Removal of chromium (VI) from water by micro-alloyed aluminium composite (MAlC) under flow conditions

Abstract

This paper deals with Cr(VI) ion removal from water, by micro-alloyed aluminium composite (MAlC), under flow conditions. In a water environment the MAlC acts as a strong reducing agent. Dissolving it in water is accompanied by the generation of Al(III) ions and reduction of water to H₂, with OH- ions. The final product is insoluble Al(OH) ₃. A series of Cr(VI) model solutions, with initial pH ranging between 1 and 5, were treated in the original semi-flow system (SFS), which simulated flow conditions well. The results demonstrate a high MAlC efficacy, considering that at the end of the treatment, concentrations of Cr(VI) were below the maximal allowed concentrations for drinking water, in all model solutions. The MAlC mechanism of action is based mainly on processes of reduction and co-precipitation by Al(OH) ₃, because Cr(VI) is removed from the water phase as metal chromium and insoluble Cr(OH) ₃. Behaviour of the composite in water is under significant influence of pH, which affects its efficacy and mechanism of action. Therefore, the rate of Cr(VI) removal is greater at the beginning, decreasing towards the end of the treatment. Additionally, the ratio of [metal chromium]/[Cr(OH) ₃] in precipitate, at the end of the treatment, decreases with increasing initial pH of the model solution. Application of the SFS significantly enlarges efficacy of the MAlC, compared to work under stationary conditions.


WaterSA Vol.30 (3) 2004: 353-359