HA Concentration Research Articles

Interactions of CeO2 nanoparticles with natural colloids and electrolytes impact their aggregation kinetics and colloidal stability

The aggregation kinetics and colloidal stability of CeO2-NPs in the presence of monovalent or divalent electrolytes, as well as inorganic (kaolin and goethite) and organic (humic acid, HA) colloids were evaluated using time-resolved dynamic light scattering, advanced spectroscopic tools, and theoretical calculations. Critical coagulation concentrations for CeO2-NPs were generally lower in CaCl2 than that in NaCl electrolyte. The negatively charged kaolin accelerated CeO2-NPs aggregation due to electrostatic attraction, whilst opposite phenomenon was observed for the positively charged goethite in NaCl solution. In CaCl2 solution, goethite destabilized CeO2-NPs because of its well-crystal structure and specific adsorption of Ca2+. The presence of 0.1 mg C/L HA decreased the surface charge of CeO2-NPs, resulting in lower critical coagulation concentrations. Increasing the HA concentration from 0.1 to 1 mg C/L improved CeO2-NPs stability, mainly via electrostatic and steric repulsion. The Ca2+-bridging and complexation contributed significantly to CeO2-NPs aggregation. Additional aggregation experiments in seven natural waters revealed that CeO2-NPs remained stable in water types with high contents of organic colloids and low levels of salts, thus having higher transport potential. These findings provided new insights into the interactive influence of naturally occurring colloids and ions on the heteroaggregation behavior and fate of CeO2-NPs.

The separation of microscale HA in aqueous solution by foam separation technique

Abstract Hyaluronic acid (HA) has important applications in fields of health care products, cosmetics and clinical medical. However, the unique physiological properties of HA make cost of its traditional separation and extraction process relatively high. Foam separation technique has simple, gentle and efficient advantages on the separation of substances with surface activity by using bubbles as the separation medium. In this paper, natural surfactant CocamideBetaine (CAPB) was used as a foaming agent to explore the technology of microscale HA in aqueous solution by foam separation. The optimum process conditions were determined based on the recovery rate and enrichment ratio of HA by single factor and orthogonal experiment: at room temperature, pH = 7, separating air velocity (v) = 350 mL/min, HA concentration (CHA) = 50 mg/L, adding liquid volume (V) = 200 mL, collecting time (tcol) = 10 min, CAPB concentration (CCAPB) = 0.035 g/L. Under these conditions, HA enrichment ratio (E) equals 6.821 and HA recovery rate (R) equals 66.425%.

Nano-hydroxyapatite enhanced double network hydrogels with excellent mechanical properties for potential application in cartilage repair

Hydrogels with desirable characteristics have been supposed to be potential materials for cartilage repair. However, the biomechanical, biotribological and biocompatible properties of hydrogels remain some crucial challenges. To address these challenges, we developed a dual physically cross-linked poly (vinyl alcohol)-(nano hydroxyapatite)/(2-hydroxypropyltrimethyl ammonium chloride chitosan) (PVA-HA/HACC-Cit) hydrogels with double-network (DN) through a simply freezing/thawing technique and an immersing process. The DN hydrogel with an optimized HA concentration exhibited outstanding fracture tensile stress (2.70 ± 0.24 MPa), toughness (14.09 ± 2.06 MJ/m3) and compressive modulus (0.88 ± 0.09 MPa). In addition, the PVA-HA/HACC-Cit DN hydrogels demonstrated remarkable anti-fatigue property, extraordinary self-recovery and energy dissipation ability due to their unique dual physically cross-linked structures. Moreover, the low friction coefficient, the predominant wear resistance property, as well as the excellent cytocompatibility were realized for the DN hydrogels because of the existence of nano-hydroxyapatite. Thus, this work puts forward a new strategy in the preparation of DN hydrogels for promising applications in cartilage repair.

