Showing papers on "Oxalic acid published in 2014"

Zirconium-carbon hybrid sorbent for removal of fluoride from water: oxalic acid mediated Zr(IV) assembly and adsorption mechanism

Abstract: When activated carbon (AC) is modified with zirconium(IV) by impregnation or precipitation, the fluoride adsorption capacity is typically improved. There is significant potential to improve these hybrid sorbents by controlling the impregnation conditions, which determine the assembly and dispersion of the Zr phases on carbon surfaces. Here, commercial activated carbon was modified with Zr(IV) together with oxalic acid (OA) used to maximize the zirconium dispersion and enhance fluoride adsorption. Adsorption experiments were carried out at pH 7 and 25 °C with a fluoride concentration of 40 mg L–1. The OA/Zr ratio was varied to determine the optimal conditions for subsequent fluoride adsorption. The data was analyzed using the Langmuir and Freundlich isotherm models. FTIR, XPS, and the surface charge distribution were performed to elucidate the adsorption mechanism. Potentiometric titrations showed that the modified activated carbon (ZrOx-AC) possesses positive charge at pH lower than 7, and FTIR analysis d...

From NdFeB magnets towards the rare-earth oxides: a recycling process consuming only oxalic acid

Abstract: A chemical process which consumes a minimum amount of chemicals to recover rare-earth metals from NdFeB magnets was developed. The recovery of rare-earth elements from end-of-life consumer products has gained increasing interest during the last few years. Examples of valuable rare earths are neodymium and dysprosium because they are important constituents of strong permanent magnets used in several large or growing application fields (e.g. hard disk drives, wind turbines, electric vehicles, magnetic separators, etc.). In this paper, the rare-earth elements were selectively dissolved from a crushed and roasted NdFeB magnet with a minimum amount of acid, further purified with solvent extraction and precipitated as pure oxalate salts. The whole procedure includes seven steps: (1) crushing and milling of the magnet into coarse powder, (2) roasting to transform the metals into the corresponding oxides, (3) the selective leaching of the rare-earth elements with acids (HCl, HNO3) to leave iron behind in the precipitate, (4) extracting remaining transition metals (Co, Cu, Mn) into the ionic liquid trihexyl(tetradecyl)phosphonium chloride, (5) precipitating the rare earths by the addition of oxalic acid, (6) removing the precipitate by filtration and (7) calcining the rare-earth oxalates to rare-earth oxides which can be used as part of the feedstock for the production process of new magnets. The magnet dissolution process from the oxides utilized four molar equivalents less acid to dissolve all rare earths in comparison with a dissolution process from the non-roasted magnet. Moreover, the less valuable element iron is already removed from the magnet during the dissolution process. The remaining transition metals are extracted into the ionic liquid which can be reused after a stripping process. Hydrochloric acid, the side product of the rare-earth oxalate precipitation process, can be reused in the next selective leaching process. In this way, a recycling process consuming only air, water, oxalic acid and electricity is developed to recover the rare earths from NdFeB magnets in very high purity.

Producing photoactive, transparent and hydrophobic SiO2-crystalline TiO2 nanocomposites at ambient conditions with application as self-cleaning coatings

Abstract: Nowadays, the enhancement of atmospheric pollution is dramatically increasing the presence of soiling on buildings in every city of the world. Thus, the development of photocatalysts as self-cleaning coatings is a promising challenge. The first object of this work was to develop a simple synthesis route for obtaining SiO2-crystalline TiO2 nanocomposites at ambient temperature. Thus, it meets the requirements to produce photoactive coatings on buildings and, additionally, it can be used in other applications requiring low temperature. The second objective was to gain insights into the structure of these materials and to establish the relationship between their structure and their performance as photocatalysts. The synthesis process involves mixing titanium and silicon alkoxides in the presence of oxalic acid. An organic silica oligomer is also added to reduce surface energy and consequently, to give hydrophobic properties to the material. These products were applied as a coating on marble specimens in order to investigate their effectiveness. The results obtained highlight that oxalic acid acts a chelating agent of the titanium precursor, giving rise to a homogeneous TiO2–SiO2 material. In addition and most importantly, oxalic acid produces photoactive anatase crystals at ambient temperature. From our investigation on the structure of these materials, we conclude that the formation of independent domains of TiO2 inside of SiO2 matrix, and the anatase crystal size are key factors for improving the photoactivity of the coatings. We also conclude that the oxalic acid concentration plays a crucial role in the formation of this optimum structure.

