(70ao) Production of a Diluted Solid Tracer by Dry Co-Grinding in a Tumbling Ball Mill

Different events may lead to an accidental pollution of grounds, present as traces. Ground cleaning up demands efficient means which are often to be developed. The development of cleaning methods goes through the production of an artificial pollution based on the dispersion of a contaminating agent, present at a very low proportion, in an inert medium having properties close to those of the ground. The present paper describes a study on the production of such a particulate system, having several imposed properties: - the proportion of the pollutant has to be lower than 5 % ; - while the two products have different sizes and densities, the pollutant has to be well dispersed in the inert medium to confer an homogeneous pollution of the ground ; - all the particles of the two products need to have final sizes lower than 10 µm. This operation was realised by dry co-grinding in a tumbling ball mill. Indeed, this process permits a reduction of the particles size. The shearing stress imposed in the grinding chamber favours a good dispersion of a product in the other one, even if the initial properties of the two constituents (size, density) are different. The two products were ground separately first and then together. The follow-up of the particles size and morphology, as well as the modelling of the grinding kinetics have permitted to propose a mechanism by which the diluted solid tracer is produced. The influence of the grinding conditions (nature and initial size of the diluting medium, ball filling rate, powder filling rate, proportion of the polluting tracer) on the properties of the final product were studied. Thus, we have defined optimum co-grinding conditions permitting to produce a tracer offering the required properties.