Effect of photoinitiator on chain degradation of hyaluronic acid

ObjectivesPhotocrosslinking systems of polymers have been widely studied using UV or visible light irradiation. However, the photodegradation behavior derived from light irradiation was rarely reported, comparing with the photocrosslinking. In this study, the tyramine-modified hyaluronic acid (HA/Tyr) hydrogel was prepared using riboflavin (RF) as a photoinitiator, and the degradation behavior of HA by the reactive oxygen species (ROS) generated in photochemical process was investigated.Materials and methodsThe HA/Tyr conjugate was synthesized by EDC/NHS chemistry to introduce phenol group. Degree of substitution (DS, %) of phenol group to HA molecule was about 25%. The structural change of HA/Tyr was measured by proton nuclear magnetic resonance (1H-NMR) and attenuated total reflectance infrared spectroscopy (ATR-FTIR), and the rheological properties of photocrosslinked HA/Tyr hydrogel were investigated by rheometer.ResultsThe HA/Tyr solution with 25% substitution formed a stable hydrogel via visible light irradiation in the presence of RF photoinitiator. Rheological data of HA/Tyr solution showed that the storage modulus (G’) was increased with increasing HA concentration. Additionally, it was found that RF initiated by visible light irradiation induced the degradation of HA molecular chain, and consequently reduced the viscosity of HA/Tyr solutions.ConclusionThe results indicate that RF-based photoinitiator system caused the degradation of HA molecule by ROS generated in photochemical process as well as the crosslinking of HA/Tyr.

Chain conformation: A key parameter driving clustering or dispersion in polyelectrolyte – Colloid systems

The work presents the characterization of Pluronic F127 micellar solutions in presence of hyaluronic acid in semi-dilute regime. The effects of the nature and salt concentration are investigated by differential scanning calorimetry and small angle neutron scattering. Hyaluronic acid reduces the critical micellar temperature to the same extend as an increase of the ionic strength. Within the investigated HA concentration range, the size and shape of the micelles are not modified by the addition of HA but their dispersion state depends on the salt concentration. By increasing the ionic strength we observe the formation of small micellar clusters which organize into a face-centered cubic liquid crystalline phase at high salt concentration. This behavior is reinforced by increasing the HA concentration or molecular weight. The nature of the salt plays also a role and divalent cations such as Ca2+ promote the clustering of micelles and their crystallization. The origin of the aggregative behavior is the change of the HA chain conformation –from stretched to coil- by addition of salt which in turn induces an excluded volume around the micelles and exerts a depletion interaction.

Application of vacuum-ultraviolet (VUV) for phenolic homologues removal in humic acid solution: Efficiency, pathway and DFT calculation

Vacuum-ultraviolet (VUV) photo-initiated oxidation of phenolic homologues in simulative natural water were investigated, including phenol, o-dihydroxybenzene (ODB), m-dihydroxybenzene (MDB), p-dihydroxybenzene (PDB), paranitrophenol (PNP) and o-chlorophenol (OCP). Results showed the phenolic homologues removal rate reached at least 90% in pure water, which was dependent on temperature, pH, concentration of HA, and functional group of HA. Experimental results indicated that 0.2 mg/L HA might be a critical point. Additionally, the rate constant of the six phenolic homologues reduced by 76.85%, 77.81%, 71.91%, 79.15%, and 55.69%, respectively in the MDB solution, and 79.73%, 82.80%, 95.36%, 80.38%, and 92.64%, respectively in the benzoic acid (BA) solution, compared to the rate constant in pure water. Moreover, quantum chemistry calculation indicated that the variances between phenolic compounds in removal rate were attributed to the substituent on the benzene ring. And, to some extent, the carboxy group of HA was supposed to arose the suppression for phenolic homologues removal rate. Mechanism involved phenolic homologues degradation using vacuum-ultraviolet (VUV) was summarized, where it underwent the formation of quinone structures, ring opening, short-chain organic acid, even eventually the transformation into NO3− and Cl− of PNP and OCP.

