Evaluation des poussières émises sur le site d'exploitation d'usines pyrométallurgiques. Cas de société pour le traitement du terril de lubumbashi (STL)

ABSTRACT

This work addresses the quantification, measurement and composition of atmospheric fallout. The theoretical part is devoted to a theoretical synthesis of the dust fallout produced during the process in the company's facilities for the treatment of Lubumbashi Heap. In fact, during the process, in the various operations, loading, unloading and transport of materials generate channeled and diffuse dust. Ducted dust is easily identifiable while diffuse dust is not. The objective of this work was to quantify the dust emitted and to classify them according to their size.

The methodology adopted in this work consisted of placing dust deposition gauges in several places or areas of the STL operating site (sheltered and semi-sheltered areas). After a given time (twenty-two days), the gauges and their contents are sent to the laboratory in order to determine the quantity of dust deposited per unit of time and area for each zone considered. Regarding the determination of the size of the particles that constitute this dust, the chosen approach consisted of placing glass plates coated with a hydrophobic fixative and glued to wooden posts. After a given exposure time of ten hours, the platelets are observed under a microscope; which makes it possible to determine the size of the constituent particles as well as their proportions. Chemical analyzes were carried out on composite samples taken from January to July 2020 by ICP-MS.

The results obtained showed that the flow of dust observed during three campaigns was not the same. In the coke storage area, the flow varied from 2 to 4.93 g/m² per day respectively during the campaign in January and July. In the drying zone, the flow recorded during the January campaign was the highest compared to the others. That is 80.1 compared to 31.93 g/m² per day in April. In the storage silo areas, between the pelletizing hall and the oven hall, pelletizing hall, oven and packaging hall, the April campaign recorded high values. Or 223.59 in April against 171.82 g/m² per day in July in the storage silo zone; 33.47 in April against 28.4 g/m² per day in January in the pelletization zone. Between the pelletizing hall and the kiln hall the flow varied from 155.67 in April against 82.84 g/m² per day in July, 18.63 in April against 15.7 in January in the kiln area. In the packing area the flow varied from 32.47 in April against 18.83 g /m² per day in January.

As regards the size, the results of the average of the observations under the microscope indicate that the fine particles whose dimensions are less than 2.5 um are in negligible proportion (less than 10%). These particles can enter the human body when exposure is prolonged. They can reach the pulmonary alveoli. The consequences are multiple at this level. While the particles whose dimensions are between 2.5 and 10 um presented a proportion of 38.9%. Those greater than 10 um presented a proportion of 51.4%.

To all of these results, the suspension of fallout is influenced by weather conditions including temperature and relative humidity. This showed that during the first three campaigns of the year 2020 the temperature values varied between 24.3 and 29.5 ° C respectively in the drying zones and the ovens during the campaigns of April and of July. Relative humidity values ranged from 30.5% to 73.0% respectively in the drying area and the area between the pelletizing hall and the ovens hall during the April and January campaigns.