Robert D. Cody

Effect of soil texture on surfactant-based remediation of hydrophobic organic-contaminated soil.

Surfactants may be used in remediation of subsoil and aquifer contaminated with hydrophobic compounds. The objectives of this study were to examine the effect of soil texture on hydrophobic organic contaminant (HOC; toluene, or 1,2,4-trichlorobenzene [TCB]) removal from six soils and to evaluate the optimal composition of soil texture for maximum HOC removal using aqueous surfactant solution. Selected surfactants were 4% (vol/vol) sodium diphenyl oxide disulfonate (DOSL) and 4% (wt/vol) sodium lauryl sulfate (LS). Toluene and TCB were selected as the lighter-than-water nonaqueous phase liquid (LNAPL) and denser-than-water nonaqueous phase liquid (DNAPL) model substances, respectively. Soil types used for this study were Ottawa sand and five Iowa soils (Fruitfield, Keomah, Crippin, Webster, and Galvar). The greatest recovery of toluene and TCB in batch tests was 73% and 84%, respectively, which was obtained with DOSL surfactant in Ottawa sand. The toluene removal of 95% in column tests has been achieved in the Ottawa sand and three Iowa soils (Fruitfield, Keomah, Crippin) with DOSL after effluent volume of 3750 ml (about 32 pore volume) passed. TCB removal of 98% in column tests has been achieved in Ottawa sand and three Iowa soils (Fruitfield, Keomah, Crippin) with DOSL after effluent volume of 2500 ml (about 21 pore volume) passed. These results were related with soil texture (clay content 30%), clay mineralogy (kaolinite and smectite), as a function of transported pore volume.

Gypsum Nucleation and Crystal Morphology in Analog Saline Terrestrial Environments

ABSTRACT Gypsum crystals were grown in experimental conditions analogous to saline terrestrial environments within bentonite clay gels by diffusion control at three different temperatures, four brine salinities, and four tannic acid (a model terrestrial humic substance) concentrations. The resulting crystals correspond to natural gypsum formed in terrestrial environments. Prismatic gypsum typically grew at both high and low temperatures in the absence of the organic additive. With increasing organic acid concentrations, the prismatic crystals progressively became flattened perpendicular to [001], and two temperature-dependent trends developed. At low temperatures, a hemi-bipyramidal habit dominated by 1111 faces developed, whereas the lenticular e103 dominated habit forme at higher temperatures. With progressively greater concentrations of organic material a(100) penetration twinning developed, secondary complex nucleation occurred near the twin interfaces, and finally, rosette and rosette-like aggregates formed. Higher temperatures generally favored better-formed and larger rosettes. The presence of 5% and 15% NaCl greatly decreased nucleation density and resulted in larger single crystals and crystal aggregates. The a(100) penetation twins appear to be diagnostic of gypsum growth in natural terrestrial sediments at a pH greater than 7.5.

Lenticular Gypsum: Occurrences in Nature, and Experimental Determinations of Effects of Soluble Green Plant Material on its Formation

ABSTRACT Lens-shaped gypsum crystals are common in both modern and ancient evaporite deposits, but laboratory experiments demonstrate that the presence of certain types of dissolved organic material is the major factor promoting growth of this particular habit rather than warm saline water conditions. A very widespread type of soluble organic material results from green plant decomposition. Experiments utilizing diffusion-controlled growth of gypsum within sediments of various types, and also utilizing evaporation-controlled solution growth indicate that this organic material promotes the growth of lenticular gypsum, but only under alkaline conditions. In acid conditions, both in the presence or absence of added plant material, only elongate prismatic gypsum develops. The type of sediment with n which gypsum grows has only minor effects on its morphology unless the sediment is contaminated with soluble organics. These observations help to explain why lenticular gypsum forms in some instances, and prismatic gypsum in others, within natural sedimentary environments.

Organo-crystalline Interactions in Evaporite Systems: The Effects of Crystallization Inhibition

ABSTRACT Supersaturated conditions in oceanic and other sedimentary environments, and the crystal morphologies of sedimentary minerals support the occurrence in nature of widespread and powerful crystallization inhibition by extremely small, substoichiometric concentrations (< 1 mg/l) of soluble organic substances. The most powerful inhibitor molecules appear to be polycarboxylic acids, polyphenols, polyphosphates, organic phosphate esters, and hydrolyzed proteins. Organic crystallization inhibition, also referred to as organic adsorption poisoning and threshold inhibition, occurs by a process that is fundamentally different from that of stoichiometric organic complexation. During chemical sedimentation in evaporite and other sedimentary environments, organic inhibition can affect crystallization processes in several distinct but related modes. Highly supersaturated solutions can be stabilized over long intervals, so that eventual destabilization may result in mineral precipitation at unexpected locations. If inhibition is overpowered by excess supersaturation or by partial destruction of inhibitor molecules, the precipitating phase also may be affected. Mineral phase kinetics can be altered so that unexpected mineral species precipitate, and habit modifications, twinning, and intergrowth of precipitates may be induced.

SURFACTANT RECYCLING BY SOLVENT EXTRACTION IN SURFACTANT-AIDED REMEDIATION

As a part of the study on the surfactant-aided remediation of organic contaminants, solvent extraction was investigated to determine its efficiency for used surfactant recycling. The experiments used a glass column 70 cm height with an internal diameter of 3 cm. The convex orifice with four holes (4 mm outer diameter) was installed at the base of the column. Four percent aqueous surfactant solutions solubilizing toluene or 1,2,4-trichlorobenzene (TCB) as model contaminants were injected in the column. Acetone, hexane, and methylene chloride were used as the solvent, and the solvent was allowed to flow upward through the surfactant solution in the column and circulated by a pump. Toluene and 1,2,4-TCB were effectively removed from the aqueous solution of anionic surfactant diphenyl oxide disulfonate (DOSL, trade name Dowfax 8390) using hexane and methylene chloride as the solvent. The times required for 98% removal of the toluene and 1,2,4-TCB were 5 h with methylene chloride or hexane flow rates of 30 ml/min. This indicates that the present solvent extraction method may help recycle anionic surfactant solutions used for remediation of contaminated soil.

