Experiments on acid digestion and gas-purification processes

Research carried out on acid digestion and gas purification started with a selection of sulphuric and nitric acid as the chemicals to be used. The design parameters for low-level waste were then determined in a pilot plant. The digestion of the waste in the pilot plant resulted in the formation of SO2 and NOx. These compounds were converted black to the corresponding acids in a gas-purification system consisting of a series of contact columns. Reconversion of sulphuric acid could be done in a relatively small column in which the SO2 formed during the digestion was oxidised by nitric acid. Nitric acid was recovered by absorbing NOx into water in three columns operating at room temperature. Both air and -preferably- hydrogen peroxide were successfully used as oxidants during adsorption. The experience thus obtained indicated that an acid-digestion plant can be run in a safe and reliable way in spite of the fact that aggressive chemicals have to be used. The burdening of the environment with NOx or SO2 is limited. The pilot plant could be run by one person, owing to the installation of a process computer. (author). 7 refs.; 12 figs.; 4 tabs