Humic Acid Aggregates Research Articles

Systematic studies on the binding of metal ions in aggregates of humic acid: Aggregation kinetics, spectroscopic analyses and MD simulations

The binding of metal ions with humic acid (HA) plays an important role in the aggregation of HA and the migration of metal ions in the environments. The effects of common cations (Na+, Mg2+, Ca2+ and Al3+) and heavy metal ions (Ag+, Cd2+, Cu2+, Cr3+ and Eu3+) on the aggregation of HA were investigated systematically by aggregation kinetics, spectroscopic techniques and molecular dynamic (MD) simulations. The critical coagulation concentration (CCC) of mono-, di- and trivalent cations could be predicted by the Schulze-Hardy rule. The aggregation of HA in the presence of Na+ and Ag+ was mainly due to the reduction of repulsive force and the hydrogen bonds between HA molecules. While the complexation of di- and trivalent cations with carboxylic/phenolic groups, or the cation-π interactions enhanced the intra- or inter-molecular bridges in HA and then contributed greatly to the aggregation of HA. Heavy metal ions could easily pass through the electric double-layer of HA compared with common cations. MD simulations further signified the strong aggregation ability of HA molecules in solutions containing high valence metal ions. These findings are important for understanding not only how the influence of metal ions on the aggregation of HA, but also the conditions which ions more efficient for aggregation.

A novel gold nanocomposite membrane with enhanced permeation, rejection and self-cleaning ability

The trade-off relationship between permeability, selectivity, and antifouling capability of nanocomposite membranes is the focal point of effective membrane technology. This study introduces a new gold nanocomposite membrane with enhanced antifouling behavior and permeability, as well as improved rejection capability for water treatment. Different (0.5, 1 and 2 wt%) concentrations of citrate-stabilized (coating) gold nanoparticles (CT-GNPs) having a core size of 50 nm were embedded into the polysulfone (PSF) membranes by the phase inversion method, resulting in alterations on PSF membrane performance. The intrinsic physicochemical properties and operational ability of all gold nanocomposite membranes were evaluated with regard to the self-cleaning, flux and selectivity criteria for water purification process. The PSF/0.5% GNPs demonstrated the optimal pore structure, morphology, and electrochemical surface properties among the gold nanocomposite and pure PSF membranes. The negative surface charge and the super hydrophilic functional group of CT-GNPs enhanced the permeation (at least three times in comparison with pure PSF membranes) and rejection ability of nanocomposite membranes. In addition, CT-GNPs showed digestive behavior towards humic acid (HA), a natural foulant, that significantly enhanced the antifouling ability (FRR = 95%) of the gold nanocomposite membranes by degrading the HA formed cake layer on the membrane surface and fragmenting the large HA aggregates that blocked the pores. The degradation of HA compounds by the embedded CT-GNPs occurred during the filtration process at room temperature and under the regular visible light. The stability of embedded GNPs into the polymeric matrix of membranes was evaluated at static and dynamic conditions for several days, and no release of CT-GNPs was observed.

New insights into the humic acid fouling mechanism of ultrafiltration membranes for different Ca2+ dosage ranges: results from micro- and macro-level analyses.

To reveal the mechanisms of the influence of Ca2+ on membrane fouling with humic acid (HA), the adhesion forces of HA with both other HA molecules and the membrane, the HA fouling layer structure, HA fouling experiments, and the HA rejections at a wide range of Ca2+ dosages were investigated. The results indicated that the effect of Ca2+ on HA fouling can be divided into three stages. At lower ionic strength (IS) of CaCl2, the change in electrostatic forces is the main factor in controlling HA fouling behavior; i.e., increasing Ca2+ dosages resulted in more serious membrane fouling. When the IS of CaCl2 reached 10 mM, HA aggregates became the dominant factor in the fouling process, which could result in a porous fouling layer accompanied by less membrane fouling. Interestingly, much weaker membrane fouling was observed when the IS increased to 100 mM and the HA rejection began to decline. This was because a stronger hydration repulsion force was generated, which could weaken the compactness of the fouling layer and the adhesion forces of HA with both the membrane and HA, while enabling smaller-sized HA to pass more easily into the permeate, which led to less membrane fouling and a lower HA rejection.

