Alkaline Oxidation Research Articles

Indirect fluorescence detection of free cyanide and related compounds by capillary electrophoresis

A capillary electrophoretic method to detect CN − and some related compounds (CNO −, SCN −, and NO 3 −) using a prototype laser-based indirect fluorescence detector has been developed. This method avoids interferences from Cl −, SO 4 2−, CO 3 2−, HCO 3 −, and ClO − and allows the detection of CN − in less than 4 min and the detection of related compounds in less than 8 min with precise migration times (R.S.D. about 1%). The measured detection limits of CN − [5 × 10 −6 M with DR = 90 (dynamic reserved)] are close to the expected theoretical value [TR CN = 0.44 (transfer ratio)]. For the related compounds, the measured detection limits ranged from 10 −5 to 2 × 10 −6 M, depending on noise conditions (DR ⩾ 300). The results showed that the chosen analytical conditions were appropriate and the detection limits could be improved using techniques to further decrease the noise (probably due to mechanical vibrations). Peak-height precision was about 10% R.S.D. and log-log regressions had slopes lower than one. These results seem to be due to instabilities in the indirect signal. The analysis of a quasi-real sample has been achieved, allowing identification of the related compounds present in a CN −/SCN − sample oxidized with ClO − and determination of the CNO − formed in this alkaline oxidation.

An Alkaline Oxidation Method for Determination of Total Arsenic and Selenium in Sewage Sludges

AbstractA simple and precise method was developed for determination of total As and Se in sewage sludges by using hydride‐generation atomic absorption spectrometry (HGAAS). It involves boiling a 50‐mg sample with sodium hypobromite (NaOBr) solution to dryness in a sand bath (260–280°C), extraction of the As and Se in the digest with 1.25 M H2SO4, and determination of these elements by HGAAS after reducing As(V) and Se(VI) to As(III) and Se(IV), respectively. The proposed method gives quantitative recovery of As and Se in standard reference materials (96–103%) and of these elements added to sewage sludges (95–100%). The average results of As (9.8 mg/kg) and Se (7.5 mg/kg) in 12 sewage sludges determined by the proposed digestion method agreed closely with those obtained by the acid digestion methods recommended by USGS and USEPA. Tests with 13 metals indicated that, at the concentrations expected in sewage sludges, none of the metals interfered with determination of As and Se by the proposed method. A single operator can complete analysis of one of the elements in 40 samples in a normal working day, or both elements in 1.5 d.

Catalytic Mechanism of Cu2+and Fe3+in Alkaline O2Oxidation of Lignin

Abstract The catalytic mechanisms of Cu2+ and Fe3+ in the alkaline oxidation of lignin are discussed. Best aldehyde yields were obtained by using Cu2+ and Fe3+ as catalysts. Without these two ions present or in the absence of one or other of them, yields were lower. It is clear that Cu2+ and Fe3+ significantly influence the reactions. Cu2+, acting as the electron acceptor, accelerates the formation of the phenoxy radical, thus speeding up the radical reaction. In order to interpret the effect of Fe3+ on oxidative degradation of lignin and formation of aldehydes, formation of an intermediate, O2-Fe3+-lignin complex and its catalytic mechanism have been proposed.

