Thermal conversion of deinking sludge to valuable cement products

Papermills produce a lot of deinking residues which have to be disposed by landfill or waste incineration. A new process is described that is cheaper than waste incineration and that produces a high-value cement product. Deinking residues contain valuable minerals such as highly dispersed china clay and chalk. In the new process, the china clay is dehydrated and the chalk is partially calcined. This combination of reactions produces a mineral product with cement-like properties. This product can be used as cement itself or as a special additive to increase cement properties such as colour or hardening. As this mineral conversion process requires a very strict temperature control, a fluidized bed is used. The organic fraction of the residue is incinerated, producing energy for the process and allowing for some additional energy production. Due to the relatively high throughput of 800 kg/m(exp 2)/h a comparably small unit can convert a large quantity of deinking residue. There are no emissions to water and emissions to air are low and legal requirements can be met without flue gas cleanup.