Solidification/Stabilization of Cresol-Contaminated Soil: Mechanical and Leaching Behavior

In this research, the effects of a solidification/stabilization (S/S) technique on the remediation of cresol-contaminated soil were investigated. The soil samples were collected from the Tehran Oil Refinery (TOR) in Ray District, Iran. Cresols are hazardous chemicals whose exposure at high dosage results in irreparable damage to animal and human health. S/S process progresses through physicochemical reactions, reducing the leachability of a waste as well as changing its physical properties in order to encapsulate the contaminants and form a solid material. The samples were spiked by certain concentrations of cresols including meta-, ortho-, and para-isomers. The treatment process was conducted using Portland cement as the binder and modified bentonite as a stabilizer. The efficiency of the S/S technique was assessed by the unconfined compressive strength (UCS) test and toxicity characteristic leaching procedure (TCLP) test. The results of the tests showed that adding 20% and 30% Portland cement in combination with 15% and 30% modified bentonite to contaminated samples increased the 28-day compressive strength of S/S blocks to a range of 2.44 to 3.08 MPa. In fact, increasing the proportion of cement in the mix design resulted in enhanced compressive strength, while modified bentonite inversely affected samples’ strength. Regarding leaching behavior, adding organophilic clay to polluted samples noticeably declined cresol's concentrations in leachate. Overall efficiency of S/S in terms of leaching was about 70%, which was obtained by adding 20% cement and 30% modified clay. A logarithmic relationship between leaching percent and modified clay ratio was also detected with high logarithmic and linear correlation coefficients of 0.96 and 0.9, respectively, hence presenting the efficiency of S/S in stabilizing the cresols in the samples.     

A molecular dynamics study on intermediate structures during transition from amorphous to crystalline state

Molecular dynamics (MD) simulations are carried out for model aluminium with 500, 864, 1372 and 2048 atoms interacting with Sutton-Chen version of embedded atom method (SCEAM) based on many body interactions. The systems equilibrated in an FCC structure have, first, been melted and then solidified with specifically selected single cooling rate which forms unstable amorphous state in the system. The local structures of the system have been analysed by bond orientational order parameters to distinguish the simple structures in the systems. The radial distribution functions (RDF) and atomic coordinates have also been analysed for determining the local structural properties. It has been observed that the phase sequences of the systems, except for those of the 2048 atoms, are FCC → Liquid → Amorphous → Mixed Crystal. Types of the crystals in the mixed state depend on the number of the atoms in the system. The final phase of the system with 2048 atoms is amorphous state.     

Solidification/Stabilization of Pb-contaminated Soils with Cement and Other Additives

In the present work, various additives, including cement, lime, montmorillonite, diatomite, sepiolite, and fly ash and their various proportions, were employed to stabilize/solidify artificially prepared Pb-contaminated soils. The unconfined compressive strength properties of the stabilized/solidified soils were measured to estimate the possibility of recycling. The efficiency of Pb²⁺ immobilization in contaminated soils was also evaluated using the US EPA TCLP toxicity test. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses were used to elucidate the mechanisms responsible for the immobilization of heavy metals. The experimental results demonstrate that the immobilization efficiency with 42.5# cement was obviously higher than that with 32.5# cement, and the additives with a mass ratio M_cement:M_{fly ash}:M_quicklime of 2:1:1 were found to be the most effective. After treatment with only 10% (weight basis) additive, contaminated soil with a Pb²⁺ contamination level of 10,000 mg/kg could be successfully remediated, which helps to reduce the cost of the remediation process. The results of the leaching tests agreed with those of XRD and SEM analyses.     

分离自活性污泥的硫酸盐还原菌用于铅锌冶炼渣重金属污染修复

【背景】从活性污泥中分离出一类具有硫酸盐还原能力的菌株,探讨了其用于铅锌冶炼渣重金属污染修复的可行性。【目的】研究硫酸盐还原菌(Sulfate reducing bacteria)对铅锌冶炼渣中重金属的固化作用。【方法】将从活性污泥中分离出的硫酸盐还原菌接种到铅锌冶炼渣中进行修复,采用X射线衍射、Tessier、电感耦合等离子体发射光谱仪检测、高通量测序等方法进行实验。检测铅锌冶炼渣中矿物组成,以及修复过程中重金属化学形态、各金属离子浓度和微生物群落结构的变化。【结果】修复实验表明,体系中电位降低、pH值提高、各重金属稳定态增加、离子浓度降低且微生物群落结构变化显著,硫酸盐还原菌成为优势菌群。【结论】接种硫酸盐还原菌后铅锌冶炼渣中的重金属原位固化效果显著,从而降低生物可利用性,将恶性循环变为良性循环,所以硫酸盐还原菌可用作重金属污染修复的固化药剂。     

Cell partitioning during the directional solidification of trehalose solutions

Previous studies have demonstrated that ice/cell interaction influences post thaw viability and specific cryoprotective agents can affect those interactions. Trehalose, a disaccharide, has been shown to have a protective benefit during conventional slow freezing. Existing theories have been put forth to explain the protective benefit of trehalose during desiccation and vitrification, but these theories do not explain the protective benefit observed during conventional freezing protocols. The overall objective of this investigation was to characterize cell/ice interactions in the presence of trehalose using non-planar freezing conditions. To that end, lymphoblasts suspended in phosphate buffered saline solution with various levels of trehalose (0, 10, 100, and 300 mM) were frozen on a directional solidification stage. The partitioning of cells into the interdendritic space or engulfment by an advancing dendrite was determined as a function of velocity and solution composition. For a given temperature gradient, the fraction of cells entrapped into the interdendritic region increased with increasing velocity. With small additions of trehalose (10 mM), the velocity at which cells were entrapped in the interdendritic region increased. At high trehalose concentrations (100, 300 mM), interface morphology was significantly different and cells were engulfed by the advancing interface. Dehydration of cells in the region shortly before and after the interface was significant and depended upon of the type of interaction experienced by the cell (entrapped vs. engulfed). These studies suggest that one potential mechanism for the action of trehalose involves changing the ice/cell interactions during conventional slow freezing.     

Foundations of modeling in cryobiology—I: Concentration,Gibbs energy,and chemical potential relationships

Mathematical modeling plays an enormously important role in understanding the behavior of cells, tissues, and organs undergoing cryopreservation. Uses of these models range from explanation of phenomena, exploration of potential theories of damage or success, development of equipment, and refinement of optimal cryopreservation/cryoablation strategies. Over the last half century there has been a considerable amount of work in bio-heat and mass-transport, and these models and theories have been readily and repeatedly applied to cryobiology with much success. However, there are significant gaps between experimental and theoretical results that suggest missing links in models. One source for these potential gaps is that cryobiology is at the intersection of several very challenging aspects of transport theory: it couples multi-component, moving boundary, multiphase solutions that interact through a semipermeable elastic membrane with multicomponent solutions in a second time-varying domain, during a two-hundred Kelvin temperature change with multi-molar concentration gradients and multi-atmosphere pressure changes. In order to better identify potential sources of error, and to point to future directions in modeling and experimental research, we present a three part series to build from first principles a theory of coupled heat and mass transport in cryobiological systems accounting for all of these effects. The hope of this series is that by presenting and justifying all steps, conclusions may be made about the importance of key assumptions, perhaps pointing to areas of future research or model development, but importantly, lending weight to standard simplification arguments that are often made in heat and mass transport. In this first part, we review concentration variable relationships, their impact on choices for Gibbs energy models, and their impact on chemical potentials.