Effect of Temperature and Solvent Composition on the Acid Dissociation Constants of 2-Pyrrol and 2-Thiophene Aldehyde Phenyl Sulphonyl Hydrazones

Acid dissociation constants, pKa, of 2-pyrrolaldehyde phenylsulphonyl hydrazone, 1, and 2-thiophenealdehyde phenylsulphonyl hydrazone, 2, have been determined spectrophotometrically in ethanol-water media of various compositions over the temperature range 25℃ - 45℃. The obtained results were used in the calculation of the enthalpy, △H°, and the entropy, △S°, of the ionization processes. The slight variations observed in the pKa values of the thiophene compound compared to the pyrrol analogue revealed that neither of the two hetero atoms in the pyrrol or thiophene rings, of the two compounds, is involved in a hydrogen bond chelation. This conclusion was also confirmed through measurements of the dipole moment, IR and NMR spectra.

Determination of the acid dissociation constants of N-carboxymethyl-N-(p-hydroxy phenyl carbamoylmethyl)-2,3-dihydroxy- 5-carbomethoxy benzylamine and the stability constants of its metal complexes

The acid dissociation constants of N-carboxymethyl-N-(p-hydroxy phenyl carbamoyl- methyl)-2,3-dihydroxy-5-carbomethoxy benzylamine(CHDCB) and the stability constants of its 1:1 complexes with alkaline earth, Cd(Ⅱ), Co(Ⅱ), Ni(Ⅱ), Cu(Ⅱ), Zn(Ⅱ), Fe(Ⅲ),Th(Ⅳ)and U(Ⅵ)ions have been determined at 25.0±0.1℃ and at an ionic strength of 0.1(KNO_3)by pH titration method. The probable coordination sites have also been discussed.

THE DISSOCIATION CONSTANT OF ARACHIDIC ACID BY IR AND LB TECHNIQUES

The dissociation constant of arachidic acid an a subphase containing Ag+ ion was measured by IR and LB techniques.

Influence of Mechanical Activation on Acid Leaching Dephosphorization of High-phosphorus Iron Ore Concentrates

High pressure roll grinding（HPRG）and ball milling were compared to investigate the influence of mechanical activation on the acid leaching dephosphorization of a high-phosphorus iron ore concentrate,which was manufactured through magnetizing roasting-magnetic separation of high-phosphorus oolitic iron ores.The results indicated that when high-phosphorus iron ore concentrates containing 54.92 mass% iron and 0.76 mass% phosphorus were directly processed through acid leaching,iron ore concentrates containing 55.74mass%iron and 0.33mass%phosphorus with an iron recovery of 84.64%and dephosphorization of 63.79% were obtained.When high-phosphorus iron ore concentrates activated by ball milling were processed by acid leaching,iron ore concentrates containing56.03mass%iron and 0.21mass% phosphorus with an iron recovery of 85.65% and dephosphorization of 77.49%were obtained.Meanwhile,when high-phosphorus iron ore concentrates activated by HPRG were processed by acid leaching,iron ore concentrates containing 58.02mass%iron and 0.10mass% phosphorus were obtained,with the iron recovery reaching 88.42% and the dephosphorization rate reaching 88.99%.Mechanistic studies demonstrated that ball milling can reduce the particle size,demonstrating aprominent reunion phenomenon.In contrast,HPRG pretreatment contributes to the formation of more cracks within the particles and selective dissociation of iron and P bearing minerals,which can provide the favorable kinetic conditions to accelerate the solid-liquid reaction rate.As such,the crystal structure is destroyed and the surface energy of mineral particles is strengthened by mechanical activation,further strengthening the dephosphorization.

Water-to-air transfer of branched and linear PFOA:Influence of pH,concentration and water type

The volatilisation of perfluorooctanoic acid(PFOA)was measured experimentally at a range of pH values using a previously published laboratory method.Water-to-air transfer was studied for five structural isomers,namely:the linear isomer(n-PFOA)and the four most commonly occurring branched isomers(3-,4-,5-and 6-PFOA).The influence of water concentration and water type on the pH-dependent waterto-air transfer was also investigated for n-PFOA.The water-to-air transfer was studied over the course of 48 h at pH values ranging from 0.2 to 5.5.Under all experimental conditions tested,the volatilisation of PFOA was negligible at pH>2.5.In experiments performed with MilliQ water,volatilisation increased with decreasing water pH.In experiments performed with tap water and lake water,maximum volatilisation was observed at pH 1.The concentration of PFOA in water had no influence on the pH value at which water-to-air transfer was observed(i.e.at pH<2.5)for the concentration range tested(0.1e50 mg/L PFOA in deionised water).Although the percentage of PFOA volatilised was significantly different for the four branched isomers at low pH,volatilisation was not observed above pH 2.5 for any branched isomer suggesting that all PFOA isomers have a low pKa.Overall,these laboratory results demonstrate that volatilisation of any structural isomer of PFOA from water is negligible at environmentally-relevant conditions.It is unlikely that PFOA isomers will be fractionated in the environment as a result of volatilisation because it is a process of negligible environmental relevance.