Digestion reactions of paper sludge combustion ash in strong alkaline solutions at 60 °C

• Published in: Journal of material cycles and waste management 2016, Vol.18 (1), p.132-145
• Main Authors: Hartmann, Andrea, Petrov, Valeriy, Buhl, Josef-Christian, Rübner, K., Lindemann, M.
• Format: Article
• Language: English
• Subjects: Alkalies; Aluminum; Analysis; Analytical chemistry; Ash; Calcite; Chemical analysis; Chemical reactions; Chemistry; Civil Engineering; Combustion; Construction industry; Crystallization; Engineering; Environmental Management; Experiments; Gravimetry; Heavy metal content; Heavy metals; Hydraulics; Lead; Low temperature; Original Article; Pulp & paper industry; Raw materials; Silica; Sludge; Sludge digestion; Sodium; Sodium hydroxide; Studies; Temperature; Waste Management/Waste Technology; Zeolites
• ISSN: 1438-4957; 1611-8227
• DOI: 10.1007/s10163-014-0320-4

Alkaline reactions of paper sludge combustion ash at low temperature (60 °C) were performed using a calcite-rich paper ash (PA 1) and a gehlenite-rich ash (PA 2). Strong alkaline conditions (8, 12, 16 M NaOH) were revealed at reaction times of 1–4 h and 12–24 h. Reactions were performed with pure ashes and in the presence of NaAlO 2 . The products were characterized by XRD, FTIR, SEM/EDX, gravimetry and chemical analysis. The conversion was found to proceed mainly in the period between 1 and 4 h. Portlandite and hydrogarnet were observed from PA 1 in 8 M NaOH. Onset of formation of Ca 4 Al 2 O 6 CO 3 . 11H 2 O beside Ca(OH) 2 could be analyzed after reaction of PA 1 in 12 M and 16 M NaOH. Addition of NaAlO 2 favored crystallization of hydrogarnet and Ca 4 Al 2 O 6 CO 3 . 11H 2 O. For PA 2 gehlenite remained stable, but a high portlandite fraction was observed. Addition of NaAlO 2 yielded hydrogarnet beside gehlenite in 8 M NaOH. Higher alkalinities favored crystallization of Ca 4 Al 2 O 6 CO 3 . 11H 2 O and onset of dissolution of gehlenite. Finally transformation of Ca 4 Al 2 O 6 CO 3 . 11H 2 O into sodium aluminum silicate hydrate was observed. All results were discussed with regard to heavy metal distribution of the initial PA between the alkaline digestion solution and the products. In conclusion suitable applications of the products were proposed.