Amount Of Humic Acid Research Articles

Isolation of humic acid from oxidized lignite and complexation with metal cations

Lignite is brown coal, which in its composition contains humic acids. Humic acids are produced by coal combustion, which leads to the enrichment of coal humic acids. Lignite, from the opet pit mine Sikulje, lignite ore ?Kreka?, Bosnia and Herzegovina, was fragmented and sieved to the appropriate size and used as a base material. The isolation of humic acid was carried out from pre-oxidized and dried lignite after which it was refined. Identification thus obtained humic acids was carried out by FTIR spectroscopy and its characterization of UV analysis which is determined by optical density of isolated humic acid and its complexation with metal cations. Data obtained by FTIR spectroscopic analysis of isolated humic acids show no significant structural and chemical difference in relation to the spectrum obtained for standard humic acids (Sigma Aldrich). UV analysis showed that isolated and standard humic acid have E4/E6 ratio in an appropriate range of 3?5, which indicates the presence of a large number of aliphatic structure. Based on the degree of humification was found that the isolated humic acids belong to the type B standard while humic acids belong to type A. The most important property of the humic substances is the ability to interact with the metal ions forming soluble or insoluble complexes which possess different chemical and biological properties and stability. The nature of the complex between humic acid and metal cation derived from the heterogeneous, polyelectric and polydispersive character humic acids that occurs due to the presence of a large number of functional groups. Complexation of humic acid is carried out with different concentrations of metal nitrate solutions and at different pH values. Different amounts of humic acids were used for the complexation. The amount of the free metal ions was measured with the ICP-OES methode. The data were also statistically analyzed with ANOVA. The results showed that increasing the pH reduces the concentration of metal ions adsorbed on humic acid and by increasing the concentrations and amounts of metal humic acid that power increases. On the basis of the difference in absorbance between metals and humic acids can be said that there is an interaction between the metal and the ligand and is based on absorbance values obtained can be determine the next set of metal binding to humic acids Pb>Zn>Ni>Cu.

Comparison of Chemical Structure of Alginite Humic Acids Isolated with Two Different Procedures with Soil Humic Acids

Abstract The different origin of alginite and soil organic matter may be the reason of differences in their humic acids (HA) chemical structure. One of the aims of this article is to compare the chemical composition of alginite HA and HA isolated from different soil types. Another aim of this article is to compare the chemical structure of humic acids of alginite isolated with two different procedures: modified IHSS (International Humic Substances Society) method and simplified extraction method. The modified IHSS method was applied for the isolation of alginite and soil HA. To obtain sufficient amount of alginate HA for biological experiments, simplified extraction method suited for large volumes of HA was applied. The differences in elemental analysis and ash proportion in HA extracted by modified IHSS method (C = 35.4, H = 43 atomic%, ash content = 0.08%) and simplified extraction method (C = 31, H = 31 atomic%, ash content = 7.42%) can be caused by different concentration of extraction solution and also differences in purification of HA. The differences in chemical structure between alginate HA and HA isolated from different soil types according to the data of elemental analysis (C content of alginite HA = 35.4 atomic%, C content in soils HA = 38.2‒49.1 atomic%) and 13C nuclear magnetic resonance (NMR) spectra (degree of aromaticity of alginite HA = 24.4% and soil HA= 35.9‒53%) were found. Results of 13C NMR show that the content of aromatic carbon was decreasing in the following order: Haplic Chernozem HA > Andic Cambisol HA > Haplic Cambisol HA > alginite HA. Based on the obtained results, it can be concluded that the differences in the chemical structure of alginite and soil HA can be explained by the difference in the origin of organic matter in alginite and soil samples. The source of organic matter in alginite is mainly type II kerogen from algae and that of soil is lignin and cellulose (type III kerogen) of higher plants.

