Experimental study on municipal solid waste incineration fly ash as a component of coal gangue geopolymer and the feasibility of making geopolymer mortar

Abstract

In this study, municipal solid waste incineration fly ash (MSWI FA) was used as a component to supplement the missing element of Ca in the coal gangue (CG) to synthesize CG-MSWI FA geopolymer (CG-MFG). The mixed NaOH and Na2SiO3 solution is adopted as alkali activator. The influence of MSWI FA content, NaOH/ Na2SiO3 ratio, liquid–solid ratio and NaON concentration on the strength and reaction on the CG-MFG is studied by unconfined compressive strength (UCS), XRD, FTIR, TGA and SEM-EDS tests. The heavy metal leaching concentration of the CG-MFG is investigated by ICP-OES test. The test results show that MSWI FA acted as a supplementary calcium source for CG is capable of effectively improving the UCS of the CG-MFG. The optimal dosage of MSWI FA is 15 %. The NaOH/ Na2SiO3 ratio significantly affects the strength of the CG-MFG and its optimal proportion is 25:75. The CG-MFG with 15 % MSWI FA content, 25:75 NaOH/ Na2SiO3, 0.45 liquid–solid ratio and 8 mol/L NaON concentration acquires the highest UCS of 30.28Mpa. The immobilization efficiency of heavy metals from MSWI FA in the CG-MFG is larger than 84.66 %. The energy consumption and carbon dioxide emission of preparing the CG-MFG is much lower than those of Ordinary Portland Cement (OPC) with reduction of 71.9 % ∼ 78.0 % and 70.1 % ∼ 82.9 %, respectively. The amorphous geopolymeric gels are observed as the main geopolymerization product of the CG-MFG. The UCS of the CG-MFG mortar reaches 4 MPa, showing possibilities of replacing cement by the CG-MFG in construction industry and shedding light on recycling of hazardous and solid wastes of MSWI FA and coal gangue.