Efficient Separation of Water-Soluble Humic Acid Using (3-Aminopropyl)triethoxysilane (APTES) for Carbon Resource Recovery from Wastewater

Humic substances are produced during the microbial degradation of biomolecules and should be recycled because they are an abundant source of carbon, hydrogen, oxygen, and nitrogen. Herein, (3-aminopropyl)triethoxysilane (APTES) was first used to recover carbon-rich water-soluble humic acid (HA) from wastewater, and the operational parameters (i.e., pH, solution temperature, APTES dosage, reaction time, and initial HA concentration) were optimized for separation efficiency. The results showed that the optimal HA separation efficiency (96.7%) could be achieved at an initial HA concentration of 250 mg/L, APTES dosage 4 mL/L, equilibration time 10 min, pH 3.0, and temperature 35 °C. Furthermore, cations (Mg2+ and Ca2+) led to a remarkable separation of HA, while anions (CO32– and SO42–) weakened the aggregation and deposition of HA. Mechanism analysis unveiled that ladderlike oligomeric aminosilanes (LAOAs) were generated by the hydrolysis, condensation, and self-assembly of APTES. The LAOAs were involved in ...

A multi-method analysis of the interaction between humic acids and heavy metal ions

ABSTRACTUnderstanding of the interaction between humic acids (HAs) and heavy metal ions (HMIs) is essential for the assessment of environmental and health risks of HMIs. Multiple analyses, including fluorescence quenching of HAs; solution pH, zeta potential, and hydrodynamic size changes; and coprecipitation of HAs and HMIs, were carried out to investigate the interaction between two HAs and four HMIs (Ag+, Pb2+, Cd2+, and Cr3+). The HA-HMI interaction mainly included chemical complexation, H+-HMI exchange, electrostatic attraction, and flocculation. The chemical complexation between HAs and HMIs revealed by the Stern–Volmer quenching constant was ordered as Ag < Cd < Pb < Cr. HMIs replaced protons in the acidic functional groups of HAs and thus lowered the pH of the solution. The electrostatic interaction between the negatively charged HAs and HMIs reduced the electronegativity of HAs. Interaction with HMIs, especially the high-valent ions, induced aggregation of HAs, causing precipitation of both HAs and HMIs in the sorptive solution. Cr3+ flocculated and precipitated HAs, but at high concentrations, it reversed the surface charge of HAs and resuspended them. The HA-HMI interaction increased as the HA acidity and solution pH increased.

Swelling and aggregation of Leonardite upon pH change and PbII binding: an AFM study

Environmental contextNatural organic materials, such as humic substances, play key roles in the binding and environmental fate of metals. We study the interaction of protons and metal ions with humic acids, and show changes to the mechanical properties of the particles and their capability to fix metal pollutants. The results will help refine current models of metal behaviour in the environment. AbstractThe swelling and aggregation of Leonardite humic acid, due to acid–base and PbII binding interactions, was studied through atomic force microscopy (AFM) tapping mode measurements and correlated with potentiometric experiments. These experiments allowed determination of parameters for the non-ideal competitive adsorption (NICA)-elastic polyelectrolyte network (EPN) model, which predicts size and electrostatic potential changes. AFM observations showed growth of agglomerates at low pH values. Height distribution analysis allowed discrimination of single particles from agglomerates. The size of individual particles increased slightly with pH increase. Agglomeration was evaluated through the dispersity, which increased at pH &lt; 5, concomitant with a decrease of the electrostatic repulsion and an increase of protonated carboxylic groups, thus the agglomeration is attributed to both factors. In the presence of PbII, agglomeration is observed to rise strongly with the increase in metal concentration, which is attributed to bridging of humic particles by PbII ions. The AFM ex situ results suggest consistency between NICA-EPN predictions and experimental behaviour.

Application of Turbiscan in the homoaggregation and heteroaggregation of copper nanoparticles

With the development of industries, copper nanoparticles (Cu NPs) have been abundantly discharged into natural water and may threaten the safety of aquatic environments. The stability (such as homoaggregation and heteroaggregation) of Cu NPs in aqueous phase may affect their toxicity. Turbiscan, including three kinds of data processing methods (transmitted intensity (T), variation of average transmitted intensity (ΔT) and Turbiscan stability index (TSI), were used to investigate the homoaggregation and heteroaggregation of Cu NPs with humic acid (HA) and kaolin in aqueous phase. T and TSI were used to analyze Cu NPs-kaolin and Cu NPs-HA-kaolin systems, respectively, whereas T and ΔT were used to analyze Cu NPs and Cu NPs-HA systems. Results showed that the stability of the system is influenced by the dissolution and sedimentation of Cu NPs, and the aggregation and sedimentation of Cu NPs, HA and kaolin. When pH is 4, the dissolution of Cu NPs is the main factor affecting the system stability. Kaolin may reduce the stability of system by sedimentation or impeding the dissolution of Cu NPs. When pH is 8, the aggregation and sedimentation of Cu NPs mainly affect the system stability. Kaolin renders the system unstable by promoting the aggregation of Cu NPs. In addition, HA improves the stability of the system by inhibiting the aggregation of Cu NPs and kaolin when pH=4 and 8. Ionic strength reduces the stability of system by condensing electric double layer. Therefore, Turbiscan can be used to study both homoaggregation and heteroaggregation in a relatively long period (12h), and three kinds of data processing methods can be applied based on the properties of the samples.

