The synthesis of humic acids graft copolymer and its adsorption for organic pesticides

humic acid graft copolymer (PSt-g-HA) was prepared by graft copolymerization of Humic acid (HA) with styrene and the sorption of three selected organic pesticides, parathion-methyl, carbaryl and carbofuran by PSt-g-HA acid and untreated humic were also examined, respectively. The PSt-g-HA had relatively high aromatic carbons content because the grafted copolymerization of polystyrene entered into condensed domains in HA, whereas the removal of the polar function groups, such as carboxyl and phenolic hydroxyl group, was performed. For above reasons, the sorption capacity of three organic pesticides (parathion-methyl, carbaryl and carbofuran) on PSt-g-HA increased by 64.1% to 95.2%.     

Adsorption of humic acid by powdered activated carbon in saline water conditions

The adsorption of humic acid (HA) by powdered activated carbon (PAC) in saline waters has been examined in the absence and presence of metal salt coagulants. The study showed that adsorption of HA by PAC can be significantly greater in saline water compared to freshwater and low conductivity water. An optimal adsorption was attained at saline concentrations corresponding to synthetic seawater diluted to 12.5-25% of its original concentration. In undiluted synthetic seawater the adsorption of HA from solution by PAC was comparable with that of local tap water in terms of initial adsorption rate and total removal. The enhanced adsorption is believed to be a combination of reduced electrostatic repulsion between the HA and PAC at high salt concentrations, and chemisorption due to chemical bonding between the functional groups. The effects of adding a metal salt coagulant, either aluminium sulphate or ferric chloride, on overall HA removal were found to depend strongly on the coagulant dose, solution pH and the sequence of addition of the PAC and metal salt coagulant. Addition of the PAC shortly before the coagulant was found to give the greatest removal of HA.     

Catalytic ozonation of humic acids with Fe/MgO

Humic acids were degraded by ozone at room temperature in a stirred tank reactor and a fixed bed reactor with Fe/MgO catalysts. Experimental results show that the ozonation with Fe/MgO induced a significant reduction in UV absorbance of humic acids as compared to ozone alone. Fe/MgO was the most efficient catalyst to degrade humic acids in the presence of ozone. GPC (gel permeation chromatography) showed that the humic acids with high molecular weight could be severely decomposed into organic compounds with low molecular weight on the Fe/MgO catalyst, indicating that humic acids could be catalytically decomposed. The continuous reaction experiments with the palletized catalysts supported that humic acids can be removed by catalysis as well as adsorption.     

Effects of heavy metals and polyelectrolytes in humic substance coagulation under saline conditions

Charge neutralisation plays a major role in heavy metal and humic substance removal in water treatment. Humic substances have no readily identifiable structure and they consist of anionic macromolecules of low to moderate molecular weight. Humic substances are easily coagulated using cationic metals and polyelectrolytes. Different concentrations of humic substances have been coagulated with different concentrations of heavy metals and/or polyelectrolytes. The charge neutralisation was determined using U.V. spectrophotometer. Humic substance removal increased with increasing salinity level until reaching a point where HS destabilization is considered complete and salinity no longer play a role in HS removal. Humic substance removal increased with increasing heavy metals concentration and precipitation was experienced at high concentrations of heavy metals (15–20 mg/L) and low concentration of humic substances (10 mg/L). In addition, HS removal also increased with increasing polyelectrolyte concentration. Diallydimethylammonium chloride (PDADMAC) polyelectrolyte was more effective in humic substance coagulation compared to copolymer of dimethyl aminoethyl acrylate (CoAA). The addition of heavy metals in polyelectrolyte coagulation increased humic substance removal due to the combined charge neutralization of the metals and polyelectrolytes.     

