Title:
Reduction of Hexavalent Chromium in Ash from Biomass Updraft Gasification Plants
Author(s):
Fernández, M.J., Barro, R., Supancic, K., Obernberger, I.
Document(s):
Paper
Poster
Abstract:
In this study, different agents for the reduction of hexavalent chromium (Cr(VI)) were evaluated, including FeCl2, FeSO4·H2O (ferrous sulphate monohydrate), as well as water only. Cr(VI) reduction in biomass ashes is of relevance as many ashes exceed the limiting value of Cr(VI) (2 mg/kg d.b.) for the utilization of ashes as a fertilizer. Various dosages of the reducing agents were applied to grate ash obtained from a commercial biomass updraft gasification plant. In addition, the influence of the moisture content of the ash (20 and 30 wt%, wet basis) was systematically investigated. All experiments were conducted at pilot scale using a commercial concrete mixer. Cr(VI) concentrations were determined immediately after mixing the ash with the reducing agents at different multiples of the stoichiometric requirement, as well as after storage periods of 5 and 10 weeks. Sampling and analytical procedures were performed in accordance with relevant ISO standards. Cr(VI) was quantified following EN 16318 (Method A). Major elements were analyzed by ICP-OES, while trace elements were determined by ICP-MS. The addition of water without any reducing agent seems to have no strong influence on the reduction of Cr(VI). The reducing agents iron sulphate and iron chloride immediately reduce the Cr(VI) content significantly. Regarding the water content of the ash, 30% water could help to obtain higher efficiencies of Cr(VI) removal but may cause problems regarding ash agglomeration, therefore, 20 wt% water seems more suitable. In general, iron sulphate works better than iron chloride. Cr(VI) tends to increase again as a function of storage duration. This fact is important because ash usually needs to be stored for a certain time before it can be applied. Therefore, this “time effect” also needs to be considered, it is most likely caused by the generation of OH- ions due to the basicity of the ash, which shifts the equilibrium over time.
Keywords:
ash, biomass, toxicity, characterization, biofertilizers
Topic:
Biomass Conversion for Bioenergy
Subtopic:
Gasification for power, CHP and polygeneration
Event:
34th European Biomass Conference and Exhibition
Session:
4BV.8.8
Pages:
612 - 616
ISBN:
978-88-89407-27-1
Paper DOI:
10.5071/34thEUBCE2026-4BV.8.8
Price:
FREE
