Preparation of nano red mud gels using red mud for the encapsulation and stabilization of arsenic in arsenic-bearing gypsum sludge

Arsenic-bearing gypsum (ABG) sludge and red mud (RM) are hazardous industrial wastes produced during the smelting of nonferrous metals. These unstable wastes are a threat to ecological environments and human health due to their massive accumulation resulting from inadequate treatment technologies. This study introduces a novel method for treating ABG sludge using RM. The aluminum, iron, calcium, and silicon separated from the RM were used to prepare red mud gel for encapsulating the sludge. Through nanogel particle polymerization and chemisorption, a core-shell structure is formed. This structure comprises Ca3(AsO4)2 and CaSO4·2H2O as the core, with CSH and CASH nanogel particles polymerized to form a gel block loaded with sulfate. The outer shell consists of complexes formed by the adsorption of arsenate ions on aluminum and iron hydroxide. Leaching tests of the encapsulated products under optimal conditions were conducted in various pH environments. The results showed that the leaching concentration of arsenic was less than 1 mg/L, demonstrating the strong environmental stability of the structure. The process effectively solidified arsenic and utilized RM in a resourceful manner, successfully demonstrating green technology to protect the environment and providing important insights into treating two types of industrial waste.