muscovite‐illite as minor mineral phases. The computed Ce anomaly values in the ores range from 0.05 to 20.84. Conservative index (e.g., Eu/Eu*) suggests that this deposit is a product of alteration and weathering of basaltic rocks. Rhythmic increment of ΣREE values of the ores with approaching to the carbonate bedrocks shows an in‐situ occurrence of lateritization processes. Mass change calculations of elements indicate that two competing processes namely leaching and fixation were the major regulating factors in concentration variation of REEs (La–Lu) in this deposit The obtained results show that pH increase of weathering solutions by carbonate bedrocks, existence of organic matters, and the degree of comlexation with organic ligands played remarkable role in distribution of REEs during lateritization. Further geochemical considerations revealed that secondary phosphates, Mn‐oxides and ‐hydroxides, diaspore, and anatase were the potential hosts for REEs in this deposit.

Emulsion synthesis of dicalcium phosphate particles for the preparation of calcium phosphate cements with improved compressive strengths and reduced setting times

AbstractThis study aimed to produce nanosized secondary calcium phosphate powders (CaHPO

Acid sulfate alteration of fluorapatite, basaltic glass and olivine by hydrothermal vapors and fluids: Implications for fumarolic activity and secondary phosphate phases in sulfate‐rich Paso Robles soil at Gusev Crater, Mars

Phosphate‐rich rocks and a nearby phosphate‐rich soil, Paso Robles, were analyzed in Gusev Crater, Mars, by the Mars Exploration Rover Spirit and interpreted to be highly altered, possibly by hydrothermal or fumarolic alteration of primary, phosphate‐rich material. To test mineral phases resulting from such alteration, we performed hydrothermal acid‐vapor and acid‐fluid experiments on olivine (Ol), fluorapatite (Ap), and basaltic glass (Gl) as single phases and a mixture of phases. Minerals formed include Ca‐, Al‐, Fe‐ and Mg‐sulfates with different hydration states (anhydrite, bassanite, gypsum; alunogen; hexahydrite, and pentahydrite). Phosphate‐bearing minerals formed included monocalcium phosphate monohydrate (MCP) (acid‐vapor and acid‐fluid alteration of fluorapatite only) and ferrian giniite (acid‐fluid alteration of the Ol + Gl + Ap mixture). MCP is likely present in Paso Robles if primary Ca‐phosphate minerals reacted with sulfuric acid with little transport of phosphate. Under fluid:rock ratios allowing transport of phosphate, a ferric phosphate phase such as ferrian giniite might form instead. Mössbauer measurements of ferrian giniite‐bearing alteration products and synthetic ferrian giniite are consistent with Spirit's Mössbauer measurements of the ferric‐bearing phase in Paso Robes soil, but are also consistent with ferric sulfate phases in the low‐P soil Arad_Samra. Therefore, Mössbauer data alone do not constrain the fluid:rock ratio. However, the excess iron (hematite) in Paso Robles soil, which implies aqueous transport, combined with our laboratory experiments, suggest acid‐sulfate alteration in a hydrothermal (fumarolic) environment at fluid:rock ratios sufficient to allow dissolution, transport, and precipitation of secondary chemical components including a ferric phosphate such as ferrian giniite.

