Examination of the hexamethylenetetramine procedure for separation of thorium from rare earths and for determination of thorium.
An examination has been made of the efficiency of the gravimetric reagent hexamethylenetetramine in the separation of thorium from rare earths and in the determination of thorium. Losses to the filtrate, beaker and filter paper are evaluated as well as the extent of rare earth and other contamination of the thorium hydroxide precipitate. When hydroxylamine is used as the reducing agent to keep cerium in the tervalent state, excellent separations are obtained. The efficacy of the reagent is offset by the loss of small amounts of thorium to the precipitation vessel, the scavenging properties of the precipitate for silica and the difficulty in evaluating a true reagent blank.
Effects of hexamethylenetetramine (HMTA) on the aqueous solution structure, dynamics and ion solvation scenario: A concentration and temperature dependent study with potential HMTA models
Abstract The local hydrogen bonding structure of water and its dynamics in hexamethylenetetramine (HMTA) solution is investigated by using classical molecular dynamics simulations. In this study, we have compared two potential HMTA models with different Lennard-Jones (L-J) combination rules. We have considered five different concentrations of HMTA, ranging from pure water to 6.181 m HMTA at 298 K, whereas to calculate the temperature dependence from 298 K to 353 K, we have used 4.187 m concentration of HMTA. From the radial distribution function, it is observed that the addition of HMTA facilitates structural making of water, whereas our calculated values of the tetrahedral order parameter and asphericity of water suggests disordered structure with increasing HMTA concentration. Also there is a significant development of self-aggregation among water and HMTA molecules at higher concentration of HMTA. The self-diffusion coefficient values of water and HMTA is found to be decreased with increasing HMTA concentration in the solution, whereas at concentrations below 1.0 m, it matches well with the experimental observations. Our calculated activation energy of diffusion for HMTA (4.10 ± 0.2 kcal/g mol for Model-II), is very close to the experimental observation (4.34–4.44 kcal/g mol). The structure of the hydration shell of ions of different charges and sizes is also investigated in the presence of HMTA. For all the models, it is observed that the structural and dynamical properties of water and the hydration shell of ion shows negligible difference with varying concentration and temperature. In contrast, the ion−HMTA correlations are model dependent. It is suggested that the HMTA model-I (AM) is the suitable model for representing ion-solvation structure and dynamics particularly at lower concentrations of aqueous-HMTA solution.
Denitrification of PVA-immobilized denitrifying photosynthetic bacterium, Rhodobacter sphaeroides
Abstract A newly isolated denitrifying strain, Rhodobacter sphaeroides NII2 was immobilized in polyvinyl alcohol (PVA) gel, and the properties of the cells in the gel were examined. The immobilized cells had low or almost no denitrification activity, but the cells were activated by incubation in light with culture medium for denitrification containing 0.5% nitrate and no other nitrogen source. Cells grown in the dark were activated by incubation at an earlier stage and to a higher rate than the light-grown cells. The activation was markedly enhanced in the PVA gel with a low cell concentration. The immobilized cells consumed nitrate with a temporary accumulation of NO 2 and evolved nitrogen gas. The immobilized cells could use various organic compounds as electron donors for denitrification. Thus, the immobilized cells were applied to a continuous treatment of synthetic wastewater using an aparatus devised by this laboratory. The results showed an efficient removal of NO 3 -N from the test water.