The mechanism of aquatic photodegradation of organophosphorus sensitized by humic acid-Fe3+ complexes

Organic phosphorus is an important source of eutrophication. In this study, to understand the mechanism of organophosphorus photodegradation, humic acid-Fe3+ (HA-Fe3+) complexes were prepared as a sensitizer, and glyphosate (GP) was used as a substrate for photodegradation. The effects of the initial GP concentration, HA concentration, Fe3+ concentration and microbial factors on photodegradation were investigated. The initial concentrations of GP, HA and Fe3+ could significantly affect the degradation rate of GP. Phosphate is the main product of GP photodegradation. Based on the identification of the active species in the reaction process, t-butanol was found to have the most significant inhibitory effect on the degradation. The reaction rate after t-butanol treatment was reduced from 0.017 to 0.003. This confirmed that OH was the main oxidant in the system, which was also demonstrated by EPR spectroscopy. A possible mechanism of GP photodegradation sensitized by HA-Fe3+ complexes was revealed for the first time. The HA-Fe3+ complexes in the reaction system were photodegraded and oxidized to finally produce OH, which promotes GP photodegradation. This study facilitates understanding the phosphorus cycle in a water environment and provides a scientific basis for the restoration of eutrophic lakes.

Adsorption, aggregation and sedimentation of titanium dioxide nanoparticles and nanotubes in the presence of different sources of humic acids.

Environmental behavior, bioavailability and risks posed by TiO2, nanomaterials (TiO2 NMs) in surface waters are affected by morphologies of the particles and geochemistry, including pH, inorganic and organic matter. Here, the adsorption, aggregation and sedimentation of TiO2 nanoparticles (TiO2 NPs) and nanotubes (TiO2 NTs) were investigated in the presence of Elliott Soil humic acid (HAE) and Suwannee River humic acids (HAS). The adsorption amount of HA on TiO2 NMs was inversely proportional to pH of solution. Maximum adsorption amount of HA on the surface of TiO2 NMs follows the order TiO2 NPs + HAE (236.05 mg/g) > TiO2 NTs + HAE (146.05 mg/g) > TiO2 NTs + HAS (70.66 mg/g) > TiO2 NPs + HAS (37.48 mg/g). Stability of TiO2 NPs and TiO2 NTs largely depended on their isoelectric point, morphology and solution pH in the absence of HA. Dispersion of TiO2 NMs was enhanced with solution pH deviated from the isoelectric point of nanomaterials due to electrostatic repulsion. Moreover, tubular structures of TiO2 NTs with higher length-diameter ratio seem to aggregate more easily than dose sphere-like TiO2 NPs. This might be due to their spherical structure enhancing steric repulsion. Notably, the adsorption of HA led to disagglomeration and significant stability of TiO2 NPs and TiO2 NTs due to steric hindrance under varying solution pH. In addition, adsorption time, concentration and sources of HA also influenced suspension/sedimentation behavior of TiO2 NPs and TiO2 NTs, and aromatic-rich HAE stabilized TiO2 NMs suspension more aggressively than aliphatic-rich HAS.

Bacterial cellulose/hyaluronic acid nanocomposites production through co-culturing Gluconacetobacter hansenii and Lactococcus lactis in a two-vessel circulating system

Bacterial cellulose (BC) based composites have been widely studied in the biomedical field. In this study, the BC/HA (hyaluronic acid) nanocomposites in the pellicle form were directly produced through co-culturing Gluconacetobacter hansenii ATCC 23769 and Lactococcus lactis APJ3 in a novel two-vessel circulating system. The concentration of HA secreted by L. lactis was controlled through adjusting the constant feed rate of glucose. The dynamic growth of the strains revealed that L. lactis was mainly growing within 48 h while G. hansenii started to grow after 48 h. XRD analysis indicated the presence of HA would not affect the crystallinity of cellulose but increase the crystalline sizes. The FESEM images showed that more ribbons within the width of 20–40 nm and larger ribbons between 180 and 360 nm were observed in BC/HA. The strain at break and the water holding capacity of BC/HA increased with the concentration of HA.

