Geochemical Transactions最新文献

{"title":"Weakly bound water structure, bond valence saturation and water dynamics at the goethite (100) surface/aqueous interface: ab initio dynamical simulations","authors":"Ying Chen,&nbsp;Eric J. Bylaska,&nbsp;John H. Weare","doi":"10.1186/s12932-017-0040-5","DOIUrl":"https://doi.org/10.1186/s12932-017-0040-5","url":null,"abstract":"<p>Many important geochemical and biogeochemical reactions occur in the mineral/formation water interface of the highly abundant mineral, goethite [α-Fe(OOH)]. Ab initio molecular dynamics (AIMD) simulations of the goethite α-FeOOH (100) surface and the structure, water bond formation and dynamics of water molecules in the mineral/aqueous interface are presented. Several exchange correlation functionals were employed (PBE96, PBE96?+?Grimme, and PBE0) in the simulations of a (3?×?2) goethite surface with 65 absorbed water molecules in a 3D-periodic supercell (a?=?30??, FeOOH slab ~12?? thick, solvation layer ~18?? thick).</p><p>The lowest energy goethite (100) surface termination model was determined to have an exposed surface Fe³⁺ that was loosely capped by a water molecule and a shared hydroxide with a neighboring surface Fe³⁺. The water molecules capping surface Fe³⁺ ions were found to be loosely bound at all DFT levels with and without Grimme corrections, indicative that each surface Fe³⁺ was coordinated with only five neighbors. These long bonds were supported by bond valence theory calculations, which showed that the bond valence of the surface Fe³⁺ was saturated and surface has a neutral charge. The polarization of the water layer adjacent to the surface was found to be small and affected only the nearest water. Analysis by density difference plots and localized Boys orbitals identified three types of water molecules: those loosely bound to the surface Fe³⁺, those hydrogen bonded to the surface hydroxyl, and bulk water with tetrahedral coordination. Boys orbital analysis showed that the spin down lone pair orbital of the weakly absorbed water interact more strongly with the spin up Fe³⁺ ion. These weakly bound surface water molecules were found to rapidly exchange with the second water layer (~0.025?exchanges/ps) using a dissociative mechanism.</p><p>Water molecules adjacent to the surface were found to only weakly interact with the surface and as a result were readily able to exchange with the bulk water. To account for the large surface Fe–OH₂ distances in the DFT calculations it was proposed that the surface Fe³⁺ atoms, which already have their bond valence fully satisfied with only five neighbors, are under-coordinated with respect to the bulk coordination.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"18 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2017-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-017-0040-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"5180548","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Global hydrogen reservoirs in basement and basins","authors":"John Parnell,&nbsp;Nigel Blamey","doi":"10.1186/s12932-017-0041-4","DOIUrl":"https://doi.org/10.1186/s12932-017-0041-4","url":null,"abstract":"<p>Hydrogen is known to occur in the groundwaters of some ancient cratons. Where associated gases have been dated, their age extends up to a billion years, and the hydrogen is assumed also to be very old. These observations are interpreted to represent the radiolysis of water and hydration reactions and migration of hydrogen into fracture systems. A hitherto untested implication is that the overwhelming bulk of the ancient low-permeability basement, which is not adjacent to cross-cutting fractures, constitutes a reservoir for hydrogen.</p><p>New data obtained from cold crushing to liberate volatiles from fluid inclusions confirm that granites and gneiss of Archean and Palaeoproterozoic (&gt;1600?Ma) age typically contain an order of magnitude greater hydrogen in their entrained fluid than very young (&lt;200?Ma) granites. Sedimentary rocks containing clasts of old basement also include a greater proportion of hydrogen than the young granites.