© 2006 by Taylor & Francis Group, LLC

72 Corrosion Control Through Organic Coatings
TABLE 4.2
Levels of Selected Compounds/Elements Found in By-Product Abrasives
Blasting media Pb Co Cu Cr Ni Zn
Copper slag [Eggen and
Steinsmo]
0.24% 0.07% 0.14% 0.05% 71 ppm 5.50%
Copper slag [Bjorgum] 203 ppm 249 ppm 5.6 ppm 1.4 ppm 129 ppm 10 ppm
Nickel slag [Eggen and
Steinsmo]
73 ppm 0.43% 0.28% 0.14% 0.24% 0.38%
Nickel slag [Bjorgum] 1.2 ppm 2.3 ppm 4.5 ppm 755 ppm 1.1 ppm 15.6 ppm
Sources: Bjorgum, A., Behandling av avfall fra bläserensing, del 3. Oppsummering av utredninger
vedrorende behandling av avfall fra blåserensing, Report No. STF24 A95326, Foundation for Scientific
and Industrial Research at the Norwegian Institute of Technology (SINTEF), Trondheim, 1995 (in
Norwegian); Eggen, T. and Steinsmo, U., Karakterisering av flater blast med ulike blåsemidler, Report
No. STF24 A94628, SINTEF, Trondheim, 1994 (in Norwegian).
and stainless steel, and to be recycled many times before significant particle breakdown
occurs.
Manufactured abrasives are more costly than by-product slags, usually by an
order of magnitude. However, the good mechanical properties of most manufactured
abrasives make them particularly adaptable for recycling as many as 20 times. In
closed-blasting applications where recycling is designed into the system, these
abrasives are economically attractive. Another important use for them is in removing
old paints containing lead, cadmium, or chromium. When spent abrasive is contaminated
with these hazardous substances, the abrasive might need to be treated and
disposed of as a hazardous material. If disposal costs are high, an abrasive that
generates a low volume of waste — due to repeated recycling — gains in interest.
Silicon carbide, or carborundum, is a dense and extremely hard angular abrasive
(specific gravity 3.2, 9 Mohr). It cleans extremely fast and generates a rough
surface profile. This abrasive is used for cleaning very hard surfaces. Despite its
name, it does not contain free silica.
Aluminium oxide is a very dense and extremely hard angular abrasive (specific
gravity 4.0, 8.5 to 9 Mohr). It provides fast cutting and a good surface profile so
that paint can anchor onto steel. This abrasive generates low amounts of dust and
can be recycled, which is necessary because it is quite expensive. Aluminium oxide
does not contain free silica.
4.3 WET ABRASIVE BLASTING AND HYDROJETTING
In dry abrasive blasting, a solid abrasive is entrained in a stream of compressed air.
In wet abrasive blasting, water is added to the solid abrasive medium. Another
approach is to keep the water but remove the abrasive; this is called hydrojetting,
or water jetting. This pretreatment method depends entirely on water impacting a
steel surface at a high enough speed to remove old coatings, rust, and impurities.
© 2006 by Taylor & Francis Group, LLC