The “NAG” was calculated in term of kg H2SO4 t-1 [7, 8, 9] and the calculation of NAG followed equation (2) [10]. The cut-off NAG pH for prediction of acid forming potential was divided into 3 ranges [9] as shown in Table 2.
NAG = 49 x V x M/W (2)
Whereas ; V = Volume of NaOH (ml)
M = Mole of NaOH (mole/l)
W = Weight of sample (g)