MINERALOGY OF SPODUMENE PEGMATITES AND RELATED ROCKS IN THE TIN-SPODUMENE BELT OF NORTH CAROLINA AND SOUTH CAROLINA, USA

The Tin–Spodumene Belt (TSB) along the border of North and South Carolina, southeastern USA, is composed of hundreds of en echelon dikes intruded into amphibolite-facies mica schist and amphibolite. The spodumene pegmatites are unzoned and consist of medium- to very coarse-grained spodumene, plagioclase, K-feldspar, quartz, muscovite, and accessory amounts of beryl, manganoan fluorapatite, triphylite, and cassiterite. The pegmatitic fabric is replaced by a fine-grained saccharoidal albite– quartz fabric that also heals fractures in spodumene and feldspar. Plagioclase (Ab95–96) in the pegmatite is only slightly less sodic than that (Ab98–99) in the replacement albite–quartz assemblage. Rare, nonperthitic K-feldspar is slightly sodic (Or95–99). Spodumene typically contains about 1% iron oxide, giving the mineral a light green color. Muscovite contains 1–2 wt% FeO and a trace of sodium (0.2–0.6 wt% Na2O). A Mn-bearing fluorapatite (altered to low-F and low-Mn apatite) and triphylite (altered to fairfieldite) occur within the pegmatite fabric and appear to be primary phosphate minerals. Secondary phosphate minerals, including several species first described from the TSB, are associated with fracture fillings in sheared pegmatite. Pre-tectonic plagioclase – quartz – muscovite – garnet (Alm71Sps26Prp3) pegmatites are folded and sheared. Muscovite and Mn-bearing fluorapatite compositions are similar to equivalent phases in the spodumene pegmatites. The spodumene pegmatites are sheared, especially in proximity to regional shear-zones, but are not folded. Post-tectonic plagioclase – quartz – K-feldspar – muscovite – biotite pegmatites have Mn-poor fluorapatite, unlike the spodumene pegmatites. The pre-tectonic pegmatites may represent a precursor to the spodumene pegmatites.

Apatite-Based Microcarriers for Bone Tissue Engineering

The current available microcarriers were mainly targeted towards pharmaceutical industries, and might not be suitable for therapeutic implantation. As such, apatite-based microcarriers intended for bone tissue engineering applications would be featured here. Hydroxyapatite-Alginate (HA-Alg) suspension was extruded drop-wise into a calcium chloride (CaCl2) crosslinking solution. The HA-Alg microcarriers were then sintered to form microcarriers of uniform size. The physicochemical properties were analysed by scanning electron microscopy (SEM), X-ray diffractometery (XRD), and fourier transform infrared (FTIR) spectrophotometry. Cell viability on these microcarriers was evaluated using human fetal mesenchymal stem cells (hfMSCs). SEM images revealed that sintered apatite-based microcarriers exhibited a rough surface topology with interconnected pores. XRD results showed that these microcarriers remained phase pure since no other secondary calcium phosphate phases were detected. FTIR analysis indicated several sharp phosphate bands coupled with a hydroxyl band (all belonging to HA). Live/dead staining showed that hfMSCs remained viable after 14 days of culture, and cells have spread and covered the surfaces of the microcarriers. Certainly, these cell-loaded microcarriers could be potentially used in bone implant science.

Relationships between nutrient stocks and inventories and phytoplankton physiological status along an oligotrophic meridional transect in the Tasman Sea

The waters of the north Tasman Sea are adjacent to the arid Australian sub-continent and are north of the circumpolar Subtropical convergence. Nutrient and phytoplankton stocks in this region were investigated on two voyages during February 2005 and March 2006 to establish the spatial extent and magnitude of oligotrophy in the region. Surface nitrate, phosphate, ammonium and nitrite were all in the nanomolar concentration range north and south of the Tasman Front (∼33°S; 165–175°E). The location of the nitracline was found to be at or above the 1% light level. The distributions of pico-eukaryotic cells, Synechococcus and Prochlorococcus showed strong latitudinal and vertical gradients, with higher abundances south of the Tasman Front that decreased northward, but consistent with changes in nutrient concentration. A nitrite maximum was observed at and below the 1% light level and results from incomplete assimilatory nitrate reduction by phytoplankton. Mixed layer dissolved iron concentrations varied between 0.05 and 0.70nmolL−1, and were dependent on the vertical supply rate of iron from below and on sporadic atmospheric dust deposition. Based on the rate of iron supply, phytoplankton located south of the Tasman Front were unlikely to be iron limited whereas phytoplankton located north of the Tasman Front were near the threshold for iron limitation. Deck-board incubation experiments involving the addition of macro- (ammonium, nitrate and phosphate) and micro- (iron, dust and zinc) nutrients confirm nitrogen availability to be the primary control on biological production, with the potential for secondary phosphate, silicate and dissolved organic carbon limitation, when nitrogen limitation was alleviated. The form of nitrogen required to stimulate the phytoplankton community also varied; ammonium stimulated Prochlorococcus growth whereas nitrate stimulated Synechococcus growth. Predator-free incubation experiments indicate that grazing was an important constraint on phytoplankton production. Water column observations and incubation results confirm that the supply of dissolved inorganic nitrogen into the euphotic zone was the primary factor controlling new primary production in the northern Tasman Sea region.