Mechanistic aspects of oxalic acid oxidation by photocatalysis and ozonation

Oxalic acid has been oxidised in acidic aqueous solutions (pH 3) using photocatalysis and ozonation alone or coupled. The simultaneous presence of ozone, titanium dioxide and near UV irradiation increases the oxidation rate of oxalic acid to values greater than those deriving from the single contributions of photocatalysis and ozonation. In particular in the present paper ozonation alone, heterogeneous photocatalysis and also combined ozonation with heterogeneous photocatalysis have been used for the oxidation of oxalic acid at acidic pH in the presence of TiO₂ Degussa P25. A likely mechanism, able to explain both the homogeneous and heterogeneous processes, is discussed.     

Site-energy distribution analysis of humic acids adsorption by zeolitic tuff

Within a research program aimed to utilize natural zeolites for pedotechnical purposes, such as to rebuild degraded soils, to improve soil fertility and to remove soil pollutants, the adsorption process of humic acids (HAs) on untreated Neapolitan Yellow Tuff and on Ca²⁺-enriched samples was investigated in the temperature range 1–45°C. Experimental data showed a negligible temperature effect indicating that ΔH ≈ 0. Moreover, Scatchard-like plots suggested the occurrence of more than one adsorption sites for both samples. A good fit of the adsorption isotherms was obtained by two-site Langmuir equation. For both sites the HAs affinity was not modified by Ca²⁺-enrichment and ΔS° was >0. The adsorption of HAs on tuff is an entropy-driven process.     

Coagulation of humic acid by aluminium sulphate in saline water conditions

Chemical coagulation has been applied in practice for the pre-treatment of saline waters in the process of water treatment by membrane desalination. The relative magnitude of the ionic strength and individual ion concentrations (cations and anions) in saline waters leads to differences in the nature of coagulation by hydrolysing metal salts compared to the treatment of freshwaters with respect to colloid destabilisation, coagulation mechanisms, and colloidal removal. In this study, the coagulation of saline solutions containing humic acid by aluminium sulphate has been examined systematically. Laboratory experiments have been undertaken over a wide range of pH (4 to 10) and alum dose (3-1000 μM Al) conditions. Coagulation has been assessed principally in terms of colloidal particle removal (change in UV-absorbance) and colloid surface charge (zeta potential). The experimental results have shown that the coagulation ofhumic substances in seawater has some distinctly different characteristics compared to the well-established coagulation behaviour in surface freshwaters. These differences can be attributed to the solution chemistry and its modification of the aluminium hydrolysis reactions and the nature of the precipitates formed. Based on the results, coagulation performance domains (Al dose vs. pH) are defined, and the mechanisms of coagulation are discussed.     

Removal of organic matter by coagulation enhanced with adsorption on PAC

The removal of humic acids and phenol from model solution by coagulation and adsorption on powdered activated carbon (PAC) was investigated. A PAX XL-69 polyaluminum chloride was applied as a coagulant. The adsorption of humic acids and phenol on activated carbon for single- and bi- component solutions was studied. It was found that coagulation without PAC addition was less effective than the adsorption-coagulation integrated system. Coagulation enhanced with adsorption on activated carbon was more effective when coagulation was preceded by adsorption than when the two processes were carried out simultaneously. The best results were obtained at pH 7. Phenol and color were removed pletely, UV₂₅₄ absorbance was reduced by about 99% and COD-Mn was reduced by 81-89%.     

Characteristics of unburned carbons and their application for humic acid removal from water

Two unburned carbons (UCs) were separated from coal fly ash and their physicochemical properties were characterised using N₂ adsorption, XRD, SEM, XPS, FT-IR and potentiometric mass titration. Chemical treatments using HNO₃ and KOH were also conducted on one of the unburned carbons. The adsorption of humic acid from aqueous solution was performed on these untreated and chemically treated UCs. It was found that the UCs showed different porous structure and surface chemical properties, which influenced their adsorption behaviour. UCs exhibited high adsorption capacity for humic acid. After chemical treatment, the textural structure and surface functional groups of the unburned carbon were changed and the adsorption behaviour showed significant difference. Acid treatment did not change the surface area but reduced the functional groups while basic treatment significantly enhanced the surface area in microporous section but still reduced the surface functional groups. Particle size and pH solution will also influence the adsorption capacity. The adsorption will increase with decreasing particle size for humic acid. Higher pH solution will reduce humic acid adsorption on unburned carbon. Ionic strength will also affect humic acid adsorption showing positive effect on adsorption capacity.     

