Mason B. Tomson

The effect of nanocrystalline magnetite size on arsenic removal

Abstract Higher environmental standards have made the removal of arsenic from water an important problem for environmental engineering. Iron oxide is a particularly interesting sorbent to consider for this application. Its magnetic properties allow relatively routine dispersal and recovery of the adsorbent into and from groundwater or industrial processing facilities; in addition, iron oxide has strong and specific interactions with both As(III) and As(V). Finally, this material can be produced with nanoscale dimensions, which enhance both its capacity and removal. The objective of this study is to evaluate the potential arsenic adsorption by nanoscale iron oxides, specifically magnetite (Fe3O4) nanoparticles. We focus on the effect of Fe3O4 particle size on the adsorption and desorption behavior of As(III) and As(V). The results show that the nanoparticle size has a dramatic effect on the adsorption and desorption of arsenic. As particle size is decreased from 300 to 12 nm the adsorption capacities for both As(III) and As(V) increase nearly 200 times. Interestingly, such an increase is more than expected from simple considerations of surface area and suggests that nanoscale iron oxide materials sorb arsenic through different means than bulk systems. The desorption process, however, exhibits some hysteresis with the effect becoming more pronounced with small nanoparticles. This hysteresis most likely results from a higher arsenic affinity for Fe3O4 nanoparticles. This work suggests that Fe3O4 nanocrystals and magnetic separations offer a promising method for arsenic removal.

Adsorption/Desorption hysteresis in organic pollutant and soil/sediment interaction.

Adsorption and desorption of pollutants to soil and sediment materials are major fate mechanisms. The hypothesis that adsorption and desorption are reversible processes has been tested. The organic pollutants naphthalene, phenanthrene, and p-dichlorobenzene have been studied in the laboratory using batch reactors at room temperature from a few hours to over 2 months. The adsorption experiments were at equilibrium within 1-4 days and could be modeled using simple linear isotherms with K p values consistent with published K oc and K ow relationships. Desorption experiments were conducted with the contaminated sediments by successive dilutions

Why Scale Forms in the Oil Field and Methods To Predict It

Predicting potential scaling problems can be difficult, and numerous saturation indices and computer algorithms have been developed to determine if, when, and where scaling will occur. The Langelier, Stiff-Davis, and the Oddo-Tomson saturation indices, all widely used in the oil field, are compared and contrasted relative to calcium carbonate scale. New saturation indices for barium, strontium, and calcium sulfate scale formation are introduced and discussed, along with an updated version of the Oddo-Tomson calcium carbonate index. An updated version of the CaCO[sub 3] saturation index is presented that includes correction terms for fugacity effects and changes in the solubility of CO[sub 2] in oil and gas wells as function of temperature, pressure, water cut, and hydrocarbons present. The CaCO[sub 3] saturation index does not require a measured pH and can accommodate the presence of weak acids, such as H[sub 2]S, and wake organic acids in the system. The sulfate scale production methods (for gypsum, hemihydrate, and anhydrite) are easy to use, reliable, and designed for field use by an operator who may be untrained in chemistry. The prediction methods can be applied to any production well where calcium carbonate, calcium sulfate, strontium sulfate, or barium sulfate scale occurs.

Transport of Fullerene Nanoparticles (nC60) in Saturated Sand and Sandy Soil: Controlling Factors and Modeling

Understanding subsurface transport of fullerene nanoparticles (nC(60)) is of critical importance for the benign use and risk management of C(60). We examined the effects of several important environmental factors on nC(60) transport in saturated porous media. Decreasing flow velocity from approximately 10 to 1 m/d had little effect on nC(60) transport in Ottawa sand (mainly pure quartz), but significantly inhibited the transport in Lula soil (a sandy, low-organic-matter soil). The difference was attributable to the smaller grain size, more irregular and rougher shape, and greater heterogeneity of Lula soil. Increasing ionic strength and switching background solution from NaCl to CaCl(2) enhanced the deposition of nC(60) in both sand and soil columns, but the effects were more significant for soil. This was likely because the clay minerals (and possibly soil organic matter) in soil responded to changes of ionic strength and species differently than quartz. Anions in the mobile phase had little effect on nC(60) transport, and fulvic acid in the mobile phase (5.0 mg/L) had a small effect in the presence of 0.5 mM Ca(2+). A two-site transport model that takes into account both the blocking-affected attachment process and straining effects can effectively model the breakthrough of nC(60).

Precipitation and dissolution kinetics and equilibria of aqueous ferrous carbonate vs temperature

Abstract In this research, aqueous ferrous carbonate, FeCO 3 , was studied in a batch reactor designed to maintain rigorously anoxic conditions in the absence of reducing agents. The precipitation kinetics were measured from 27 to 80°C and were found to be approximately 100 times slower than any measured precipitation rate previously reported for a 2:2 sparingly soluble salt. Dissolution kinetics results are reported at 26 and 60°C. Solubility product constant measurements are reported from 25 to 94°C. Statistical analyses and application of the Nielsen theory of surface reaction rates suggest that the precipitation of ferrous carbonate is surface reaction rate limited with an Arrhenius activation energy of 108.3 kJ/mol. The dissolution of ferrous carbonate is probably also surface reaction rate limited.