</p><p>The data support the case for a global reservoir of hydrogen in both the ancient basement and in the extensive derived sediments. These reservoirs are susceptible to the release of hydrogen through a variety of mechanisms, including deformation, attrition to reduce grain size and diagenetic alteration, thereby contributing to the hydrogen required by chemolithoautotrophs in the deep biosphere.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"18 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2017-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-017-0041-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4801315","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A survey of photogeochemistry","authors":"Timothy A. Doane","doi":"10.1186/s12932-017-0039-y","DOIUrl":"https://doi.org/10.1186/s12932-017-0039-y","url":null,"abstract":"<p>The participation of sunlight in the natural chemistry of the earth is presented as a unique field of study, from historical observations to prospects for future inquiry. A compilation of known reactions shows the extent of light-driven interactions between naturally occurring components of land, air, and water, and provides the backdrop for an outline of the mechanisms of these phenomena. Catalyzed reactions, uncatalyzed reactions, direct processes, and indirect processes all operate in natural photochemical transformations, many of which are analogous to well-known biological reactions. By overlaying photochemistry and surface geochemistry, complementary approaches can be adopted to identify natural photochemical reactions and discern their significance in the environment.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"18 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2017-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-017-0039-y","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4416571","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"How long do natural waters “remember” release incidents of Marcellus Shale waters: a first order approximation using reactive transport modeling","authors":"Zhang Cai,&nbsp;Li Li","doi":"10.1186/s12932-016-0038-4","DOIUrl":"https://doi.org/10.1186/s12932-016-0038-4","url":null,"abstract":"<p>Natural gas production from the Marcellus Shale formation has significantly changed energy landscape in recent years. Accidental release, including spills, leakage, and seepage of the Marcellus Shale flow back and produced waters can impose risks on natural water resources. With many competing processes during the reactive transport of chemical species, it is not clear what processes are dominant and govern the impacts of accidental release of Marcellus Shale waters (MSW) into natural waters. Here we carry out numerical experiments to explore this largely unexploited aspect using cations from MSW as tracers with a focus on abiotic interactions between cations released from MSW and natural water systems. Reactive transport models were set up using characteristics of natural water systems (aquifers and rivers) in Bradford County, Pennsylvania. Results show that in clay-rich sandstone aquifers, ion exchange plays a key role in determining the maximum concentration and the time scale of released cations in receiving natural waters. In contrast, mineral dissolution and precipitation play a relatively minor role. The relative time scales of recovery τ_rr, a dimensionless number defined as the ratio of the time needed to return to background concentrations over the residence time of natural waters, vary between 5 and 10 for Na, Ca, and Mg, and between 10 and 20 for Sr and Ba. In rivers and sand and gravel aquifers with negligible clay, τ_rr values are close to 1 because cations are flushed out at approximately one residence time. These values can be used as first order estimates of time scales of released MSW in natural water systems. This work emphasizes the importance of clay content and suggests that it is more likely to detect contamination in clay-rich geological formations. This work highlights the use of reactive transport modeling in understanding natural attenuation, guiding monitoring, and predicting impacts of contamination for risk assessment.