Comparative assessment of thermal and thermochemical activation methods of South African kaolinite for effective adsorptive sequestration of humic acid from aqueous media

Adsorptive removal of humic acid from aqueous solution on polyaniline/attapulgite composite

Adsorption of low concentration humic acid from water by palygorskite

Adsorption and desorption of humic and fulvic acids on SiO 2 particles at nano- and micro-scales

This investigation compared the adsorption behavior of humic acid (HA) on cellulose, chitosan and nano zerovalent iron/chitosan (nZVI/chitosan). Results show that nZVI/chitosan is very effective in the adsorption of HA from aqueous media. The feasibility of using nZVI/chitosan as an adsorbent for the simultaneous removal of nitrate and HA from aqueous media was also studied. Structural analyses of the samples were identified by TEM, FT-IR, EDX, XRD and N2 isotherms. The effects of pH, amount of composite, nitrate concentration, HA concentration and contact time and their interactions on responses were explored by central composite design (CCD) and response surface methodology (RSM). The optimal conditions of pH (5.5), adsorbent amount (0.098 g), reaction time (27 min) and initial concentrations (110 mg/L for nitrate and 30 mg/L for HA) were obtained from the desirability function. The adsorption properties of the resulting nanocomposite toward nitrate and HA were investigated through kinetic and isotherm studies. The adsorption kinetics was found to fit the pseudo-second order model. The obtained results indicate that nitrate uptake fitted well with Langmuir model while Freundlich isotherm was the best model for describing the multilayer uptake of HA from aqueous solutions. Moreover, nZVI/chitosan nanocomposite illustrates a very high antibacterial activity against pathogen bacteria strains such as Staphylococcus aureus ATCC 25935, ATCC 25923, and Pseudomonas aeruginosa ATCC 27853. The findings reported in this investigation highlight the potential of using nZVI/chitosan as a promising adsorbent for the simultaneous removal of nitrate and HA from aqueous solutions.

Adsorption of lignite-derived humic acids on coal-based mesoporous activated carbons

In this paper, a quartz crystal microbalance with dissipation monitoring (QCM-D) is used to investigate humic acid (HA) adsorption onto alumina (Al(2)O(3)). The amount of adsorption and layer structures of HA were determined by the real-time monitoring of resonance frequency and energy dissipation changes (Δf and ΔD). The effect of HA concentration, HA molecular characteristics (molecular weight and polarity), and pH on HA adsorption onto Al(2)O(3) were investigated. The mass of HA adsorption increases as the concentration of HA increases. The masses are about 24, 60, and 87 ng cm(-2) as the concentration of DOC is 1.0, 4.85, and 92.0 mg L(-1), respectively. The adsorbed layer of HA is more nonrigid, and the mass of HA adsorption is higher at weakly acidic pH values. It was 20, 80, 65, and 45 ng cm(-2) at pH values of 4.5, 5.5, 6.5, and 8.0, respectively. This reveals that efficient HA removal by coagulation at weakly acidic pH values is not just due to the hydrolysis of Al ions as previously presumed. The adsorbed layer of hydrophobic HA is more nonrigid than hydrophobic HA (fractionated by Amberlite XAD-8 resin), and the mass adsorption for the hydrophobic fraction is about four times higher than the hydrophilic fraction (120 ng cm(-2) and 30 ng cm(-2)). The method is of value in the research to establish a quantified calculation model for the coagulation process.

Humic acid (HA) impairs water quality due to its reactivity with many substances present in water. During the drinking-water treatment process and water distribution via water supply system, HA present in water may react with chlorine and other disinfects <br /> producing harmful disinfection by-products (DBPs), which are categorized by the International Agency for Research on Cancer (IARC) in groups 2A (probably carcinogenic to humans) or 2B (possibly carcinogenic to humans). Several studies have investigated and reported increased HA removal by iron-coated sorbents. Therefore, the aim of this study was to examine the removal of HA from water by two commercially available bituminous coal-based activated carbons (ACs), Cullar D (Cm) and Hydraffin 30N (Hm). Prior to testing the chosen adsorbents were chemically modified according to two protocols: (1) oxidation by acid mixture (m1), and (2) oxidation with acid mixture followed by iron-ions impregnation (m2). The batch adsorption tests were used to test their efficiency in HA removal under various values of process parameters (initial HA concentration, pH, contact time, adsorbent mass, and temperature). The results showed that up to 96 % of HA removal can be obtained by Cullar D modification Cm1, while maximum uptake of HA by Hydraffin 30N modification was achieved with Hm1 (62.1 %). After surface saturation with Fe3+ –ions (m2), both activated carbons showed similar and lower performances in HA removal (Cm2 up to 66.5 %, and Hm2 up to 50.3 %). FTIR analysis confirmed differences in modified AC structures, as well as favorable structure of Cm1 for HA adsorption.

