Geopolymers as a material suitable for immobilization of fly ash from municipal waste incineration plants

Figures & data

Table 1. Labels and descriptions of samples.

Sample label	Sample description
FA	Coal fly ash (as delivered)
MK	Metakaolin (as delivered)
W1	Waste no. 190107* as delivered (Waste 1)
W2	Waste no. 190113* as delivered (Waste 2)
G-MK	Geopolymer obtained from metakaolin
70W1-G-MK	Geopolymer obtained from 70 mass% W1 and 30 mass% metakaolin
70W2-G-MK	Geopolymer obtained from 70 mass% W2 and 30 mass% metakaolin
50W1-G-FA	Geopolymer obtained from 50 mass% W1 and 50 mass% coal fly ash
50W2-G-FA	Geopolymer obtained from 50 mass% W2 and 50 mass% coal fly ash

Table 2. Chemical composition of coal fly ash (FA), metakaolin (MK), and waste fly ashes (W1, W2).

Component	mass% of components in the investigated samples
	FA	MK	W1	W2
SiO2	50.5	51.7	2.5	10.1
Al2O3	25.3	32.1	1.0	7.2
Fe2O3	13.9	1.5	0.4	1.0
Na2O	1.1	0.1	6.8	5.4
K2O	3.2	0.3	3.0	2.2
CaO	3.6	0.3	43.6	41.6
MgO	2.2	0.3	0.5	1.8
TiO2	1.0	1.4	0.3	1.6
SO3	0.4	0.1	5.8	14.0
Cl	—	—	18.6	6.9
LOI	2.4	6.1	16.2	6.0
Residuals	1.9	6.2	1.6	2.2

Table 3. Selected physical properties of the investigated wastes.

Property	W1	W2
Fineness (%)	13.1 ± 0.6	64.2 ± 1.2
Moisture content, as delivered (%)	1.1 ± 0.1	0.3 ± 0.1
The quantity of dioxins (ng/g)	0.0170 ± 0.0044	0.0009 ± 0.0002
D10 (µm)	3.8 ± 0.6	10.2 ± 1.1
Median D50 (µm)	14.9 ± 5.1	59.1 ± 4.6
D90 (µm)	30.6 ± 8.2	164.1 ± 7.6
Span (D90 − D10)/D50 (µm)	1.8 ± 0.5	2.6 ± 0.2
Mean (µm)	16.6 ± 5.0	75.1 ± 4.3
Mode (µm)	18.2 ± 6.9	78.9 ± 5.0

Figure 1. Particle size distributions and cumulative curves of the samples W1 and W2.

Figure 2. SEM images of the wastes: (a) W1 and (b) W2, as delivered.

Table 4. Leaching of the examined waste samples as delivered and after washing of W1.

Analyzed substance		Leaching (mg/kg)
	Criteria for admission of waste for storage at a hazardous waste landfill	W1	W1 after washing	W2
Antimony (Sb)	5	<0.5	<0.5	<0.5
Arsenic (As)	25	<0.5	<0.5	<0.5
Barium (Ba)	300	54.4	7.6	2.3
Chlorides (Cl^−)	25,000	171,930	29,000	43,190
Chromium(VI)	—	0.5	<0.5	42.1
Cr (total amount) (Cr)	70	<1	2.3	42.6
Zinc (Zn)	200	31.5	7.2	12.9
Fluorides (F^−)	500	73.3	20.2	83.7
Cadmium (Cd)	5	<1	<1	<1
Copper (Cu)	100	<1	<1	<1
Molybdenum (Mo)	30	<0.5	<0.5	2.8
Nickel (Ni)	40	<1	<1	1
Lead (Pb)	50	191	<1	13.7
Dissolved organic carbon (DOC)	1000	2300	<300	<300
Selenium (Se)	7	<0.5	<0.5	<0.5
Sulfates (SO4^2−)	5000	16,500	8510	23,910
Total dissolved solids (TDS)	100,000	373,980	107,000	135,530

Table 5. Leaching of geopolymers made from fly ash or metakaolin containing W1 and W2 wastes.

Analyzed substance	Leaching (mg/kg)
	50W1-G-FA	50W2-G-FA	70W1-G-MK	70W2-G-MK	MK-G
Antimony (Sb)	<0.5	1.7	1.5	<0.5	<0.5
Arsenic (As)	42.0	1.8	<0.5	<0.5	8.2
Barium (Ba)	<0.5	<0.5	<0.5	<0.5	1.3
Chlorides (Cl^−)	5530	21,050	2460	5400	367
Chromium(VI)	<0.5	25.5	<0.5	4.9	0.5
Cr (total amount)	<1	27.4	<1	5.9	<1
Zinc (Zn)	<1	<1	<1	<1	<1
Fluorides (F^−)	46.3	38.2	18.6	62.0	17.1
Cadmium (Cd)	<1	<1	<1	<1	<1
Copper (Cu)	<1	<1	<1	<1	<1
Molybdenum (Mo)	17.8	3.9	<0.5	0.5	<0.5
Nickiel (Ni)	<1	<1	<1	<1	<1
Lead (Pb)	<1	<1	<1	<1	<1
Dissolved organic carbon (DOC)	<300	<300	<300	615	491
Selenium (Se)	4.9	1.7	<0.5	<0.5	<0.5
Sulfates (SO4^2−)	7720	55,440	617	17,070	401
Total dissolved solids (TDS)	43,180	116,150	21,200	50,440	15,380

Table 6. The compressive strength tests of two geopolymer matrices with the introduced wastes, examined after 28 and 90 days of curing.

Label of the sample	Compressive strength after 28 days of curing (MPa)	Compressive strength after 90 days of curing (MPa)
50W1-G-FA	4.6 ± 0.3	10.1 ± 0.2
50W2-G-FA	13.2 ± 0.2	18.9 ± 0.1
70W1-G-MK	18.2 ± 0.4	18.9 ± 0.3
70W2-G-MK	14.4 ± 0.4	14.4 ± 0.4
G- MK	57.3 ± 0.7	62.1 ± 0.5