Removal of Reactive Black 5 Azo Dye from Aqueous Solutions by a Combination of Reduction and Natural Adsorbents Processes

In this study, a combined process of reduction and adsorption for the degradation of azo dye with nanocrystalline Fe80Si10B10 powder as a reducing agent is analyzed. A mechanical alloying technique produced the powdered alloys needed for the redox process. The synthesized nanocrystalline structure favors the efficiency of the reduction step of Reactive Black 5 (RB5) azo dye. According to the UV-Vis analysis, the reductive process alone allowed for nearly complete color removal after 3 min of reaction. In this regard, the nanocrystallized FeSiB powder has excellent application potential in the first step of the reduction processes for degrading azo dye solutions. Indeed, the nanocrystalline FeSiB powder outperforms commercial Fe powders in terms of degradation efficiency because of the formation of multiple micro-batteries between the α-Fe solid solution and the Fe3Si nanocrystalline phases, favoring the loss of electrons from iron and exhibiting different corrosion resistance. In the second step, the adsorption process, the efficient removal of intermediate undesired compounds from the reduction processes, principally aromatic amines, is analyzed. Different adsorbents, including wood, graphene oxide, activated carbon, and pine particles, were used. The results suggest that graphene oxide and activate carbon performed the best for secondary product adsorption following RB5 degradation. The current study could serve as a guide for environmental applications, such as industrial wastewater treatment, using metallic powders produced by high-energy mechanical alloying.