Interaction between Dissolved Organic Matter and Long-Chain Ionic Liquids: A Microstructural and Spectroscopic Correlation Study.

The production and use of ionic liquids (ILs) increase the potential risk after their emission into the environment. After entering the environment, ILs will readily interact with dissolved organic matter (DOM), and their environmental behavior will be impacted by DOM, which is abundant in the environment and has various functional groups. However, to date, the interaction between DOM and ILs, especially long-chain ILs, remains unclear. In this work, the interaction between long-chain ILs and humic acid (HA), a representative DOM, was investigated using synchronous fluorescence, Fourier transform infrared spectroscopy, dynamic light scattering, and zeta potential techniques, which were integrated with two-dimensional correlation spectroscopy (2DCOS), hetero-2DCOS, and perturbation-correlation moving-window analyses. The results show that cation exchange by the carboxylic groups in humic-like fractions was primarily responsible for interaction at low IL concentrations. As a result, the decrease in electrostatic repulsion and the increase in hydrophobicity facilitated the loose aggregation of HA. With an increase in IL concentration, the aromatic and carbonyl groups were involved in the interaction via the π-π interaction and dipole-dipole interaction, respectively, which resulted in the disruption of the intramolecular hydrogen bond and promoted the compaction of HA under the hydrophobic effect. The intensity transition sequence of various groups in HA was elucidated more specifically by 2DCOS. With these results, a comprehensive view of the structural changes of DOM in its IL-binding process was obtained, and the fate and environmental impact of ILs could be better understood. Furthermore, the superior potential of such an integrated approach in investigating the complex interactions in the environment was also demonstrated.

Wheat straw biochar-supported nanoscale zerovalent iron for removal of trichloroethylene from groundwater.

This study synthesized the wheat straw biochar-supported nanoscale zerovalent iron (BC-nZVI) via in-situ reduction with NaBH4 and biochar pyrolyzed at 600°C. Wheat straw biochar, as a carrier, significantly enhanced the removal of trichloroethylene (TCE) by nZVI. The pseudo-first-order rate constant of TCE removal by BC-nZVI (1.079 h−1) within 260 min was 1.4 times higher and 539.5 times higher than that of biochar and nZVI, respectively. TCE was 79% dechlorinated by BC-nZVI within 15 h, but only 11% dechlorinated by unsupported nZVI, and no TCE dechlorination occurred with unmodified biochar. Weakly acidic solution (pH 5.7–6.8) significantly enhanced the dechlorination of TCE. Chloride enhanced the removal of TCE, while SO42−, HCO3− and NO3− all inhibited it. Humic acid (HA) inhibited BC-nZVI reactivity, but the inhibition decreased slightly as the concentration of HA increased from 40 mg∙L-1 to 80 mg∙L-1, which was due to the electron shutting by HA aggregates. Results suggest that BC-nZVI was promising for remediation of TCE contaminated groundwater.

Using flow field-flow fractionation (Fl-FFF) for observation of salinity effect on the size distribution of humic acid aggregates

ABSTRACTFlow field-flow fractionation (Fl-FFF) was used to investigate the effect of salinity on the size distribution of humic acid (HA) aggregates in estuarine water. In water with high salinity as estuarine water, size distributions were slightly broadened with increasing contact time between HA and estuarine water. At the longest contact times (89 days) and highest salinity value (28 psu, g kg−1), the peak maxima were observed at 1.7 and 8.6 nm when detected at 254 nm, and at 1.9 and 9.1 nm when detected at 400 nm. In addition, Fl-FFF with an inductively coupled plasma mass spectrometry was applied to examine the effect of salinity on the size distribution of Cd, Ce, Cu, Mn and Pb-binding HA aggregates in estuarine water with different salinity values. At 1 day contact time, the peak maxima of Cd, Ce, Cu, Mn and Pb-binding HA aggregates in water with increased salinity values were increased and gave the larger breadth of size distribution. The larger size fraction of HA aggregates showed more affinity for Pb, Cd, Ce and Mn than Cu whereas the smaller size fraction of humic aggregates showed preferential binding towards Cu.

