Leaching behaviour of rock materials and a comparison with slag used in road construction
Abstract: Leaching characteristics are used for the evaluation of secondary materials used in road construction. In order to form a basis for comparison of the leachability, Swedish rock material have been investigated using the availability test NT ENVIR 003. Microscopic studies of the mineral composition, Acid-Base-Accounting and pH-measurements have been used to explain the leaching results. Overall, the content of identified opaque minerals is low and the leachable amounts of the heavy metal elements and sulphur are very small. At oxidising conditions the leachability of sulphide bound elements increases notably. Chromium and vanadium present as substituted ions in the crystal lattice of oxides show very low solubility. The results have been compared to similar leaching tests of metallurgical slags used in road construction. The dissolution of the major phase, the solubility of the heavy metal mineral and the total concentration of the element are factors influencing the dissolved amount of the heavy metal element. 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. X-ray diffraction analysis has been performed on two rock materials. The objective was to identify potential structural changes due to ageing and mechanical activation. Line broadening caused by lattice disturbance could not be observed, most likely because of too low energy input. The investigation did not provide evidence of surface changes due to ageing. Two Swedish rock materials have been investigated regarding the influence of Thiobacillus ferrooxidans to enhance the leaching of zinc and copper. A substantial part of the elements were dissolved due to chemical leaching already during the pH stabilisation to pH2. The experiments were run as single tests and no final conclusions can be drawn regarding the bacterial influence on the leaching of copper and zinc in the rock materials.
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