Continuous treatment of heavy metal contaminated clay soils by extraction in stirred tanks and in a countercurrent column

Abstract

Extraction of metals from two contaminated waste site clay soils by 0.1–0.3 N HCl solutions was tested in three laboratory scale, continuous processes: two stirred tank reactors (CSTR’ s) in series; a countercurrent sieve‐plate column fed with flocculated. clay soil material; and a combination of tank reactor and column. After extraction clay soil suspension and extractant were separated by means of flocculation and sedimentation. The countercurrent process gave greater efficiencies in removing the metal than the CSTR process but the difference was only small. The following type of cleaning process seemed to be promising: first an extraction in a stirred tank followed by a further second extraction in a countercurrent column. Residence time in the CSTR could be short (15–30 minutes) while it should be as long as possible in the column.