High-temperature electrocoagulation of colloidal calcareo-argillaceous suspension

Abstract

In this work, the temperature-dependent electrocoagulation behavior of the highly stable calcareo-argillaceous colloids was studied. The response surface methodology was implemented to explain the performance of this physicochemical process. Since the preliminary standard quadratic models were proved to be non-satisfactory, Box-Cox transformation technique was applied to the related responses. After the reliable and capable models were obtained with Box-Cox technique, the whole system was characterized based on the response surface meshes constructed on these models. According to the results of the statistical study, the suspension pH was proved as a critical parameter. In the slightly acidic range between pH 5–6, the supernatant turbidity was effectively eliminated with the electrocoagulation owing to the formation of the hydrolyzed aluminum species (Al(OH)2+, Al2(OH)2+4, Al3(OH)4+5, Al(OH)+2). On the other hand, the increase in the electrical current promoted the electrocoagulation and the formation of the agglomerates leading to the larger volumes of the final sediment (mud). The increase in the solution temperature from 25 °C to 85 °C also significantly contributed to the turbidity elimination process and decreased the cost of the electricity consumption. This temperature-dependent improvement was explained by the increasing concentration of Al(OH)2+. This physicochemically active species became more dominant at 85 °C and coagulated the colloidal particles in a more effective way. In parallelism with these inferences, the desirability-based optimization estimations strongly suggested that the applied electrical current for the electrocoagulation should be low (0.2 A), the suspension should be hot (85 °C) and slightly acidic (pH 5) for the minimization of the supernatant turbidity (3 NTU), the sediment thickness (0.8 cm) and the cost of the electricity consumed (0.003$). Conclusively, the high-temperature electrocoagulation of the colloidal mineral matters seems to be a promising technique in terms of its effectiveness and significantly diminished cost of the process at the higher suspension temperatures.