硝酸氧化对风化煤中腐植酸含量的影响

研究了硝酸浓度、氧化时间及煤酸比对提高风化煤中腐植酸含量的影响。结果表明,当煤酸比为０．４、硝酸浓度为３３％、氧化时间３０ｍｉｎ时,风化煤的腐植酸含量可由２９．５％提高到６１．４％     

Adsorption of humic acid onto pillared bentonite

Pillared bentonite, a clean and cost-effective adsorbent with high specific areas of 111.3 m²/g and high basalspacing of 1.98 nm, was prepared for the removal of humic acid from water. It is effective for the removal of humic acid with a high adsorption capacity of 537 mg/g, and adsorption is favored under acid conditions. Adsorption is dependent on ionic strength and dissolved NaCl enhanced adsorption. Over 97% removal was observed under natural pH conditions from humic acid solutions containing 10 mg/L Ca²⁺ or Mg²⁺, which suggests that pillared bentonite can be an effective adsorbent for the removal of humic acid for drinking water purification. Pillared bentonite can be regenerated with NaOH, and the regeneration efficiency reaches 83% and 85% when the concentration of NaOH reaches 0.025 and 0.05 mol/L. The mechanism for adsorption of humic acid to pillared bentonite is discussed.     

Modeling of cadmium(II) adsorption on kaolinite-based clays in the absence and presence of humic acid

Cadmium adsorption on kaolinite-based clays in the absence and presence of humic acid was modeled with the aid of the FITEQL 3.2 computer program using a modified Langmuir approach for capacity calculations. Formation of surface–metal ion and surface–humate–metal ion complexes was assumed using the DLM approach. As Cd(II) adsorption was ionic strength-dependent, the adsorption experiments were carried out in solutions containing two different concentrations of an inert electrolyte (0.1 M and 0.005 M NaClO₄). The surface sites responsible for the adsorption were assumed to be the permanent charges, ≡S₁OH silanol groups and carboxyl groups having pK_a values close to that of the silanol groups, and ≡S₂OH aluminol groups and phenol groups with pK_a values close to that of the aluminol groups, because the studied clays (partly composed of clay soil) contained organic carbon. Cd²⁺ ions were assumed to bind to the surface in the form of outer-sphere X₂²⁻ Cd²⁺ and inner-sphere ≡SOCd⁺ monodentate complexes. When humic acid was added, Cd(II) adsorption was modeled using a multi-site binding model by the aid of FITEQL3.2. The fit between model and experimental values was excellent in each case. Since the stability of the ternary surface complexes in the presence of humic acid was higher than that of the corresponding binary surface–cadmium ion complexes, the adsorption vs. pH curves were much steeper (and distinctly S-shaped) compared to the tailed curves observed in binary clay–cadmium ion systems. The clay mineral in the presence of humic acid probably behaved more like a chelating ion-exchanger for heavy metal ions than as a simple inorganic ion exchanger.     