Dermal targeting of Centella asiatica extract using hyaluronic acid surface modified niosomes

The work aimed to develop Centella asiatica extract-loaded niosomes (CAE-Nio) and surface modified niosomes by hyaluronic acid (CAE-Nio-HA) to enhance transdermal penetration. Niosome formulations were prepared by film hydration method using Tween 60 and Span 60 as nonionic surfactants, cholesterol and various CAE contents. Various HA concentrations were investigated to obtain optimized CAE-Nio enhancing further skin penetration. Results showed that niosomes prepared from Tween 60 yielded suitable CAE encapsulated niosomes with mean particle size and zeta-potential of 155 nm and −15 mV, respectively. The niosomes exhibited high encapsulation efficiency (%EE) and drug loading capacity (%DL) of 71–77% and 3–7%, respectively. Incorporating HA to niosome decreased %DL and caused larger particle size and increased zeta-potential in a dose dependent manner while %EE remained unaffected. The sustained-release behaviour of CAE from all niosomes was under a diffusion controlled mechanism. Asiaticoside, a relatively polar compound from CAE-Nio-HA could penetrate through the stratum corneum and dermis in a larger amount than from CAE-Nio and CAE solution. CAE-Nio-HA formulations showed good stability under low temperature (4 °C and 25 °C) for periods longer than 4 months. In conclusion, the developed Nio-HA is a promising delivery system for asiaticoside to enhanced dermal absorption, permeation and accumulation in viable epidermis and dermis layers. This system can also be applied to other hydrophilic natural active compounds.

Enhanced fluoride uptake by bimetallic hydroxides anchored in cotton cellulose/graphene oxide composites.

A novel hybrid nanomaterial was synthesized by embedding the bimetallic Zr and La (hydro)xides onto the cotton cellulose/graphene oxide composites (CC/GO composites), forming the Zr-La-CC/GO nanocomposites. Selective uptake of fluoride onto the Zr-La /GO hybrids in multiple competitive environments were evaluated. Morphological characteristics of Zr-La-CC/GO nanocomposites reflected the well distributions of embedded Zr and La hydroxides in the nanocomposites. Results also indicated that the encapsulated bimetallic hydroxides in Zr-La-CC/GO hybrids exhibited extremely high fluoride adsorption capacity and stability. XPS investigation exhibited the strong ZrF and LaF bonds in spent Zr-La-CC/GO nanocomposites, and the bonds were weakened at higher pH, which was consistent with the adsorption results. In addition, CC/GO composites using as the host could also exert the strong shielding effect to improve the stability of embedded La and Zr species so as only a low La dissolution (<4.2%) and almost no Zr leaching (0.1%) were observed in high HA concentration. What's more, the Zr-La-CC/GO nanocomposites have also shown great potential application for defluoridation in field.

Phosphorus availability and soybean growth in contrasting Oxisols in response to humic acid concentrations combined with phosphate sources

ABSTRACTHumic acid (HA) use can improve phosphorus (P) availability in soils with high P fixation capacity. The aim of this study was to evaluate soil P availability and soybean growth in both medium-texture (MT) and clayey (CL) Oxisols under humic acid carbon (C-HA) concentrations: 0, 5, 10, 50 and 100 mg kg−1, combined with Araxá phosphate rock (APR) and single superphosphate (SS). Mixtures of C-HA with P sources were incubated for 15 d. In sequence, the soil solution was extracted and analyzed for soil solution C (SSC), soil solution P (SSP) and soil solution electrical conductivity (EC). Soil initial resin-P and pH were determined before soybean sowing and, after harvest, shoot (SDM), root (RDM), total dry matter (TDM), soil residual resin-P and soil pH were determined. In CL fertilized with SS, the addition of C-HA increased SSP by 17%, residual resin-P by 42%, SDM, P and N accumulated in the shoot. Addition of C-HA reduced SSP and initial resin-P in MT treated with SS and increased in 18% residual resin-P in MT fertilized with APR. Effects of HA on soil attributes, soybean growth and nutritional status rely on HA concentration, soil texture and P source used.

