Characterization of nitrate reduction with magnesium using the pH change

Nitrate contamination of drinking water is a dangerous. problem. The removal of nitrate presents a challenge because of the ion's high stability and soluble nature. Current technologies for removal of nitrate are lengthy and have several disadvantages. To avoid these disadvantages, chemical reducing agents are preferred to use. In recent years chemical methods of nitrate removal using zerovalent metals like iron [Fe[o]] and aluminum [Al[o]] have been studied intensively. Zero-valent magnesium [Mg[o]] is considered as a nontoxic and environmental benign metal, having high reduction potential as compared to Feoand Al[o]. It is tried here to develop a simplified quick and easy procedure to trace the extent of reduction of nitrate with Mg by just measuring the pH of the solution

Corrosion behaviour of some stainless steels in chloride solutions

The pitting corrosion of various types of stainless steels was studied in different anions. The effect of temperature was also examined. The most well known aggressive anion is the chloride ion. The open circuit potential and the potentiodynamic techniques were used. The pitting potential, Ep and the protection potential, Epp were determined for stainless steels.The pitting and protection potentials depend linearly on the concentration of Cl - ion according to the equations. Ep = a + b log [Cl -]. Epp=a -+b - log [Cl -]. Pitting potential is shifted to more negative values with the increase of Cl - content, as well as the temperature according to the composition of the alloy. The concentration necessary for pitting and the critical pitting temperature increases with increasing Cr content. The effect of different concentrations of SO 4 -2 ion at temperature up to 80°C was also investigated

study of the behaviour of AI, Cu and AI-Cu couple in sodium carbonate solutions.

In case of copper, oxide film thickening occurred and the open circuit steady state potential shifted slightly towards more negative values; while in case of Al, either alone or coupled with copper, oxide film thickening occurred at lower concentrations <10-3 but at higher than 10-3 M; dissolution of the oxide took place and the potential was shifted to more negative values. Potentiostatic polarization confirmed the above results. The galvanic potential measurements of Al-Cu couple in different aerated or oxygenated carbonate solutions indicated that at concentrations <10-3 M, the potential shifted to less negative values; while at higher concentrations, a more negative shift was recorded and Al anode was severely attacked. Addition of 3.5% NaCl shifted the potential to more negative values at lower carbonate concentrations. Galvanic current Ig measurements indicated a decrease in the current strength values at the moment of contact followed by a steady state value. The steady state galvanic current Ist against logarithm of carbonate concentration showed a more or less regular increase of Ist with increase of electrolyte concentration

Zinc-steel polarity reversal. I. Effect of bicarbonate concentration and temperature

The open circuit potentials of 2 types of zinc and mild steel were followed with time in different NaHCO3 solutions [10-5-10-1 M] at different temperatures [25-80 degree]. No potential reversal of polarity was observed between zinc and mild steel at room temperature. At higher temperatures, passivation of zinc and mild steel would preferentially occur, and potential reversal was manifested, particularly for pure zinc. Impurities, even in minute amounts, enhanced the activation of zinc, as well as sodium hydroxide at adequate concentration even in presence of the bicarbonate. AES survey analysis of the electrode surface gave more insight on the corrosion products

Some electrochemical behavior of low corrosion metals III- Tantalum in aqueous solutions

The oxide film growth on Ta in 0.1 M solutions of HCl, HNO3, H2SO4, H2CrO4 and their respective sodium salts was examined at low current densities. The kinetics of film formation was stated and the local current density at open circuit was calculated in the tested media. The variation of the open circuit potential of Ta with time was traced in buffer solutions covering the range from pH 1 to 13. The results showed that the possibility of the metal to be used as an indicator electrode and was tested for acid-base and precipitation potentiometric titration. The equivalent point obtained was satisfactory and in accordance with other standard recommended electrodes