Synergism effect of mixed surfactant solutions in remediation of soil contaminated with PCE

The purpose of this research was to evaluate the effect of mixed surfactant solution for removal of perchlorethylene (PCE) in sandy soil. Ten different surfactant solutions were used in column studies. Mixed surfactant solutions (anionic and nonionic) were most effectively worked in the sandy soil for removal of PCE as a result of synergism between the two types of surfactants. The effectiveness of the mixture of surfactants [anionic DOSL (Diphenyl Oxide Disulfonates) and nonionic Tween 60] was 35–38% greater than that for the anionic or nonionic surfactant alone. However, synergism between the anionic SDS (Sodium N-dodecyl Sulfate) and the anionic DOSL was not observed. Cause of the lack of synergism in a mixture of the two anionic surfactants is uncertain but may result from the twin head structure of DOSL. The results indicate that mixed surfactant solution (1∶1 mixture of anionic and nonionic) leaching is a promising candidate for the remediation of PCE contaminated sandy soil.

Growth and early diagenetic changes in artificial gypsum crystals grown within bentonite muds and gels

Experiments designed to simulate muddy environments failed to nucleate anhydrite or cause replacement of initially formed gypsum crystals by anhydrite during five months at temperatures to 80°C and with pore solutions containing as much as 20 percent sodium chloride. Gypsum and bassanite (at higher temperatures and salinities) were the only species produced. In addition, gypsum crystals experimentally grown for several months in Wyoming bentonite gels and pastes and in the presence of dissolved monovalent salts underwent major habit changes. The habit produced by these early diagenetic changes is characteristic of many natural crystals found in saline sediments and probably is diagnostic of evaporite sedimentation.

Reduction of Concrete Expansion by Ettringite Using Crystallization Inhibition Techniques

Many researchers have proposed that secondary or delayed ettringite is responsible for serious, premature deterioration of concrete highways. The current research project was designed to determine experimentally if secondary ettringite formation in concrete can be reduced by treating the concrete with commercial crystallization-inhibitor chemicals. The hypothesis is that if ettringite is reduced, a concomitant reduction of concrete expansion and cracking will occur. If ettringite formation and concrete deterioration are simultaneously reduced, then the case for ettringite-induced expansion/cracking is strengthened. Our experiments used four commercial inhibitors—two phosphonates, a polyacrylic acid, and a phosphate ester. Concrete blocks were subjected to continuous-immersion, wet/dry cycling, and freeze/thaw cycling in sodium sulfate solutions and in sulfate solutions containing an inhibitor. The two phosphonate inhibitors were effective in reducing ettringite nucleation and growth in the concrete. Two other non-phosphonate inhibitors were somewhat effective, although less so than the two phosphonates. Reduction of new ettringite formation in concrete blocks also reduced expansion and cracking of the blocks. This relationship clearly links concrete expansion with ettringite formation. Secondary ettringite nucleation and growth must cause concrete expansion, because the only effect of these inhibitor chemicals is to reduce crystal nucleation and growth. These inhibitors cannot be responsible in any other way for reduction in expansion.

Anomalous Boron Content of Two Continental Shales in Eastern Colorado

ABSTRACT Boron content and clay mineralogy were determined on samples from a continental facies of the Fountain Formation of Permo-Pennsylvanian age and a pre-Fountain fossil soil developed during late Mississippian time. All samples from both units were found to contain far more boron than amounts previously proposed as indicative of shales deposited in continental environments. The results of the study cast doubt on the reliability of boron analyses of sedimentary rocks as an index of their depositional salinity.

Variation of soil hydraulic conductivity by anionic surfactants in soil column

Remediation techniques using surfactants to flush hydrophobic organic contaminants from soils have recently been investigated. However, less attention has been given to evaluating the effects of surfactants on the hydraulic properties of porous media. The objective of this study was to investigate the effects on saturated hydraulic conductivity of the interactions between soil type (sand, clay loam) and anionic surfactants (DOSL, SLS, TDCA). Saturated hydraulic conductivities of two Iowa soils, Fruitfield sand and Webster clay loam, were measured in constant-head laboratory columns. The two soils were leached with solution of 4% (v/v) sodium diphenyl oxide disulfonate (DOSL, trade name Dowfax 8390) or 4% (w/v) sodium lauryl sulfate (SLS, trade name SLS) or 4% (v/v) trideceth-19-carboxylic acid (TDCA, trade name Sandopan JA36). As controls, soils were also leached with deionized water. Reductions in hydraulic conductivity due to surfactant leaching ranged from 9% to 85% relative to the initial values measured with deionized water. The most severe reductions in saturated hydraulic conductivity occurred in Webster soil leached with solution of TDCA. For three surfactants, more clogging occurred in the Webster clay loam than the Fruitfield sand. For both soils, the least clogging occurred with DOSL. Doubling the DOSL concentration to 8.2% did not change its effect on hydraulic conductivity for either soil. Results of this study suggest that the surfactant DOSL is a good candidate for surfactant-assisted remediation based on its relatively small effects on soil hydraulic conductivity. These results indicate that potential surfactant-assisted hydraulic conductivity losses should be considered prior to in-situ surfactant remediation.