Novel aspects of utilization of mineral-rich lignite as an efficient sorbent of heavy metals and polycyclic aromatic hydrocarbons

Abstract

In this study low quality, mineral-rich lignite taken from the Kostolac Basin (Serbia), containing 45.36 % of ash, 33.42 % of total organic carbon and having low net calorific value of 9.5 MJ/kg was tested as a sorbent for heavy metals and polycyclic aromatic hydrocarbons (PAHs), considering that due to the low maturity (huminite reflectance, 0.30±0.03 %) it contains numerous oxygenic electron-donor functional groups (carboxylic, phenolic, alcoholic) available to complex metal ions, as well as that petrographic analysis indicated a high amount of clays in mineral matter, which have good adsorption properties. The obtained results indicated very efficient sorption of heavy metals on lignite ranged from 87.34 % for Co2+ ion to more than 99.40 % for Cu2+ and Pb2+ ions (Table 1). The slightly lower percent of adsorption of Cd2+ ion can be attributed to its order of magnitude smaller concentration in model solution, which however corresponds to generally lower concentration of this very toxic element in natural waste waters. Almost quantitative sorption of PAHs having 3 or more aromatic rings was observed. This is very important considering that toxicity and persistency of PAHs rise with increase of number of condensed aromatic rings. Significantly smaller percent of sorption of low-molecular weight PAHs can be partly attributed to their volatility. The obtained results showed that used lignite has good sorption properties against heavy metals, particularly Cu2+ and Pb2+ ions, as well as PAHs containing 3 or more aromatic rings.