fines and water with the coarse fraction returned to the screen. Typically, screen are more effective classifiers than hydrocyclones giving a sharper cut and more effective removal of undersize materials. The test arrangement is shown in figure 2. Typically, screens produce a cleaner sand because the classification efficiency of DW Screens is (65-85%) with inefficiency close to the cut size vs Hydrocyclones (45-65%) where inefficiency is entrained slimes. Clays tend to stick to coarser material exaggerating cyclone inefficiency. The critical variables were the tailings physical characterization, including PSD, clay percentage (montmorillonite and illite between 3-15%), mineralogy by XRD, and specific gravity (2.7 g/cc). operating conditions included pressure (100-150 Kpa), solids in the screen feed (6872%), apex (1.25”-1.50”) and vortex (1.25”-1.50”). Screen characteristics included slot aperture(0.3-0.8 mm), open area percentage (30-45%), flow rate (35-45 m3/h), bed depth (10-15 cm), and fines <75 um (10-15%). The fresh feed to come from current cyclone underflow to go dewatering screen. The final product is the oversize screen and the retorn of water from the overflow hydrocyclones. Figure 3 Pilot plant arrangement
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