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Leaching behaviour of rock material and slag used in road construction ‐ amineralogical interpretation
Author(s) -
Tossavainen Mia,
Forssberg Eric
Publication year - 2000
Publication title -
steel research
Language(s) - English
Resource type - Journals
eISSN - 1869-344X
pISSN - 0177-4832
DOI - 10.1002/srin.200005713
Subject(s) - dissolution , leaching (pedology) , silicate minerals , silicate , metallurgy , base metal , solubility , metal , mineralogy , geology , chemistry , materials science , soil water , soil science , organic chemistry , welding
Rock materials used in road construction contain heavy metal elements bound in minerals that are more or less soluble. There are no requirements for investigations of leaching behaviour before use of rock materials in Sweden, which is the case regarding other materials as, e.g., slags. This implies that there is a lack of data to be used when other materials are evaluated. Seven rock materials and two gravels representing non‐weathered material for use in base or sub‐base course from three counties in Sweden have been investigated regarding mineral composition in order to explain the leaching behaviour. Microscopic studies of the mineral composition, acid‐base‐accounting and pH ‐measurements have been used to explain the leaching results achieved with the availability test. The identified transparent minerals were the expected silicate minerals for the sampled rock‐forming materials. Overall, the content of identified opaque minerals was low. How an element is bound in the mineral is decisive for the dissolution of the heavy metal elements. Sulphide bound elements have a notably high fraction that is soluble, especially under oxidising conditions. Chromium and vanadium present as substituted ions in the crystal lattice of oxides are not dissolved. The dissolution of the buffering rock forming silicates is much slower than the dissolution of the acid‐producing sulphides. The results have been compared to similar leaching tests of metallurgical slag used in road construction. The dissolution of the major phase, the solubility of the heavy metal mineral and secondary reactions are factors influencing the dissolved amounts of heavy metal elements. Compared to the crystalline rock materials, the amorphous fuming slag from a copper smelter has very low solubility, while blast furnace slag is easily dissolved due to hydrolysis. The soluble amounts of sulphide bound elements in rock material is higher compared to blast furnace slag. The kinetics of the acid‐producing and acid‐consuming reactions of the rock materials needs to be further investigated. The blast furnace slag and the fuming slag can be used in road construction without any risk of harmful environmental impact due to heavy metal leaching.