Clarification of a laterite suspension using a mixed two-layer filter based on limestone and pozzolan

Coagulation and flocculation are essential in water clarification but rely on costly chemical reagents that can leave harmful residues and generate polluting sludge. This study aims to evaluate and compare the effectiveness of bilayer (limestone/pozzolan) and mixed (homogeneous blend) filters for clarifying lateritic suspensions. A suspension with 30 ± 1 NTU turbidity and pH 6.00 ± 0.05 was prepared. Filters were composed of pozzolan and limestone granules (1–2 mm) and characterized by porosity, permeability, bed surface area, and Reynolds number. Flow behavior was determined using a 1 M glucose solution. The bilayer and mixed filters showed porosities of 67.24% and 62.49%, permeabilities of 3.51×10⁻⁷ and 5.73×10⁻⁷ m², and bed surface areas of 2911.99 and 3334.22 m², respectively. Reynolds numbers were 1.42 and 1.75, indicating piston flow in both systems. The mixed filter achieved 65% turbidity removal, outperforming the bilayer filter’s 50%, and had a lower pressure drop (780 Pa vs. 820 Pa). These results suggest that the mixed filter offers better performance and efficiency, making it a promising alternative for the clarification of lateritic suspensions.