Academic literature on the topic 'Nitrilotriacetic acid (NTA)'

Abstract This study describes a fast and accurate method for the sample preparation, identification, and quantitation of nitrilotriacetic (NTA) acid in environmental aqueous samples at a concentration of ppb level. The method is sensitive, specific, and free from the interferences of fatty and amino acids. The tri-n-propyl- and tri-n-butyl-NTA acid esters were prepared by the reaction of n-propyl-HCl and n-butyl-HCl solutions and NTA acid, respectively. The derivatives were analyzed by a gas chromatograph equipped with a mass spectrometric detector. The method detection limit, 0.006 mg/L of each NTA ester, was determined and validated by an analysis of a fortified water sample. The overall recoveries were 103–115%, n = 8. The method was applied to a real sample and a 0.90 mg/L concentration of NTA acid was found. Mass fragmentation patterns of the derivatives are also reported.

The inhibition efficiency of nitrilotrimethylene phosphonic acid (NTP) in controlling mild steel corrosion in sea water has been evaluated by galvanostatic polarization, electron scanning for chemical analysis (ESCA), and scanning electron microscope (SEM) methods. The results are compared with those obtained for nitrilotriacetic acid (NTA). NTP is found to be more effective in protecting mild steel against sea water corrosion as compared to NTA. The surface of mild steel in presence and absence of NTP and NTA is characterized by ESCA and SEM. From the ESCA studies, it is found that NTP formed a stable and compact film over the mild steel.

The mobilization of heavy metals in river water and sediment by NTA during river bank filtration was investigated in the laboratory under oxygen-deficient conditions. Four PVC-columns, 1.20 m long, 0.18 m diameter, filled with river bed sediment, were percolated for 7 months with river water spiked with NTA. Water and sediment were collected from a branch of the river Rhine, where the sediment has high metal contents. The percolation rate was 10 cm. day−1. Supply water for three columns was kept oxygen-deficient. Water for the fourth column had an oxygen content of 6 mg.dm−3. To the anoxic river water NTA was added to concentrations of 0, 100 and 600 µg.dm−3 respectively. The oxic water obtained an NTA-concentration of 100 µg/l. Leachate and pore water were analysed for heavy metals, inorganic macroparameters and NTA. After percolation the sediment was analysed for bound metals. When river water and sediment contained adapted micro-organisms, NTA was degraded within two weeks in all columns. Degradation was nearly absent during the first three weeks of percolation, due to the necessary adaptation. Except for the first month, NTA was not detected in the pore water below 10-30 cm. In the first month it penetrated into the leachate. Within the concentration range considered, neither NTA- nor O2-content of the supply water affected the mobilization of the heavy metals considered.

A Cd-tolerant plant species named Boehmeria nivea (L.) Gaudich (ramie) was applied to study its Cd accumulation and translocation mechanisms with the addition of ethylene diamine tetracetic acid (EDTA) or nitrilotriacetic acid (NTA).

