Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Aquatic Geochemistry (v.8, #4)
Pb (II) Sorption with Calcite: A Radiotracer Study by ASHAKI A. Rouff; RICHARD J. Reeder; NICHOLAS S. Fisher (pp. 203-228).
A 210Pb radiotracer was used to monitor Pb solid-aqueousphase partitioning in sorption experiments at ambient temperature, pH = 8.2, and atmospheric PCO2 in 0.15 M NaNO3 solutions. A 24 h isotherm is linear up to Pb concentrations of 4 × 10-6 M, above which an increase in slope suggests precipitation. The effect of Pb concentration, calcite loading, and ionic strength on Pb sorption with time was monitored. Sorption kinetics are rapid, followed by a slower sorption step.At a constant calcite loading500 mg L-1,fractional sorptiondecreases with increasing initialPb concentration. The reverse isobserved for surface coverage, with0.6, 5.6 and 40.2% of availableCa2+sites occupied at10-8,10-7 and10-6 MPb after 96 h. At a constant Pb concentration of10-6 M,fractional sorption increases with increasing particleloading, however surface coverage decrease with72.5 and 22.1%Ca2+sites occupied at 100 and200 mg L-1calcite after 96 h.The adsorption coefficient (Kd) is approximately 103,increases with initial Pb concentration, but remains unaffected by variable calcite loading. Absence of an ionic strength effect on Pb sorption is interpreted as the dominance of inner-sphere complexation. For desorption experiments conducted over a range of initial sorption times, an average desorption index > 0.8 but < 1 indicates that sorption is largely reversible, but is accompanied by slight incorporation. Solid-solution formation increases with time, as observed by slower initial desorption rates for samples with longer sorption times. These findings indicate that Pb may be effectively sequestered by calcite; however re-release via desorption is likely as Pb does not become significantly incorporated into the mineral structure.
Keywords: lead; calcite; sorption; desorption; radiotracers
Stable Isotope Ratios and the Evolution of Acidulous Ground Water by Martin Dietzel; Thorsten Kirchhoff (pp. 229-254).
Ground waters in North Hesse (Germany) are conspicuous by high amounts of dissolved inorganic carbon (DIC) at low pH. The DIC is received from the uptake of soil CO2 and CO2 of volcanic origin and the subsequent dissolution ofTriassic and Permian limestone and dolomites. The volcanic CO2 is related to Miocene basaltic magma which has liberated gaseous CO2 during thebreakthrough to Triassic and Permian sediments. The volcanic CO2 (-6 < δ13CCO2 < -3‰, PDB) was trapped within pore spacesand intra- and intergranulares of Permian evaporites and Triassic sandstones and was stored within such reservoirs until recent times. The uptake of volcanic CO2 occurs as ground water migrates through such reservoirs. The 13 C/12 C-signatures of the DIC indicate mixture of soil-CO2and CO2 of volcanic origin for the dissolution of marine limestone and dolomites. The obtained two types for CO2 of volcanic origin with δ13CCO 2-values of -10 ± 3 and +2 ± 2‰ can be explained by diffusion of CO2 through micropores, faults, and interfacesof solids. This mobilisation of CO2 is accompanied with a kinetic fractionation of ≈ -9‰. 13 C-depleted CO2 is liberated from the reservoir,whereas 13 CO2 is accumulated in the residue
Keywords: acidulous ground water; calcite; dolomite; carbonic acid; stable isotopes; isotope fractionation; volcanic CO2
Sorption Model for Dissolved Aluminium in Freshwaters by S. Upadhyay; P. S. Liss; T. D. Jickells (pp. 255-275).
A series of aluminium speciation measurements were madein the freshwaters of the Yare and Great Ouse rivers (England). Samples were analysedfor dissolved and particulate Al, suspended particulate matter (SPM), and other alliedchemical species in order to assess the role of sorption processes on the suspended phasesin controlling dissolved Al levels. Partitioning of Al occurs between solid andsolution phases with a distribution coefficient (Kd) which varies over about one anda half orders of magnitude for suspended particle concentrations of comparablemagnitude. A sorption model is proposed for dissolved Al concentrations in thesefreshwaters with most of the data fitting the model defined by a zone with Kdvalues of 0.316 × 106 and 107. However, a few data points lie outside thiszone, suggesting that other processes may also influence dissolved Al distributions.Nevertheless, the model may serve as a starting point for predicting concentrations ofdissolved Al in rivers where SPM levels are moderate to high (>1 mg l-1 but< 75 mg l-1), and indeed, this model works reasonably well for the Conway system(Wales). Further, the empirical distribution coefficient, Kd, decreases withincreasing suspended particle concentration, which may be due in part to colloidal phenomena.
Keywords: river water; dissolved aluminium; partitioning; sorption model; particle concentration effect