Treatment of wood ash containing soluble chromate

The “TA Siedlungsabfall” issued in Germany in May 1993 will entail severe problems concerning the disposal of wood ash. One particular problem is associated with the occurrence of soluble chromium compounds in the leachates of wood ash. During combustion of wood, wood residues or waste wood, Cr-III which is generally found in wood is partly oxidized to Cr-VI. Under the conditions of the leaching test DIN 38 414 part 4, which is the compulsory test procedure according to the “TA Siedlungsabfall”, Cr-VI is partly soluble. Thus, the comparatively low limit value for the leachates is exceeded by many wood ash samples. To achieve significant reduction of the soluble Cr-VI content of wood ash, a procedure termed wet ash removal was applied. Investigations were carried out both under industrial conditions and in the laboratory. It is shown that wood ash leachates with Cr-VI concentrations of up to about 2 mg/l can be treated effectively with this procedure.