NEUTRALIZING PROCESSES IN LEACHING OF SOLID-WASTE - MODELING OF INTERACTIONS BETWEEN SOLID-WASTE AND STRONG ACID

The neutralizing characteristics of MSWI bottom ash over a pH range be tween 4 and 12 were investigated using a reaction path model. Experime ntal data on the pH titration combined with the geochemical simulation were used to obtain the reacted fractions of the main constituents th at are Ca hydroxide and carbonate and Al and Si oxides/hydroxides. The simulation results combined with the sensitivity analysis of the reac tion system provided an insight into the neutralizing processes of MSW I bottom ash. The geochemical simulations showed the reactivities of m ajor constituents of the solid waste in neutralizing reactions. In the most interesting pH range (pH4-12), the calcium-containing constituen ts and carbonates made large contributions to the acid neutralizing ca pacity of the solid waste. The contributions of Si- and Al-component t o the neutralizing reactions were more complex, which could be explain ed by the interaction of multiple phases and equilibria in the system. Secondary phases played an important role in the neutralization react ions. Although the composition of individual secondary phases to a lar ge extent was not known in detail, the system was robust in the sense that several possible secondary phases gave similar acid neutralizatio n curves. Furthermore, they predicted similar aqueous phase concentrat ions. The predicted concentrations agree reasonably well with the expe rimentally found values.