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Cr(VI) Formation Related to Cr(III)-Muscovite and Birnessite Interactions in Ultramafic Environments
Rajapaksha, Anushka Upamali,Vithanage, Meththika,Ok, Yong Sik,Oze, Christopher American Chemical Society 2013 Environmental science & technology Vol.47 No.17
<P>Chromium is abundantly and primarily present as Cr(III) in ultramafic rocks and serpentine soils. Chromium(III) oxidation involving chromite (FeCr<SUB>2</SUB>O<SUB>4</SUB>) via interactions with birnessite has been shown to be a major pathway of Cr(VI) production in serpentine soils. Alternatively, Cr(III)-bearing silicates with less Cr(III) may provide higher Cr(VI) production rates compared to relatively insoluble chromite. Of the potential Cr(III)-bearing silicates, Cr(III)-muscovite (i.e., fuchsite) commonly occurs in metamorphosed ultramafic rocks and dissolution rates may be comparable to other common Cr(III)-bearing phyllosilicates and clays. Here, we examine the formation of Cr(VI) related to Cr(III)-muscovite and birnessite (i.e., acid birnessite) interactions with and without humic matter (HM) via batch experiments. Experimentally, the fastest rate of Cr(VI) production involving Cr(III)-muscovite was 3.8 × 10<SUP>–1</SUP> μM h<SUP>–1</SUP> (pH 3 without HM). Kinetically, Cr(III)-muscovite provides a major pathway for Cr(VI) formation and Cr(VI) production rates may exceed those involving chromite depending on pH, available mineral surface areas in solution, and the abundance of Cr(III) present. However, when HM is introduced to the system, Cr(VI) production rates decrease by as much as 80%. This highlights that HM strongly decreases but may not completely suppress the formation and mobilization of Cr(VI). A Sri Lankan serpentine soil was utilized to provide context with regards to the experimental results. Despite Cr(VI) in the soil solids and Cr(VI) formation being favorable from Cr(III)-bearing minerals, no detectable Cr(VI) was released into soil solutions potentially due to the abundance of HM. Overall, the dynamic interactions of Cr(III)-bearing silicates and birnessite provide a kinetically favorable route of Cr(VI) formation which is tempered by humic matter.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2013/esthag.2013.47.issue-17/es4015025/production/images/medium/es-2013-015025_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/es4015025'>ACS Electronic Supporting Info</A></P>
Rajapaksha, Anushka Upamali,Alam, Md. Samrat,Chen, Ning,Alessi, Daniel S.,Igalavithana, Avanthi Deshani,Tsang, Daniel C.W.,Ok, Yong Sik Elsevier BV 2018 Science of the Total Environment Vol.625 No.-
<P><B>Abstract</B></P> <P>Biochar is an emerging low-cost sorbent used for removing trace metals from water. In this study, we evaluated the removal potential of aqueous hexavalent chromium (Cr(VI)) by biochars produced from soybean (<I>Glycine</I> <I>max</I> L.) and burcucumber (<I>Sicyos angulatus</I> L.) residues. The highest Cr(VI) removal from solution occurred at low pH values (pH2–5), and adsorption decreased approximately tenfold when the pH increased from 2 to 10. Synchrotron-based X-ray absorption spectroscopy (XAS) investigations showed that Cr(VI) species were reduced to trivalent chromium (Cr(III)) at the biochar surface following Cr(VI) adsorption. Linear combination fitting (LCF) of X-ray absorption near edge structure (XANES) data indicated that approximately 90% of the total Cr(VI) (962μM) was reduced to Cr(III). Extended X-ray absorption fine structure (EXAFS) fitting results yielded interatomic chromium (CrCr) distances consistent with the formation of Cr(III) precipitates as Cr(OH)<SUB>3</SUB>. Trivalent chromium is far less soluble than Cr(VI) and typically precipitates as amorphous Cr(III) solids. Thus, biochars produced by soybean and burcucumber residues are a promising technique for both adsorbing and reductively immobilizing Cr(VI) from aqueous solutions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Removal potential of aqueous Cr(VI) by biochar was evaluated. </LI> <LI> The highest Cr(VI) removal occurred at low pH values. </LI> <LI> Cr(VI) species can be reduced to Cr(III) at the biochar surface. </LI> <LI> Biochar properties determine the coordination environment of Cr(III) products. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Acid-activated biochar increased sulfamethazine retention in soils.