AN EVALUATION OF WATER QALITY OF AKPINAR STREAM (DENİZLİ) WHERE TROUT PRODUCTION TAKES PLACE

In this study, 20 physicochemical parameters were measured mountly in 2007 and seasonaly in 2008 and 2009 on Akpinar Stream, which is located within the borders of Denizli and has 13 trout production facility. The data obtained were evaluated according to the fresh water fish directive which was agreed by the Commision of European Union (EC Directives) and Water Pollution Control Regulation Criteria. We determined that, the measured parameters on the first station do not constitute any risk for Salmonids and Cyprinids according to EC Directives and in the second station, the values of biological oxygen demand and nitrite were high enough to adversely affect the health of fish. There is not a significant difference between two stations for the parameters of oxygen, nitrate, total nitrogen, pH, chemical oxygen demand, acid binding capacity, total hardness and chlorine. The parametes of total suspended solids, ammonium, nitrite, secondary phosphate, total phosphorus, organic matter, ammonia, biological oxygen demand, turbidity, temperature and flow rate were significantly high in second station (p<0.05). The reason of high levels of the parameters especially origin of organic pollution in the secod station is fish feces and feed wastes which directly given into the water. Settling ponds should be used properly and controls should be provided to increase for more healty production.

The phosphate mineral sigloite Fe3+Al2(PO4)2(OH)3·7(H2O), an exception to the paragenesis rule – A vibrational spectroscopic study

The secondary phosphate mineral sigloite Fe3+Al2(PO4)2(OH)3·7H2O is the exception to the rule that phosphate mineral paragenesis is related to the final phase of hydrothermal mineralization at low temperatures. Sigloite was formed as an oxidation pseudomorph after paravauxite, during the last supergene paragenetic stage.We have studied the secondary phosphate mineral sigloite Fe3+Al2(PO4)2(OH)3·7H2O using vibrational spectroscopic techniques. Because the mineral is a phosphate mineral, it is readily studied by spectroscopic techniques as the phosphate and hydrogen phosphate units are readily measured. Indeed, sigloite shows the presence of both phosphate and hydrogen phosphate units in its structure. Raman bands at 1009cm−1 with shoulders at 993 and 1039cm−1 are assigned to stretching vibrations of PO43- and HPO42- units. The Raman band at 993cm−1 is assigned to the ν1 symmetric stretching mode of the POH units, whereas the Raman band at 1009cm−1 is assigned to the ν1PO43- symmetric stretching mode. Raman bands observed at 506, 528, 571, 596, 619 and 659cm−1 are attributed to the ν4 out of plane bending modes of the PO4 and H2PO4 units. The Raman bands at 2988, 3118 and 3357cm−1 are assigned to water stretching vibration. The series of bands at 3422, 3449, 3493, 3552 and 3615cm−1 are assigned to the OH stretching vibrations of the hydroxyl units. The observation of multiple bands gives credence to the non-equivalence of the OH units in the sigloite structure.

