Effect of Alkali Fusion Methods on the Preparation of One-Part Geopolymer From Coal Gasification Slag

This study investigated the one-part geopolymer synthesis by coal gasification slag through a calcination treatment. Two preparation methods, the traditional alkali fusion method (M-I) and the alkali fusion and modification method (M-II), were compared to illustrate the more suitable way for coal gasification slag-based one-part geopolymer (CGS-based geopolymer) synthesis. The reaction products and structure of the geopolymer were tested by XRD, FTIR, TG-DTG, and SEM. The results showed that the compressive strength of geopolymers prepared by M-I was raised as the NaOH amount increased, and the maximum compressive strength of geopolymers was achieved at 8.44 MPa. The low compressive strength suggested that M-I failed to be used for CGS-based geopolymer synthesis. When solid NaOH was selected for one-part geopolymer synthesis by M-II, the geopolymer possessed a compressive strength of 25.52 MPa and exhibited a well-combined and dense matrix. More Si and Al species in F-SH could be released for geopolymerization, and the coal gasification slag additive could be partially dissolved and act as the filler in the geopolymer matrix, which enhanced the geopolymerization degree. The M-II has been proven to be more suitable for preparing CGS-based geopolymers than the M-I.