Integrated pyrolucite fluidized bed-membrane hybrid process for improved iron and manganese control in drinking water

Newly developed ceramic membrane technologies offer numerous advantages over the conventional polymeric membranes. This work proposes a new configuration, an integrated pyrolucite fluidized bed (PFB)-ceramic MF/UF hybrid process, for improved iron and manganese control in drinking water. A pilot-scale study was undertaken to evaluate the performance of this process with respect to iron and manganese control as well as membrane fouling. In addition, the fouling of commercially available ceramic membranes in conventional preoxidation-MF/UF process was compared with the hybrid process configuration. In this regard, a series of experiments were conducted under different influent water quality and operating conditions. Fouling mechanisms and reversibility were analyzed using blocking law and resistance-in-series models. The results evidenced that the flux rate and the concentration of calcium and humic acids in the feed water have a substantial impact on the filtration behavior of both membranes. The model for constant flux compressible cake formation well described the rise in transmembrane pressure. The compressibility of the filter cake substantially increased in the presence of 2 mg/L humic acids. The presence of calcium ions caused significant aggregation of manganese dioxide and humic acid which severely impacted the extent of membrane fouling. The PFB pretreatment properly alleviated membrane fouling by removing more than 75% and 95% of iron and manganese, respectively.

Role of Humic Substances on Cr(VI) Removal from Groundwater with Pyrite

Groundwater composition may have a pronounced impact on long-term performance of permeable reactive barriers (PRBs). Here, batch and column experiments were conducted to investigate the effects of humic acid (HA) on Cr(VI) removal by pyrite in systems containing cations such as Ca2+ and Mg2+. HA was observed to have inhibitory effect on Cr(VI) uptake by pyrite under the experimental conditions studied (e.g., pH 3 to 8). HA sorbed onto pyrite surface and thus (1) competed against Cr(VI) for pyritic surface sites and/or (2) increased electrostatic repulsion between Cr(VI) and pyrite. In systems with HA and Ca2+/Mg2+, the Cr(VI) uptake by pyrite decreased drastically relative to HA alone due to the aggregation of HA with Ca2+/Mg2+. The formation of such HA aggregates/precipitates blocked Cr(VI) ions to reach its binding sites, thereby resulting in a substantial decrease in Cr(VI) uptake. Overall, the results have major implications for proper design and operation of PRBs with pyrite as the reactive material.

Effect of Natural Organic Matter on Plutonium Sorption to Goethite.

The effect of citric acid (CA), desferrioxamine B (DFOB), fulvic acid (FA), and humic acid (HA) on plutonium (Pu) sorption to goethite was studied as a function of organic carbon concentration and pH using batch sorption experiments at 5 mgC·L-1 and 50 mgC·L-1 natural organic matter (NOM), 10-9-10-10 M 238Pu, and 0.1 g·L-1 goethite concentrations, at pH 3, 5, 7, and 9. Low sorption of ligands coupled with strong Pu complexation decreased Pu sorption at pH 5 and 7, relative to a ligand-free system. Conversely, CA, FA, and HA increased Pu sorption to goethite at pH 3, suggesting ternary complex formation or, in the case of humic acid, incorporation into HA aggregates. Mechanisms for ternary complex formation were characterized by Fourier transform infrared spectroscopy in the absence of Pu. CA and FA demonstrated clear surface interactions at pH 3, HA appeared unchanged suggesting HA aggregates had formed, and no DFOB interactions were observed. Plutonium sorption decreased in the presence of DFOB (relative to a ligand free system) at all pH values examined. Thus, DFOB does not appear to facilitate formation of ternary Pu-DFOB-goethite complexes. At pH 9, Pu sorption in the presence of all NOM increased relative to pH 5 and 7; speciation models attributed this to Pu(IV) hydrolysis competing with ligand complexation, increasing sorption. The results indicate that in simple Pu-NOM-goethite ternary batch systems, NOM will decrease Pu sorption to goethite at all but particularly low pH conditions.