The humic acid influenced the behavior and reactivity of Ni/Fe nanoparticles in the removal of deca-brominated diphenyl ether from aqueous solution.

The removal of contaminants by iron-based nanomaterials was inevitably affected by the natural organic matter (NOM), which is one of the most abundant material on earth and exists in natural waters. This study was performed to investigate the main influence of humic acid (HA, representing NOM) on the behavior and reactivity of Ni/Fe nanoparticles in the removal of deca-brominated diphenyl ether (BDE209). Generally, the inhibitory effect of HA on the removal of BDE209 by Ni/Fe showed greater significance with an increase of HA concentration. The zeta potential and sedimentation experiments showed that the HA enhanced the dispersion and stabilization of Ni/Fe particles; however, the removal of BDE209 was found to be inhibited. Moreover, the corrosion capacity of the Ni/Fe nanoparticles showed a positive correlation with the effect of HA on the reactivity of Ni/Fe nanoparticles. Meanwhile, typical quinone compounds in HA had an adverse effect on the removal of BDE209. Additionally, the competitive adsorption experiments and characterization illustrated that the adsorption of HA by Ni/Fe nanoparticles was superior to BDE209. Overall, it was proposed that the corrosion of Ni/Fe was reduced as the contact between the nanoparticles and H2O was hindered due to the surface of Ni/Fe was occupied by the adsorbed HA, and thus inhibited the reactivity of Ni/Fe nanoparticles in the removal of BDE209.

Mild stir-assisted membrane dispersion for enhancing propionic acid extraction

Abstract Mild stir-assisted membrane dispersion extraction (MDE) method was employed to enhance propionic acid (HA) extraction and compared to the mechanical stirred extraction (MSE) method. Triocylamine (TOA) and tributyl phosphate (TBP) were chosen as model extractant to extract HA. Firstly, droplet size and the size distribution of organic phase were analyzed, and then the effects of phase ratio, extractant and HA concentration on extraction performance were investigated. Comparing the two extraction methods, the results show mild stir-assisted MDE method reduced the mass transfer equilibrium time compared to MSE method. The mass transfer mechanism was explored by analyzing mass transfer resistance. Mild stir-assisted MDE had less total mass transfer resistance than MSE. When the extractant concentration was 40%, the extraction process was controlled by organic phase mass transfer process with HA volume fraction was 1% and controlled by both of reaction process and organic phase mass transfer process when HA concentration increased to 5%. This work may provide a new type of extraction method for the recovery of organic carboxylic acid.

Adsorption of HA (humic acid) using sulfuric acid-crosslinked chitosan/pectin polyelectrolyte complex film

A sulphuric acid-crosslinked chitosan/PEC film had been synthesized and applied for adsorption of HA from aqueous solution. The parameters for adsorption study were an optimum ratio of chitosan/pectin composition, contact time, the effect of the solution pH, and HA concentration. The model for adsorption kinetics and isotherm adsorption as well as desorption study were also conducted. The result showed that the film was durable in water at pH 2 to 12. The analysis using FTIR indicated a shift of absorption peak at 1527 cm−1 (bending vibration N−H in −NH3+). Analysis with SEM showed the morphological differences of the film before and after adsorption and after desorption. Adsorption reached its optimum capacity in the film with a ratio of chitosan and pectin composition 70:30, at pH 6, contact time of 480 mins and HA concentration of 450 mg L−1. The kinetic model of HA adsorption could be explained by the second-order kinetic model of Ho & McKay and the adsorption isotherm follows the Langmuir isotherm model with a maximum adsorption capacity of 50.0 mg g−1, the Langmuir constant (KL) of 1.49×105 L mol−1 and the adsorption energy was found to be 29.7 kJ mol−1. The highest desorption was 82.5% using 1 M NaOH.