Vithanage, Meththika,Rajapaksha, Anushka Upamali,Zhang, Ming,Thiele-Bruhn, S?ren,Lee, Sang Soo,Ok, Yong Sik Ecomed 2015 Environmental Science and Pollution Research Vol.22 No.3
<P>Sulfamethazine (SMZ) is an ionizable and highly mobile antibiotic which is frequently found in soil and water environments. We investigated the sorption of SMZ onto soils amended with biochars (BCs) at varying pH and contact time. Invasive plants were pyrolyzed at 700 C and were further activated with 30 % sulfuric (SBBC) and oxalic (OBBC) acids. The sorption rate of SMZ onto SBBC and OBBC was pronouncedly pH dependent and was decreased significantly when the values of soil pH increased from 3 to 5. Modeled effective sorption coefficients (K D,eff) values indicated excellent sorption on SBBC-treated loamy sand and sandy loam soils for 229 and 183 L/kg, respectively. On the other hand, the low sorption values were determined for OBBC- and BBC700-treated loamy sand and sandy loam soils. Kinetic modeling demonstrated that the pseudo second order model was the best followed by intra-particle diffusion and the Elovich model, indicating that multiple processes govern SMZ sorption. These findings were also supported by sorption edge experiments based on BC characteristics. Chemisorption onto protonated and ligand containing functional groups of the BC surface, and diffusion in macro-, meso-, and micro-pores of the acid-activated BCs are the proposed mechanisms of SMZ retention in soils. Calculated and experimental q e (amount adsorbed per kg of the adsorbent at equilibrium) values were well fitted to the pseudo second order model, and the predicted maximum equilibrium concentration of SBBC for loamy sand soils was 182 mg/kg. Overall, SBBC represents a suitable soil amendment because of its high sorption rate of SMZ in soils.</P>
Ahmed, Mohamed Bedair M.,Rajapaksha, Anushka Upamali,Lim, Jung Eun,Vu, Ngoc Thang,Kim, Il Seop,Kang, Ho Min,Lee, Sang Soo,Ok, Yong Sik American Chemical Society 2015 Journal of agricultural and food chemistry Vol.63 No.2
<P>Veterinary antibiotics can be released to environment by the animals’ excretions, which thereby poses human health and ecological risks. Six antibiotics (tetracycline, oxytetracycline, chlortetracycline, sulfamethazine, sulfamethoxazole, and sulfadimethoxine) at three concentrations (5, 10, and 20 mg kg<SUP>–1</SUP> soil) were employed in pots filled with a loamy sand upland soil. Three types of vegetable seedlings, including cucumber (<I>Cucumis sativus</I>), cherry tomato (<I>Solanum lycopersicum</I>), and lettuce (<I>Lactuca sativa</I>), were also cultivated during 45 d in the greenhouse. All antibiotics taken up by tested plants showed negative effects on growth. Relatively high levels of tetracyclines and sulfonamides (SAs) were detected in the nonedible parts, roots, and leaves of cucumber and tomato, but fruit parts accumulated them lower than acceptable daily intake. Indeed, cucumber roots accumulated SAs by up to 94.6% of total addition (at 5 mg kg<SUP>–1</SUP> soil).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jafcau/2015/jafcau.2015.63.issue-2/jf5034637/production/images/medium/jf-2014-034637_0002.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jf5034637'>ACS Electronic Supporting Info</A></P>