Investigation of UV/H2O2 pretreatment effects on humic acid fouling on polysulfone/titanium dioxide—And polysulfone/multiwall carbon nanotube—Nanocomposite ultrafiltration membranes

Membrane fouling is an important concern for membrane separation technology. Preparation of the feed before entering into the membrane and physicochemical modifications of membrane are both important approaches toward enhancing the permeability and separation in membrane processes. The present report combines both approaches. In terms of membrane characterization, scanning electron microscopy (SEM) images showed that the addition of titanium dioxide (TiO2) nanoparticles and multiwall carbon nanotube (MWCNT) resulted in increased pore numbers at the top surface and more interconnected pores in the porous membrane structure. The surface hydrophilicity and porosity of the PSF/TiO2 and PSF/MWCNT increased compared with pure PSF membranes. PSF/TiO2 nanocomposites showed just 10% flux decline and improved 95% flux recovery ratio (FRR%). UV/H2O2 pretreatment changed the physicochemical properties of humic acid (HA) aggregates by reducing the super‐micrometer size range (&gt;1 μm) aggregates to a bimodal distribution of two submicrometer size ranges &lt;1 μm (10–100 nm and 100–1000 nm) and increased the zeta potential of HA solution due to the production of new functional groups. The oxidation pretreatment alone improved flux decline at 120 min from 21% to 80% and increased the FRR from 58% to 80% for the pure PSF. The oxidative pretreatment also improved purification for the PSF/TiO2 nanocomposite membranes. The flux decline improved from 81% to 95% with only a slight improvement on the 94% FRR increasing to about 99% FRR. The FRR in the case of PSF/MWCNT actually declined with the pretreatment. The hybrid process of UV/H2O2 pretreatment and PSF/TiO2 nanocomposite membranes exhibited optimal permeability and antifouling properties. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 27–37, 2017

Dynamic modeling of copper bioaccumulation by Mytilus edulis in the presence of humic acid aggregates

Copper (Cu) complexation by humic acids (HA) is expected to decrease Cu bioavailability for aquatic organisms as predicted by metal bioavailability models, such as the biotic ligand model (BLM). This has been confirmed for non-feeding organisms such as marine invertebrate embryos or microalgae, but for filter-feeding organisms such as the mussel Mytilus edulis, Cu bioaccumulation was higher in the presence of HA, suggesting that part of the Cu-HA complexes were available for uptake. This study shows the dynamic modeling of Cu accumulation kinetics in the gills and rest of the soft-body of M. edulis in the absence and presence of HA. Assuming that truly dissolved Cu is taken in the body via the gills following BLM premises, and including uptake of Cu-HA aggregates via the gut into the rest compartment, this two-compartmental model could successfully explain the observed bioaccumulation data. This modeling approach gives strong evidence to the hypothesis that Cu-HA aggregates can be ingested by mussels leading to Cu absorption in the digestive system.

Study on PVDF-TiO2 mixed-matrix membrane behaviour towards humic acid adsorption

Despite the expansion and successful application of membrane systems in water industry, membrane fouling which predominantly caused by the irreversible adsorption is still a critical problem. The objective of this work is to study the adsorptive behaviour of membrane for the removal of humic acid (HA). Apart of neat membrane that has very often been used in adsorption study, PVDF-TiO2 mixed-matrix membranes (MMMs) with varied titanium dioxide (TiO2) concentration (0.001g/L, 0.01g/L, and 0.1g/L) were explored in the present work. A dynamic stirring cell with continuous stirring for 24h at 250rpm was applied in this study. Different operating parameters such as initial HA solution concentration, calcium chloride (CaCl2) concentration, and HA solution pH were performed in this study. HA adsorption ratio in each single batch of experiment was determined by measuring the HA adsorbance as a function of time. The results, interpreted in terms of adsorption ratio (A/A0) yield severe HA adsorption at low pH and high initial HA solution concentration. In addition, it was found that, increased CaCl2 concentration reduces the electrostatic repulsion between HA aggregates and membrane surface, consequently appears to be more adapted to HA adsorption.

