The effect of residual flocculants in the circulating water on dewatering of Gol-e-Gohar iron ore

Abstract

While flocculant type and concentration have been extensively reported in the literature for sedimentation of iron ores and its respective mono-minerals, little information is known regarding the effect of residual flocculant in the circulating water. To this end, inlet slurry to the tailings thickener of the Gol-e-Gohar iron ore processing plant was sampled for four days. Flocculant type (anionic, cationic, and nonionic polyacrylamide), their dosage (10–90 g/t), pH (1–12.5), solid content (5–23%), and for the first-time residual flocculant dosage in the circulated water were investigated. Experimental tests including zeta potential measurements, batch sedimentation trials, and flocculant adsorption tests were performed. An experiential design (Taguchi L27) was applied for conducting the settling tests. The results showed that the isoelectric point (IEP) of the bulk material was 4.3. The principal flocculant adsorption mechanism was based on the hydrogen bond formation, and there was an interaction between flocculant type and pH. Among the flocculants, the anionic one demonstrated desirable settling efficiency due to its strong hydrogen bonding property and large flocs formed through repulsive force between the flocculant and particle surfaces. Finally, the experimental data indicated that the optimum conditions to achieve maximum settling rate (48 m/h), minimum flocculant concentration in the circulated water (0.5 mg/L), and desirable clarity were obtained at 9% (w/w) solid content, 20 g/t high molecular anionic polyacrylamide (APAM) and pH of 8.3. It was concluded that exceeding flocculant dosage to more than 20 g/t resulted in higher residual flocculant concentration in the circulating water leading to a considerable attenuation in the solid-liquid separation efficiency.