Comparative study on the sorption capacity of cyhalofop Acid on polymerin, ferrihydrite, and on a ferrihydrite-polymerin complex

Removal of Agrochemicals from Waters by Adsorption: A Critical Comparison among Humic-Like Substances, Zeolites, Porous Oxides, and Magnetic Nanocomposites

The use of humic-like substances, zeolites, various porous oxides (i.e., Al, Fe, or Si oxides), and magnetic nanocomposites in the adsorption of agrochemicals from water was critically reviewed. Firstly, the adsorbents were characterized from the structural, textural, and physico-chemical points of view. Secondly, the fundamental aspects of the adsorption of various agrochemicals on the solids (dependence on pH, kinetics, and isotherm of adsorption) were studied and interpreted on the basis of the adsorbent features. Thirdly, iterative processes of agrochemical removal from water by adsorption on the reported solids were described. In particular, in some cases the residual concentration of agrochemicals in water was lower than the maximum concentration of agrochemicals that the Italian regulations allow to be released in wastewater, surface waters, or sink water.

Gibberellic acid surface complexation on ferrihydrite at different pH values: Outer-sphere complexes versus inner-sphere complexes

Gibberellic acid (GA₃) is a widely used plant growth regulator and environmental toxin especially in China, but no study has focused on the mechanism of the interactions between GA₃ and minerals/soils. In this study, the GA₃ surface complexation mechanism on ferrihydrite (Fh) was investigated by combining sorption-desorption batch experiments with Fourier transform infrared (FTIR) spectroscopy and moving-window two-dimensional (MW2D) correlation spectroscopy. The results showed that the Fh-GA₃ surface complexes and retention after desorption depended strongly on the pH. For pH > 2.9, electrostatic interactions played an important role in GA₃ sorption on Fh in two ways. One was directly forming an outer-sphere complex by electrostatic attraction to a minor extent. The other was acting as a driving force to facilitate the formations of surface hydration-shared ion pair (mainly formed at pH < 5.7) and solvent-surface hydration-separated ion pair (mainly formed at pH > 5.7). Those three outer-sphere complexes were partially reversible according to the high total desorption percentage of GA₃ (69-80%). For pH ≤ 2.9, the generated monodentate complex was observed and increased with decreasing pH, which showed more retention on Fh after desorption than the outer-sphere complexes according to the lower total desorption percentage of GA₃ (37%). At the typical soil and groundwater pH values (4.5-9), the outer-sphere complexes predominate, where GA₃ could be out-competed by nitrate and other anions and then easily desorbed from Fh. This increases the risk of groundwater contamination.

Sorption specificity and desorption hysteresis of gibberellic acid on ferrihydrite compared to goethite, hematite, montmorillonite, and kaolinite

The pesticide gibberellic acid (GA₃) is a potential endocrine disruptor and environmental toxin; therefore, research into its environmental fate is warranted. Batch studies were conducted to investigate the sorption and desorption characteristics of GA₃ on aquifer media. The results demonstrated special sorption characteristic of GA₃ on ferrihydrite compared to goethite, hematite, montmorillonite, and kaolinite, where the sorption kinetics of GA₃ on ferrihydrite was fitted well with the pseudo-second-order, Elovich, and intra-particle diffusion models. The sorption kinetics of GA₃ on ferrihydrite indicated an initial high sorption rate followed by a slow reaction process. The initial high GA₃ sorption rate may be related to electrostatic sorption and surface complexation reactions on the outer surfaces and at the macropore entrances of ferrihydrite. While the slow step was controlled by GA₃ diffusion into mesopore of ferrihydrite. Analysis of the desorption hysteresis indicated a high hysteresis index (HI) ranging from 0.68 to 17.32, and a low desorption percentage ranging from 18 to 48%. After sufficient desorption, the calculated maximum residual GA₃ quantity due to surface complexation reactions with the ferrihydrite coordinated unsaturated sites was 9.05 ± 0.12 mg g^-1. The calculated maximum quantity of GA₃ trapped within the mesopore was 16.23 ± 0.91 mg g^-1. Graphical Abstract Schematic overview of GA₃ sorption and desorption on five minerals in groundwater.

Polymerin and lignimerin, as humic acid-like sorbents from vegetable waste, for the potential remediation of waters contaminated with heavy metals, herbicides, or polycyclic aromatic hydrocarbons

Polymerin is a humic acid-like polymer, which we previously recovered for the first time from olive oil mill waste waters (OMWW) only, and chemically and physicochemically characterized. We also previously investigated its versatile sorption capacity for toxic inorganic and organic compounds. Therefore, a review is presented on the removal, from simulated polluted waters, of cationic heavy metals [Cu(II), Zn, Cr(III)] and anionic ones [Cr(VI)) and As(V)] by sorption on this natural organic sorbent in comparison with its synthetic derivatives, K-polymerin, a ferrihydrite-polymerin complex and with ferrihydrite. An overview is also performed of the removal of ionic herbicides (2,4-D, paraquat, MCPA, simazine, and cyhalofop) by sorption on polymerin, ferrihydrite, and their complex and of the removal of phenanthrene, as a representative of polycyclic aromatic hydrocarbons, by sorption on this sorbent and its complexes with micro- or nanoparticles of aluminum oxide, pointing out the employment of all these sorbents in biobed systems, which might allow the remediation of water and protection of surface and groundwater. In addition, a short review is also given on the removal of Cu(II) and Zn from simulated contaminated waters, by sorption on the humic acid-like organic fraction, named lignimerin, which we previously isolated for the first time, in collaboration with a Chilean group, from cellulose mill Kraft waste waters (KCMWW) only. More specifically, the production methods and the characterization of the two natural sorbents (polymerin and lignimerin) and their derivatives (K-polymerin ferrihydrite-polymerin, polymerin-microAl(2)O(3) and -nanoAl(2)O(3), and H-lignimerin, respectively) as well as their sorption data and mechanism are reviewed. Published and original results obtained by the cyclic sorption on all of the considered sorbents for the removal of the above-mentioned toxic compounds from simulated waste waters are also reported. Moreover, sorption capacity and mechanism of the considered compounds on polymerins and lignimerins are evaluated in comparison with other known natural sorbents, especially of humic acid nature and other organic matter. Some of their technical aspects and relative costs are also considered. Finally, the possible large-scale application of the considered sorption systems for water remediation is briefly discussed.