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"17 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2016-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-016-0038-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4527401","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Oxidation of arsenite to arsenate on birnessite in the presence of light","authors":"Samantha L. Shumlas,&nbsp;Soujanya Singireddy,&nbsp;Akila C. Thenuwara,&nbsp;Nuwan H. Attanayake,&nbsp;Richard J. Reeder,&nbsp;Daniel R. Strongin","doi":"10.1186/s12932-016-0037-5","DOIUrl":"https://doi.org/10.1186/s12932-016-0037-5","url":null,"abstract":"<p>The effect of simulated solar radiation on the oxidation of arsenite [As(III)] to arsenate [As(V)] on the layered manganese oxide, birnessite, was investigated. Experiments were conducted where birnessite suspensions, under both anoxic and oxic conditions, were irradiated with simulated solar radiation in the presence of As(III) at pH 5, 7, and 9. X-ray absorption spectroscopy (XAS) was used to determine the nature of the adsorbed product on the surface of the birnessite. The oxidation of As(III) in the presence of birnessite under simulated solar light irradiation occurred at a rate that was faster than in the absence of light at pH 5. At pH 7 and 9, As(V) production was significantly less than at pH 5 and the amount of As(V) production for a given reaction time was the same under dark and light conditions. The first order rate constant (k_obs) for As(III) oxidation in the presence of light and in the dark at pH 5 were determined to be 0.07 and 0.04?h^?1, respectively. The As(V) product was released into solution along with Mn(II), with the latter product resulting from the reduction of Mn(IV) and/or Mn(III) during the As(III) oxidation process. Post-reaction XAS analysis of As(III) exposed birnessite showed that arsenic was present on the surface as As(V). Experimental results also showed no evidence that reactive oxygen species played a role in the As(III) oxidation process.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"17 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2016-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-016-0037-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4277928","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sources of salinity and arsenic in groundwater in southwest Bangladesh","authors":"John C. Ayers,&nbsp;Steven Goodbred,&nbsp;Gregory George,&nbsp;David Fry,&nbsp;Laura Benneyworth,&nbsp;George Hornberger,&nbsp;Kushal Roy,&nbsp;Md. Rezaul Karim,&nbsp;Farjana Akter","doi":"10.1186/s12932-016-0036-6","DOIUrl":"https://doi.org/10.1186/s12932-016-0036-6","url":null,"abstract":"<p>High salinity and arsenic (As) concentrations in groundwater are widespread problems in the tidal deltaplain of southwest Bangladesh. To identify the sources of dissolved salts and As, groundwater samples from the regional shallow Holocene aquifer were collected from tubewells during the dry (May) and wet (October) seasons in 2012–2013. Thirteen drill cores were logged and 27 radiocarbon ages measured on wood fragments to characterize subsurface stratigraphy.</p><p>Drill cuttings, exposures in pits and regional studies reveal a?&gt;5?m thick surface mud cap overlying a?~30?m thick upper unit of interbedded mud and fine sand layers, and a coarser lower unit up to 60?m thick dominated by clean sands, all with significant horizontal variation in bed continuity and thickness. This thick lower unit accreted at rates of?~2?cm/year through the early Holocene, with local subsidence or compaction rates of 1–3?mm/year. Most tubewells are screened at depths of 15–52?m in sediments deposited 8000–9000 YBP. Compositions of groundwater samples from tubewells show high spatial variability, suggesting limited mixing and low and spatially variable recharge rates and flow velocities. Groundwaters are Na–Cl type and predominantly sulfate-reducing, with specific conductivity (SpC) from 3 to 29 mS/cm, high dissolved organic carbon (DOC) 11–57?mg/L and As 2–258?ug/L, and low sulfur (S) 2–33?mg/L.</p><p>Groundwater compositions can be explained by burial of tidal channel water and subsequent reaction with dissolved organic matter, resulting in anoxia, hydrous ferric oxide (HFO) reduction, As mobilization, and sulfate (SO₄) reduction and removal in the shallow aquifer. Introduction of labile organic carbon in the wet season as rice paddy fertilizer may also cause HFO reduction and As mobilization. Variable modern recharge occurred in areas where the clay cap pinches out or is breached by tidal channels, which would explain previously measured ¹⁴C groundwater ages being less than depositional ages. Of samples collected from the shallow aquifer, Bangladesh Government guidelines are exceeded in 46?