Simultaneous destruction of Nickel (II)-EDTA with TiO2/Ti film anode and electrodeposition of nickel ions on the cathode

Abstract: Ethylenediaminetetraacetic acid (EDTA) forms stable complexes with toxic metals such as nickel. A combined photocatalytic-electrochemical system using TiO 2 /Ti plate as anode and stainless steel as cathode achieves the simultaneous decomplexation of Ni-EDTA and recovery of nickel. Ni-EDTA was efficiently destroyed in photoelectrocatalytic process in comparison with individual photocatalytic and electro-oxidation process. At 60 min, removal efficiencies of Ni-EDTA were 75%, 12%, and 5%, respectively. At 180 min, the removal efficiency of Ni-EDTA in the photocatalysis and electrolysis processes is only 21% and 18%, respectively. By contrast, nearly 90% Ni-EDTA is removed in the photoelectrocatalytic process. The recovery percentage of nickel was determined to be 45%, 21%, and 5% in the photoelectrocatalysis, electrolysis, and photocatalysis process, respectively. The deposition of nickel ions at the cathode was confirmed by scanning electron microscopy analysis and the nickel species were identified via X-ray photoelectron spectra as nickel with zero value. The removal of Ni-EDTA and recovery of nickel ions increased with the current density and favored at acid conditions. Intermediates detected using a capillary electrophoresis and a high performance liquid chromatography includes Ni-NTA, glycine, maleic acid, glycolic acid, formic acid, acetic acid, oxalic acid, and oxamic acid were identified. The decomplexation pathway of Ni-EDTA was proposed.

Promoting effect of nitration modification on activated carbon in the catalytic ozonation of oxalic acid

Abstract: A commercial activated carbon (AC) was modified with a nitration or amination method, and the effects of textural and chemical properties on the ability of the AC samples to destroy oxalic acid (OA) using ozone was investigated in this work. The degradation rates of OA on the nitrated and aminated AC samples increased by 38.5% and 9.6%, respectively. The adsorption capacity of the AC sample was not enhanced after modification, but the decomposition rate of ozone in solution increased. The surface area of AC significantly decreased after nitration because the entrance of micropores and some larger pores were blocked by the modified functional groups. In addition, the surface area was recovered when the nitrated AC was further aminated. We demonstrated that the enhancement in the catalytic activity was primarily caused by the differences in surface chemistry. The pH(pzc) values and Boehm titration results showed that nitration increased the acidity of the AC, while more basic groups were grafted after amination. X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) results confirmed that-NO2 and acid oxygenated groups were simultaneously grafted onto AC during nitration. Meanwhile, the-NO2 group was completely reduced to-NH2 and the carboxylic groups were partially reduced during amination. The basic groups (-NH2 and possible pyrone groups) enhanced the catalytic activity of the aminated AC sample, and the increased activity of the nitrated AC material was mainly due to the acid oxygenated surface groups. (C) 2013 Elsevier B.V. All rights reserved.

Phosphorus recovery from sewage sludge char ash.

Abstract: Phosphorus was recovered from the ash obtained after combustion at different temperatures (600 °C, 750 °C and 900 °C) and after gasification (at 820 °C using a mixture of air and steam as fluidising agent) of char from sewage sludge fast pyrolysis carried out at 530 °C. Depending on the leaching conditions (extraction time, acid load and acid concentration, and type of acid) 90% mass of the original P was recovered. Regarding char combustion ash, higher phosphorus yields are obtained from ash obtained at 900 °C than at 600 °C and 750 °C when using sulphuric acid. Combustion temperature does not affect phosphorus leaching with oxalic acid. A contact time of 2 h and an oxalic acid load of 10 kg kg−1 of P seem sufficient for phosphorus extraction. Almost all phosphorus present in gasification ash is leached after 2 h with both sulphuric and oxalic acid using an acid load of 14 kg kg−1 of P. Char ash is a possible renewable source of phosphorus and it can be an alternative to rock phosphate in fertilizer production. The combination of sewage sludge pyrolysis, combustion or gasification of the char and phosphorus extraction from the final solid residue contributes to the integral exploitation of sewage sludge.

