Suitability study of secondary raw materials for prevention of acid rock drainage generation from waste rock

Prevention of sulfide oxidation in waste rock by the addition of lime kiln dust

“…A previous study by Nyström et al (2019) showed that the LKD consisted of anhydrite, calcite, gypsum, Mg-rich calcite, Na-rich sylvine, portlandite, and quicklime. Moreover, the study showed that the LKD, compared with many other secondary raw materials, was a rather pure material with low content of easily water-soluble minerals and generally low leachability of trace metals and metalloids such as As (0.08 μg/L), Cu (< 0.5 μg/L), Mn (0.5 μg/L), Pb (0.1 μg/L), Sb (0.08 μg/L), and Zn (< 2 μg/L).…”

“…As previously described, the success of passivation of sulfide surfaces by the formation of secondary minerals highly relies on the ability for sulfides to oxidize under near-neutral pH. To meet one of these requirements, waste rock was selectively chosen based on sulfur content, previously described by Alakangas et al (2013) and Nyström et al (2019) and included screening of waste rock piles with a handheld X-ray fluorescence (XRF) of the brand Olympus Innov-x systems, USA, for selectively choosing waste rock with high sulfur content. Alakangas et al (2013) characterized the waste rock for its major and minor elements showing that it had an average sulfur content of 30%.…”

“…Alakangas et al (2013) characterized the waste rock for its major and minor elements showing that it had an average sulfur content of 30%. Nyström et al (2019) characterized the waste rock for its major mineral content showing that it was dominated by pyrite and quartz (17%) with smaller amounts of sericite (6%), chlorite (4%), and calcite (1%). Approximately 99% of the sulfide content in the waste rock consisted of pyrite with the remaining 1% comprising of, e.g., chalcopyrite, bournonite, sphalerite, arsenopyrite, and pyrrhotite (in descending order of abundance).…”

“…Moreover, the study showed that the LKD, compared with many other secondary raw materials, was a rather pure material with low content of easily water-soluble minerals and generally low leachability of trace metals and metalloids such as As (0.08 μg/L), Cu (< 0.5 μg/L), Mn (0.5 μg/L), Pb (0.1 μg/L), Sb (0.08 μg/L), and Zn (< 2 μg/L). The LKD had, before sampling, been stored in piles outdoors, which likely hydrated and re-carbonated the quicklime in the LKD (Nyström et al 2019).…”

“…There is thus a need for alternative materials, with properties that limit the addition amounts (≤ 5 wt.%) to consider economic and space perspective. Several tests of different secondary raw materials’ suitability for passivation purposes resulted in the selection of lime kiln dust (LKD) (Nyström et al 2019) as an alternative additive. Results from 52 weeks of leaching of sulfide-rich waste rock covered with a thin layer of LKD (5 wt.%) showed a substantial decrease in acid, metals, and metalloids.…”