Removal of humic acid from aqueous solution by magnetically separable polyaniline: Adsorption behavior and mechanism

The presence of natural organic matter (NOM) in drinking water can increase the levels of copper released from copper pipes to water and inhibit the formation of protective deposits such as malachite. Since adsorption of NOM on copper pipes surfaces is believed to be one of mechanisms that explains this phenomenom, the objective of this study was to determine kinetics and the adsorption equilibrium of main components of NOM, humic acid (HA) and fulvic acid (FA), onto copper surfaces. The kinetics and equilibrium adsorption of HA and FA on copper foils were examined using batch experiments at 22°C. HA and FA followed pseudo second-order kinetics adsorption. Rate constants measured were 2.59 × 10−1 (mgTOC cm−2 h−1) for HA and 3.13 × 10−1 (mgTOC cm−2 h−1) for FA. The adsorption behavior of HA and FA on the copper surface is in accordance with the Langmuir adsorption isotherm. Langmuir adsorption constants measured were 5.98 × 10−2 L mg−1 for HA and 4.78 × 10−2 L mg−1 for FA. The copper foils exposed during five months to FA formed malachite deposits, whereas those exposed to HA did not and just cuprite was found. The results of this study showed that both HA as well as FA adsorption on copper surfaces is favored and no significant differences were found in the adsorption parameters calculated for both compounds. However, the inhibition of the malachite precipitation could be attributed to the HA adsorption.

Removal of humic acid from aqueous solution by cetylpyridinium bromide modified zeolite

Sorption of hydrophobic organic compounds (HOCs) to natural organic matter (NOM) is an important process that affects the transport, transformation, bioavailability, and fate of HOCs in the environment. Manufactured nanoparticles (NPs) such as nano-oxides will inevitably enter the environment in the processes of their production, transfer, and use and could be coated by the ubiquitous NOM. Thus, sorption of HOCs to NOM in the environment could be affected by the NP interactions with NOM. Furthermore, the toxicity of nano-oxides could be increased due to the adsorbed HOCs. Therefore, sorption of phenanthrene by nano-Al(2)O(3) coated with humic acid (HA) was examined in this study to explore the possible effect of nanoparticles (NPs) on the environmental behavior of HOCs and the potential environmental and health risks of NPs. Four HAs were sequentially extracted with 0.1 mol/L NaOH from a peat soil. HAs, nano-Al(2)O(3), and HA-coated nano-Al(2)O(3) were characterized by techniques such as elemental analysis, solid-state (13)C NMR, N(2) surface area analysis, and zeta potential measurement. Adsorption isotherms of HAs by nano-Al(2)O(3) and phenanthrene by HAs and HA-coated nano-Al(2)O(3) were obtained using a batch equilibration technique at 25 +/- 1 degrees C. HA concentrations were measured by total organic carbon analysis. Phenanthrene concentrations were measured by liquid scintillation counting. The adsorption maxima of HAs by nano-Al(2)O(3) was one order of magnitude higher than that by soil inorganic minerals. Phenanthrene isotherms of HA-coated nano-Al(2)O(3) were more nonlinear than that of their respective bulk HAs. Concentration-dependent organic carbon-normalized sorption coefficients (K' (oc)) of phenanthrene by HA-coated nano-Al(2)O(3) were lower than those for their respective bulk HAs, especially at relatively high concentrations. Isotherm nonlinearity of phenanthrene could be interpreted by a combination of partitioning accompanied by linear isotherm with adsorption accompanied by nonlinear isotherm. HA conformation changes during their adsorption on nano-Al(2)O(3) could play an important role in phenanthrene sorption and were responsible for higher nonlinearity of phenanthrene isotherms and lower phenanthrene K' (oc) on the adsorbed HAs than their respective bulk HAs. Adsorption of HA on nano-Al(2)O(3) would form a more condensed HA state with higher pi-polarity/polarizability and lower partitioning affinity than the respective bulk HA, leading to an increase of relative contribution of adsorption to the total sorption and more nonlinear phenanthrene isotherms in the adsorbed HA due to the increase in phenanthrene adsorption affinity and decrease in phenanthrene partitioning affinity. Adsorption of HA on nano-Al(2)O(3) was much higher than that on soil oxide minerals and could form a more condensed HA state with higher pi-polarity/polarizability and lower partitioning affinity than the bulk HA, causing the significant difference in phenanthrene sorption between the adsorbed HA and the respective bulk HA. Therefore, once released in the environment, NPs such as nano-Al(2)O(3) will strongly alter the environmental transport, fate, and bioavailability of HOCs and could be potentially more toxic due to the adsorbed toxic chemicals. Due to the high adsorption of HA on nano-Al(2)O(3) and its significant effect on phenanthrene sorption, interactions of NOM with nano-oxides and their mechanistic relations with NOM conformation changes and HOC sorption merit further research. In addition, due to the higher sorption of phenanthrene on the HA-coated nano-Al(2)O(3) than the pure counterpart, the effect of NOM and HOCs on the ecotoxicity of NPs should be addressed in the future.

