RAPPORT F2007:03 - Avfall Sverige

Summary
In the past, zinc oxide has had no classification in the databases that exist for dangerous properties. In
the classifications that have been made in accordance with the Ordinance of waste (Avfallsförordningen,
SFS 2001:1063), it has been convenient as well as cautious to use zinc oxide as a reference substance
in spite of the fact that the availability of zinc (i e the leachability) in ash is much lower than
that for zinc oxide.
However, from the end of 2005, zinc oxide has received a much stricter classification. Avfall Sverige
has therefore commissioned Tekedo AB to investigate the availability and to identify, if possible, what
reference substance to select in order to achieve a more realistic but yet still cautious representation of
the properties of zinc in ash.
Information searches and literature compilations have been carried out in scientific data bases and
papers, in books and on the Internet. The analyses have included availability in combination with
properties over time. Comparison has been made with similar high and low temperature type of materials
such as high temperature modified rock (metamorphic rock), lime and cement, and natural soil
material, sediment, and cured lime and cement mortar, respectively. The compilation and analyses
have included “traditional” investigation techniques such as leaching, thermodynamic calculations and
x-ray crystallography as well as EXAFS (Extended X-ray Absorption Fine Structure).
All the sources found have unanimously provided a single interpretation and view. Most likely, zinc
appears as a minor element in phases where other elements are the major ones. Thus, the availability
of zinc becomes that of the major elements that form the “mother” phase, i e the availability of zinc in
ash becomes typically very low. In these phases, zinc occurs together with iron-II, magnesium and
manganese-II which have similar ionic radii and chemical properties. These elements form mixed oxides
with iron (e g spinels) as well as certain silicates with infinite sheet structures (micas). One such
mixed oxide with iron is franklinite, which has an ideal composition (i e there are exact and simple
ratios between atoms of different kinds). This mineral represents the availability of zinc in ash in a
reasonable way and it also occurs in data bases for dangerous substances. On these grounds, franklinite
has been selected as the proposed reference substance for zinc in ash.
This selection is not warranted under all conditions, however. The ash should have a relatively “normal”
chemical composition, and also tests should prove that the availability of zinc in aged ash is actually
low.
Moreover, the zinc that actually leashes out should be figured as zinc oxide, and thereby contribute in
the summations of the dangerous properties in accordance with Appendix 3 of the Ordinance of waste.
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