An association of secondary Al-Li-Be-Ca-Sr phosphates in the San Elias pegmatite, San Luis, Argentina

The complex association of secondary phosphates from the Li-bearing, rare-element San Elias pegmatite in the Eastern Pampean ranges of Argentina shows widespread albite-hosted dendritic montebrasite in its northern part and lepidolite in the south. This dendritic montebrasite survived low-temperature processes virtually intact, but subrectangular blocks of montebrasite along the margins of quartz core were extensively modified in three stages: (i) two generations of secondary montebrasite intimately intergrown with hydroxylherderite, augelite, and fluorapatite, (acid hydrous fluids, locally channeled, at ~450°–420°C, ~2 kbar); (ii) goyazite–crandallite and hydroxylapatite formed after P–T equilibration between the pegmatite and its host rock along the path of metamorphic cooling, which introduced Ca, Sr and minor S from the host rocks into the pegmatite (at about

Substantial biologically mediated phosphorus depletion from the surface of a Middle Cambrian paleosol

Despite recent work, a comprehensive understanding of pre-Devonian terrestrial ecosystems remains elusive, resulting in frequent speculation about their composition. Terrestrial microbial mats are known from the Precambrian paleosol record, and bryophytes are known from the Middle Ordovician palynological record. The intervening time, however, remains enigmatic, although recent studies indicate a progressive greening of the Precambrian prior to the first unambiguous fossil evidence for land plants. In this study, an older than 503 Ma, heavily weathered, clay-rich soil was identified and provides a window to a probable Cambrian terrestrial landscape. The paleosol developed on the ancient continent of Laurentia in a dry, subtropical climate. Mobilization of Si, Al, and P indicate the influence of organic acids. Apatite, a recalcitrant mineral present throughout the majority of the weathered section, is notably absent from the top 30 cm of the paleosol. Few secondary phosphates and a complete absence of oxide- or carbonate-bound P indicate that once biologically weathered, P remained in an ecosystem-available form during the lifetime of this paleosol. The zone of apatite dissolution coincides with intense argillan development, indicating clay flocculation in the presence of soil solutions rich in labile Ca 2+ . Enhanced P weathering coupled with high Ca 2+ concentrations as a result of in situ apatite dissolution is a biosignature previously linked to the activities of mycorrhizal fungi. Biosignatures of mycorrhizal fungi in a Middle Cambrian paleosol add further evidence to the notion that there was an important terrestrial fungal presence prior to the first unequivocal evidence for terrestrial land plants.

Steady-state dissolution kinetics of mineral ferric phosphate in the presence of desferrioxamine-B and oxalate ligands at pH = 4–6 and T = 24 ± 0.6 °C

