Analysis of Leachate Characteristics to Study Coal Ash Usability - Management of Natural Resources in a Changing Environment - page 235

Table 4 Trace elements analysis of leachate
Element
name

Sample 1
(mg/L)

Sample 2
(mg/L)

Sample 3
(mg/L)

Sample 4
(mg/L)

Sample
5 (mg/L)

Fe 0.10 0.03 0.02 0.06 0.03

Mn 0.04 0.04 0.05 0.04 0.05

Pb ND ND ND ND ND

Cu 0.09 0.06 0.12 0.13 0.12

Ni ND ND ND ND ND

Cd ND ND ND ND ND

Cr 0.01 0.01 0.01 0.01 0.01

ND not detected

more accessible to leaching in an aqueous environment. Therefore, the mode of
occurrence in the parent coal controls to a large extent whether a given element will
be immobile or will be easily released to the environment (Izquierdo 2012 ). During
these studies, leaching behaviours of various heavy metals like Fe, Mn, Pb, Cu, Ni,
Cd and Cr from coal ash samples was studied. The concentrations of the heavy met-
als that were leached out with deionised water as a result of the batch leaching test
are shown in Table 4 .
Ni, Pb and Cd did not leach from the coal ash samples. Cu concentrations were
low (0.06-0.13 mg/L); this is probably because Cu gets precipitated as their insolu-
ble hydroxides. Mn and Cr are leached in samples but shows very low concentration
i.e. 0.04-0.05 mg/L and 0.01 mg/L respectively. Fe leached from ash is probably
precipitated as hydroxides due to the alkaline nature of ash, hence found in low
amount i.e. 0.02-0.1 mg/L.
Research shows that elements in the ash particles were mainly associated with
the surface, and these surface-associated fractions might dominate the leachate
chemistry at the early stages of fl y-ash disposal in contact with water. However,
the elements incorporated within the interior of the fl y ash dissolved at a slower
rate compared with the readily leachable surface associated elements (Choi et al.
2002 ).

Calcium, Potassium and Sodium Salts Analysis

Soluble salts like Ca, K and Na leached from coal ash samples are shown in Table 5 .
Low values of calcium leached in samples, i.e. 1.8-3.9 mg/L, indicate that low
amount of Ca was present as free lime.
Calcium is not regarded as an element of concern, but it does play a primary
role in the environmental quality of the ash. The amount of Ca states the pH of the
ash-water system, and most trace elements display a pH-dependent solubility
(Izquierdo 2012 ). Potassium and sodium are tightly bound within the glassy
matrix, and therefore less than 2 % is available for leaching (Ward et al. 2003 ;
Moreno et al. 2005 ). Result shows potassium and sodium were leached in very less
amount i.e. 3.2-4.9 mg/L and 2.2-4.7 mg/L respectively.