This thesis describes a study of the remobilisation of heavy metals from sediments by three aminopolycarboxylic acids (APCAs). They are nitrilotriacetic acid, ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid. The investigation is introduced by examining the sources, uses and chemistry of these acids. The introduction also includes a discussion of what is known about the inclusion of heavy metals into sediments and their remobilisation from sediments. Typical concentrations of APCAs in natural waters and sediments have been catalogued from the literature. The advantages and disadvantages of various laboratory techniques employed for the remobilisation of heavy metals by APCAs from sediments are assessed, as is the use of such experiments in quantifying the role of APCAs in the remobilisation of heavy metals from sediments. Sediments from three areas were sampled for this study; they were the Alexandra Canal, Captains Flat and Jenolan Caves in New South Wales, Australia. In each area several sites were sampled. For each site there is a brief description of the catchment geology and hydrology. Selected sediment-associated waters in the areas were analysed for their metal concentrations as well as for ultratrace levels of APCAs employing a method developed in the present study. The waters were analysed for the major ions Ca2+, Mg2+, K+, Na+, Cl-, NO3- and SO42-. The sediments from selected sites in each of the areas were dried and fractionated. The dry total and fine sediments were analysed for their metal content and the latter was found to adequately represent the former in this respect. Water samples from the three areas showed different chemistries and exhibited more subtle differences between sites. In general, the Alexandra Canal waters are saline and alkaline and are a mixture of urban runoff and seawater; the Captains Flat waters are acidic and contain high sulfate from acid mine and tailings drainage; the Jenolan Caves waters are neutral and have the features characteristic of waters draining through limestone. The APCA contamination in all water samples when ranked against other global sites is very low. Although the current APCA levels in the waters appear low, it was concluded that they should be closely monitored so that efforts can be made to minimise the risk of APCAs being hazardous environmental contaminants and also that any remobilisation of heavy metals from sediments by APCAs can be controlled. Agitation and column laboratory-scale experiments were carried out in order to obtain an understanding of the remobilisation of metals by contamination levels of APCAs in water, both as the individual APCAs and as a mixture of APCAs. Complimentary experiments were carried out using a molar excess of APCAs calculated from the metal concentrations obtained by acid digestion (assuming 1:1 metal complex formation). Both types of remobilisation experiments were designed to investigate the role that redox potential (Eh) and concentration of APCAs in natural waters have on the remobilisation of heavy metals from the sediments. The agitation experiments were employed to assess metal remobilisation for the situation where the sediments are disturbed while the column experiments explored metal remobilisation for the case where the sediments are left undisturbed in situ. The major conclusions from the agitation experiments that used fine sediment from the Alexandra Canal were that 100 ppm APCA solutions will remobilise metals from the sediments under oxic conditions but only remobilise infinitesimally small amounts of metal under anoxic conditions. The use of fine sediments for the duplicate agitation experiments was found to give adequate duplication of results. A mixture of APCAs in solution acts similarly to the average of the three individual APCA solutions, showing that there are no antagonistic or synergistic effects likely to occur when they are found together in the environment. It was found that the mmoles of the metals remobilised exceeded the mmoles of the APCAs added when 500.0 mL of 100 ppm APCA solution was used on 50.00 g of sediment. This might be due to APCAs remobilising metals from the sediments in ways other than by complexation. Even though an excess of APCAs was available, metal remobilisation was not complete when the experiments were forced to terminate. During the 14 days of the experiment, only one quarter of the metals liberated from the sediment by HNO3 and 30 % H2O2 digestion were remobilised by the APCAs. Therefore an excess of free APCAs remains in solution. Fine sediments from Alexandra Canal, Captains Flat and Jenolan Caves were employed in the oxic agitation experiments using excess APCAs in solution. These experiments resulted in the following major conclusion: when producing an APCA remobilisation signature for trace and ultratrace metals, the geochemistry of the site is of secondary importance to the source of the contaminating metals. This is a feature of the trace and ultratrace metal speciation in the source rather than their concentration in it. From the different levels of calcium present in the three areas it was found that calcium is unlikely to form stable 1:1 APCA complexes at the pH values employed and is unlikely to compete with the heavy metal remobilisation by APCAs. Total sediments from Alexandra Canal and 100 ppm APCA solutions were employed for the column leaching experiments. From mass, pore water volumes and flow measurements it was shown that the ten mini cores taken from the same site were not true replicates. Despite this, when the sediments have settled and the pore waters removed from the cores, the levels of metal being leached stabilise and may represent a clearer picture of the in situ metal leaching from sediment with time. The levels of metal leached from the cores in 14 days suggest that during this period the cores are essentially anoxic, with the oxygen supplied from the oxic leaching solutions used for inorganic and microbial processes in the sediments. Agitation experiments appeared to yield an adequate picture of what would happen if free APCA solution came in contact with fine sediments suspended in the water column. Column leaching experiments employing total sediment were found to be only of limited value in assessing heavy metal remobilisation from undisturbed sediment. These experiments do not give a reliable assessment of the bioavailability of heavy metals and further testing of the acute and chronic toxicity of the sediments is recommended. APCA solutions that have been used in sediment and soil washing under conditions related to those used in the present study may contain an excess of the free APCAs as well as APCA heavy metal complexes and hence may be toxic to biota.

Nitrilotriacetic Acid (NTA) is an organic ligand which has been extensively studied due to its biological significance and excellent chelating properties. Nitrilotripropionic Acid (NTPA) is a ligand that is believed to possess similar properties to NTA, but has not been as extensively studied. It has been experimentally determined that metal complexes of NTA are orders of magnitude stronger than those formed with NTPA. This is surprising, especially considering that the ligands do not differ that much from each other. NTPA contains an additional –CH2– group in each of the acid containing arms as compared to NTA. The aim of these studies were to explain, theoretically, why this is the case. Analyses were conducted with a number of software programs including, Gaussian 03, Schrödinger Maestro and AIM 2000. All Density Functional Theory (DFT) studies were conducted in solvent at the RB3LYP/6-311+G(d,p) level of theory in conjunction with a number of different solvation models. En route to explaining why the complexes differ in stability a new methodology was utilized (isodesmic reactions) in which the four stepwise protonation constants of both NTA and NTPA were successfully predicted; in fact these were the most accurate values predicted to date by DFT methods. The final step of these studies focused on predicting stability constants of metal (Zn2+ and Ni2+) complexes of NTA and NTPA. These predictions were not as accurate as those achieved for the prediction of protonation constants; however, success was achieved in predicting the trend – complexes with NTA are orders of magnitude stronger than complexes formed with NTPA. The most important observation revealed that H–clashes and C–H∙∙∙O hydrogen bonds present in M(NTPA) complexes, which are not present in M(NTA) complexes, result in the formation of additional rings which contributes to the formation of a cage. It was discovered that the H-clashes present in the M(NTPA) complexes were contributing to the overall stability of the molecule. This is completely contradictory to a previous explanation in which H-clashes, being a result of steric crowding, resulted in destabilization of a complex. If the H-clashes were not present in the M(NTPA) complexes there would not be enough stabilizing factors present in the molecule which will inevitably result in the non-existence of M(NTPA) complexes. Copyright
Dissertation (MSc)--University of Pretoria, 2010.
Chemistry
unrestricted