Influence of NOM and SS on the BPA removal via peroxidase catalyzed reactions: Kinetics and pathways

Abstract In the present study, horseradish peroxidase (HRP) was employed to removal bisphenol A (BPA) with the presence of natural organic matter (NOM) and suspended solids (SS). Humic acid (HA) and kaolin have been selected as the typical NOM and SS in the experiment. According to the results, HA has shown a very interesting performance, which has both inhibitory and facilitation effects on BPA removal. For the low enzyme concentration (20 u/L and 50 u/L), small amount of HA could facilitate the BPA removal, while large amount of HA could inhibit the BPA removal. For the higher enzyme concentration (100–300 u/L), the addition of HA reduced the removal transformation of BPA and the inhibition effect of HA raised with the increase of HA concentrations. The facilitation nature of HA on enzyme catalytic processes can be attributed to the mitigation of enzyme inactivation, which has been proven by HRP inactivation rate. The inhibitory effect could be caused by the inhibition effect of HA on the enzyme activity, which has been suggested by both kinetic study and enzyme inactivation analysis. Kaolin showed a negative effect on BPA removal by HRP catalyzed reactions due to the inhibition effect of kaolin on HRP activity. The results have important implications for the engineering design by employing HRP in water and waste water treatment.

Adsorption of Humic Acid from Aqueous Solution onto PVDF Nanofiber: Effect of Temperature

The sorption of humic acid from aqueous solution onto polyvinyl difluoride nanofiber under the influence of temperature has been investigated. Batch adsorption experiments were carried out using humic acid (HA) as an adsorbate. It was observed that the amount of humic acid adsorbed increase with increasing temperature. Thermodynamic parameters data indicated that the humic acid adsorption was non-spontaneous and endothermic under the experimental conditions, with the enthalpy (∆H) and entropy (∆S) of +16.32 kJ mol-1 and +41.92 J mol-1, respectively.

Modification of ultrafiltration membrane with iron/aluminum mixed hydrolyzed precipitate layer for humic acid fouling reduction

Iron/aluminum mixed flocs were pre-deposited onto an ultrafiltration (UF) membrane surface to test their antifouling properties in the presence of humic acid (HA). Membranes modified with higher aluminum mole ratios in the mixture were more effective in controlling membrane fouling. Relatively strong adhesion was observed between the mixed flocs and the UF membrane used. The differences in the structure of the deposited layer were an important contributing factor for antifouling properties, which was significantly influenced by solution pH. Scanning electron microscopy showed that dense deposition layers were formed by small flocs at pH 6.0, while loose deposition layers were formed by large flocs at pH 8.0. Atomic force microscopy showed that the surface roughness of the deposition layer was much larger at pH 6.0 than that at pH 8.0. The corresponding positive charge of the mixed flocs was also higher at pH 6.0, resulting in stronger adsorption ability to the negatively charged HA molecules. These factors reduced the amount of HA getting to the membrane surface and thus helped increase membrane flux at lower pH values. In addition, HA molecules with various molecular weights were removed much faster at pH 6.0 than at pH 8.0.

Interactions in Ternary Mixtures of MnO2, Al2O3, and Natural Organic Matter (NOM) and the Impact on MnO2 Oxidative Reactivity.