Removal of natural organic matter from water using chemically activated coffee husk

The presence of natural organic matter (NOM) in source water has posed many challenges for conventional water treatment facilities. Small organic acids, such as humic acid, present in NOM, have a high potential to influence the performance of water treatment processes. Uncontrolled application of agricultural chemicals leads to the simultaneous presence of toxic substances. In this work, batch adsorption experiments were conducted to examine the biosorption of HA onto chemically activated coffee husk. The biosorption process was studied as a function of operating conditions, such as contact time, pH of the solution, HA concentration, adsorbent dose and agitation speed parameters. Experimental results showed that the adsorption has an equilibrium time of 60 min with a maximum adsorption of 93.7%. The optimum pH for maximum HA adsorption was found to be 5.5, with a maximum adsorption of 94.3%. . As the dose of adsorbent increased from 1 to 25 g/L, the concentration of HA was observed to reduce from 10 to 1.67 mg/L which is below the WHO (World Health Organization) guideline value of 2 mg/L. The amount of HA adsorbed increased with increasing the initial adsorbent concentration from 0.5 to 20 mg/L. The adsorption kinetics well fitted the pseudo-second order model with the correlation coefficient R2 = 0.997 and Ks = 0.078. The experimental sorption equilibrium can be represented by the Langmuir isotherm (R2 = 0.998, SSE = 0.006). An average desorption capacity of 87.3% was observed. The study shows that chemically activated coffee husk can be a potential candidate to be used as a biosorbent in the removal of NOM from aqueous solutions.

Effect of humic acid concentration on pharmaceutically active compounds (PhACs) rejection by direct contact membrane distillation (DCMD)

In this study, a direct contact membrane distillation process was used to achieve rejection of 25 pharmaceutically active compounds (PhACs) in water. The influence of natural organic matter (NOM), a common contaminant in waters that are used for water supply, on PhACs removal was investigated. Humic acid was used as an organic model in order to represent major constituents of NOM. Results indicated that flux decline slightly increased from 0 to 8% as HA feed concentration increased from 0 to 80 mg L−1. Flux decline was mainly associated with membrane fouling which added hydraulic resistance to the transfer of liquid water. Pore wetting was observed when HA concentration increased, which indicated changes in the hydrophobic character of the membrane. MD process showed a rejection of ≥ 99% for the 25 assessed PhACs for all HA concentration evaluated even at high permeate recovery rate (60%), whereas, 24 PhACs presented concentrations below limit detection. The retention of PhACs by MD membrane occurs predominantly by membrane rejection which is mainly governed by volatility and, to a lesser extent, by hydrophobia. The adsorption contribution to PhACs retention was low (<8%) and was significantly associated with positively charged compounds. Although the feed side of the membrane became hydrophilic due to the HA deposit, the PhACs retention by DCMD was not affected, which reinforces the robustness of the process and the ability to produce safe water. Thus, in general, DCMD is less influenced by the feed composition than nanofiltration or reverse osmosis, implicating in higher PhACs rejections.

Effect of aqueous concentration of humic acid on the sorption of polychlorinated biphenyls onto soil particle grain sizes

The role of initial aqueous humic acid concentrations (dose), as well as secondary environmental conditions on the sorption of PCB congeners PCB 28, 52, 77, 101, 105, 138, 153, and 180 onto soil particle grain sizes, was investigated in this study. Scanning electron microscopy equipped with energy dispersive X-ray and Fourier transform infrared spectroscopy were used for the internal morphology and qualitative elemental analysis, as well as identification of possible functional groups found in commercial HA. Batch adsorption experiments were used for sorption studies. The results showed that the sorption of PCBs onto soil decreased with an increase in the aqueous HA concentrations. The adsorption of the selected PCBs onto the soils was found to decrease with an increase in the solution pH of humic acid. Thermodynamic studies showed that the partition coefficient values increased with an increase in solution temperature. All the standard free energy were negative indicating the spontaneity and feasibility of the sorption process with positive and high enthalpy and entropy values of the system. The sorption was best fitted with the Freundlich isotherm with the intensity parameter 1/n found to be greater than 1. The outcome of this study revealed that secondary pollution of river water may possibly be altered depending on variations in the environmental conditions such as pH and temperature. The presence of organic pollutants in alkaline soils having less organic matter content could increase the chances of leaching of organic pollutants causing groundwater contamination.