% for As and 100?% for salinity.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"17 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2016-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-016-0036-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4460155","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A study on the dissolution rates of K-Cr(VI)-jarosites: kinetic analysis and implications","authors":"Iván A. Reyes,&nbsp;Ister Mireles,&nbsp;Francisco Patiño,&nbsp;Thangarasu Pandiyan,&nbsp;Mizraim U. Flores,&nbsp;Elia G. Palacios,&nbsp;Emmanuel J. Gutiérrez,&nbsp;Martín Reyes","doi":"10.1186/s12932-016-0035-7","DOIUrl":"https://doi.org/10.1186/s12932-016-0035-7","url":null,"abstract":"&lt;p&gt;The presence of natural and industrial jarosite type-compounds in the environment could have important implications in the mobility of potentially toxic elements such as lead, mercury, arsenic, chromium, among others. Understanding the dissolution reactions of jarosite-type compounds is notably important for an environmental assessment (for water and soil), since some of these elements could either return to the environment or work as temporary deposits of these species, thus would reduce their immediate environmental impact.&lt;/p&gt;&lt;p&gt;This work reports the effects of temperature, pH, particle diameter and Cr(VI) content on the initial dissolution rates of K-Cr(VI)-jarosites (KFe&lt;sub&gt;3&lt;/sub&gt;[(SO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2???X&lt;/sub&gt;(CrO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;X&lt;/sub&gt;](OH)&lt;sub&gt;6&lt;/sub&gt;). Temperature (T) was the variable with the strongest effect, followed by pH in acid/alkaline medium (H&lt;sub&gt;3&lt;/sub&gt;O&lt;sup&gt;+&lt;/sup&gt;/OH&lt;sup&gt;?&lt;/sup&gt;). It was found that the substitution of CrO&lt;sub&gt;4&lt;/sub&gt;\u0000 &lt;sup&gt;2?&lt;/sup&gt;in &lt;i&gt;Y&lt;/i&gt;-site and the substitution of H&lt;sub&gt;3&lt;/sub&gt;O&lt;sup&gt;+&lt;/sup&gt; in &lt;i&gt;M&lt;/i&gt;-site do not modify the dissolution rates. The model that describes the dissolution process is the unreacted core kinetic model, with the chemical reaction on the unreacted core surface. The dissolution in acid medium was congruent, while in alkaline media was incongruent. In both reaction media, there is a release of K&lt;sup&gt;+&lt;/sup&gt;, SO&lt;sub&gt;4&lt;/sub&gt;\u0000 &lt;sup&gt;2?&lt;/sup&gt; and CrO&lt;sub&gt;4&lt;/sub&gt;\u0000 &lt;sup&gt;2?&lt;/sup&gt; from the KFe&lt;sub&gt;3&lt;/sub&gt;[(SO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2???X&lt;/sub&gt;(CrO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;X&lt;/sub&gt;](OH)&lt;sub&gt;6&lt;/sub&gt; structure, although the latter is rapidly absorbed by the solid residues of Fe(OH)&lt;sub&gt;3&lt;/sub&gt; in alkaline medium dissolutions. The dissolution of KFe&lt;sub&gt;3&lt;/sub&gt;[(SO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2???X&lt;/sub&gt;(CrO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;X&lt;/sub&gt;](OH)&lt;sub&gt;6&lt;/sub&gt; exhibited good stability in a wide range of pH and T conditions corresponding to the calculated parameters of reaction order &lt;i&gt;n&lt;/i&gt;, activation energy &lt;i&gt;E&lt;/i&gt;\u0000 &lt;sub&gt;\u0000 &lt;i&gt;A&lt;/i&gt;\u0000 &lt;/sub&gt; and dissolution rate constants for each kinetic stages of induction and progressive conversion.&lt;/p&gt;&lt;p&gt;The kinetic analysis related to the reaction orders and calculated activation energies confirmed that extreme pH and T conditions are necessary to obtain considerably high dissolution rates. Extreme pH conditions (acidic or alkaline) cause the preferential release of K&lt;sup&gt;+&lt;/sup&gt;, SO&lt;sub&gt;4&lt;/sub&gt;\u0000 &lt;sup&gt;2?&lt;/sup&gt; and CrO&lt;sub&gt;4&lt;/sub&gt;\u0000 &lt;sup&gt;2?