Our previous work reported that Al2O3 inhibited the oxidative reactivity of MnO2 through heteroaggregation between oxide particles and surface complexation of the dissolved Al ions with MnO2 (S. Taujale and H. Zhang, "Impact of interactions between metal oxides to oxidative reactivity of manganese dioxide" Environ. Sci. Technol. 2012, 46, 2764-2771). The aim of the current work was to investigate interactions in ternary mixtures of MnO2, Al2O3, and NOM and how the interactions affect MnO2 oxidative reactivity. For the effect of Al ions, we examined ternary mixtures of MnO2, Al ions, and NOM. Our results indicated that an increase in the amount of humic acids (HAs) increasingly inhibited Al adsorption by forming soluble Al-HA complexes. As a consequence, there was less inhibition on MnO2 reactivity than by the sum of two binary mixtures (MnO2+Al ions and MnO2+HA). Alginate or pyromellitic acid (PA)-two model NOM compounds-did not affect Al adsorption, but Al ions increased alginate/PA adsorption by MnO2. The latter effect led to more inhibition on MnO2 reactivity than the sum of the two binary mixtures. In ternary mixtures of MnO2, Al2O3, and NOM, NOM inhibited dissolution of Al2O3. Zeta potential measurements, sedimentation experiments, TEM images, and modified DLVO calculations all indicated that HAs of up to 4 mg-C/L increased heteroaggregation between Al2O3 and MnO2, whereas higher amounts of HAs completely inhibited heteroaggregation. The effect of alginate is similar to that of HAs, although not as significant, while PA had negligible effects on heteroaggregation. Different from the effects of Al ions and NOMs on MnO2 reactivity, the MnO2 reactivity in ternary mixtures of Al2O3, MnO2, and NOM was mostly enhanced. This suggests MnO2 reactivity was mainly affected through heteroaggregation in the ternary mixtures because of the limited availability of Al ions.

The effects of humic acid and soil on black carbon-mediated reduction of 2,4-dinitrotoluene

Black carbon (BC) can act as a catalyst to promote the reductive transformation of redox-sensitive organic chemicals in electron-rich conditions. This process is called a BC-mediated reduction. To determine the effects of natural organic matter and the existence of soil on the BC-mediated reduction of nitroaromatics (NACs) in subsurface environments, a BC-mediated reduction of 2,4-dinitrotoluene (DNT) by dithiothreitol was investigated using graphite, humic acid (HA), and soil. The presence of dissolved HA in the graphite–dithiothreitol–DNT system showed different yields of reduction intermediates and pathways, indicating that different reduction/removal mechanisms are involved. Control experiments with HA alone confirmed that the HA-mediated reduction of DNT and HA–DNT complexation are existed. Kinetically, HA did not slow the reductive removal of DNT in the graphite–dithiothreitol system. In contrast, the existence of soil in the system retarded the BC-mediated reduction of DNT, probably due to competitive sorption and hindrance of mass transfer. Our results suggest that the amounts of BC and HA may affect the BC-mediated reduction of NACs in soils and sediments.

Effect of humic acids, sesquioxides and silica on the pore system of silt aggregates measured by water vapour desorption, mercury intrusion and microtomography

SummaryMost of the information on soil aggregation and porosity comes from studies of natural soil in which the effects of the different constituents that form the structure overlap. The aim of this research was to study the effects of these constituents separately on well‐characterized artificial aggregates in order to understand them better. To do this, the pore system of model silt aggregates, amended with different amounts of humic acids, iron and aluminium hydroxides or colloidal silica, was investigated at three levels of magnification with water vapour desorption (nanometre sizes), mercury intrusion (micrometre sizes) and microtomography (tens of micrometres). Humic acid and aluminium hydroxide increased aggregate porosities measured by all methods. An increase in porosity with increasing additions of each constituent was indicated only by water desorption. We did not observe any well‐defined trends in the dynamics of average pore radii. The pore surface fractal dimension determined by mercury intrusion was negatively correlated with that measured by water desorption. The pore system in granular media comprises larger voids joined by narrower necks; therefore, we attempted to relate their sizes with a novel approach that combined microtomography with mercury intrusion and extrusion data. We observed a decrease in the size of pore necks that give access to voids of the same sizes with increasing additions of all constituents. With additions of humic acid this effect was the smallest. The mercury intrusion data showed the formation of separate concretions of iron hydroxides and silica in silt aggregates.