Removal of malachite green dye from wastewater by different organic acid-modified natural adsorbent: kinetics, equilibriums, mechanisms, practical application, and disposal of dye-loaded adsorbent

Abstract: Natural adsorbent (Cinnamomum camphora sawdust) modified by organic acid (oxalic acid, citric acid, and tartaric acid) was investigated as a potential adsorbent for the removal of hazardous malachite green (MG) dye in aqueous media in a batch process. The extent of MG adsorption onto modified sawdust increased with increasing organic acid concentrations, pH, contact time, and temperature but decreased with increasing adsorbent dosage and ionic strength. Kinetic study indicated that the pseudo-second-order kinetic model could best describe the adsorption kinetics of MG. Equilibrium data were found to fit well with the Langmuir model, and the maximum adsorption capacity of the three kinds of organic acid-modified sawdust was 280.3, 222.8, and 157.5 mg/g, respectively. Thermodynamic parameters suggested that the sorption of MG was an endothermic process. The adsorption mechanism, the application of adsorbents in practical wastewater, the prediction of single-stage batch adsorption system, and the disposal of depleted adsorbents were also discussed.

Degradation of Eight Relevant Micropollutants in Different Water Matrices by Neutral Photo-Fenton Process under UV254 and Simulated Solar Light Irradiation – a comparative study

Abstract: This is a comparative study of photolytic degradation under exposure to UV254 nm and solar-simulator irradiation of a mixture of eight equally concentrated relevant micropollutants in the presence of H2O2 and Fe(II) in ultrapure water, Lake Geneva water, and effluent from a wastewater treatment plant (WWTP). The electron-spin resonance (ESR) experiments point to a low efficiency of singlet oxygen formation by the mixture of micropollutants. This finding corroborates with the chemical stability of the micropollutants under UVC irradiation (in decreasing order: gabapentin, metformin, metoprolol, atenolol, clarithromycin, primidone, methylbenzotriazole, and benzotriazole). The oxidation rate increased in the presence of low-concentration H2O2 and Fe(II), except for metformin and gabapentin. Gabapentin and metformin were the most persistent compounds, less than 24% were removed after 60 minutes of UV254/H2O2/Fe(II) treatment. The low micropollutant removal rates were observed in WWTP effluent and lake water, and using sunlight simulation. Guanylurea, phenol, oxalic acid, tartronic acid, glycolic acid, oxamic acid, and maleic acid, could also be detected as fragmental oxidation products. Furthermore, up to 300 µg/L of nitrate and ammonia were identified as final degradation products. Ecotoxicological tests showed that the degradation products are more toxic for algae Chlamydomonas reinhardtii than the parent compounds themselves.

Mechanochemical Reaction of Sulfathiazole with Carboxylic Acids: Formation of a Cocrystal, a Salt, and Coamorphous Solids

Abstract: The anhydrous solvent-free mechanochemical reaction of sulfathiazole, STZ, polymorphs I, III, and V with 10 carboxylic acids was monitored by powder X-ray diffraction (PXRD), attenuated total reflectance infrared (ATR-IR), and near-infrared (NIR) spectroscopy. A 1:1 cocrystal was observed with glutaric acid and the strongest acid, oxalic acid, gave a 1:1 salt. A principal components analysis of the glutaric acid NIR data showed that forms I and V proceeded to the cocrystal, but that form III transformed to form IV before cocrystal formation. The oxalic acid salt was formed via complete amorphization. The crystal structures of the cocrystal and the salt were determined. Sulfathiazole comilled with l-tartaric and citric acids gave coamorphous systems that were stable at 10% RH for up to 28 days. Comilling sulfathiazole with dl-malic acid gave mixtures of form V and the amorphous form.