Bacterial heap leaching of refractory gold/sulphide ores

Low-grade refractory sulphide gold ores exist in which the gold values are too low to economically justify the use of pre-concentration processes. The pre-concentration process (usually flotation) is followed by the oxidation of the sulphidic concentrate to render the gold amenable to a subsequent cyanide leach. Oxidation processes that have been used are acidic and alkaline pressure oxidation, roasting and the BIOX® process. The latter process is a commercial process developed by GENMIN of South Africa, and involves grinding and tank leaching of the ground concentrate in the presence of bacteria. The BIOX® and other oxidation processes are, however, relatively expensive and it would be uneconomic to apply them to low-grade ore deposits. It may well be economic, however, to use a bacterial pre-leach of crushed material to release the encapsulated gold and make it amenable to a standard alkaline cyanide heap-leaching process or to a heap-leaching process using alternative gold lixiviants. The GENMIN Group has being carrying out research on the bacterial heap leaching process for a number of years, and has successfully demonstrated the process on a laboratory and large column scale for ores containing acid-consuming gaugue and for ores where the gangue is not acid-consuming. In addition, mathematical models have been used to predict the results of laboratory column leaches and to extrapolate the results to larger scales. In this paper the results of experimental and theoretical investigations into the bacterial heap-leaching process for low-gold-grade sulphide ores are given, and the economics of the process discussed.

The oxidation of ortho-anisidine in alkaline medium. A product characterization and an EPR study

Alkaline oxidation of ortho-anisidine by potassium ferricyanide in alkaline aqueous solution was examined. Azo compounds, a diamine, and para-iminoquinones were isolated from the highly coloured reaction mixture. The reaction was also carried out within the cavity of an EPR spectrometer and two radical species have been detected. Following these product results and EPR studies, a radical mechanism is proposed for the process.

Brief overview of activities and operations of Hydrometal S.A.

Numerous papers discuss the mechanism of alkaline oxidation of pyrite but there is limited information available describing the actual kinetics of the pyrite sulphide to thiosulphate reaction. A previous investigation in this series determined the rate of sulphide sulphur oxidation and thiosulphate yield in the reaction of pyrite with sodium hydroxide under various testing conditions. The goal of the current study is to validate these rates using two different gold-containing pyrite concentrates. A further objective of the current work is to investigate the simultaneous dissolution of gold with in situ formed thiosulphate during pyrite oxidation.It was found that at 20 psi oxygen overpressure and a temperature of 80 °C, the initial rate of sulphide oxidation and thiosulphate yield were close to 0.08 mol/h and 0.0155 mol/h, respectively. These rates are in agreement with previously published data. However, a shift from linearity occurred when the pH decreased below 12. A rapid decay of thiosulphate was evidenced at pH 8.3–9.2 while EH was in the range of 22–141 mV. Based on relevant thermodynamic analysis of metastable thiosalts system, such rapid decomposition is not expected at these pH and EH values. It is believed that the presence of unreacted pyrite acting as a catalyst caused this behaviour. It appears that under mildly alkaline conditions, the rate of oxidation of sulphide to thiosulphate becomes slower than the rate of thiosulphate degradation, which causes a net loss of thiosulphate in the system. The maximum extraction of gold and silver (96% and 75% respectively) was achieved under conditions of pH < 12.

Improved Alkaline Oxidation Process for the Production of Aldehydes (Vanillin and Syringaldehyde) from Steam-Explosion Hardwood Lignin

The production of aldehydes from a steam-explosion hardwood lignin is the main objective. It is demonstrated that the combined aldehydes yield (vanillin + syringaldehyde + hydroxybenzaldehyde) can reach 14.6 wt% of the lignin isolated from the steam-explosion process. This represents 12.2 wt% of the Klason lignin present in the initial hardwood (Populus tremuloides) and 2.5 wt% of the dry wood. The process steps are relatively simple: aqueous alkaline (13.5 wt% NaOH) oxidation (pure O 2 ) of lignin in the presence of Cu 2+ and Fe 3+ as catalysts, at 170°C and with 10 min as reaction time. The high yields of aldehydes far exceed those obtained in the conventional alkaline air oxidation of spent sulfite liquors. The results support the concept that biomass-derived oxyaromatic chemicals via improved process strategies may soon challenge existing petroleum-derived routes (vanillin currently produced via the sequence benzene → cumene → phenol → guaiacol → vanillin)

A surface study of the chemical pretreatment before coil coating of hot dip zinc‐coated steel

AbstractZinc‐coated steel strip is painted in coil‐coating plants in order to improve corrosion resistance and to provide a decorative surface. We have used Auger and x‐ray photoelectron spectroscopy to characterize the conversion coating formed during pretreatment of hot dip zinc‐coated steel prior to coil coating. The pretreatment process includes alkaline cleaning of the strip, alkaline oxidation and a chromic acid after‐rinse treatment. The composition and the chemical state of the surface have been examined after the different pretreatment steps.

