A semi-industrial scale plant for Ferrox®-stabilisation of APC-residues.

Mixing

The mixing process includes the residue to be mixed with water and ferrous sulphate solution in a Liquid-Solid ratio of approx 3-4 m3/tonnes. The residue is stored dry and added directly to the process by a screw conveyor. The ferrous sulphate (FeSO4x7H2O) arrives by truck or ship and is stored in a tank with water. The water saturated with ferrous sulphate is added to the process.

Aeration

The aeration process oxidises the ferrous iron into iron oxides by a simple dispersion of atmospheric air into the suspension. pH is adjusted, if necessary, either with additional ferrous sulphate or with sulphuric acid.

Filtration

Finally, a filtration process on a vacuum belt filter removes most of the water. The wastewater contains a large amount of salts but only traces of heavy metals. The treated residues can be washed on the filter to improve the removal of salts. The water used for washing is then reused in the mixing process and the washing is thereby neutral with respect to water consumption. The treated residue leaves the filtration unit as filter cakes with dry matter content of approx. 50-55 % (w/w) ready for disposal. If desired the treated residue can be dried even further.