Ammonium Addition (and Aerosol pH) Has a Dramatic Impact on the Volatility and Yield of Glyoxal Secondary Organic Aerosol

Abstract: Glyoxal is an important precursor to secondary organic aerosol (SOA) formed through aqueous chemistry in clouds, fogs, and wet aerosols, yet the gas-particle partitioning of the resulting mixture is not well understood. This work characterizes the volatility behavior of the glyoxal precursor/product mix formed after aqueous hydroxyl radical oxidation and droplet evaporation under cloud-relevant conditions for 10 min, thus aiding the prediction of SOA via this pathway (SOACld). This work uses kinetic modeling for droplet composition, droplet evaporation experiments and temperature-programmed desorption aerosol-chemical ionization mass spectrometer analysis of gas-particle partitioning. An effective vapor pressure (p'L,eff) of ∼10(-7) atm and an enthalpy of vaporization (ΔHvap,eff) of ∼70 kJ/mol were estimated for this mixture. These estimates are similar to those of oxalic acid, which is a major product. Addition of ammonium until the pH reached 7 (with ammonium hydroxide) reduced the p'L,eff to 80 kJ/mol, at least in part via the formation of ammonium oxalate. pH 7 samples behaved like ammonium oxalate, which has a vapor pressure of ∼10(-11) atm. We conclude that ammonium addition has a large effect on the gas-particle partitioning of the mixture, substantially enhancing the yield of SOACld from glyoxal.

Enhanced efficiency of cadmium removal by Boehmeria nivea (L.) Gaud. in the presence of exogenous citric and oxalic acids

Abstract: Boehmeria nivea (L.) Gaud. is a potential candidate for the remediation of Cd contaminated sites. The present investigation aims to explore Cd tolerance threshold and to quickly identify the role of exogenous organic acids in Cd uptake and abiotic metal stress damage. Elevated Cd levels (0–10 mg/L) resulted in an obvious rise in Cd accumulation, ranging from 268.0 to 374.4 in root and 25.2 to 41.2 mg/kg dry weight in shoot, respectively. Citric acid at 1.5 mmol/L significantly facilitated Cd uptake by 26.7% in root and by 1-fold in shoot, respectively. Cd translocation efficiency from root to shoot was improved by a maximum of 66.4% under 3 mmol/L of oxalic acid. Citric acid exhibited more prominent mitigating effect than oxalic acid due to its stronger ligand affinity for chelating with metal and avoiding the toxicity injury of free Cd ions more efficiently. The present work provides a potential strategy for efficient Cd remediation with B. nivea.

The role of O- and S-containing surface groups on carbon nanotubes for the elimination of organic pollutants by catalytic wet air oxidation

Abstract: Multi-walled carbon nanotubes (CNTs) were subjected to several liquid-phase chemical treatments (using HNO 3 , H 2 SO 4 , a mixture of HNO 3 /H 2 SO 4 , HCl or bubbling O 3 in water) as well as gas-phase thermal treatments under nitrogen atmosphere (at 200, 400 and 600 °C) in order to obtain CNTs with different chemical properties. The modified CNTs were characterized by common techniques including nitrogen adsorption at −196 °C, temperature programmed desorption, thermogravimetry, X-ray photoelectron spectroscopy and point of zero charge (pH pzc ). The HNO 3 and HNO 3 /H 2 SO 4 treatments induced a pronounced acidic character to the pristine CNTs (originally with a neutral pH pzc of 6.8), creating a large amount of carboxylic acids, anhydrides and phenol surface groups, and also lactones and carbonyl/quinone surface groups. The treatment with H 2 SO 4 alone, or with the HNO 3 /H 2 SO 4 mixture, led to the additional introduction of S-containing groups (such as sulphonic groups), while O 3 and HCl treatments did not affect significantly the surface chemistry. The pristine and modified CNTs were studied as catalysts in the catalytic wet air oxidation (CWAO) process by using oxalic acid and phenol as model pollutants (at 140 and 160 °C, respectively, and 40 bar of total pressure). At the selected operating conditions, these pollutants are quite stable in the absence of a catalyst. However, a marked degradation of both compounds was observed in the presence of CNTs. The O-containing surface groups in CNTs (carboxylic acids, phenols, anhydrides) contribute to the acidic character of the surface, and, simultaneously, decrease the catalytic activity for degradation of the tested pollutants. The presence of S-containing groups also increases the acidity of the CNTs, but a marked increase of the catalytic activity was observed in this particular case (complete degradation of the pollutants, 56% of TOC reduction in 120 min when phenol was the pollutant, and complete mineralization of oxalic acid). Therefore, the presence of S-containing groups and the absence of carboxylic groups (such as carboxylic acids and anhydrides) seem to improve the catalytic performance of CNTs; however, the S-containing materials are not stable in consecutive runs, probably as a result of the high temperatures and pressures employed in the CWAO process.