Seawater flocculation of emulsified oil and alkaline wastewaters

Abstract Seawater flocculation at high pH was investigated for the removal of emulsified oil and suspended solids from wastewater. As little as 2% seawater by volume, in conjunction with lime or caustic for pH adjustment, was required to achieve good flocculation of the oil-water emulsion. The same amount of seawater allowed efficient removal of suspended solids from alkaline industrial wastewaters and oxidation pond effluent having pH of 10.6 and higher, without addition of an OH − source. Effective flocculation was associated with the precipitation of 2–3.5 g equiv m −3 of Mg 2+ . The minimum seawater concentration for effective flocculation, in relation to pH, was predicted successfully based on the solubility of magnesium in wastewater-seawater mixtures.

Production of humic acids from lignites and subbituminous coals by alkaline-air oxidation

The alkaline oxidation of four Spanish coals by air was studied using a two-level factorial design with four variables: temperature, time, alkali concentration and coal-to-alkali ratio. The main aim was to increase the humic acid content of these coals. The best results were obtained at the highest temperature, longest time and lowest alkali concentration and coal-to-alkali ratio. Lower rank coals yielded the highest humic acid concentrations after oxidation, while the subbituminous coals were only slightly affected by treatment under the test conditions. A detailed study of the elemental composition of the coal and the generation of oxygen-containing functional groups is reported. The evolution of sulphur forms during the process is also described.

Chemistry of alkali extraction of brown coals—I. Kinetics, characterisation and implications to coalification

Three Australian brown coals have been separated into humin and humic acid fractions and studied by high resolution solid state 13C NMR spectroscopy and Fourier transform IR spectroscopy. The aromatic rings of the humic acids are highly substituted showing that extensive cross linking must have occurred during formation from wood lignin and tannin. However, the humins contain more aliphatic carbon and hydrogen than the corresponding humic acids. This shows that little cross linking has occurred with other components of the brown coal such as resins, waxes cutin and algal detritus, and cross linking has not rendered the aromatics alkali insoluble. The kinetics of extraction are complex and not simple first order. This is reflected in the chemical composition of the humic acid which is extraction temperature dependent. We also observed that there is a conversion of aromatic carbon to aliphatic carbon and gas during extraction, probably by alkaline oxidation, resulting in ring opening. A range of suitable model compounds have been studied to confirm this finding. Such a mechanism may account for the modification of lignin in oxidising environments such as those occurring in the initial stages of coalification (lignite or brown coal formation) and in soils.

Bishomocamphenilon, Bishomocamphen und Bishomocamphenilans�ure: Synthesen in der Isocamphanreihe, 32. Mitt.

Syntheses of the title compounds are described and their olfactive properties discussed. Bishomocamphenilone (2) has been prepared by a Diels-Alder reaction of acrylonitril and cycloheptadiene-1,3 via the bicyclonitril5 which upon geminal chlorination and alkaline oxidation furnished the bishomonorbornanone9 which then could be transformed into2 by twofold methylation.14 has been prepared by action ofMeLi upon2 and bishomocamphene by dehydration of14. Hydroboration of this olefine3 yielded the alcohol15, which could be oxidized to the corresponding aldehyde13 and bishomocamphenilanic acid (4). The configurations of all new compounds has been ascertained.

ChemInform Abstract: n‐Heptanoic Acid by the Caustic Oxidation of 2‐Octanol.

AbstractThe alkaline oxidation is achieved by introducing 2‐octanol (I), saturated with water, into a hot melt of NaOH and KOH.

