Ashes (residues), coal

Additional physico-chemical information

Administrative data

Endpoint:

other: morphology and mineralogy of ashes

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well-documented publication meeting basic scientific principles.

Data source

Reference

Reference Type:

publication

Title:

The occurrence of quartz in coal fly ash particles

Author:

Meij, R. et. al.

Year:

2000

Bibliographic source:

Inhalation Toxicology, 12 (Supplement 3): 109-116

Materials and methods

Principles of method if other than guideline:

1) XRD analyses for the determination of mineral phases
2) scanning electron microscopy (SEM)
3) EDX (X-ray microanalyses or XMA with a light-element detector)
4) SEM/XMA applied on polished embedded particles in epoxy resin (examination of a cross section of ash particles)

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Ashes (residues), coal

EC Number:

931-322-8

Cas Number:

68131-74-8

Molecular formula:

Not applicable (UVCB substance)

IUPAC Name:

Ashes (residues), coal

Results and discussion

Results:

Conclusions
Coal gasification ash (CG slag and CG fly ash), as produced in the Netherlands, consists entirely of glass and does not contain any crystalline silica forms. No cristobalite or tridamite could be demonstrated in any of the ashes studied.
In Dutch power plants after combustion of the coal, about 50% of the original quartz remains in the ash, which is mostly present in the coarse fraction as free angular particles. The quartz content of the health-relevant respirable fraction is lower: less than 1% of the original quartz in coal. However, the major part of the quartz in the respirable fraction is embedded in the glass matrix of the fly ash particle. Since the effects of quartz are surface related, these findings explain the negative results of quartz related effects of PFA (pulverized fuel ash) in epidemiological, in vitro and in vivo studies. Besides, the amount of the total α-quartz in the respirable fraction of the ashes studied is less than 0.2%, so in practice the occupational quartz standard will not be exceeded.
There is no reason to assume that coal ash, as produced in the Netherlands, induces PMF (progressive massive fibrosis), so occupational limits of quartz should be applicable.

Any other information on results incl. tables

Quartz content, relative enrichment factor, density and mass medium diameter

		α-Quartz content (XRD)		Density (kg/dm³)	D50 (µm)
	n	Mean± SD (%)	RE factor		Physical	Aerodynamic
Coal	50	2.1± 1.4^a		1.2	75.5± 13.5	82.7± 14.9
PFBA	1	10.8	0.39		Coarse
PFA-C	13	9.2± 3.0	0.47± 0.12	2.2	20.4± 5.2	30.8± 7.9
PFA-4 or 5	5	3.6± 1.3	0.16± 0.02	2.7	6.0± 3.8	9.9± 6.2
CG slag	4	n.d.^b			Coarse
CG fly ash	4	n.d.		2.6	2.7	4.3

^a As a weighted average of the coal as fired in the Netherlands

^b In one sample some quartz was found present as arr impurity of unburned coal.

Occurrence of quartz in pulverized coal and coal fly ash particles

Α-Quartz content, % (w/w)
SEM / XMA
				Total fraction			Respirable fraction (PM4)
Code	Power station	Sample type	XRD total	Total	Enclosed	Free	Total	Enclosed	Free
21	AC-9	p.coal	4.2	4.0 ± 3.2	1.4 ± 1.2	2.6 ± 3.9	0.022 ± 0.023	0.018 ± 0.023	0.004 ± 0.006
22	AC-9	PFA-C	14.1	14.5 ± 4.1	4.7 ± 0.9	9.8 ± 4.0	0.10 ± 0.05	0.06 ± 0.02	0.04 ± 0.03
23	AC-9	PFA-5	4.4	5.6 ± 1.3	3.9 ± 0.6	1.7 ± 1.5	0.61 ± 0.16	0.55 ± 014	0.06 ± 0.06
47	CG-13	PFA-C	9.9	11.2 ± 3.6	5.6 ± 1.4	5.6 ± 2.9	0.14 ± 0.07	0.12 ± 0.05	0.02 ± 0.03
48	CG-13	PFA-4	5.2	7.1 ± 2.3	4.9 ± 1.2	2.2 ± 1.6	0.17 ± 0.07	0.15 ± 0.05	0.02 ± 0.02
Number of particles studied
				Quartz-containing particles			Respirable (PM4) quartz-containing particles
Code	Part PM4, % (w/w)	PM4	Total	Total	Enclosed	Free	Total	Enclosed	Free
21	0.17	24	217	98	88	10	11	11	0
22	1.2	346	5594	1996	1636	360	80	73	7
23	20	616	996	156	149	7	60	59	1
47	2.3	273	1822	544	488	56	62	58	4
48	3.5	347	2501	646	611	35	67	66	1
Total		1606	11130	3440	3272	468	280	267	13