Electrochemical studies on the anodic polarization of silver

The potentio-dynamic anodic polarization of silver exhibit different peaks at different potentials depending on the selectrolyte used. In neutral sulfate solutions the major process is the Ag2O formation, while in presence of NaNO3, as an oxidizing agent, a peak which may represent the AgO formation appears at a later more anodic potential. The two peaks can be found together depending on the ambient concentration of both Na2SO4 and NaNO3. The presence of Cl- ions, either as HCl or NaCl, causes the rise of current at approximate 0.1 V which increases with increase of Cl- concentration independent of pH. This study showed that the early stages of growth occur by two- dimensional surface process on the Ag electrode forming a porous lager of AgCl giving a chance for nucleation of three-dimensional phase. The presence of NaNO3 with chloride solutions causes the appearance of the peak representing AgO formation

Polarographic behaviour of mononitrophenols in aqueous buffered solutions

The electroreduction of o-m- and p- nitrophenol has been extensively studied using the dropping mercury electrode. It was shown that in acid media, nitrophenols generally produce along two polarographic steps. The first is usually well-defined, and is attributed to the reduction of the nitro group to the corresponding hydroxylamine via a four-electron process. The second step usually somewhat drawn-out, is ascribed to further reduction to the amine via a two-electron transfer process. In alkaline media, on the other hand, the three isomers, are reduced quite differently

Effect of proton donors and proton acceptor on the Polarographic reduction waves of o-,m- and p- nitrophenol in methanolic media

The polarographic behaviour of o, m- and p-nitrophenol is studied in methanolic solutions. Due to the poor proton availability of this medium reduction of part of the depolarizer proceeds with the uptake of the necessary protons from the other part. The anions thus formed are reduced along a second, more negative wave. This conclusion was supported through study on the effect of addition of acid proton donors [mono-and poly percent weak and strong acids], basic proton donors [e.g. [NH4]2CO3] or proton acceptor [e.g. NaOH]. The results were interpreted on the basis of Ruetschi and Trumpier's theory of H[+] ion impoverishment in the reduction layer. In presence of sodium hydroxide, reduction occurs in a single wave, at negative potentials, due to the ionization of the phenolic groups of the depolarizers. The difference in the behaviour of the three isomers is discussed

Polarographic study on the electrochemistry and hydrolysis of cations I-zirconium

Metal ions in aqueous solutions interact strongly with water molecules. The latter are bound to the ionic species via the oxygen atoms to form strong coordinate linkages by virtue of the lone electron pairs. The actual state of such species in solution is that of an aquo complex in which water molecules are regarded as ligands. Hydrolysis reactions are common to most cations and their degree differs from an ion to the other. Zirconium is a typical transition element with valence-electron configuration 4d[2]-5s[2], and its properties in aqueous solutions are determined by the electrostatic characteristic of the Zr4+ ion. The high charge, small radius and comparatively low ionization potential make it possible to classify Zr[4+]among the electrostatic complex forming ion. For the formation of a stable complex with ionic bonding, it is necessary not only that the central ion has a high charge and a small radius, but also that the ligand is able to satisfy conditions for ion-dipole interaction to a sufficient extent. Water has a considerable dipole moment and high electron affinity and is capable of forming stable aquo ions with Zr[4+] characterized by ionic bonding. Little work on the direct polarography of zirconium has been reported. Laubengayer and Eaton reported two reduction steps over a narrow pH range and limited zirconium concentration. They attributed the first wave to be due to hydrogen discharge, whilst the second one was ascribed to the reduction of quadrivalent zirconium to the metal. Potzak and Zaki reported a linear relationship between zirconium-dye reduction current and the zirconium concentration. Graham et al. reported an indirect method for zirconium estimation involving the precipitation of the metal with m-nitro benzoic acid. The polarography of zirconium salts in non-aqueous methanolic media of 0-1N LiCl was examined, and also of zirconium complexes with Solochrome Violet R.S. in various supporting electrolytes. In the present investigation a study of the hydrolysis of zirconium in aqueous media using the polarographic technique is undertaken