Humic acid fouling mitigation by ultrasonic irradiation in membrane distillation process

A novel ultrasonic assisted direct contact membrane distillation hybrid process was designed and the effect of ultrasonic irradiation on humic acid (HA) fouling mitigation during membrane distillation process was investigated. Although permeate flux declines were negligible (less than 5%) for the ranges of HA concentration studied, ultrasonic irradiation could enhance the permeate flux more than 30% without destroying HA rejection. The higher the concentration factor was, the larger the ultrasonic enhancement of permeate flux could be obtained. Severe permeate flux decline can be found when CaCl2 was added into the HA solution. The presence of Ca2+ would aggravate HA organic fouling phenomenon and resulted in a thick and dense HA fouling layer on membrane surface. The HA fouling increased heat transfer resistance and reduced the pores available for vapor transfer, both the permeate flux and thermal efficiency of the FIFE membrane declined. Under ultrasonic irradiation, ultrasonic wave refreshed the liquid-membrane interface continuously and alleviated the deposition of HA aggregates. Therefore, although there were still some HA fouling scattered on membrane surface, most of the membrane pores could be kept open and clean, the relative permeate flux can maintain above 94% and was hardly affected by concentration factor increasing. (C) 2015 Elsevier B.V. All rights reserved.

Conductivity-Dependent Flow Field-Flow Fractionation of Fulvic and Humic Acid Aggregates

Fulvic (FAs) and humic acids (HAs) are chemically fascinating. In water, they have a strong propensity to aggregate, but this research reveals that tendency is regulated by ionic strength. In the environment, conductivity extremes occur naturally—freshwater to seawater—warranting consideration at low and high values. The flow field flow fractionation (flow FFF) of FAs and HAs is observed to be concentration dependent in low ionic strength solutions whereas the corresponding flow FFF fractograms in high ionic strength solutions are concentration independent. Dynamic light scattering (DLS) also reveals insight into the conductivity-dependent behavior of humic substances (HSs). Four particle size ranges for FAs and humic acid aggregates are examined: (1) &lt;10 nm; (2) 10 nm–6 µm; (3) 6–100 µm; and (4) &gt;100 µm. Representative components of the different size ranges are observed to dynamically coexist in solution. The character of the various aggregates observed—such as random-extended-coiled macromolecules, hydrogels, supramolecular, and micellar—as influenced by electrolytic conductivity, is discussed. The disaggregation/aggregation of HSs is proposed to be a dynamic equilibrium process for which the rate of aggregate formation is controlled by the electrolytic conductivity of the solution.

Effects of ionic strength and cationic type on humic acid facilitated transport of tetracycline in porous media

The occurrence of antibiotics in subsurface environments is increasingly reported recently in addition to the widespread distribution in surface waters. However, the mechanisms governing the transport of antibiotics from surface into subsurface are not well understood. In this study, the transport of tetracycline in saturated sand columns were investigated in the presence and absence of humic acid (HA) at different ionic strengths and cationic types. NaCl (0–0.1M) and CaCl2 (0–0.1M) were used as representatives of mono- and divalent cations in subsurface. The presence of HA moderately facilitated the transport of tetracycline in sand columns. The presence of Na+ inhibited the transport of tetracycline and HA through increasing the deposition of HA aggregates on the sands. The inhibition increased slightly with the increase in Na+ concentration from 0 to 0.1M. In contrast, the presence of Ca2+ dramatically inhibited the transport of tetracycline and HA even at a low concentration of 0.001M, which was attributed to the increased aggregation of HA and the greater electrostatic attractive interactions. Results from this study improve our understanding on the penetration of antibiotics from surface into subsurface waters and the transport of antibiotics in saturated aquifers at environmentally relevant conditions.

Spontaneous aggregation of humic acid observed with AFM at different pH

Atomic force microscopy in contact (AFM-C) mode was used to investigate the molecular dynamics of leonardite humic acid (HA) aggregate formed at different pH values. HA nanoparticles dispersed at pH values ranging from 2 to 12 were observed on a mica surface under dry conditions. The most clearly resolved and well-resulted AFM images of single particle were obtained at pH 5, where HA appeared as supramolecular particles with a conic shape and a hole in the centre. Those observations suggested that HA formed under these conditions exhibited a pseudo-amphiphilic nature, with secluded hydrophobic domains and polar subunits in direct contact with hydrophilic mica surface. Based on molecular simulation methods, a lignin–carbohydrate complex (LCC) model was proposed to explain the HA ring-like morphology. The LCC model optimized the parameters of β-O-4 linkages between 14 units of 1–4 phenyl propanoid, and resulted in an optimized structure comprising 45–50 linear helical molecules looped spirally around a central cavity. Those results added new insights on the adsorption mechanism of HA on polar surfaces as a function of pH, which was relevant from the point of view of natural aggregation in soil environment.