&lt;/sup&gt; from the KFe&lt;sub&gt;3&lt;/sub&gt;[(SO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2???X&lt;/sub&gt;(CrO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;X&lt;/sub&gt;](OH)&lt;sub&gt;6&lt;/sub&gt; structure, although CrO&lt;sub&gt;4&lt;/sub&gt;\u0000 &lt;sup&gt;2?&lt;/sup&gt; is quickly adsorbed by Fe(OH)&lt;sub&gt;3&lt;/sub&gt; solid residues. The precipitation of phases such as KFe&lt;sub&gt;3&lt;/sub&gt;[(SO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2???X&lt;/sub&gt;(CrO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;X&lt;/sub&gt;]","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"17 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2016-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-016-0035-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4545268","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characterization, dissolution and solubility of the hydroxypyromorphite–hydroxyapatite solid solution [(PbxCa1−x)5(PO4)3OH] at 25 °C and pH 2–9","authors":"Yinian Zhu,&nbsp;Bin Huang,&nbsp;Zongqiang Zhu,&nbsp;Huili Liu,&nbsp;Yanhua Huang,&nbsp;Xin Zhao,&nbsp;Meina Liang","doi":"10.1186/s12932-016-0034-8","DOIUrl":"https://doi.org/10.1186/s12932-016-0034-8","url":null,"abstract":"&lt;p&gt;The interaction between Ca-HAP and Pb&lt;sup&gt;2+&lt;/sup&gt; solution can result in the formation of a hydroxyapatite–hydroxypyromorphite solid solution [(Pb&lt;sub&gt;x&lt;/sub&gt;Ca&lt;sub&gt;1?x&lt;/sub&gt;)&lt;sub&gt;5&lt;/sub&gt;(PO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;(OH)], which can greatly affect the transport and distribution of toxic Pb in water, rock and soil. Therefore, it’s necessary to know the physicochemical properties of (Pb&lt;sub&gt;x&lt;/sub&gt;Ca&lt;sub&gt;1?x&lt;/sub&gt;)&lt;sub&gt;5&lt;/sub&gt;(PO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;(OH), predominantly its thermodynamic solubility and stability in aqueous solution. Nevertheless, no experiment on the dissolution and related thermodynamic data has been reported.&lt;/p&gt;&lt;p&gt;Dissolution of the hydroxypyromorphite–hydroxyapatite solid solution [(Pb&lt;sub&gt;x&lt;/sub&gt;Ca&lt;sub&gt;1?x&lt;/sub&gt;)&lt;sub&gt;5&lt;/sub&gt;(PO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;(OH)] in aqueous solution at 25?°C was experimentally studied. The aqueous concentrations were greatly affected by the Pb/(Pb?+?Ca) molar ratios (X&lt;sub&gt;Pb&lt;/sub&gt;) of the solids. For the solids with high X&lt;sub&gt;Pb&lt;/sub&gt; [(Pb&lt;sub&gt;0.89&lt;/sub&gt;Ca&lt;sub&gt;0.11&lt;/sub&gt;)&lt;sub&gt;5&lt;/sub&gt;(PO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;OH], the aqueous Pb&lt;sup&gt;2+&lt;/sup&gt; concentrations increased rapidly with time and reached a peak value after 240–720?h dissolution, and then decreased gradually and reached a stable state after 5040?h dissolution. For the solids with low X&lt;sub&gt;Pb&lt;/sub&gt; (0.00–0.80), the aqueous Pb&lt;sup&gt;2+&lt;/sup&gt; concentrations increased quickly with time and reached a peak value after 1–12?h dissolution, and then decreased gradually and attained a stable state after 720–2160?h dissolution.&lt;/p&gt;&lt;p&gt;The dissolution process of the solids with high X&lt;sub&gt;Pb&lt;/sub&gt; (0.89–1.00) was different from that of the solids with low X&lt;sub&gt;Pb&lt;/sub&gt; (0.00–0.80). The average &lt;i&gt;K&lt;/i&gt;\u0000 &lt;sub&gt;sp&lt;/sub&gt; values were estimated to be 10&lt;sup&gt;?80.77±0.20&lt;/sup&gt; (10&lt;sup&gt;?80.57&lt;/sup&gt;–10&lt;sup&gt;?80.96&lt;/sup&gt;) for hydroxypyromorphite [Pb&lt;sub&gt;5&lt;/sub&gt;(PO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;OH] and 10&lt;sup&gt;?58.38±0.07&lt;/sup&gt; (10&lt;sup&gt;?58.31&lt;/sup&gt;–10&lt;sup&gt;?58.46&lt;/sup&gt;) for calcium hydroxyapatite [Ca&lt;sub&gt;5&lt;/sub&gt;(PO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;OH]. The Gibbs free energies of formation (Δ&lt;i&gt;G&lt;/i&gt;\u0000 &lt;span&gt;\u0000 &lt;sup&gt;&lt;i&gt;o&lt;/i&gt;&lt;/sup&gt;&lt;sub&gt;\u0000 &lt;i&gt;f&lt;/i&gt;\u0000 &lt;/sub&gt;\u0000 \u0000 &lt;/span&gt;) were determined to be ?3796.71 and ?6314.63?kJ/mol, respectively. The solubility decreased with the increasing Pb/(Pb?+?Ca) molar ratios (X&lt;sub&gt;Pb&lt;/sub&gt;) of (Pb&lt;sub&gt;x&lt;/sub&gt;Ca&lt;sub&gt;1?x&lt;/sub&gt;)&lt;sub&gt;5&lt;/sub&gt;(PO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;(OH). For the dissolution at 25?