Modeling of chlorophenols competitive adsorption on soils by means of the ideal adsorbed solution theory

Development of a Multicomponent Adsorption Isotherm Equation and Its Validation by Modeling

Researchers have made significant efforts over the past few decades to understand adsorption by developing various simple adsorption isotherm models. However, though many contaminants usually occur as multicomponent mixtures in nature, multicomponent adsorption isotherms have received limited attention and remain an area of inadequate research. We have presented here in a new multicomponent adsorption isotherm model, named the Jeppu Amrutha Manipal Multicomponent (JAMM) isotherm, that can alleviate this problem. We first developed the JAMM multicomponent isotherm using our experimental data sets of arsenic and fluoride competitive adsorption on activated carbon. We then tested the JAMM multicomponent isotherm for a case study of cadmium and zinc competitive adsorption. Next, we further assessed the JAMM isotherm using another competitive adsorption case study of copper and chromium. Through extensive validation studies and error analysis, the JAMM isotherm was able to demonstrate its efficacy in predicting the adsorption behavior in several multicomponent adsorption systems accurately. The main advantage of JAMM isotherm over other multicomponent isotherms is that it utilizes and leverages the single-component adsorption parameters to simulate multicomponent isotherms. The proposed JAMM analytical isotherm model furthermore incorporates the interaction between the components, a mole fraction parameter, and a heterogeneity index, providing a more comprehensive modeling framework for multicomponent adsorption. The mole fraction term was introduced for the distribution of adsorption sites based on the relative number of molecules of each component. An additional term for interaction coefficient was introduced for the representation of interactions. During the validation of JAMM with three experimental case studies with negligible, small, and high competition systems of adsorbates, impressive predictions were exhibited, with the average normalized absolute percentage error as 6.05% and average R2 as 0.86, highlighting the model's robustness, versatility, and reliability. We propose that the new JAMM isotherm modeling framework might profoundly help in chemical engineering, environmental engineering, and materials science applications by providing a potent tool for analyzing and predicting multicomponent adsorption systems.

Treatment of industrial contaminants with zero-valent iron- and zero-valent aluminium-activated persulfate: a case study with 3,5-dichlorophenol and 2,4-dichloroaniline

Zero-valent iron (ZVI)- and zero-valent aluminium (ZVA)-activated persulfate (PS) oxidation procedure was applied to remove the industrial pollutants 3,5-dichlorophenol (3,5-DCP; 12.27 µM) and 2,4-dichloroaniline (2,4-DCA; 12.34 µM) from aqueous solutions. The effects of PS concentration and pH were investigated to optimize heterogeneous treatment systems. Negligible removals were obtained for both pollutants by individual applications of nanoparticles (1 g/L) and PS (1.00 mM). PS activation with ZVI resulted in 59% (1.00 mM PS; 1 g/L ZVI; pH 5.0; 120 min) and 100% (0.75 mM PS; 1 g/L ZVI; pH 5.0; 80 min) 3,5-DCP and 2,4-DCA removals, respectively. The ZVA/PS treatment system gave rise to only 31% 3,5-DCP (1.00 mM PS; 1 g/L ZVA; pH 3.0; 120 min) and 47% 2,4-DCA (0.25 mM PS; 1 g/L ZVA; pH 3.0; 120 min) removals. The pH decreases from 5.0 to 3.0 and from 3.0 to 1.5 enhanced contaminant removals for ZVI/PS and ZVA/PS treatments, respectively. Pollutant removal rates were in correlation with the consumption rates of the oxidants. Metal ion (Al, Fe) release increased in the presence of PS and with decreasing pH.

Synthesis of chitosan/γ-Fe2O3/fly-ash-cenospheres composites for the fast removal of bisphenol A and 2,4,6-trichlorophenol from aqueous solutions

The chitosan/fly-ash-cenospheres/γ-Fe(2)O(3) (CTS/γ-Fe(2)O(3)/FACs) magnetic composites were prepared by microemulsion process. The resulting composites were characterized by XRD, FT-IR, SEM, TGA, DTG and VSM, and the results indicated that CTS/γ-Fe(2)O(3)/FACs exhibited magnetic property (M(s)=6.553 emu g(-1)) and thermal stability, and composed of chitosan wrapping magnetic γ-Fe(2)O(3) and fly-ash-cenospheres (thickness of the cross-linked chitosan was about 5.2 μm). Then the CTS/γ-Fe(2)O(3)/FACs were employed as adsorbents for the fast removal of bisphenol A (BPA) and 2,4,6-trichlorophenol (TCP) from aqueous solutions. The adsorption performances of CTS/γ-Fe(2)O(3)/FACs were investigated by batch mode experiments with respect to pH, temperature, initial concentration, contact time and binary solution system. The Langmuir isotherm model was fitted to the equilibrium data better than the Freundlich model, and the kinetic properties were well described by the pseudo-second-order equation. The effects of binary solution systems also demonstrated that BPA adsorption onto CTS/γ-Fe(2)O(3)/FACs was more affected by the simultaneous presence of competitive phenolic compound than that of TCP. In addition, the resulting composite reusability without obviously deterioration in performance was demonstrated by at least three repeated cycles.

Competitive and complementary adsorption of bisphenol A and 17alpha-ethinyl estradiol on carbon nanomaterials

Competitive adsorption between organic chemicals is an important process affecting their environmental behavior and risk. Overlapping of adsorption sites between solutes was often emphasized in the literature. However, chemicals with different properties may complementarily occupy different sorption sites. The objective of this study was to test this hypothesis by collecting detailed information on competitive and accumulative adsorption of different chemicals on carbon nanomaterials (CNMs). Bisphenol A (BPA) and 17alpha-ethinyl estradiol (EE2) are different with regard to their hydrophobicity and molecular structures, and they were selected as model chemicals. The cumulative adsorption of both BPA and EE2 in bisolute adsorption experiments resulted in much higher total adsorption than in single-solute adsorption experiments. A new competitive-complementary adsorption concept was proposed. This information indicates that the modeling concept of competitive adsorption should be improved to better understand the fate and risk of both CNMs and organic chemicals.

Enhanced chlorophenol sorption of soils by rice-straw-ash amendment

Rice-straw burning is a common post-harvest practice on rice paddy land, which results in the accumulation of rice-straw ash (RSA) in paddy soil. Because the occurrence of RSA in soil may affect the fate and transport of contaminants, this study investigated the sorption of 3-chlorophenol (3-CP) on RSA and RSA amended soils to evaluate the sorptive properties of RSA in soils. The results showed that the sorption of 3-CP to RSA proceeds through a surface reaction rather than through partitioning and that the neutral form of 3-CP is preferentially sorbed to the surface when compared to the deprotonated anionic form of 3-CP. The addition of RSA to the soils enhanced the overall 3-CP sorption, indicating that RSA amendment may be applied to retard the movement of 3-CP in contaminated soils. As the RSA content in the soils was increased from 0% to 2%, the Langmuir sorption maximum of the soils increased from 18-80 to 256-274 mg kg(-1). Thus, RSA contributed more to the total sorption of the soils than other major components in the soils. Nonetheless, the 3-CP sorption of the soils containing RSA was less than the combination of pure RSA and the soils, thereby indicating that the 3-CP sorption of RSA was suppressed. This may be attributed to the competition of organic matter or other soil components for the surface binding sites of RSA.