Abstract Aminopolycarboxylate-based chelants are used to control iron precipitation during acidizing operations by interacting directly with the iron, resulting in water-soluble complexes. This paper highlights that, in order to improve the effectiveness of iron control during acidizing operations, the type and the concentration of the chelants should be based on the formation properties and the well characteristics by comparing the cheltors’ performance as iron-control agents at different temperatures and pH environments with different levels of iron concentrations and chelant to iron molar ratios in acid (HCl). This study also addresses the interactions between the tested iron-control additives and acid, as well as the performance of the chelants in carbonate cores. Laboratory experiments were conducted to investigate the performance of nitrilotriacetic acid (NTA), glutamic acid, N, N-diacetic acid (GLDA), diethylenetriaminepentaacetic acid (DTPA), ethylenediamine-tetraacetic acid (EDTA), and hydroxyethylethylenediaminetriacetic acid (HEDTA) as iron control additives in 5 wt% HCl at pH values 0 to 4.5 to simulate carbonate acidizing at temperatures of 70 to 300°F, and initial iron concentrations of 2000 ppm. The performance of NTA and EDTA was also compared at higher initial iron concentration (4000 ppm). This work also quantified the effects of acid additives such as corrosion inhibitor and non-ionic surfactant on the chelation performance. Coreflood experiments using carbonate cores in acid with chelant helped determine its influence on permeability. Testing chelant-to-acid molar ratios of 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, and 2:1 relative to iron concentration yielded optimal values. Additional tests monitored iron precipitation in solution using an inductively coupled argon plasma (ICAP) emission spectroscopy. Precipitates were filtered and analyzed using X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Without chelant, at 70°F and 2000 ppm initial iron concentration, precipitation began at pH 1.45 and completed by pH 2.42. At 150 and 210°F, iron precipitated at pH 0.68 and 0.3 and completed by pH 1.3 and 1, respectively. At 70°F, NTA showed a minimum of 98% chelation at pH 4.3; however, its performance declined at 150°F to 74% chelation at pH 4.24, and at 210°F to 53% chelation at pH 4.0. Although DTPA dissolves completely in live acid, precipitations occurred at partially spent acid. At pH 0.15, SEM-EDS showed that the precipitate contains as much as 13 wt% iron. Thus, DTPA is not a suitable iron-control agent. HEDTA showed a 90% chelation at 210°F and pH 4.8. GLDA's performance declined to less than 50% at 150°F. At higher iron concentrations of 4000 ppm, Na3NTA kept all iron in solution in a 5 wt% HCl up to pH 4.0 at 70°F and its performance declined to a minimum of 97% at pH 4.7 at same temperature. At 150°F, and 210°F, Na3NTA started to gradually decline at pH values greater than 3.9, and 3.5, respectively. The minimum chelation reached by NTA was 91% at pH 4.4, at 150°F, and 73% at pH 4 at 210°F. Upon comparing the NTA's results at high iron concentrations to the popular EDTA, Na4EDTA at 1-to-1 mole ratio with iron exceeded its maximum solubility in 5 wt% HCl and precipitated in the original solution. For NTA, a molar ratio of 1.4:1 is optimal at 70 and 150°F, showing chelation performance of 95% and 94%, respectively, while a molar ratio of 1.5:1 is optimal at 210°F, showing a chelation performance of 87%. This study's results improve field operations by identifying NTA and HEDTA as having the best iron-control chelation performance of the five additives tested, thus reducing guesswork and streamlining production. The work also provided recommendations for choosing the best type of iron-control agent based on solubility and coreflood analysis. The results can be used to design more efficient acidizing fluids. This work won second place in the Masters division of the 2020 Gulf Coast Regional Student Paper Contest, April 2020.