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Risk assessment of the utilization of basic oxygen furnace slag (BOFS) as soil liming material: Oxidation risk and the chemical bioavailability of chromium species

Reijonen, Inka, Hartikainen, Helinä
Environmental technology & innovation 2018 v.11 pp. 358-370
bioavailability, chromium, environmental factors, furnaces, heavy metals, leachates, liming, liming materials, manganese, manganese dioxide, manufacturing, oxidation, oxygen, risk, slags, soil, solubility, steel, toxicity, water content, water holding capacity
Basic oxygen furnace slag (BOFS), a by-product of steel manufacturing, is efficient as liming material. It contains, however, trace amounts of heavy metals such as chromium (Cr). Under environmental conditions Cr exists in two stable oxidation states: +III and +VI. From those, CrIII is an essential nutrient, whereas CrVI is highly toxic. In soils, soluble CrIII is potentially oxidized to CrVI by manganese (hydr)oxides (MnO2). We investigated the release of bioaccessible CrIII or CrVI from BOFS to field soil. Prior to characterization of the bioaccessible, as well as less bioavailable Cr fractions, field soil was incubated with BOFS in quantities equivalent to 10 and 100 t ha−1 (7 weeks at 22ºC, moisture content at 50% of water holding capacity). Liming with BOFS elevated the acid soluble (known as semi-total) Cr but not the bioaccessible CrIII or CrVI. In addition, potential oxidation of initially soluble CrIII (mimicking leachates of BOFS) was determined by a short-term net-oxidation test in soil suspension with 1 mM CrCl3 (1:10 soil to solution). In field soil incubated with BOFS, the net-oxidation (oxidized CrIII–CrVI reduced back to CrIII) of added CrIII into CrVI without MnO2 was negligible. To produce highly oxidizing conditions, the test was further modified with excessive addition of synthetic MnIVO2. Liming with BOFS diminished the production of CrVI, whereas added MnIVO2 notably promoted oxidation of CrIII. Overall, the oxidation risk of CrIII in BOFS to CrVI by innate soil MnO2 can be expected to be minimal due to the low solubility of CrIII in field soil.