The adsorption of Selenium by δ - MnO2 was studied under varying pH conditions and amounts of adsorber. The methods of analysis for trace amounts of selenium included those of colorimetry and gamma ray spectroscopy. Of the two methods the latter proved to be the most effective in terms of precision, accuracy and conciseness.
The adsorption of selenium on δ - MnO2 was adequately described through the use of the Langmuir isotherm equation. The pH conditions varied from 2.0, 3.5, 5.0 to 8.0 with an increase of pH, the ability of the - MnO2 to absorb selenium decreased. It is proposed that this is primarily due to an increased electrostatic repulsion on - MnO2 surface with increasing pH.
The surface area of δ - MnO2 was determined using the BET - Kr method and was found to be 156 m2/gm. with increasing amounts of adsorber the ability to adsorb more selenium increased. When the amount adsorbed per gram was calculated it was seen to decrease with an increase in the amount of adsorber. This is probably due to an increase in the number of available sites with a greater amount of adsorber. This trend was observed at pH levels of 2.0 and 8.0 and the acidic conditions showed the best results. The ability of δ - MnO2 to adsorb a certain amount of selenium regardless of pH conditions may infer the adsorption mechanism is a two-stage mechanism. This would include an initial site filling and release of Mn2+ or H+ which would then result in a change of surface character. The trends seen with selenium adsorption by δ - MnO2 closely paralleled those of adsorption by ferrous hydroxide, montmorillonite and kaolinite.