Antimony leaching from MSWI bottom ash: Modelling of the effect of pH and carbonation

• Development of treatment methods to reduce Sb leaching from municipal solid waste incinerator (MSWI) bottom ash, such as accelerated carbonation, is being complicated by insufficient understanding of Sb geochemistry. The leaching of antimonate (Sb(V)) and antimonite (Sb(III)) in MSWI bottom was studied as a function of pH and degree of carbonation. While total (Sb(V)+Sb(III)) leaching was lowest (1.2mgkg-1) at the natural pH (i.e. 10.6) of uncarbonated bottom ash, HPLC-ICP-MS analysis showed that acidification and carbonation increased Sb(V) leaching, but decreased Sb(III) leaching, probably because Sb(III)(OH)4- became less stable. PHREEQC geochemical modelling suggested that Sb(V) concentrations approached equilibrium with the romeites, i.e. calcium antimonates, Ca1.13Sb2(OH)0.26·0.74H2O at pH=10.6 and Ca[Sb(OH)6]2at pH=8. It is hypothesised that not interaction with ettringite but dissolution of romeite controls antimonate leaching in the pH range 8-11 in MSWI bottom ash, because while Ca is preferentially leached from romeite, the mineral structures containing more Ca at higher pH are less soluble. A model was proposed where acidification and carbonation both lead to lower Ca2+and/or hydroxyl concentration, which removes Ca2+and hydroxyls from the romeite structure and leads to comparably higher Sb(V) concentration in equilibrium with romeite. Sb solubility depends on pH and Ca2+availability in this model, which has implications for bottom ash valorisation and risk assessment. © 2011 Elsevier Ltd.

Subject headings

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Keyword

Accelerated carbonation

Antimony

Leaching

Precipitation

Publication and Content Type

ref (subject category)

art (subject category)