Geochemical Transactions最新文献

{"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}

{"title":"Interaction mechanisms and kinetics of ferrous ion and hexagonal birnessite in aqueous systems","authors":"Tianyu Gao,&nbsp;Yougang Shen,&nbsp;Zhaoheng Jia,&nbsp;Guohong Qiu,&nbsp;Fan Liu,&nbsp;Yashan Zhang,&nbsp;Xionghan Feng,&nbsp;Chongfa Cai","doi":"10.1186/s12932-015-0031-3","DOIUrl":"https://doi.org/10.1186/s12932-015-0031-3","url":null,"abstract":"<p>In soils and sediments, manganese oxides and oxygen usually participate in the oxidation of ferrous ions. There is limited information concerning the interaction process and mechanisms of ferrous ions and manganese oxides. The influence of air (oxygen) on reaction process and kinetics has been seldom studied. Because redox reactions usually occur in open systems, the participation of air needs to be further investigated.</p><p>To simulate this process, hexagonal birnessite was prepared and used to oxidize ferrous ions in anoxic and aerobic aqueous systems. The influence of pH, concentration, temperature, and presence of air (oxygen) on the redox rate was studied. The redox reaction of birnessite and ferrous ions was accompanied by the release of Mn²⁺ and K⁺ ions, a significant decrease in Fe²⁺ concentration, and the formation of mixed lepidocrocite and goethite during the initial stage. Lepidocrocite did not completely transform into goethite under anoxic condition with pH about 5.5 within 30?days. Fe²⁺ exhibited much higher catalytic activity than Mn²⁺ during the transformation from amorphous Fe(III)-hydroxide to lepidocrocite and goethite under anoxic conditions. The release rates of Mn²⁺ were compared to estimate the redox rates of birnessite and Fe²⁺ under different conditions.</p><p>Redox rate was found to be controlled by chemical reaction, and increased with increasing Fe²⁺ concentration, pH, and temperature. The formation of ferric (hydr)oxides precipitate inhibited the further reduction of birnessite. The presence of air accelerated the oxidation of Fe²⁺ to ferric oxides and facilitated the chemical stability of birnessite, which was not completely reduced and dissolved after 18?days. As for the oxidation of aqueous ferrous ions by oxygen in air, low and high pHs facilitated the formation of goethite and lepidocrocite, respectively. The experimental results illustrated the single and combined effects of manganese oxide and air on the transformation of Fe²⁺ to ferric oxides.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"16 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2015-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-015-0031-3","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4876261","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":"The influence of environmental conditions on kinetics of arsenite oxidation by manganese-oxides","authors":"Matthew H. H. Fischel,&nbsp;Jason S. Fischel,&nbsp;Brandon J. Lafferty,&nbsp;Donald L. Sparks","doi":"10.1186/s12932-015-0030-4","DOIUrl":"https://doi.org/10.1186/s12932-015-0030-4","url":null,"abstract":"<p>Manganese-oxides are one of the most important minerals in soil due to their widespread distribution and high reactivity. Despite their invaluable role in cycling many redox sensitive elements, numerous unknowns remain about the reactivity of different manganese-oxide minerals under varying conditions in natural systems. By altering temperature, pH, and concentration of arsenite we were able to determine how manganese-oxide reactivity changes with simulated environmental conditions. The interaction between manganese-oxides and arsenic is particularly important because manganese can oxidize mobile and toxic arsenite into more easily sorbed and less toxic arsenate. This redox reaction is essential in understanding how to address the global issue of arsenic contamination in drinking water.</p><p>The reactivity of manganese-oxides in ascending order is random stacked birnessite, hexagonal birnessite, biogenic manganese-oxide, acid birnessite, and δ-MnO₂. Increasing temperature raised the rate of oxidation. pH had a variable effect on the production of arsenate and mainly impacted the sorption of arsenate on δ-MnO₂, which decreased with increasing pH. Acid birnessite oxidized the most arsenic at alkaline and acidic pHs, with decreased reactivity towards neutral pH. The δ-MnO₂ showed a decline in reactivity with increasing arsenite concentration, while the acid birnessite had greater oxidation capacity under higher concentrations of arsenite. The batch reactions used in this study quantify the impact of environmental variances on different manganese-oxides’ reactivity and provide insight to their roles in governing chemical cycles in the Critical Zone.</p><p>The reactivity of manganese-oxides investigated was closely linked to each mineral’s crystallinity, surface area, and presence of vacancy sites. δ-MnO₂ and acid birnessite are thought to be synthetic representatives of naturally occurring biogenic manganese-oxides; however, the biogenic manganese-oxide exhibited a lag time in oxidation compared to these two minerals. Reactivity was clearly linked to temperature, which provides important information on how these minerals react in the subsurface environment. The pH affected oxidation rate, which is essential in understanding how manganese-oxides react differently in the environment and their potential role in remediating contaminated areas. Moreover, the contrasting oxidative capacity of seemingly similar manganese-oxides under varying arsenite concentrations reinforces the importance of each manganese-oxide mineral’s unique properties.</p>","PeriodicalId":12694,"journal":{"name":"Geochemical Transactions","volume":"16 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2015-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s12932-015-0030-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4664373","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}