Valorization of aluminum scrap via an acid-washing treatment for reductive removal of toxic bromate from water

Abstract

Aluminum scrap (AS) is adopted for the first time as a readily available aluminum source to prepare zero-valent aluminum (ZVAl) for removing bromate from water via a reductive reaction. Since aluminum is easily oxidized to aluminum oxide (Al2O3) on exposure to air, an acid-washing pretreatment on AS is developed to remove the layer of Al2O3. HCl is found as the most effective acid to pretreat AS and the HCl-pretreated or acid-washed AS (AWAS) is able to remove bromate from water and convert it to bromide. Factors, such as temperature, pH, co-existing anions, and particle size, which influence the bromate removal using AWAS are also investigated. The mechanism of bromate removal by AWAS can be attributed to both reduction and adsorption. The elevated temperature also significantly improves bromate removal capacity of AWAS as well as the reaction kinetics. The bromate removal capacity of AWAS is substantially improved under acidic conditions. However, the basic conditions and co-existing anions suppress or interfere with the interaction between bromate and AWAS, leading to much lower removal capacities. The recyclability of AWAS is also evaluated and the acid-washing regeneration is necessary to restore its capacity. However, the mass of AWAS can gradually decrease due to multi-cycle acid-washing regeneration. Through this study, the valorization of AS via acid-washing is demonstrated and optimization of acid-washing parameters is presented. Our findings reveal that the acid-washing is a useful technique to utilize AS as an inexpensive and efficient material for removing bromate from water.