Isotherm and kinetic studies on the adsorption of humic acid molecular size fractions onto clay minerals

Regulation of SiO2 Nanoparticles on the Adsorptive Fractionation of Dissolved Organic Matter by Goethite

“…Studies have indicated that the adsorption of NOM on iron-bearing minerals is predominantly regulated by ligand exchange and/or electrostatic interactions with the surface hydroxylated groups. , At first, a decrease in the adsorption of DOM as the pH increases can be partly associated with the electrostatic interactions due to the less positively charged on the goethite surface under circumneutral conditions (Figure S2). In addition, this pH-dependent adsorption of DOM is consistent with the decrease of symmetric carboxylic stretching for DOM-reacted goethite (peak at 1393–1400 cm –1 shifted from 1408 cm –1 for DOM) (Figure ), suggesting that ligand exchange of carboxyl to hydroxyl groups on the iron oxide surface governs the adsorption of DOM in a low pH system. ,, However, a higher OM adsorption capacity at pH 8 (<pH IEP of goethite) relative to that at pH 6.5 can be ascribed that some active phenols with ortho-positioned hydroxyls (e.g., plant-derived polyphenols) can play a significant role in OM adsorption via ligand exchange at alkaline pH, ,− as evidenced by the elevated stretching vibrations of phenolic hydroxyl (−OH) groups for DOM-reacted goethite (peak at 3428 cm –1 from 3421 cm –1 for DOM) at pH 8 (Figure ). Besides, the strengthening of carbohydrate-like hydroxyl for DOM-reacted goethite (1110–1118 cm –1 bands shifted from 1039/1089 cm –1 for DOM) from pH 5 to pH 8 (Figure ) provides evidence that plant-derived carbohydrates are also linked to more OM adsorption on the hydroxylated mineral surface (e.g., goethite) at near pH IEP of minerals. , Meanwhile, the adsorption of DOM on SiO 2 NPs was only slightly decreased (2.08–5.37%) from pH 5 to 8 (Table S3), likely due to the attenuated aggregation behavior (particle sizes refer to Figures S3 and S4) partially offsetting the effects of decreased high-energy hydroxyl groups on SiO 2 NPs from acidic to alkaline conditions.…”

“…Compared with goethite or SiO 2 NPs, the coexisting SiO 2 NPs strongly hindered the highly and completely sorbed molecules of PCA and aromatic compounds by the goethite-SiO 2 NPs complex at all pHs, and reduced the highly and completely sorbed molecules of all compounds at pH 5, while it significantly increased the high and complete adsorption of Aliphatic_No N and Aliphatic_N compounds at pH 6.5 and increased the high and complete adsorption of lignin-like, Aliphatic_No N and carbohydrate-like compounds at pH 8 (Table S5). These results could be explained that the coexisting of SiO 2 NPs reduced the exchange of minerals surface hydroxyl moieties with carboxylic groups by covering mineral surface hydroxyls and increasing electron densities (or negatively charged) of the bond at the mineral-water interface under different pH conditions. , The SiO 2 nanoparticle surfaces are three-dimensional network structures with diverse hydroxyl and more unsaturated chemical bonds, and can easily disperse on goethite surface due to a smaller aggregate size at high pH conditions and the high-energy adsorption sites become completely occupied, resulting in the hydrophobic partitioning and hydrogen bonding of highly unsaturated phenolic/aliphatic compounds in the DOM controls the adsorption at the mineral-water interface under circumneutral and acidic conditions.…”

“…In the terrestrial and aquatic systems, the interaction between natural organic matter (NOM) and iron (hydroxyl)­oxides plays a critical role in its biogeochemical cycling. , Iron (hydroxyl)­oxides, as an efficient “rusty sink”, have a greater potential to trap the terrestrially derived NOM compared to the clay aluminosilicates, and they can improve the stability of NOM by forming complexes and coprecipitates with minerals, thus mediating the long-term carbon storage or toward gaseous release and altering the bioavailability of contaminants and nutrients. , Dissolved organic matter (DOM), as a heterogeneous continuum of organic substances with diverse functionalities, contains the most active fractions of NOM that can help enhance its stability via the formation of organo-mineral complexes in soil and water environments. Iron oxides and oxyhydroxides can selectively sorb specific components in DOM through mechanisms such as ligand exchange, hydrophobic partitioning, H-bonding, and electrostatic interaction, − resulting in its molecular fractionation. , Molecular fractionation at the mineral-water interface is usually driven by the compositional diversity and molecular properties of DOM. DOM molecules with greater affinity to iron-bearing mineral matrices of varying crystallinity, often high molecular weight, highly unsaturation or oxygenated moieties, can be preferentially bound, ,, while the hydrophobic aliphatic compounds tend to remain in soil solutions or natural waters, ultimately having a bottom-up effect on ecosystem structures and functions .…”

Production of bio-coal based on empty fruit bunches by torrefaction method with fixed bed and tubular continuous reactors

“…Peat water is acidic due to the presence of humic acid and fulvic acid [13]. As a result, peat water is effective in dissolving potassium and chlorine because humic acid has the ability to adsorb minerals [14], making it more efficient in dissolving these elements compared to regular water. Several studies have been carried out previously to reduce the potassium and chlorine content in EFB.…”