Holistic insight into the viability of employing cerium(IV) sulphate to oxidise toxic contaminants in effluent from the coal gasification process: Optimisation studies

The coal gasification (CG) process, while beneficial for producing syngas, poses environmental risks due to the production of highly toxic wastewater containing high concentrations of polycyclic aromatic hydrocarbons (PAHs), phenolics, and cyanides. This study examines the oxidation of pollutants in wastewater from a simulated underground coal gasification (UCG) process, with initial pollutant levels of pH 1.8, total cyanides 21.00 mg/L, total phenols 61.95 mg/L, heavy metals 7.68 mg/L, PAHs 2459 μg/L, and dissolved organic carbon (DOC) 148.0 mg/L. Three oxidation systems (Ce(SO 4 ) 2 ·4H 2 O, Ce(SO 4 ) 2 ·4H 2 O + H 2 O 2 , and Fenton process with FeSO 4 + H 2 O 2 ) were used to remove pollutants from wastewater from the coal gasification process. In the first system, the oxidising agent was Ce 4+ ions, while in the second and third systems, where hydrogen peroxide was added, the oxidising agents were hydroxyl radicals. Using central composite design and response surface methodology (CCD/RSM), the most favourable oxidation conditions were identified for Ce(SO 4 ) 2 ·4H 2 O (35 min, Ce 4+ :C molar ratio of 5:1, pH 2.5, temp. 40 °C). For the Ce(SO 4 ) 2 ·4H 2 O + H 2 O 2 system DOC:Ce 4+ :H 2 O 2 molar ratio of 1:2:10. Results showed significant reduction in pollutants: Ce(SO 4 ) 2 ·4H 2 O reduced PAHs, phenols, cyanides, DOC, and heavy metals by 99.40 %, 99.97 %, 97.67 %, 65.34 %, and 90.01 %, respectively; Ce(SO 4 ) 2 ·4H 2 O + H 2 O 2 achieved reductions of 99.91 %, 99.66 %, 98.14 %, 76.35 %, and 81.45 %; and the Fenton process achieved reductions of 99.91 %, 99.95 %, 95.07 %, 56.49 %, and 89.33 %. An application of alternative oxidation processes (Ce(SO 4 ) 2 ·4H 2 O and Ce(SO 4 ) 2 ·4H 2 O + H 2 O 2 ) is a viable option in removing toxic pollutants with simultaneously cerium recovery. • Cerium(IV) oxidants reduce over 99 % of PAHs, 97 % of cyanides, and 99 % of phenolics. • Oxidising with a cerium(IV) and hydrogen peroxide system produces stable sediments. • Cerium compounds utilised in the process can be recovered from the sediments.