Analysis of sulfur in soil, plant and sediment materials: Sample handling and use of an automated analyzer

Methods for analyzing soil, vegetation and sediment samples for total S and handling soil samples for analysis of S constituents were examined. A LECO automated total S analyzer (SC-132) was used for the analysis of vegetation, sediments and soil samples. Results from the LECO analyzer compared favorably with other currently used total S techniques such as alkaline oxidation. Calibrating the instrument on soil or vegetation standards using two combusion accelerators improved accuracy and recovery. The upper 99% confidence interval RSD values for duplicate samples using the LECO analyzer were < 15% for mineral soil, < 8% for forest floor and < 3% for sediment samples. Sample analysis takes < 3 min and provides a direct readout of the total S value. Freeze-drying soil samples caused minor changes (< 15%) in S constituent analyses (Zn-HCl reduction, HI-S and extractable sulfate) when compared to fresh (field moist, refrigerated) samples. Oven-drying at 65°C caused greater changes in soils than freeze-drying, primarily in extractable sulfate.

Determination of total sulfur in soils and plant materials by ion chromatography

Abstract An accurate and precise ion Chromatographie (IC) method is described for determination of total S in soils and plant materials. It involves ignition of a mixture of soil and NaHCO3or plant material and NaHCO3containing Ag2O at 550°C for 3 h. The residue is dissolved in 1MHOAc, diluted with deionized water, filtered, and analyzed for S02‐ 4by a Dionex model 2002i ion Chromatograph. Results by the IC method of seven Iowa soils, three Chilean soils, and 10 plant materials agreed closely with those obtained by the methylene blue method after alkaline oxidation with NaOBr. In general, the IC method was more precise than the methylene blue method. The method is simple and requires a minimum of analytical skill. A single operator can analyze 30–40 soil or plant samples in a normal working day.

Complexation and Catalyzed Oxidative Polymerization of Catechol by Aluminum in Acidic Solution

AbstractThe role of soluble Al in catalyzing the abiotic oxidation of phenolic compounds has been investigated by monitoring the slow oxidation of aerated aqueous solutions of catechol containing Al. Spectroscopic analysis of the various oxidation products has demonstrated that aqueous Al3+ increases the rate of oxidation of catechol by O2, favoring the formation of highly colored polymeric products which may possess charge‐transfer properties. Spectral (UV‐visible, nuclear magnetic resonance, infrared, and electron spin resonance) properties of these products suggest that they have some similarities to polymers generated by alkaline oxidation of polyphenols, but they also have properties which suggest that they are related to melanins generated enzymatically byu fungi and plants. A proposed low‐pH mechanism for the role of Al in promoting oxidative polymerization is based on the concept that Al3+ cations tend to stabilize o‐semiquinone radicals at low pH and direct the manner in which these radicals polymerize. Aluminum may also stabilize charge‐transfer complexes by bridging oxidized and reduced molecules. Preliminary evidence is presented to suggest that the surfaces of Al oxides in soils may, by a similar mechanism, catalyze the oxidation of phenolic compounds by O2.

