Correlations and nonlinear partition of nonionic organic compounds by humus-like substances humificated from rice straw

The debate on whether the nonlinear sorption of nonionic organic compounds (NOCs) by soil organic matter (SOM) is captured by nonlinear partition or adsorption has been going on for decades because the used SOM samples are complex mixtures from various precursors with varied humification degrees in natural environment. Therefore, in this study, hydrothermal method was employed to prepare humus-like substances from a sole precursor (i.e., rice straw) with various humification degrees for nonlinear sorption of 25 aromatic compounds, then to have an insight into the underlying mechanisms of the nonlinear sorption of NOCs by SOM. It was observed that the increasing humification degree of humus-like substances, i.e., decreasing in the polarity ((O + N)/C) and increasing in the aromaticity, result in the increase of isotherm nonlinearity and sorption capacity/affinity of NOCs. Sorption capacity of NOCs, obtained by isotherm fitting using Dubinin-Astakhov (DA) model and Dual-Mode (DM) model, are positively correlated with their solubility in water and octanol, indicating the nonlinear sorption could be captured by nonlinear partition mechanism. Specific interactions including hydrogen-bonding interaction and π-π interaction between aromatic structures of humus-like substances and organic molecules could be responsible for the nonlinear partition and the increase of sorption affinity with the enhancement of humification degree. These obtained correlations are valuable for understanding the underlying mechanisms of nonlinear sorption and elucidating the transport of NOCs in the environment.

Multireaction Modeling of Lead (Pb) and Copper (Cu) Sorption/Desorption Kinetics in Different Soils

Batch kinetic experiments were carried out to quantify and describe the sorption/desorption of Cu and Pb in ten soils that exhibited a wide range of properties. Sorption isotherms were quantified using the Langmuir equation, whereas modeling of sorption/desorption kinetics was described using multireaction model (MRM). Results revealed the nonlinear sorption behavior of Cu and Pb in all soils. The ten soils exhibited higher affinity to Pb (6.4 to 36.5 mmol kg−1) in comparison to Cu (3.6 to 22.4 mmol kg−1). Simulation of Cu and Pb kinetic data indicated that the rate of sorption reaction was two orders of magnitude higher than the rate of release. Considering one irreversible site in addition to one-reversible kinetic site improved the estimation of rates of reaction for both Cu and Pb in acidic and alkaline soils. All soils exhibited sorption/desorption hysteresis where Pb-releases ranged between <0.2% and 14.4% of the total sorbed. The respective Cu releases ranged from <0.85% and 23.4%. The multireaction model, which was successful in describing Cu and Pb for all ten soils, provided insight into the processes of sorption/desorption of Cu and Pb in all soils.

A Review on Water Vapor Pressure Model for Moisture Permeable Materials Subjected to Rapid Heating

This paper presents a comprehensive review and comparison of different theories and models for water vapor pressure under rapid heating in moisture permeable materials, such as polymers or polymer composites. Numerous studies have been conducted, predominately in microelectronics packaging community, to obtain the understanding of vapor pressure evolution during soldering reflow for encapsulated moisture. Henry's law-based models are introduced first. We have shown that various models can be unified to a general form of solution. Two key parameters are identified for determining vapor pressure: the initial relative humidity and the net heat of solution. For materials with nonlinear sorption isotherm, the analytical solutions for maximum vapor pressure are presented. The predicted vapor pressure, using either linear sorption isotherm (Henry's law) or nonlinear sorption isotherm, can be greater than the saturated water vapor pressure. Such an “unphysical” pressure solution needs to be further studied. The predicted maximum vapor pressure is proportional to the initial relative humidity, implying the history dependence. Furthermore, a micromechanics-based vapor pressure model is introduced, in which the vapor pressure depends on the state of moisture in voids. It is found that the maximum vapor pressure stays at the saturated vapor pressure provided that the moisture is in the mixed liquid/vapor phase in voids. And, the vapor pressure depends only on the current state of moisture condition. These results are contradictory to the model predictions with sorption isotherm theories. The capillary effects are taken into consideration for the vapor pressure model using micromechanics approach.