Laboratory and greenhouse studies compared the ability of water treatment residuals (WTRs) to alter P solubility and leaching in Immokalee sandy soil (sandy, siliceous, hyperthermic Arenic Alaquod) amended with biosolids and triple superphosphate (TSP). Aluminum sulfate (Al-WTR) and ferric sulfate (Fe-WTR) coagulation residuals, a lime softening residual (Ca-WTR) produced during hardness removal, and pure hematite were examined. In equilibration studies, the ability to reduce soluble P followed the order Al-WTR > Ca-WTR = Fe-WTR >> hematite. Differences in the P-fixing capacity of the sesquioxide-dominated materials (Al-WTR, Fe-WTR, hematite) were attributed to their varying reactive Fe- and Al-hydrous oxide contents as measured by oxalate extraction. Leachate P was monitored from greenhouse columns where bahiagrass (Paspalum notatum Flugge) was grown on Immokalee soil amended with biosolids or TSP at an equivalent rate of 224 kg P ha(-1) and WTRs at 2.5% (56 Mg ha(-1)). In the absence of WTRs, 21% of TSP and 11% of Largo cake biosolids total phosphorus (PT) leached over 4 mo. With co-applied WTRs, losses from TSP columns were reduced to 3.5% (Fe-WTR), 2.5% (Ca-WTR), and <1% (Al-WTR) of applied P. For the Largo biosolids treatments all WTRs retarded downward P flux such that leachate P was not statistically different than for control (soil only) columns. The phosphorus saturation index (PSI = [Pox]/ [Al(ox) + Fe(ox)], where Pox, Al, and Fe(ox) are oxalate-extractable P, Al, and Fe, respectively) based on a simple oxalate extraction of the WTR and biosolids is potentially useful for determining WTR application rates for controlled reduction of P in drainage when biosolids are applied to low P-sorbing soils.

a b s t r a c tDuring CO 2 storage, mineral trapping is the safest long-term storage mechanism, and it is therefore important to estimate the correct CO 2 portion trapped in secondary mineral phases. The storage potential for cold, quartz-rich reservoirs, hereafter termed Utsira-type reservoirs, were solved using the numerical code PHREEQC, using a rate model that took into account both nucleation and growth of secondary mineral phases. This represented a modification of earlier simulations where growth rates were calculated from dissolution rate data. Because growth rate and nucleation rate parameters were largely unknown for the secondary carbonates, we did a sensitivity study on the potential for carbonate growth on rate parameters.The simulations suggest that the total amount of CO 2 trapped as mineral carbonates is given by the amount of glauconite, chlorite, and smectite present in the reservoir prior to injection, as they were nearly completely dissolved. The fast dissolution of the silicates provided divalent cations for the growth of ankerite and siderite. The timing of precipitation and the secondary mineral assemblage were seen to be highly sensitive to the nucleation and growth rates. Moreover, at high nucleation rates, the secondary carbonates started to precipitate at fairly low supersaturations and formed rapidly after the dissolution of the primary minerals.Finally, a comparison of earlier simulations on the Utsira-type system with the present model and natural analogues, suggests that the earlier models have largely overestimated the growth potential of carbonates such as dolomite, magnesite and dawsonite.

a b s t r a c tLong term containment of stored CO 2 in deep geological reservoirs will depend on the performance of the caprock to prevent the buoyant CO 2 from escaping to shallow drinking water aquifers or the ground surface. Here we report new laboratory experiments on CO 2 -brine-caprock interactions and a review of the relevant literature.The Eau Claire Formation is the caprock overlying the Mount Simon sandstone formation, one of the target geological CO 2 storage reservoirs in the Midwest USA region. Batch experiments of Eau Claire shale dissolution in brine were conducted at 200• C and 300 bars to test the extent of fluid-rock reactions. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis indicate minor dissolution of K-feldspar and anhydrite, and precipitation of pore-filling and pore-bridging illite and/or smectite, and siderite in the vicinity of pyrite.We also reviewed relevant reactivity experiments, modeling work, and field observations in the literature in an attempt to help define the framework for future studies on the geochemical systems of the caprock overlain on geological CO 2 storage formations. Reactivity of the caprock is generally shown to be low and limited to the vicinity of the CO 2 -caprock interface, and is related to the original caprock mineralogical and petrophysical properties. Stable isotope studies indicate that CO 2 exists in both free phase and dissolved phase within the caprock. Carbonate and feldspar dissolution is reported in most studies, along with clay and secondary carbonate precipitation. Currently, research is mainly focused on the micro-fracture scale geochemistry of the shaly caprock. More attention is required on the potential pore scale reactions that may become significant given the long time scale associated with geological carbon storage.

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