Electrochemical treatment of industrial sulfidic spent caustic streams for sulfide removal and caustic recovery

• Published in: Journal of hazardous materials 2020-04, Vol.388, p.121770-121770, Article 121770
• Main Authors: Ntagia, Eleftheria, Fiset, Erika, Truong Cong Hong, Linh, Vaiopoulou, Eleni, Rabaey, Korneel
• Format: Article
• Language: English
• Subjects: Electrochemistry; Environmental Sciences; Industrial wastewater treatment; NaOH; Resource recovery; Sulfide oxidation
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2019.121770

[Display omitted] •Industrial spent caustic stream (SCS) is electrochemically treated.•Sulfide (H2S) is removed at 3.7 kW h kg−1 S.•Caustic (NaOH) is recovered at 6.3 kW h kg−1 NaOH.•Electrolysis is key to sustainable recovery of caustic soda on-site.•Electrolysis can replace the H2O2 in oxidative SCS treatment. Alkaline spent caustic streams (SCS) produced in the petrochemical and chemical manufacturing industry, contain high concentrations of reactive sulfide (HS−) and caustic soda (NaOH). Common treatment methods entail high operational costs while not recovering the possible resources that SCS contain. Here we studied the electrochemical treatment of SCS from a chemical manufacturing industry in an electrolysis cell, aiming at anodic HS− removal and cathodic NaOH, devoid of sulfide, recovery. Using a synthetic SCS we first evaluated the HS− oxidation product distribution over time, as well as the HS− removal and the NaOH recovery, as a function of current density. In a second step, we investigated the operational aspects of such treatment for the industrial SCS, under 300 A m−2 fixed current density. In an electrolysis cell receiving 205 ± 60 g S L−1 d−1 HS− over 20 days of continuous operation, HS− was removed with a 38.0 ± 7.7 % removal and ∼80 % coulombic efficiency, with a concomitant recovery of a ∼12 wt.% NaOH solution. The low cell voltage obtained (1.75 ± 0.12 V), resulted in low energy requirements of 3.7 ± 0.6 kW h kg−1 S and 6.3 ± 0.4 kW h kg−1 NaOH and suggests techno-economic viability of this process.