The sorption interactions of humic acid onto Beishan granite

Abstract To explore the sorption phenomenon and mechanism between humic acid (HA) and Beishan granite (BsG), the influence of factors such as pH, contact time, ionic strength, temperature, HA concentration and solid-to-liquid ratio were investigated using the batch technique. The sorption process was significantly affected by pH and ionic strength. The maximum adsorption capacity of HA on BsG was approximately 0.9493 mg g −1 at pH = 6.7 and T = 305 K, and the thermodynamic parameters indicated that the sorption process was spontaneous and endothermic. The SEM–EDS results indicated the presence of a certain amount of HA on BsG after sorption with HA. The results of FT-IR spectroscopy and the change in pH demonstrated that ligand exchange–surface complexation may be an important mechanism. BET analysis showed that parts of the HA tended to enter the pores formed by close-packing of BsG particles, and albite and muscovite might have played a role in the sorption process, as indicated by the XRD analysis. Overall, it is speculated that the mechanisms governing the sorption behaviors of HA on BsG are precipitation, ligand exchange–surface complexation and electrostatic interaction. Moreover, the colloidal properties of HA under certain conditions may also significantly affect its sorption interactions with BsG.

Antioxidant properties of garlic as affected by selenium and humic acid treatments

Garlic is an important bulb vegetable because of its medicinal and nutritional values. Selenium, an important trace element, and humic acid, a soil amendment, can positively affect garlic's nutritional values. To evaluate the impact of selenium and humic acid on antioxidant activity and phenol, flavonoid and allicin contents in garlic, Na2SeO4 solution was sprayed in concentrations of 0, 10, 20 and 30 μg Se/mL, and humic acid was used in fertigation at rates of 0, 10 and 20 kg/ha. Results showed the applied treatments had positive effects on the total antioxidant activity in garlic. The application of low concentrations of Se with moderate amounts of humic acid caused the highest antioxidant activity, as did the application of high Se concentrations with no humic acid. Humic acid at the rate of 10 kg/ha contributed more to the lower total phenol content than did the 20 kg/ha (H20) rate. The Se treatment decreased flavonoid content, and the control plants (Se0) had the highest amount of flavonoids. The results regarding sulphur and allicin contents were greatly similar in that they were both at their maximum level in the Se0H20 treatment. Se0 led to the highest allicin content, and its difference from other Se treatments was significant (P < 0.01). A strong negative correlation was found between selenium concentration and allicin content (R2 = 0.881). The findings showed that humic acid positively affects most tested traits, but negative or no effects were seen for the Se treatment. Therefore, if the production of Se-enriched garlic is the aim, a decrease in some nutritional values must be accepted.

Stability of coprecipitated natural humic acid and ferrous iron under oxidative conditions

Goethite and lepidocrocite are considered the stable species of Fe oxyhydroxides formed from Fe2+ oxidation in mildly acidic soil environments, while maghemite is formed in mildly alkaline conditions. Complexing ligands, especially humic acid (HA), can change the pathway formation of these iron oxyhydroxides from Fe2+ oxidation. This research aimed to assess the influence of HA on Fe2+ oxidation and its effect on crystalline Fe mineral products. Ferrous iron was added to HA at increasing initial COOH/Fe(II) charge ratios (R) at pHs of 5.0 and 8.0 and aged at 70°C for 1month and up to 8years at room temperature. The precipitated products after aging were analysed using XRD, FT-IR, TEM and AFM. The results indicate that oxidation of Fe2+ at pH5.0, in the presence of large amounts of HA (R=0.1) promoted the formation of goethite together with ferrihydrite. Oxidation of Fe2+ in slightly alkaline conditions (pH8.0) yielded maghemite with small amounts of goethite. Further, long-term aging of HA coprecipitated with Fe2+ perturbed the stacking of the Fe hydroxyl sheets at pH5.0, favouring the formation of ferrihydrite. At pH8.0 the presence of humic acid does not influence the crystallinity of the precipitation products and maghemite was still stable after 8years of aging. This research confirms that the oxidation of Fe2+ in soil and its subsequent hydrolysis is a very common process of Fe hydroxides/oxide formation in acidic soil environments. The type of Fe oxide formed depends strictly on the pH and secondly on the rate of oxidation, especially on the presence and amount of organic compounds that inhibit crystal growth. Humic acid are the main organic molecules in soils, particularly in cool, humid weathering environments where they lead to a decrease in crystalline perfection and promote the formation of ferrihydrite instead of goethite or lepidocrocite. These results provide significant insights into the effect of the mobility of HA in association with Fe minerals.

