Surface complexation of U(VI) on goethite (α-FeOOH)

Sorption of U(VI) to goethite is a fundamental control on the mobility of uranium in soil and groundwater. Here, we investigated the sorption of U on goethite using EXAFS spectroscopy, batch sorption experiments and DFT calculations of the energetics and structures of possible surface complexes. Based on EXAFS spectra, it has previously been proposed that U(VI), as the uranyl cation , sorbs to Fe oxide hydroxide phases by forming a bidentate edge-sharing (E2) surface complex, >Fe(OH)₂UO₂(H₂O)_n. Here, we argue that this complex alone cannot account for the sorption capacity of goethite (α-FeOOH). Moreover, we show that all of the EXAFS signal attributed to the E2 complex can be accounted for by multiple scattering. We propose that the dominant surface complex in CO₂-free systems is a bidentate corner-sharing (C2) complex, (>FeOH)₂UO₂(H₂O)₃ which can form on the dominant {101} surface. However, in the presence of CO₂, we find an enhancement of UO₂ sorption at low pH and attribute this to a (>FeO)CO₂UO₂ ternary complex. With increasing pH, U(VI) desorbs by the formation of aqueous carbonate and hydroxyl complexes. However, this desorption is preceded by the formation of a second ternary surface complex (>FeOH)₂UO₂CO₃. The three proposed surface complexes, (>FeOH)₂UO₂(H₂O)₃, >FeOCO₂UO₂, and (>FeOH)₂UO₂CO₃ are consistent with EXAFS spectra. Using these complexes, we developed a surface complexation model for U on goethite with a 1-pK model for surface protonation, an extended Stern model for surface electrostatics and inclusion of all known UO₂-OH-CO₃ aqueous complexes in the current thermodynamic database. The model gives an excellent fit to our sorption experiments done in both ambient and reduced CO₂ environments at surface loadings of 0.02-2.0 wt% U.     

Kinetic studies of the rate of dissolution of silica and diatom tests in sea water

Kinetic studies have been carried out on the dissolution of 10μm beads of silica and of the siliceous tests of two species of diatoms (Thalassiosira fluviatus andSkeletonema costatum) in sea water at 10–50°C and over the pH range 6–9. At all temperatures dissolution of the biogenous silica occurred most rapidly at pH 8 and most slowly at pH 6. First order kinetics were closely followed when the silica was present in a considerable excess over that required for saturation, the rate being proportional to the area of the silica. Apparent deviation from this type of kinetics occurred when there was insufficient silica to bring about saturation. This was undoubtedly due to the progressive decrease in the surface area which takes place as the particle dissolves. Application of the rather simplistic model developed by Kamataniet al. (1980), which makes allowance for this decrease, gave a close correspondence with the data until ∼ 90% of the silica had dissolved.     

Cross inoculation studies: Response of Vigna mungo to inoculation with rhizobia from tree legumes growing under arid Environment

Cross-inoculation experiments were conducted in the greenhouse to test the rhizobia isolated from nodules of seven tree legumes for their effectiveness in Vigna mungo plants. The tree legumes included Albizia lebbeck, Dalbergia sissoo, Leucaena leucocephala, Pithecellobium dulce, Prosopis cineraria, Prosopis glandulosa and Prosopis juliflora, all growing under arid environment. Rhizobia from these legumes formed nodules on the roots of Vigna mungo except isolates from Albizia lebbeck. Dry weight and nitrogen contents of Vigna mungo plants increased significantly (P<0.05) in response to cross inoculation as compared to uninoculated control. Rhizobia from Leucaena leucocephala and Prosopis glandulosa showed significant increase in dry weight (P<0.05) and nitrogen contents (P<0.05) than other inoculated treatments. The natural rhizobia of wild tree legumes growing under arid environment show higher tolerance to prevailing adverse conditions like salt stress, elevated temperatures and drought. These rhizobia may be used to inoculate wild as well as crop legumes cultivated in reclaimed desert lands. These rhizobia may have specific traits that can be transferred to other rhizobia through genetic engineering tools. The cross infection of agriculturally important legumes with isolates from wild legumes may prove a useful means of increasing nitrogen contents within these plants.     

Bioaccumulation of heavy metals in organs of fresh water fish Cyprinus carpio (Common carp)

The objective of the present study is to determine the bioaccumulation of heavy metals in various organs of the fresh water fish exposed to heavy metal contaminated water system. The experimental fish was exposed to Cr, Ni, Cd and Pb at sublethal concentrations for periods of 32 days. The elements Cd, Pb, Ni and Cr were assayed using Shimadzu AA 6200 atomic absorption spectrophotometery and the results were given as μ/g dry wt. The accumulation of heavy metal gradually increases in liver during the heavy metal exposure period. All the results were statistically significant at p < 0.001. The order of heavy metal accumulation in the gills and liver was Cd > Pb > Ni > Cr and Pb > Cd > Ni > Cr. Similarly, in case of kidney and flesh tissues, the order was Pb > Cd > Cr > Ni and Pb > Cr > Cd > Ni. In all heavy metals, the bioaccumulation of lead and cadmium proportion was significantly increased in the tissues of Cyprinus carpio (Common carp).     

Is C/O enhanced in NGC 253?

We have mapped the nuclear region of the starburst galaxy NGC 253 in the³ P ₁ ³ P ₀ line of neutral carbon using the JCMT. Carbon is widespread across the nuclear region with a similiar distribution to CO as expected. Previous studies of Galactic star-forming regions showed that carbon emission is enhanced in photon-dominated regions (where UV photons impinge upon molecular clouds). Previous observations of other PDR tracers such as ionized carbon and FIR continuum constrain the physical conditions in the PDR gas of NGC 253. The carbon we have observed is far brighter than predicted by theoretical models of PDRs with solar elemental values. This indicates that carbon emission is not a reliable diagnostic of the physical conditions in the nuclear region of a galaxy undergoing a burst of star formation.     

The Jovian surface condition and cooling rate

A theory which is almost fully analytic is used to investigate Jupiter's cooling rate. We find that a simple model of contraction with adiabatic interior structure gives a total cooling time to the present which is in good agreement with the age of the solar system. The interplay between the surface condition and the cooling rate is exhibited and discussed. The current rate of change of the effective temperature is calculated to be ?1°K/0.145×10⁹ yr. Discrepancies with fully numerical investigations of the Jovian age and cooling rate are noted.     

High rate anaerobic treatment of Sago wastewater using HUASB with PUF as carrier

Sago industry is one of the major small-scale sectors in India and over 800 units are located in the southern State of Tamilnadu. Processing of sago generates enormous quantities of high strength wastewater requiring systematic treatment prior to disposal. The present study is an attempt to treat the sago wastewater using Hybrid Upflow Anaerobic Sludge Blanket (HUASB) reactor, which offers the advantages of both fixed film and up flow anaerobic sludge blanket treatment. HUASB reactor with a volume of 5.6 L was operated at Organic Loading Rates varying from 10.7 to 24.7 kg COD/m³.day. After 130 days of startup, the reactor produced appreciable decrease in COD of wastewater and removed solids efficiently. The COD removal varied from 91–87%. While the removal of Total Solids was in the range of 61–57%, that of volatile solids varied from 70–67%. The ideal OLR for the reactor was 23.5 kg COD/m³.day. The findings of the study open up newer possibilities of design low cost and compact onsite treatment systems with very short retention periods.