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Rheological measurements are carried out on aqueous magnetic suspensions (10% ⩽ Φv ⩽ 30%) submitted to a low magnetic field. The suspended particles are micronic latex spheres made of very small ((10 ÷ 100) Å) grains of iron oxyde embedded in a polystyrene matrix. The suspension exhibit a strong increase of the apparent viscosity which is measured by capillary flow experiments. The rheological behaviour is interpreted on the basis of a Bingham model with a yield stress due to the fibrinated structure induced by the magnetic field.

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Présenté par Jacques Villain RésuméNous présentons des résultats sur la structuration d'une suspension colloïdale sous l'effet d'un champ électrique alternatif. La croissance des fibrilles est étudiée par un dispositif d'analyse d'image qui a permis la détermination de la loi temporelle de la formation des chaînes de particules, à différentes intensités du champ appliqué. De même, l'effet du changement de la fréquence a été étudié.

A new multibranch Integrated Catchment (INCA) model INCA-Metals has been developed to simulate the impact of tannery discharges on river systems. The model accounts for the key chemical reaction kinetic processes operating as well as sedimentation, resuspension, dilution, mixing and redistribution of pollutants in rivers downstream of tannery discharge points and for mine discharges or acid rock drainage sites. The model is dynamic and simulates the daily behaviour of hydrology and eight metals, including cadmium, mercury, copper, zinc, lead, arsenic, manganese and chromium, as well as cyanide and ammonia. The model is semi-distributed and can simulate catchments, tributaries and instream river behaviour. The model can also account for diffuse pollution from rural runoff as well as point sources from effluent and trade discharges. The model has been applied to the new Savar tannery complex on the Dhaleshwari River system in Bangladesh to assess the impacts on pollution levels in the river system and to evaluate a set of treatment scenarios for pollution control, particularly in the dry season. It is shown that the new effluent treatment plant at Savar needs to significantly improve its operation and treatment capability in order to alleviate metal pollution in the downstream Dhaleshwari River System and also protect the Meghna River System that falls in the Bay of Bengal.