Preparation of novel magnetic chitosan nanoparticle and its application for removal of humic acid from aqueous solution

Modified humic acid (MHA) binder based on lignite humic substances is a novel sort of promising organic binder for iron ore pellets. Humic acid (HA) is one of the main ingredients of MHA binder. Pure HA was firstly isolated from lignite and then adsorption of HA onto magnetite particle surface was investigated. The final results indicate that the adsorption of HA onto magnetite surface accords with Langmuir model well, and it is evidently influenced by the initial HA concentration and solution pH value. Adsorption depends on chemical interaction at pH values above the PZC (the pH where the Zeta potentials of minerals are zero) of magnetite, while electrostatic attraction and chemical interaction both contribute to the adsorption at pH values below the PZC.

Dissolved organic matter (DOM) affects arsenite [As(III)] toxicity by altering its sorption equilibrium at the cell wall interface. A better understanding of such mechanism is of great importance to assess As(III) ecotoxicity in aquatic systems. Batch experiments were conducted to study the effects of DOM on the regulation of As(III) sorption and toxicity in the diatom Navicula sp. The influence of humic acid (HA) on As(III) toxicity was assessed by measuring algal growth, chlorophyll a, and reactive oxygen species (ROS), whereas As(III) mobility across the cell wall was estimated by determining the concentration of intracellular, cell-wall-bound, and free As(III) ions in cell media. Results showed that the effects of HA on arsenite toxicity varied depending on various combinations of As(III)-HA concentrations. EC50 had an approximate threefold increase from 8.32 (HA-free control) to 22.39 μM (at 20 mg L(-1) HA) when Navicula sp. was exposed to 1.0-100.0 μM of As(III), compared to an overall low complexation ratio of HA-As(III) in a range of 0.91-6.00 %. The cell wall-bound and intracellular arsenic content decreased by 19.8 and 20.3 %, respectively, despite the lower arsenite complexation (2.10 ± 0.16 % of the total As). Meanwhile, intracellular ROS was decreased by 12.6 % in response to 10.0 μM As(III) and 10 mg L(-1) HA vs. the HA-free control. The significant contrast indicated that complexation alone could not explain the HA-induced reduction in arsenite toxicity and other factors including HA-cell surface interactions may come into play. Isotherms describing adsorption of HA to the Navicula sp. cells combined with morphological data by scanning electron microscopy revealed a protective HA floccule coating on the cell walls. Additional Fourier transform infrared spectroscopic data suggested the involvement of carboxylic groups during the adsorption of both HA and As(III) on the Navicula sp. cell surface. Collective data from this study suggest that cell wall-bound HA can moderate As(III) toxicity through the formation of a protective floccule coating occupying As(III) sorption sites and decreased effective functional groups capable of binding As(III). Our findings imply that As(III) toxicity can be alleviated due to the increased hindrance to cellular internalization of As(III) in the presence of naturally abundant DOM in water.

Enhanced removal of humic acid from water by micelle-montmorillonite composites: Comparison to granulated activated carbon