Chemical Properties
Mineral wools are calcium–magnesium–aluminum silicate
fibers. The fibers differ in composition from batch to batch,
depending upon the raw materials used. The following is
guideline for the range of components, by percentage: SiO2,
43–50%; Al2O3, 6–15%; CaO, 10–25%; MgO, 6–16%;
MgOtCaO, 16–41%; Na2O, 1–3.5%; K2O, 0.5–2%;
B2O3, ,1%; FeO, 3–8%; ,1–1%; TiO2, 0.5–3.5%; P2O5,
,1%; S, 0–2%. Nominal fiber diameters at manufacture are 3–8 μm.
Production Methods
Rock wool is produced from a mixture of natural and synthetic rock, depending upon the final desired specifications. Slag wool is produced from a mixture of iron ore slags removed from blast furnaces and other raw materials such as sand, limestone, and clay.
The mix is melted in a cupola furnace. The mineral wool product is formed by introducing a molten stream onto a rotating wheel to form the fiber. Fibers are 3–8 mm in diameter, with variable length that is difficult to evaluate because they break readily. Chemically, slag wool fibers contain calcium, magnesium, and aluminum silicates with trace amounts of other metal compounds.
The final product may be bagged as raw, unbonded fiber for use as blown-in insulation or shipped in bales to end users for the manufacture of products such as ceiling tiles or acoustical and thermal insulation batts. The raw material may be cured with urea–phenolic resins; this bonded product is used in the manufacture of insulation batts, boards, blankets, and pipe covering materials (17, 20, 22a).
Carcinogenicity
Clinical Cases.
Four out of 21 workers studied by
Malmberg et al., reported slight skin, eye, and nose
symptoms in response to a standardized questionnaire.
Eleven employees at mineral wool factories included in
the Enterline et al. cohort were included in an evaluation
of lung dust burden at autopsy (51a).
Four of the six who
worked in a single plant had amosite concentrations exceeding
1.0 f/mg dry lung; none of the referents for these workers
had any detectable amosite. No man-made fibers were found
in the mineral wool workers.
Analysis of lung tissue from 17 lung cancer cases
employed in the rock and slag wool industry did not show
a relation between cumulative exposure and lung retention at
autopsy (51b). MMVF was found in all samples; smaller
amounts of asbestos minerals were found in 16 of the cases.
Acute toxicity.
In the industrial environment,
fibers with diameters larger than 3 mm have been associated
with irritation of the upper respiratory passages, skin, and the
mucosa of the eyes. The European Union classifies all
MMVF as irritants (16d).
