title: Electrochemical sulfide removal and caustic recovery from spent caustic streams.
abstract: Spent caustic streams (SCS) are produced during alkaline scrubbing of sulfide containing sour gases. Conventional methods mainly involve considerable chemical dosing or energy expenditures entailing high cost but limited benefits. Here we propose an electrochemical treatment approach involving anodic sulfide oxidation preferentially to sulfur coupled to cathodic caustic recovery using a two-compartment electrochemical system. Batch experiments showed sulfide removal efficiencies of 84 ± 4% with concomitant 57 ± 4% efficient caustic production in the catholyte at a final concentration of 6.4 ± 0.1 wt% NaOH (1.6 M) at an applied current density of 100 A m(-2). Subsequent long-term continuous experiments showed that stable cell voltages (i.e. 2.7 ± 0.1 V) as well as constant sulfide removal efficiencies of 67 ± 5% at a loading rate of 47 g(S) L(-1) h(-1) were achieved over a period of 77 days. Caustic was produced at industrially relevant strengths for scrubbing (i.e. 5.1 ± 0.9 wt% NaOH) at current efficiencies of 96 ± 2%. Current density between 0 and 200 A m(-2) and sulfide loading rates of 50-200 g(S) L(-1) d(-1) were tested. The higher the current density the more oxidized the sulfur species produced and the higher the sulfide oxidation. On the contrary, high loading rate resulted in a reduction of sulfide oxidation efficiency. The results obtained in this study together with engineering calculations show that the proposed process could represent a cost-effective approach for sodium and sulfur recovery from SCS.
authors.affiliation: Laboratory of Microbial Ecology & Technology, Faculty of Bioscience Engineering, University of Ghent, Coupure Links 653, 9000, Ghent, Belgium.
authors.forename: Eleni
authors.initials: E
authors.lastname: Vaiopoulou
authors.affiliation: Laboratory of Microbial Ecology & Technology, Faculty of Bioscience Engineering, University of Ghent, Coupure Links 653, 9000, Ghent, Belgium.
authors.forename: Thomas
authors.initials: T
authors.lastname: Provijn
authors.affiliation: Laboratory of Microbial Ecology & Technology, Faculty of Bioscience Engineering, University of Ghent, Coupure Links 653, 9000, Ghent, Belgium.
authors.forename: Antonin
authors.initials: A
authors.lastname: Prévoteau
authors.affiliation: School of Civil Engineering, The University of Queensland, Brisbane, QLD, 4072, Australia.
authors.forename: Ilje
authors.initials: I
authors.lastname: Pikaar
authors.affiliation: Laboratory of Microbial Ecology & Technology, Faculty of Bioscience Engineering, University of Ghent, Coupure Links 653, 9000, Ghent, Belgium. Electronic address: korneel.rabaey@UGent.be.
authors.forename: Korneel
authors.initials: K
authors.lastname: Rabaey
mesh_terms: D002424:Caustics / Q000302:isolation & purification*; D004560:Electricity; D004563:Electrochemistry / Q000295:instrumentation / Q000379:methods*; D004566:Electrodes; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D045483:Rivers / Q000737:chemistry*; D013440:Sulfides / Q000302:isolation & purification*; D014865:Waste Disposal, Fluid; D018508:Water Purification / Q000379:methods
chemical_list: D002424:Caustics; D013440:Sulfides
keywords: Electrochemical treatment; Recovery; Sodium hydroxide; Spent caustic; Sulfide