Neutralising processes of municipal solid waste incineration bottom ash in a flow-through system

The neutralising processes of MSWI bottom ash in a flow-through system were investigated by pH titration in a serial batch system. A one-dimensional coupled transport (advection) and geochemical reaction model was used to simulate the neutralising reactions. It has been found that the formation and movement of pH fronts are essential features of neutralising processes in flow-through systems. This characteristic and the washing-out effect makes the neutralising capacity obtained from batch experiment difficult to apply directly to a flow-through system. The neutralising ability of the MSWI bottom ash was significantly less in a flow-through system than in a batch system. It was found that the available neutralising ability of the MSWI bottom ash in the flow-through system is only a third of the neutralising capacity in a batch system. Carbonation reactions have a large influence on the neutralising processes of the MSWI bottom ash. The carbonation transformation plays an important role in the formation of controlling minerals for the MSWI bottom ash in the neutralising processes. Geochemical simulations combined with experiments provided valuable information about the neutralising processes in the flow-through system. This approach provides needed insights into reaction mechanisms and helps to check the basic assumptions for a geochemical model.