Adsorption of glucosinolates to metal oxides, clay minerals and humic acid

Glucosinolates are thioglucosides produced by plants belonging to the Capparales order. Glucosinolates can upon hydrolysis be transformed into a variety of bioactive compounds with a potential to serve as naturally produced pesticides. This paper presents results on the adsorption of prop-2-enyl and benzyl glucosinolate to two metal oxides (amorphous aluminium hydroxide and goethite), two clay minerals (kaolinite and montmorillonite) and to humic acid at different initial concentrations and at pH 4 and 8. The results show that the glucosinolates are weakly adsorbed to the variable-charge minerals with K_d ranging from 0.00 to 1.85 L kg^− 1 and that adsorption was higher at pH 4 than 8 indicating that adsorption takes place by electrostatic interactions between the negatively charged glucosinolates and positive sites on the minerals. On the humic acid higher K_d values were observed for prop-2-enyl glucosinolate (7.22 and 12.3 L kg^− 1), indicating that hydrophobic interactions may take place between the glucosinolate and humic acid. On the montmorillonite anion exclusion was observed as an effect of the negatively charged glucosinolates being repelled from the negatively charged montmorillonite surface. Thus glucosinolates will be very mobile in the soil environment with the potential of leaching to ground and surface waters where the toxic hydrolysis products may be formed.     

Specific adsorption of arsenic and humic acid on Pt and PtO films

A study of specific adsorption of arsenic (As) and humic acid (HM) onto Pt and PtO films using cyclic voltammetry and cyclic massogram in 0.5-M H₂SO₄ is presented, which may serve as an alternative to studies involving specific adsorption of these species on soil minerals. Adsorption of As is normally evaluated by conducting batch adsorption experiments, followed by analysis using hydride-generation atomic absorption spectrophotometry (HGAA) or inductively coupled plasma-optical emission spectrometry (ICP-OES). We found that specific adsorption of As and HM depends both on the surface and on these species present in the adsorption solution. HM does not desorb previously adsorbed As at the HM concentrations used in the present study, but it does co-adsorb with As from a 1 × 10⁻⁶-M aqueous solution of As₂O₃ containing 1 mg of carbon L⁻¹ HM. Arsenic adsorbs strongly on Pt in the presence of HM or during sequential specific adsorption with HM.     

Specific adsorption of propiconazole and humic acid on Pt and PtO films

We herein report a study of specific adsorption of propiconazole (PPC) and humic acid (HM) on Pt and PtO films, using cyclic voltammetry (CV) and cyclic massogram (CM) in 0.5 M H₂SO₄. This approach serves as an alternative to studies involving specific adsorption on soil minerals (e.g., clays, Al/Fe oxides), in which adsorption is evaluated by conducting batch or column sorption experiments and analysis by liquid scintillation counter, high performance liquid chromatography (HPLC), gas chromatography (GC), or capillary electrophoresis. We found that HM adsorbs specifically on Pt and does not interfere with PPC adsorption at the HM concentration ranges examined (10 mg of carbon L⁻¹). PPC adsorbs strongly on Pt in the presence of HM. Also, PtO films were utilized to study HM and PPC adsorption.     

Sorption and desorption characteristics of cobalt in clay: Effect of humic acids

The effect of humic acid (HA) on the sorption and desorption of Co(II) on kaolin was investigated. Cobalt ions interact with carboxylic and phenolic groups in HA and form HA-cobalt complex. The solubility of HA was affected by the surrounding pH. The presence of HA reduced the equilibrium time for the Co(II) sorption on kaolin compared to the absence of HA. Solution pH, not HA concentration, was a main factor to affect sorption of Co(II) on kaolin in the presence of HA. In the kinetic sorption and desorption of Co(II) on kaolin, the presence of HA shortened the breakthrough of Co(II) sorption on kaolin compared to bare kaolin, and HA solution enhanced the displacement of Co(II) from kaolin compared with deionized water.     

Inactivation of Bacteria E. coli and photodegradation of humic acids using natural sunlight

