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Radiolytic transformation of sulfides in sulfate black liquors

University of British Columbia

The potentially volatile, malodorous sulfides (H₂S, CH₃SH, CH₃SCH₃ and CH₃SSCH₃) in sulfate black liquros were transformed to stable compounds by exposure to gamma photon radiolysis. The product complex following radiolysis of sulfides in aqueous solution is partly resolved ass polysulfide (from H₂S) sulfate (H₂S, CH₃SH, and CH₃SSCH₃), an intermediate, CH₃SSCH₃ (from CH₃SH), and a high molecular weight, amorphous substance (especially from CH₃SCH₃). Variables studied with aqueous solutions and commercial black liquors have included sulfide concentration, solution pH, temperature, oxygen saturation and effects of soluble lignin, all of which.adjusted to some extent the sulfide degradation kinetics. Lowering solution pH and increasing initial sulfide concentration, temperature and/or oxygen pressure increased apparent degradation yields (G), while lignin (thiolignin) acted as a radical scavenger in the process. In gamma radiolysis of strong and weak black liquors (pH 12.85 -13.40) at Gammacell temperature (34°C), and atmospheric oxygen pressure, the apparent degradation yields of sulfide are proportional to the respective initial concentrations. Apparent degradation yields were 0.001-0.003 for CH₃SCH₃ at 0.20 x 10⁻³ -1.10 x 10⁻³g/l and 0.002-0.085 for CH₃SSCH₃ at 0.44 x 10⁻³g/l-39.71 x 10⁻³g/l concentration. Similarly, in carbonated black liquors (pH 8.20 – 9.15), the apparent degradation yields of sulfides significantly correlated with their initial concentration. The apparent sulfide degradation yields are 0.015 to 3.427 for H₂S at 0.89 x 10⁻³-265.20 x 10⁻³g/l, 0.006-0.230 for CH₃SH at 0.48 x 10⁻³- 28.70 x 10⁻³g/l, 0.003 - 0.020 for CH₃SCH₃ at 0.60 x 10⁻³ - 5.22 x 10⁻³g/l and 0.004-0.035 for CH₃SSCH₃ at 1.03 x 10⁻³-9.11 x 10⁻³g/l concentration. The presence of oxygen( 1 atmosphere pressure) at higher concentration of H₂S (247.75 x 10⁻³g/l) and CH₃SH(967.50 x 10⁻³g/l) in carbonate black liquor (pH 7.50) showed high apparent degradation yields of 17 and 28 for H₂S and CH₃SH, respectively. This is considered to be due to a chain reaction occurring during degradation of sulfides. Polysulfide may be generated by radiolysis of acidified sodium sulfide and sulfate green liquor. The apparent yields of polysulfide excess sulfur were 3 and 5 for acidification with carbon dioxide (120 psi) and hydrogen sulfide (270 psi), respectively. As part of these studies, new techniques have been developed for recovery and analysis of sulfides at low concentrations in aqueous solution.

Text

2011-03-02

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http://hdl.handle.net/2429/31925

Forestry

University of British Columbia

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