Partitioning of humic acids between aqueous solution and hydrogel. 2. Impact of physicochemical conditions.

The effects of the physicochemical features of aqueous medium on the mode of partitioning of humic acids (HAs) into a model biomimetic gel (alginate) and a synthetic polyacrylamide gel (PAAm) were explored. Experiments were performed under conditions of different pH and ionic strength as well as in the presence or absence of complexing divalent metal ions. The amount of HA penetrating the gel phase was determined by measuring its natural fluorescence by confocal laser scanning microscopy. In both gel types, the accumulation of HA was spatially heterogeneous, with a much higher concentration located within a thin film at the gel surface. The thickness of the surface film (ca. 15 μm) was similar for both types of gel and practically independent of pH, ionic strength, and the presence of complexing divalent metal ions. The extent of HA accumulation was found to be dependent on the composition of the medium and on the type of gel. Significantly more HA was accumulated in PAAm gel as compared to that in alginate gel. In general, more HA was accumulated at lower background salt concentration levels. The distribution of different types of HA species in the gel body was linked to their behavior in the medium and the differences in physicochemical conditions inside the two phases.

A further study on adsorption interaction of humic acid on natural magnetite, hematite and quartz in iron ore pelletizing process: Effect of the solution pH value

Humic acid (HA) was the predominant component of the MHA (modified humic acid) binder invented by the authors. This work aims to study the effect of the solution pH value on the HA adsorption onto natural magnetite/hematite/quartz particles and the strength of green pellets with the MHA binder. The SEM images for HA indicated that HA had distinct morphology at different pH values. The adsorption density of HA on the three oxide minerals was significantly pH-dependent and decreased with increasing pH value. The zeta potential values of the magnetite, hematite and quartz particles coated by HA became negative and the isoelectric point of the three natural oxide minerals disappeared in the tested pH value range. The electrostatic interaction and the ligand exchange were the two leading interactions for the HA sorption onto the magnetite/hematite particles, while the small adsorption amount of HA onto the quartz was attributed to the hydrogen-bond interaction. The pH value of the MHA binder solution affects markedly the strength of green pellets from magnetite and hematite concentrates. At pH ~7.0, the HA molecule was expanded and dispersed well and the relatively strong bonding bridges were formed among the iron ore particles. The optimal pH value was founded to be around 7.0 for preparing high-quality iron ore green pellets.

Effect of Humic Acid Application on the Yield and Quality of Flue-Cured Tobacco

The field experiment was conducted to investigate the effect of of humic acid amount (600 kg/hm 2 , 900 kg/hm 2 , 1200 kg/hm 2 ) at different fertilization time (base fertilization, topdressing fertilization and both) on the potassium content and chemical quality of Yunyan 97. The results showed that humic acid can significantly increase the potassium content in tobacco leaves. The coordination of potassium content in upper, middle and lower leaves reached for 1.52%, 2.55%, 2.63% respectively in the treatment of humic acid (1200 kg/hm 2 ) at base fertilization and topdressing fertilization (1/2 respectively), The content of nicotine and total nitrogen remained in appropriate range in all treatments. Both base and/or topdressing fertilization of humic acid in high level leaded to a more reasonable Potassium/Chloride ratio, and the coordination chemical quality was better.