Ferric phosphate (FePO4·2H2O) is one of the most common secondary phosphate minerals in the environment. Nevertheless, few studies address the biological dissolution mechanism(s) of FePO4·2H2O. This paper reports steady-state dissolution rates of synthetic FePO4·2H2O at 4≤pH0≤6 by desferrioxamine-B (DFO-B) and oxalate (Ox) ligands. The composition of the influent solution was 10mM NaClO4, 5mM MES buffer. The influent solution was adjusted to 4≤pH0≤6 by adding aliquots of HNO3 or NaOH stock solution. The initial concentrations of DFO-B and Ox, [DFO-B]0 and [Ox]0, ranged from 0 to 135μM, and 0 to 345μM. Geochemical thermodynamic equilibrium modeling was conducted using MINEQL+ (Schecher and McAvoy, 1998). Speciation calculations were based on thermodynamic formation constants at 298.17K, K298 (infinite dilution reference state). Ligand-promoted dissolution rates were determined after steady-state values. Iron concentrations in the effluent solution were quantified (t>500h). Typical effluent-flow rate was maintained at 0.10±0.01mLmin−1. The measured dissolution rate of FePO4·2H2O by DFO-B and Ox, RDFO–OxObs, was compared to the sum of dissolution rates by DFO-B (RDFO-B) or Ox (ROx), RDFO–OxSum (RDFO–OxSum=RDFO‐B+ROx). Results were analyzed using the t student test. Obtained data values with p≤0.05 (⁎) and ≤0.01 (⁎⁎) were considered to differ statistically from control experiments. Dissolution rates by DFO-B (RDFO-B) increased with [DFOB]0, and no evidence of surface masking became apparent. By contrast, dissolution rates by Ox (ROx) varied with [Ox]0 and pH0. The kinetics of dissolution by Ox was not explained by a first-order mineral dissolution behavior. Dissolution rates by DFO-B and Ox (RDFO–OxObs) surpassed RDFO-B or ROx, and increased with proton activity. Reacting FePO4·2H2O with DFO-B and high amounts of Ox resulted in higher values for RDFO–OxObs relative to RDFO-B. Observed (RDFO–OxObs) to calculated (RDFO–OxSum=RDFO‐B+ROx) ratio was found to be highest at [DFOB]0=50μM and [Ox]0=49μM. Increases in the proton activity favors the dissolution of FePO4·2H2O by DFO-B and Ox, explained because the sequestration of Fe(III) at the surface vicinity in the form of adsorbed Fe(III)-oxalate complexes. A direct comparison between the dissolution behavior of FePO4·2H2O by DFO-B and Ox against those for goethite (α-FeOOH) and Al goethite (AlFeOOH) was conducted. The dissolution behavior was found to be a function of the mineral structure. RDFO-B values for FePO4·2H2O by 22.5μM DFO-B surpassed those for α-FeOOH or α-AlFeOOH by 20μM DFO-B, namely, 37, and 11.6 and 3–5μmolkg−1h−1, respectively. ROx values for FePO4·2H2O by 49mM Ox surpassed that for α-FeOOH by 70μM Ox or α-AlFeOOH by 50μM Ox, namely, i.e., 12, and 0.7 and 0.1μmolkg−1h−1. The latter results agree with the idea of the inhibition of Fe release in goethite because its sequestration in the form of adsorbed Fe(III) oxalate complexes. In contrast, a different scenario holds true for dissolution by 50μM DFO-B and 49μM Ox. The dissolution rates for FePO4·2H2O, α-FeOOH, and α-AlFeOOH correspond to 50, and 39–42 and 71–129μmolkg−1h−1, respectively. The high extent of iron release from Al goethite is best explained because high-energy surface sites formed after Al substitution in goethite.

The Estimation of Acidic Behavior of Wood by Treatment with Aqueous Solution

As a new approach, the acidity that wood exhibits under moderate conditions is assayed by stimulated dissociation of weak wood acids in lightly basic secondary phosphate solutions. To assure a sufficient dissociation of hardly soluble weak acids in the solution, the amount of wood suspended in Na2HPO4 solutions should be small but vary depending on the degree of acidity of wood species. However, the difficulties are associated with the titration of very dilute acids limiting the precision of the measurement. If the disintegrated wood is suspended in a secondary phosphate solution, the weak woods acids form the conjugate acid Na2HPO4 from secondary phosphate Na2HPO4 resulting in a pH fall of the solution. The decrease in the pH value in phosphate solution, which depends on the wood acidity, can be evaluated to estimate the acidity arising from wood under moderate conditions.

A chronology for Late Quaternary weathering in the Murray Basin, southeastern Australia: evidence from 230Th/U dating of secondary uranium phosphates in the Lake Boga and Wycheproof granites, Victoria