Synthesis of Bi nanowire networks and their superior photocatalytic activity for Cr(vi) reduction.

Abstract: Interconnected Bi nanowire networks were synthesized for the first time via a solvothermal route by using ethylene glycol (EG) as both a solvent and a reducing agent, and citric acid (CA) as a stabilizing agent at a molar ratio of CA/Bi3+ = 5. Among various reaction conditions including the temperature, reaction time and precursor concentration, the molar ratio of CA/Bi3+ was the dominant experimental parameter to influence the morphology and structures of the Bi crystals. Highly dispersed Bi microspheres and network-like Bi thick wires were obtained if the molar ratio of CA/Bi3+ was changed to 2.5 and 10, respectively. As compared to other additives including trisodium citrate, cetyltrimethylammonium bromide (CTAB) and oxalic acid, good solubility of CA in EG together with its coordination effect played a crucial role in the formation of network-like Bi nanowires. The Bi nanowire networks exhibited excellent photocatalytic performance for Cr(VI) reduction. Cr(VI) was completely reduced to less toxic Cr(III) after 8 min and 55 min of UV and visible-light irradiation, respectively.

Efficient removal of insecticide "imidacloprid" from water by electrochemical advanced oxidation processes.

Abstract: The oxidative degradation of imidacloprid (ICP) has been carried out by electrochemical advanced oxidation processes (EAOPs), anodic oxidation, and electro-Fenton, in which hydroxyl radicals are generated electrocatalytically. Carbon-felt cathode and platinum or boron-doped diamond (BDD) anodes were used in electrolysis cell. To determine optimum operating conditions, the effects of applied current and catalyst concentration were investigated. The decay of ICP during the oxidative degradation was well fitted to pseudo-first-order reaction kinetics and absolute rate constant of the oxidation of ICP by hydroxyl radicals was found to be k abs(ICP) = 1.23 × 109 L mol−1 s−1. The results showed that both anodic oxidation and electro-Fenton process with BDD anode exhibited high mineralization efficiency reaching 91 and 94 % total organic carbon (TOC) removal at 2 h, respectively. For Pt-EF process, mineralization efficiency was also obtained as 71 %. The degradation products of ICP were identified and a plausible general oxidation mechanism was proposed. Some of the main reaction intermediates such as 6-chloronicotinic acid, 6-chloronicotinaldehyde, and 6-hydroxynicotinic acid were determined by GC-MS analysis. Before complete mineralization, formic, acetic, oxalic, and glyoxylic acids were identified as end-products. The initial chlorine and organic nitrogen present in ICP were found to be converted to inorganic anions Cl−, NO3 −, and NH4 +.

Interaction of organic acids and pH on multi-heavy metal extraction from alkaline and acid mine soils

Abstract: Vegetation at mining sites can produce increased heavy metal leaching by the organic acids and protons originating from root secretion and litter degradation. Batch experiments were conducted to investigate the effects of organic acids and pH on the extraction of Pb, Cd, Zn and Cu from an alkaline mine soil (sampled from a mining site of Chenzhou City, Hunan Province) and an acid mine soil (sampled from a mining site of Daxin county, Guangxi Province). The results showed that in the presence of organic acids (acetic, oxalic, malic, fumaric, tartaric and citric acids) at pH 7, the extraction of Pb, Cd, Zn and Cu from the acid mine soil was much higher than that from the alkaline mine soil, in which only citric acid with higher concentration was capable of extracting some heavy metals. Citric acid had the strongest ability in extracting heavy metals, followed by oxalic acid. Heavy metal extraction dramatically decreased with increasing pH. Moreover, at low pH, oxalic acid promoted the risk of Cu leaching; at high pH, the leaching of Pb, Zn, Cd and Cu was enhanced by both oxalic and citric acids. This indicated that those plants, which can produce substantial citric acid or oxalic acid by root secretion and litter degradation, should not be selected for the revegetation of mining sites.