Application of a set of complementary techniques to understand how varying the proportion of two wastes affects humic acids produced by vermicomposting

A better understanding of how varying the proportion of different organic wastes affects humic acid (HA) formation during vermicomposting would be useful in producing vermicomposts enriched in HAs. With the aim of improving the knowledge about this issue, a variety of analytical techniques [UV–visible spectroscopic, Fourier transform infrared, fluorescence spectra, solid-state cross-polarization magic-angle spinning (CPMAS) 13C nuclear magnetic resonance (NMR) spectra, and thermal analysis] was used in the present study to characterize HAs isolated from two mixtures at two different ratios (2:1 and 1:1) of tomato-plant debris (TD) and paper-mill sludge (PS) before and after vermicomposting. The results suggest that vermicomposting increased the HA content in the TD/PS 2:1 and 1:1 mixtures (15.9% and 16.2%, respectively), but the vermicompost produced from the mixture with a higher amount of TD had a greater proportion (24%) of HAs. Both vermicomposting processes caused equal modifications in the humic precursors contained in the different mixtures of TD and PS, and consequently, the HAs in the vermicomposts produced from different waste mixtures exhibited analogous characteristics. Only the set of analytical techniques used in this research was able to detect differences between the HAs isolated from each type of vermicompost. In conclusion, varying the proportion of different wastes may have a stronger influence on the amount of HAs in vermicomposts than on the properties of HAs.

Effect of the chemical structure of anion exchange resin on the adsorption of humic acid: Behavior and mechanism

Polystyrenic (PS) anion-exchange resin and polyacrylic (PA) anion-exchange resin were used to investigate the effect of resin chemical structure on the adsorption of humic acid (HA). Due to the rearrangement of HA to form layers that function as barricades to further HA diffusion, PS resin exhibited 12.4 times slower kinetics for the initial adsorption rate and 8.4 times for the diffusion constant in comparison to that of the PA resin. An HA layer and a spherical cluster of HA can be observed on the surface of the PS and PA resins after adsorption, respectively. The considerable difference in HA adsorption between the PS and PA resins was due to the difference in molecule shape for interaction with different resin structures, which can essentially be explained by the hydrophobicity and various interactions of the PS resin. A given amount of HA occupies more positively charged sites and hydrophobic sites on the PS resin than were occupied by the same amount of HA on the PA resin. Increased pH resulted in an increase of HA adsorption onto the PA resin but a decrease in adsorption onto PS resin, as the non-electrostatic adsorption led to electrostatic repulsion between the HA attached to the resin and the HA dissolved in solution. These results suggest higher rates of adsorption and higher regeneration efficiency for interaction of HA with more hydrophilic anion exchange materials.

Factors affecting the adsorptive removal of bisphenol A in landfill leachate by high silica Y-type zeolite.

Although bisphenol A (BPA), a representative endocrine-disrupting compound, has been detected frequently in landfill leachate, effective technologies for BPA removal from landfill leachates are limited. We used high silica Y-type zeolite (HSZ-385) for the selective adsorption of BPA from landfill leachate, and factors affecting this adsorption are discussed. Higher removal efficiencies at pH 5.0-9.0 imply that neutral BPA is adsorbed more easily onto HSZ-385 than monomeric or divalent BPA anions. An increase in ionic strength and sodium acetate concentration did not affect BPA adsorption significantly, while the removal efficiency decreased slightly when more than 50 mgC/L of humic acid was added. HSZ-385 was applied to synthetic leachates that simulate the composition of landfill leachate at various degradation stages. In young acidic leachates that contain sodium acetate, the use of HSZ-385 for the adsorptive removal of BPA appears to be more effective than in old alkaline leachates, which contain large amounts of humic acid. In addition, 82 % BPA removal was achieved from young raw leachates using HSZ-385, which demonstrates that selective BPA removal from actual landfill leachate has been achieved.