Enhanced removal of organic contaminants in water by the combination of peroxymonosulfate and carbonate

In this study, a favorable CO32−/PMS system for efficient degradation of organic contaminants (acid orange 7 (AO7), acetaminophen, para-aminobenzoic acid, phenol, methylene orange, methylene blue) in water was firstly reported. Under optimal conditions, the decolorization ration of AO7 was 100% within 40 min. Data fitting showed that the AO7 decolorization could be described by the pseudo-first-order kinetics, and the rates constant values ranging from 0.0006 to 0.2297 min−1 depending on the operating parameters (initial PMS, CO32−, AO7 concentrations). Radical scavenging studies revealed that superoxide anion radical (O2−) and singlet oxygen (1O2) rather than sulfate (SO4−) nor hydroxyl (HO) were the dominant oxidants might be responsible for AO7 degradation. The presence of NO3−, HPO42− and low concentration of Cl−, NO2−, HCO3−, H2PO4−, HA had no significantly effect on the decolorization of AO7. Adding a higher Cl− concentration displayed favorable effects on the removal efficiencies of AO7, but adding a higher NO2−, HCO3−, H2PO4− and HA concentration apparently inhibited this process. The decolorization of AO7 was lower in wastewater in comparison to other natural waters and ultrapure water, which was probably due to the presence of higher concentration of colloids in wastewater. Nevertheless, up to 94.8%, 97.0% and 85.1% of AO7 were degraded from the filtrate, permeate, and retentate phases of wastewater within 60 min, respectively. Consequently, CO32−/PMS would be promising for removal methodology for AO7 in wastewater containing considerable colloids. Finally, three intermediates were identified and degradation pathways of AO7 were proposed.

Fe–colloid cotransport through saturated porous media under different hydrochemical and hydrodynamic conditions

To investigate the effect of different colloids on Fe migration in saturated porous media under different hydrochemical and hydrodynamic conditions, experiments were performed using colloidal silicon (inorganic) and colloidal humic acid (HA, organic), which are representative of the colloids in groundwater. Transport of Fe with and without colloid was investigated by column experiments using various porous media, colloid concentrations, ionic strengths (ISs), cation valences, and flow rates. The results show that colloidal silicon promotes and colloidal HA inhibits Fe transport, which is mainly because of their different bonding ratio, bonding modes with Fe and opposite surface charges between Fe–colloidal silicon and Fe–colloidal HA. Almost 100% of HA binds to Fe through the deprotonated functional groups, whereas only 13.3% of colloidal silicon binds to Fe, which is by electrostatic forces. Cotransport is also dependent on the hydrochemical and hydrodynamic conditions. For the Fe–colloidal silicon system, increasing the colloid concentration and flow rate, and decreasing the IS enhances Fe transport. Compared with colloidal silicon concentration = 10 mg/L, flow rate = 0.25 mL/min, and IS = 0.05 with CaCl2, a higher colloidal silicon concentration (20 mg/L), a higher flow rate (0.50 mL/min), and a lower IS (<0.0005 M) increase Fe recovery by 1.69%, 94.49% and 38.92%, respectively. Fe migration is also different in different porous media. For the Fe–colloidal HA system, Fe recovery decreases by 81.46% as the colloidal HA concentration increases from 0 to 20 mg/L. The type of porous medium and flow rate conditions have the same effects on Fe–colloidal HA transport as for colloidal silicon, although the electrical conditions have the opposite effect. With increasing IS, Fe–colloidal HA transport is enhanced because of competitive adsorption of the cations and Fe to colloidal HA and the porous medium.