The Lake Boga Granite in northern Victoria contains a suite of well-crystallised secondary uranyl phosphates, including torbernite, saléeite, metanatroautunite and ulrichite. The minerals crystallised in miarolitic cavities and on joints, after dissolution of primary uraninite and fluorapatite by oxidising groundwater. A more restricted assemblage occurs in the nearby Wycheproof Granite. The 230Th/U dating method was used to reveal any links between formation ages of these minerals and climatic fluctuations during the Quaternary. Out of 104 analyses, 77 gave apparent ages less than about 500 ka, the upper limit beyond which secular equilibrium in the 230Th/U decay series is closely approached. The age distribution curve shows a broad peak around 400 ka, coinciding with a global interglacial period (Marine Isotope Stage 11). Thereafter, there is a slow tapering off towards younger ages, but with no direct correlation with interglacial peaks and with no ages less than 100 ka. Throughout this time interval (ca 500–100 ka), the southeastern Australian region was undergoing aridification, suggesting that regional rather than global climate was the more significant influence on uranium phosphate crystallisation. While caution needs to be applied when interpreting these results, the overall distribution pattern might be best explained by fluctuating weathering affecting a finite primary uranium source that was progressively depleted from about 400 ka and exhausted by around 100 ka. The study has also revealed that the Lake Boga and Wycheproof granites acted as natural reservoirs for the sequestration of uranium in phosphate-rich assemblages over periods of several hundred thousand years.

Electrokinetic properties of wavellite and its floatability with cationic and anionic collectors

The reverse apatite flotation with fatty acids has been widely used for the reduction of phosphorus content of magmatic origin iron ores. However, the occurrence of phosphorus intensely disseminated as secondary minerals such as wavellite renders the anionic reverse flotation a challenge. Zeta potential measurements and microflotation tests of wavellite with the use of anionic and cationic collectors were carried out in this work. The wavellite’s IEP value was achieved at pH 4.5. Below the IEP value, the surface positively charged sites are made up of aluminum ions. The species H+,Al(OH)2+,Al(OH)2+,Al3+,OH-,H2PO4-,HPO42-, and PO43- play a role in the protonation and deprotonation reactions that will determine the wavellite-solution interface properties. The highest values of wavellite’s floatability under basic pH conditions were achieved in the presence of cationic collectors (1×10−4molL−1). The formation of surface complexes and the precipitation of insoluble salt of aluminum onto wavellite surface seems to be the most likely hypothesis for the chemical nature interactions between amines and wavellite. The surface formation of aluminum oleate on the wavellite’s surface seems to be the most probable hypothesis for the adsorption mechanism and the resultant high floatability of wavellite between pH 7.5 and pH 10.0 in the presence of sodium oleate (1×10−4molL−1). The results showed that the cationic reverse flotation of secondary phosphates is a promising route to reduce the phosphorus content of iron ores from deposits that underwent a supergene enrichment process, since wavellite floatability in the alkaline pH range, using amine as collector, was not significantly affected by the presence of corn starch.

In vivo degradation of low temperature calcium and magnesium phosphate ceramics in a heterotopic model

Bone replacement using synthetic and degradable materials is desirable in various clinical conditions. Most applied commercial materials are based on hydroxyapatite, which is not chemically degradable under physiological conditions. Here we report the effect of a long-term intramuscular implantation regime on the dissolution of various low temperature calcium and magnesium phosphate ceramics in vivo. The specimens were analysed by consecutive radiographs, micro-computed tomography scans, compressive strength testing, scanning electron microscopy and X-ray diffractometry. After 15 months in vivo, the investigated materials brushite (CaHPO 4·2H 2O), newberyite (MgHPO 4·3H 2O), struvite (MgNH 4PO 4·6H 2O) and hydroxyapatite (Ca 9(PO 4) 5HPO 4OH) showed significant differences regarding changes of their characteristics. Struvite presented the highest loss of mechanical performance (95%), followed by newberyite (67%) and brushite (41%). This was accompanied by both a distinct extent of cement dissolution as well as changes of the phase composition of the retrieved cement implants. While the secondary phosphate phases (brushite, newberyite, struvite) completely dissolved, re-precipitates of whitlockite and octacalcium phosphate were formed in either particulate or whisker-like morphology. Furthermore, for the first time the possibility of a macropore-free volume degradation mechanism of bioceramics was demonstrated.