Insight into the thermal kinetics and thermodynamics of sulfuric acid plant sludge for efficient recovery of sulfur

Abstract

The disposal and management of sulfur-rich sludges (SRS) are challenging issues for the industries due to their adverse environmental impact. The present study reports the detailed characterizations and assessment of the thermo-kinetics of sludge generated from the sulfuric acid plant. In addition, the sulfur was retrieved with the help of the evaporation–condensation method. In the active devitalization zone (200–400 °C), a substantial mass loss (91 ± 3%) was observed, primarily due to the vaporization of sulfur. The isoconversional model-free methods were used to appraise kinetic parameters for the pyrolytic process. The average activation energy (64.5 kJ mol−1) estimated by the Starink method admired the less energy-intensive process and validated the occurrence of thermochemical reactions at low temperatures. The thermodynamic parameters and frequency factor calculated at 10 °C min−1 were ΔG* = 149.1 kJ mol−1, ΔH* = 59.8 kJ mol−1, ΔS* = −0.157 kJ mol−1K−1, and A = 2.1 × 105 s−1. Criado's Z-master plot revealed the dominance of the diffusion mechanism on the process. The efficient recovery of sulfur (≈96% with purity 99 ± 0.5%) was achieved at 440 °C by evaporation–condensation technique, and the findings closely complemented the kinetic and thermodynamic parameters. This study provides a background for a better understanding SRS and efficient sulfur recovery.