Discriminant analysis in predicting the leaching behaviour of Ca/Na/K in cardboard tube waste biomass/biochar

• The predicted leaching behaviours followed the geochemical partitioning coefficients • Stepwise DA mode predicted that Na had a faster rate of dissolution into water • Standard DA mode predicted that K had a faster rate of dissolution into NH 4 OAc • The predicted leaching behaviours proceeded via dissolution at the solid-phase • The predicted leaching behaviours completed with diffusion into the bulk solution. Studies integrating the leaching behaviour of alkaline/alkali earth metal species (AAEMs; Ca/ Na, K) in the context of the rate of ion dissolution from the solid-phase and subsequent migration into the bulk solution are scarce. Similarly, studies always considered the faster rate of ion migration in the bulk solution in terms of greater diffusion coefficients of K/Na relative to those of the divalent species. Accordingly, the leaching behaviours of AAEMs were investigated in biomass/(biochar produced at 500 °C) under different extractants: Melich-1 (M-1), Ammonium Acetate (AA), and water. The Univariate ANOVA accounted for group differences, with M-1 yielding the greatest extractable-Ca ( p < 0.04) relative to AA and water. Stepwise discriminant analysis (DA) enabled the discrimination of the AAEMs into two Discriminant functions (DFs). Function 1 (F1) classified the AAEMs as belonging to their geochemical partitioning coefficients, in the order of Ca > Na as the best discriminators/predictors, with M-1 as the best extractant for greater yield of extractable-Ca and Na. Conversely, F2 classified the AAEMs according to their rates of solid-phase dissolution and migration into the bulk solution, in the order of Na > Ca, with Na being the best discriminator/predictor for faster rate of dissolution at the solid-phase and migration in water relative to Ca and K. It is concluded that the leaching behaviour of the AAEMs in biomass/biochar is not a function of the rate of ion migration/diffusion coefficient within the bulk solution alone, but a combined process, which proceeds with the rate of dissolution from the solid-phase step, to diffussion/transport in the bulk solution step, respectively.