In this work, the disinfection of bacteria Escherichia coli and degradation of humic acids, using sunlight, sunlight + TiO₂ (Degussa P25) in suspension or TiO₂ supported on Ahlstrom paper (NW10) fixed around concentric tubes inside the photoreactor, were investigated in a pilot plant. The inactivation of bacteria E. coli proved to be more efficient (only 1 kJ_UV/L for 5-log decrease in concentration) when using sunlight and TiO₂ in suspension. However, true disinfection was not achieved under the conditions reported in this work. A first-order model was able to fit the photocatalytic deactivation of E. coli ([TiO₂] = 50 mg/L) with an inactivation rate constant of 8.21 L/kJ. A Langmuir–Hinshelwood-like model was successfully applied for modelling photolysis and supported-TiO₂ photocatalysis of bacteria E. coli, considering an initial latency period, a classical log-linear behaviour and a tail region. The effect of the flow rate between 5 and 15 L/min was negligible in the inactivation of E. coli in the presence of sunlight and supported TiO₂. The inactivation rate constant increased with the initial concentration of E. coli. Almost no bacterial regrowth was observed in dark conditions during 24 h after illumination of E. coli suspension until complete deactivation. The humic acids (HA) degradation was also investigated by solar photocatalysis with suspended and supported TiO₂ and exposure to sunlight-only, in a CPC photoreactor. Supported-TiO₂ photocatalysis of HA originated 70% concentration reduction after Q_UV ≈ 14 kJ/L, whereas only 20% reduction was obtained by photolysis and slurry photocatalysis. First-order kinetic constants of 0.088 and 0.010 L/kJ were obtained, respectively, for suspended and supported TiO₂.     

Evaluation of humic acid photocatalytic degradation by UV–vis and fluorescence spectroscopy

Photodegradation of humic substances causes drastic changes in the UV–vis absorption and fluorescence properties of humic acids. In this study it is intended to fulfill the lack of knowledge about the spectral changes of humic acids during photocatalytic oxidation processes and elucidate the effects observed on the molecular size distribution of humic acid focusing on their analysis by UV–vis and fluorescence spectroscopy.

As confirmed by the spectroscopic evaluation of the molecular size distribution data, photocatalytic degradation of humic acid leads to the formation of lower molecular size (small fractions) and higher UV absorbing compounds. For fractions less than 10 kDa, UV₂₅₄ absorbing moieties in treated humic acid samples become higher than that of raw humic acid designating the generation of new species during photocatalysis. UV–vis spectroscopic changes were also evaluated by the parameters relating to the concomitant removal of the total organic carbon as well as by the ratios using absorption values at discrete wavelengths. Moreover, the fluorescence spectra of treated humic acid samples show decreasing intensity profiles with increasing photocatalytic irradiation time.     

腐植酸类物质凝聚及沉淀特性的研究

通过对不同产地，不同提取方法获得的煤炭腐植酸和经过生物发酵人工合成的生化黄腐酸分别进行铝离子絮凝实验和酸化沉淀实验，发现煤炭腐植酸、腐植酸盐、棕惰酸、黄腐酸都同时具有被铝离子定量絮凝和在酸性条件下定量沉淀的特性，这类物质具有极其相近的化学特性。生化黄腐酸在上述两方面显示出与煤炭腐植酸十分不同的特性。     

Fouling effects of humic and alginic acids in nanofiltration and influence of solution composition

The objectives of this research were to investigate the combined and individual influence of hydrophobic and hydrophilic fractions of NOM on the fouling of thin-film composite nanofiltration (NF) membranes, and also the roles of solution chemistry on the permeate flux and fouling. Combined fouling is compared to the individual fouling behaviors (i.e., alginate or humic acid alone).Experiments were conducted using a “cross-flow” pilot-scale membrane unit with a full circulation mode. Fouling experiments were performed with individual and combined humic acid and alginate.The results demonstrated that increasing organic concentration increased greatly the rate and extent of flux reduction. Individual alginate fouling was more detrimental than individual humic acid fouling, and alginate exhibited greater flux decline than humic acid fouling alone at the same conditions. A higher flux decline was observed with increasing proportions of aliginate in combined fouling. In other word, there are antagonistic effects during combined fouling because the charge functional groups of two above foulants are negative and increase electrostatic repulsion between two foulants and also foulant-membrane. The flux reduction increased with increasing ionic strength, foulant concentrations, and with lower pH. This observation implies the importance of interaction between various foulants for deeper understanding of fouling phenomena. The membrane fouling was largely dependent on organic properties and fractions.