°C with an initial pH of 2.00, the experimental data plotted on the Lippmann diagram showed that the solid solution (Pb&lt;sub&gt;x&lt;/sub&gt;Ca&lt;sub&gt;1?x&lt;/sub&gt;)&lt;sub&gt;5&lt;/sub&gt;(PO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;(OH) dissolved stoichiometrically at the early stage of dissolution and moved gradually up to the Lippmann &lt;i&gt;solutus&lt;/i&gt; curve and the saturation curve for Pb&lt;sub&gt;5&lt;/sub&gt;(PO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;OH, and then the data points moved","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"17 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2016-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-016-0034-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4264130","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effects of common groundwater ions on chromate removal by magnetite: importance of chromate adsorption","authors":"Amanda H. Meena,&nbsp;Yuji Arai","doi":"10.1186/s12932-016-0033-9","DOIUrl":"https://doi.org/10.1186/s12932-016-0033-9","url":null,"abstract":"<p>Reductive precipitation of hexavalent chromium (Cr(VI)) with magnetite is a well-known Cr(VI) remediation method to improve water quality. The rapid (&lt;a few hr) reduction of soluble Cr(VI) to insoluble Cr(III) species by Fe(II) in magnetite has been the primary focus of the Cr(VI) removal process in the past. However, the contribution of simultaneous Cr(VI) adsorption processes in aged magnetite has been largely ignored, leaving uncertainties in evaluating the application of in situ Cr remediation technologies for aqueous systems. In this study, effects of common groundwater ions (i.e., nitrate and sulfate) on Cr(VI) sorption to magnetite were investigated using batch geochemical experiments in conjunction with X-ray absorption spectroscopy.</p><p>In both nitrate and sulfate electrolytes, batch sorption experiments showed that Cr(VI) sorption decreases with increasing pH from 4 to 8. In this pH range, Cr(VI) sorption decreased with increasing ionic strength of sulfate from 0.01 to 0.1?M whereas nitrate concentrations did not alter the Cr(VI) sorption behavior. This indicates the background electrolyte specific Cr(VI) sorption process in magnetite. Under the same ionic strength, Cr(VI) removal in sulfate containing solutions was greater than that in nitrate solutions. This is because the oxidation of Fe(II) by nitrate is more thermodynamically favorable than by sulfate, leaving less reduction capacity of magnetite to reduce Cr(VI) in the nitrate media. X-ray absorption spectroscopy analysis supports the macroscopic evidence that more than 75?% of total Cr on the magnetite surfaces was adsorbed Cr(VI) species after 48?h.</p><p>This experimental geochemical study showed that the adsorption process of Cr(VI) anions was as important as the reductive precipitation of Cr(III) in describing the removal of Cr(VI) by magnetite, and these interfacial adsorption processes could be impacted by common groundwater ions like sulfate and nitrate. The results of this study highlight new information about the large quantity of adsorbed Cr(VI) surface complexes at the magnetite-water interface. It has implications for predicting the long-term stability of Cr at the magnetite-water interface.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"17 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2016-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-016-0033-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"5104883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Erratum to: Zn (II) and Cu (II) adsorption and retention onto iron oxyhydroxide nanoparticles: effects of particle aggregation and salinity","authors":"Rebecca B. Chesne,&nbsp;Christopher S. Kim","doi":"10.1186/s12932-015-0032-2","DOIUrl":"https://doi.org/10.1186/s12932-015-0032-2","url":null,"abstract":"","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"16 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2015-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-015-0032-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4764344","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}