Removal of Humic Acid by Organo-Montmorillonites: Influence of Surfactant Loading and Chain Length of Alkylammonium Cations

In this study, the characterization and adsorption properties of montmorillonite (MMT) and organomontmorillonites with different surfactant/cationic exchange capacity (CEC) ratios (1 and 2) of tetradecyl trimethylammonium (TDTMA+) and hexadecyl trimethylammonium (HDTMA+) cations were evaluated. The particle apparent diameter, determined by laser and scanning electron microscopy showed aggregate formation, which varied with loading and cation length of the surfactant used. X-ray diffraction analysis revealed the formation of a pseudotrilayer arrangement of both surfactants in the interlayer space, FTIR showed the characteristic bands of the surfactants and micelle formations, and zeta potential determinations indicated neutral or negative surface charge values, except for sample obtained with one CEC concentration exchanged with HDTMA+ (HDTMA1-MMT) where a charge reversal to positive was found. Higher adsorption amounts of humic acid (HA) were found for HDTMA1-MMT and TDTMA1-MMT samples than for MMT sample, while the increase in the loading of both surfactants decreased the amounts of HA adsorbed could be assigned to a higher micelle formation and different packing density of alkyl chain, in the external surface. The correlation found between the total surface area and negative zeta potential values and the HA adsorption rate, within each surfactant, indicated the strong influence that these properties have on HA adsorption.

Aggregation and dissolution of ZnO nanoparticles synthesized by different methods: Influence of ionic strength and humic acid

Zinc oxide (ZnO) nanoparticles (NPs) are widely used in various industries, and studies on the aggregation and dissolution of this material in an aqueous environment are being actively conducted these days. In this study, ZnO-NPs (i.e., nZnO-1 versus nZnO-2) with two different particle sizes, particle shapes, specific surface areas, and functional groups (OH group and carboxylic acid) were prepared through two different synthesis methods. Aggregation tests at circumneutral pH (∼7.5) confirmed that both ZnO-NPs, which have different zeta potentials, were largely affected by the ionic strength and the amounts of humic acid. In the absence of humic acid, their sedimentation behavior was observed to differ from each other due to the different surface charges of the ZnO-NPs and the aggregation behavior of ZnO-NPs according to the ionic strength corresponded to the classic Derjaguin–Landau–Verway–Overbeek (DLVO) theory. The presence of humic acid significantly enhanced the dispersion stability of both ZnO-NPs, but the stability was not explained by the classic DLVO theory due to steric repulsion. In both ZnO-NPs, the Zn2+ dissolution level increased in the presence of humic acid, and the level increased with the increasing humic acid amount. In particular, in the presence of humic acid at pH 9.0, the dissolution level of nZnO-1 was confirmed to be significantly higher than that of nZnO-2. Although nZnO-2 had a smaller particle size and a greater specific surface area than nZnO-1, the humic acid adsorption amount of nZnO-1 was confirmed to be greater than that of nZnO-2 due to the lower hydrophilicity and the stronger electrostatic attraction between humic acid and nZnO-1 caused by less water content and positive zeta potential of nZnO-1.

Carbon Sequestration in Soil Humic Substances Under Long-Term Fertilization in a Wheat-Maize System from North China

The changes in humic substances (HS) is fundamental in detecting soil carbon sequestration mechanisms in natural and cultivated environments. Based on a long-term trial, the amounts of water dissolved substances (WSS), humic acid (HA), fulvic acid (FA) and humin (HU) were determined to explore the impact of long-term fertilization on HS. Increases in the amounts of WSS, HA, FA and HU were significant different among the treatments with manure. A significant correlation was found between the increased soil organic carbon (SOC) and HS (R2=0.98, P<0.01). The change in the E4/E6 ratio was significantly correlated with the increased SOC (R2=0.88, P<0.01), HA (R2=0.91, P<0.01), FA (R2=0.91, P<0.01) and HU (R2=0.88, P<0.01). The cluster was mainly divided into two parts as manure fertilization and inorganic fertilization, based on the increases in HA, FA and HU. These results suggest that long term fertilization with manure favours carbon sequestration in HS and is mainly stabilized as HU, while the HA becomes more aliphatic. We conclude that increases in SOC can be linked to changes in the molecular characteristics of HS fractions under long term fertilization.