The temperature dependence of the solubility product constant of vivianite

Abstract Vivianite Fe3(PO4)2 · 8H2O is an important phosphate mineral in many natural and environmental aquatic systems. Yet, the solubility product constant of vivianite has been determined only at room temperature. A new apparatus has been designed to facilitate the study of redox sensitive elements. Using this apparatus the solubility product constant of vivianite has been determined from 5 to 90°C. The equilibrium aqueous model MINTEQA2 used for data interpretation assumes the formation of all possible aqueous complexes. The temperature dependence of the negative logarithm of vivianite solubility (pKsp) product can be described between 5 to 90°C by pKsp = −234.205 + 12,242.6/T + 92.510 log10T, where T is temperature in Kelvin, yielding log Ksp = −35.767 ± 0.076 at 25°C. Using this expression, the calculated values of ΔG°, ΔH°, ΔS°, and ΔC°p at 25°C and 0.969 atm total pressure are 204.1 kJ mol−1, 5.05 kJ mol−1, −667.8 J K−1 mol−1, and −769 J K−1 mol−1, respectively.

The inhibition of gypsum and barite nucleation in NaCl brines at temperatures from 25 to 90°C

Abstract The inhibition of gypsum and barite nucleation in NaCl brines by phosphonates and polycarboxylates was studied at 25, 50, 70 and 90°C in terms of the prolonged induction period. Hexamethylene-diaminetetra (methylene phosphonic) acid (HDTMP) was found to be an effective inhibitor for the scaling of calcium sulfate dihydrate. Hydroxyethylene-1, 1-diphosphonic acid (HEDP) and phosphinopolycarboxylic acid (PPPC) were found to be effective inhibitors for barium sulfate scaling. The inhibition of nucleation through prolongation of the nucleation induction period likely resulted from an increase in the interfacial tension between the crystal and aqueous solution due to the presence of the inhibitors. It was observed that the inhibition of nucleation depends highly on the lattice cation/anion molar ratio and the pH of the solution as well as the degree of supersaturation and temperature for a given inhibitor.

pH-dependent effect of zinc on arsenic adsorption to magnetite nanoparticles.

UNLABELLED The effect of Zn(2+) on both the kinetic and equilibrium aspects of arsenic adsorption to magnetite nanoparticles was investigated at pH 4.5-8.0. At pH 8.0, adsorption of both arsenate and arsenite to magnetite nanoparticles was significantly enhanced by the presence of small amount of Zn(2+) in the solution. With less than 3 mg/L of Zn(2+) added to the arsenic solution prior to the addition of magnetite nanoparticles, the percentage of arsenic removal by magnetite nanoparticles increased from 66% to over 99% for arsenate, and from 80% to 95% for arsenite from an initial concentration of ∼100 μg/L As at pH 8.0. Adsorption rate also increased significantly in the presence of Zn(2+). The adsorption-enhancement effect of Zn(2+) was not observed at pH 4.5-6.0, nor with ZnO nanoparticles, nor with surface-coated Zn-magnetite nanoparticles. The enhanced arsenic adsorption in the presence of Zn(2+) cannot be due to reduced negative charge of the magnetite nanoparticles surface by zinc adsorption. Other cations, such as Ca(2+) and Ag(+), failed to enhance arsenic adsorption. Several potential mechanisms that could have caused the enhanced adsorption of arsenic have been tested and ruled out. Formation of a ternary surface complex by zinc, arsenic and magnetite nanoparticles is a possible mechanism controlling the observed zinc effect. Zinc-facilitated adsorption provides further advantage for magnetite nanoparticle-enhanced arsenic removal over conventional treatment approaches. SYNOPSIS Arsenic adsorption to magnetite nanoparticles at neutral or slightly basic pH can be significantly enhanced with trace amount of Zn(2+) due to the formation of a ternary complex.

Simplified Calculation of CACO3 Saturation at High Temperatures and Pressures in Brine Solutions

A simplified method to calculate CaCO/sub 3/ saturation is developed using only commonly measured field parameters. The calculated saturation index, I/sup S/, and pH values are accurate at high temperatures and pressure in brines and are compared with less sophisticated and more complex calculations. The final forms of I/sub S/ and pH calculations are derived using conditional equilibrium constants dependent on temperature, pressure, and ionic strength, which eliminate the need for activity coefficients. The I/sub S/ equation is presented in forms for calculation with known or derived pH and where the pH of the solution is known. Practical application of I/sub S/ is shown by calculating the scaling tendency of several geopressure energy wells of the U.S. Gulf Coast region. 18 refs.

Inhibition of calcium carbonate precipitation in NaCl brines from 25 to 90°C

Abstract The nucleation induction period of CaCO3 in NaCl brines in the absence and presence of scale inhibitors was experimentally measured at temperatures from 25 to 90°C. A semi-empirical mathematical inhibitor model is presented for the CaCO3 scale control in industrial processes based upon nucleation theory and experimental observations. Results show that the minimum inhibitor dosage (Cinh) may be obtained from: Cinh=f(s)/binh log [tinh/t0], where tinh is the inhibition time, e.g., 20 min, t0 is the nucleation induction period in the absence of inhibitors, binh is the inhibitor efficiency, and f(s) is the safety factor, e.g., 2. Important factors for the kinetics of both nucleation and inhibition have been incorporated in this model including the calcite saturation index (SI), temperature (T), and the molar ratio of Ca to HCO3 alkalinity (R). In this paper, model parameters are presented for commonly used inhibitors, including 1-hydroxyethylidene-1,1-diphosphonic-acid (HEDP) and nitrilotri(methylene phosphonic) acid (NTMP). Results show that HEDP and NTMP are the best inhibitors for calcite scaling in the systems examined.