Mechanism and kinetics for the carbothermal reduction of arsenic-alkali mixed salt produced from treatment of arsenic-alkali residue

Abstract

Arsenic-alkali mixed salt (AAS) is a hazardous by-product of the treatment of arsenic-alkali residue (AAR). Although direct carbothermal reduction can enable the harmless and resourceful disposal of AAS, the specific reaction pathway and mechanism of the reduction process remain unclear. To gain further insight into the reaction process, the non-isothermal kinetics and reaction mechanism of AAS carbothermal reduction were investigated. The results indicate that AAS reduction involves three pathways: (1) direct reduction of Na2As4O11 to As(g), (2) reduction of Na2As4O11 to As2O3 and subsequent reduction to As(g), and (3) direct reduction of Na3AsO4 to As(g). Calculations using the Flynn-Wall-Ozawa (FWO) and integral master-plot methods indicate that the kinetic model conforms to the two-dimensional diffusion function, with an average activation energy of 164.30 kJ/mol and a pre-exponential factor of 1.764 × 106 1/s. These results are significant for further in-depth research into the carbothermal reduction of AAS.