Investigation on leaching behaviour of toxic metals from biomedical ash and its controlling mechanism

It is comprehensible that disposal of biomedical ash (BMA) is a serious threat to human life and to the environment compared to any other type of waste without proper treatment. In the present study, it is focused in studying the leaching behaviour and its controlling mechanism to predict the contamination levels of BMA. Experimental investigation was carried out to determine the physico-chemical properties of BMA. The morphological and mineralogical composition was performed by SEM equipped with EDAX and XRD. A leaching pattern was identified for various heavy metals simultaneously (Hg, Se, As, Fe, Cd, Zn, Pb, Ca, Co, Ni, Cr and Cu) by varying pH (3, 5, 7, 9, and 11) via a pH-dependent batch leaching test using AAS and ICP. Major oxidation states of leached mineral/metal were established by Visual MINTEQA 3.1. Leaching test results show that a high concentration of Hg (9.3 mg/l), Se (2.4 mg/l) and As (9.7 mg/l) at pH 11 was obtained. Characterisation studies substantiate 60% of calcium silicate presence and major minerals like ettringite, calcite and thermonatrite. Geochemical modelling reveals that leached elements were solubility controlled except As and Se. It is inferred that, presence/formation of ettringite, calcite and thermonatrite minerals are responsible for immobilizing/reduced leaching of toxic heavy metals in alkaline environment except for Hg, Se and As as they are highly mobile in an alkaline condition which can be reduced by adopting a suitable pretreatment option so as to reduce the contamination levels of handling even untreated waste disposal.