Atmospheric Sulfur Deposition to Agricultural Land in Northeastern Ohio

AbstractIn certain forms, S is an important acid‐forming substance deposited from the atmosphere to the earth's surface. Controversy surrounds estimates of total S deposition because of an inability to accurately measure S in dry deposition (particulate fallout and gaseous sorption). In a field experiment in northeastern Ohio, the amount of S in dry deposition was determined over a 3‐yr period using 20 lysimeters (4.8 m by 1.7 m) cropped with soybean [Glycine max (L.) Merr.]. Two treatments consisting of tillage (conventional or no‐tillage) and elemental S addition (0 or 50 kg ha−1) were applied to the lysimeters. Sulfur inputs to the lysimeters as precipitation and agricultural amendments and S outputs, as runoff and leachate waters, were determined using ion chromatography or alkaline oxidation techniques. The net S output (total outputs minus measured inputs) was considered to equal dry deposition. Precipitation and agricultural amendment inputs of S were 10.2 and 3.8 kg ha−1 yr−1, respectively. In comparison, S in dry deposition ranged from 14 to 26 kg ha−1 yr−1 for the conventional tilled treatment and from 25 to 39 kg ha−1 yr−1 for the no‐tilled treatment, with the upper values of these ranges considered most accurate. Dry deposition is clearly as important as precipitation in contributing to the total S load at this location. A sulfur dry deposition estimate of only 15 kg ha−1 yr−1 was made based on average deposition velocity and ambient SO2 levels. Total deposition models, which rely on dry deposition estimates obtained by the use of SO2 concentrations and an average deposition velocity, may yield inaccurate values of total S additions to the earth's surface.

Kinetics of Hydrolysis and Oxidation of Carbon Disulfide by Hydrogen Peroxide in Alkaline Medium and Application to Carbonyl Sulfide

Kinetic studies of the oxidation of carbon disulfide by hydrogen peroxide in alkaline medium were made spectrophotometrically. The reaction of CS/sub 2/ with OH/sup -/ ion was found to be rate controlling and proceeded by the formation of a dithiocarbonate complex. The major reaction product was sulfate with sulfur occurring as colloidal suspensions only at pH values less than 8. The formation of sulfate increased exponentially with time and was also found to be dependent on the rate of hydrolysis of CS/sub 2/. In addition, the production of sulfate showed large induction periods, suggesting either a complex mechanism or formation by secondary reactions. The results obtained for carbon disulfide were extended to carbonyl sulfide (OCS) oxidation in alkaline solutions. The removal of OCS (acid gas) from mixtures of gases by alkaline liquid absorbents (e.g. NaOH) and oxidation of subsequent solutions to sulfate is an important industrial practice. 42 references, 14 figures, 2 tables.

Acid pyrophosphate extraction of soil fulvic acids

SUMMARYA simple three step method is described for isolation of soil fulvic acids in high yield. The complexing agent H2P2O72− (at pH 2) is used to release soil‐bound fulvic acids. Extraction of humic acids is minimal. Selective separation of the protonated fulvic acids from the ionic extractant is achieved on a non‐ionic polyacrylate resin (Amberlite XAD‐7); after washing the resin, fulvic acids were retrieved in &gt;98% yield by adjusting the pH to 6.5. Two problems associated with the classical alkali extraction method are avoided: possible alkaline oxidation of phenolic components, and their oxidation by Fe3+ under the acidic conditions employed to precipitate humic acids. The product typically has an ash weight of &lt;0.6% after one XAD treatment. The method has been applied to three soils and one IHSS peat sample.

3] Determination of thiamin and its phosphate esters by high-performance liquid chromatography

This chapter describes high-performance liquid chromatography (HPLC) of thiamin and its phosphate esters, which is considered the most sensitive method to determine these compounds at the subpicomole level within lo-20 min. This method is applicable to the analysis of thiamin and its phosphates not only in animal tissues but also in body fluids, foods, and pharmaceutical preparations. This method is also useful in the study of intermediary metabolism of thiamin. In the chromatographic mode, two systems, straight-phase HPLC and reversed-phase HPLC, are used. In the former system, thiamin, thiamin monophosphate (ThMP), thiamin diphosphate (ThDP), and thiamin triphosphate (ThTP) are eluted from a column in this order. In the latter system, the elution order of thiamin phosphates is the reverse. When detection of thiamin phosphates is carried out fluorometrically, two different procedures are used—namely, pre- and postcolumn derivatization methods. The mobile phase used in the precolumn derivatization method of HPLC for thiamin and its phosphates should contain a buffer solution of pH above 8, as thiochrome fluoresces at pH values above 8. All phosphate bonds remain intact when thiamin phosphates are converted to thiochrome phosphates by alkaline oxidation.