The potential leaching of road-making material and potential influences on the leaching behavior: Fid-Bau Portal

The potential leaching of road-making material and potential influences on the leaching behavior

Tossavainen, M.

Rock material used in road building contains heavy metal minerals that are more or less soluble. However, not only the mineral and the leaching conditions, but also storing and sample preparation might influence the leaching behaviour. Grinding implies mechanical activation and the high reactivity is utilised in e.g. hydrometallurgy. Sample preparation for leaching tests, in many cases, includes grinding to a specific particle size, which can change the surface structure of the specimen. Acidophilic iron- and sulphur oxidising bacteria present in the environment might enhance the actual leaching of sulphide bound elements in the rock material through oxidation. Typical Swedish roadmaking materials have been tested regarding the potential of leaching with respect to heavy metals. The teachability of some heavy metal elements is higher in the rock materials as compared to air-cooled blast furnace slag and a granulated slag-fuming slag from a copper smelter. High contents of heavy metal elements are inclosed in the granulated slag-fuming slag. Of the zinc in the rock material, 30.3 % is dissolved under oxidising conditions due to presence as a sulphide. More than 90 % of the zinc in the blast furnace slag is soluble but the amount is less than 3 mg/kg. The granulated slag-fuming slag contains more than 1.3 % of zinc, but only 80 mg/kg is dissolved. XRD studies showed that the sample preparation (grinding) did not cause lattice disturbance. However, differences in surface energy due to ageing could not be excluded. Two samples of rock material have been exposed to leaching with Thiobacillus ferrooxidans at pH 2. Chemical leaching was dominating. However, an enhanced solubility of zinc due to bioleaching was indicated. (VDEh)