IMPROVED METHOD FOR PREDICTION OF HEAVY-METAL RECOVERIES FROM SOIL USING HIGH-INTENSITY MAGNETIC SEPARATION (HIMS)

In recent years the soil cleaning industry has developed a number of c leaning strategies mostly based on classification techniques. Sometime s, however, those strategies fail for a number of reasons and as a res ult cleaning targets are not met. Therefore, some soil cleaning facili ties have experimented with HIMS as an alternative process step. This paper describes a prediction method based on magnetic separation techn iques for use of HIMS separators in soil cleaning plants. Two types of HIMS separators were used. First a (dry) Frantz isodynamic separator (FIS) and secondly a (wet) Jones high gradient magnetic separator (mod el P40 KHD and model DP 90 Humboldt Wedag). The FIS was used to separa te heavy metals from soil and for observation of heavy metal behaviour in magnetic fields, With the Jones P40, pilot-scale experiments were performed to confirm the FIS results. In total six soil samples unclea nable by soil washing plants and three soil samples prepared by labora tory classification were used in the experiments. Furthermore, three s oils were treated on full plant scale. FIS experiments indicated that soils can be distinguished by their different magnetic properties and that each soil shows its own characteristic magnetic susceptibility fi ngerprint. A similarity, however, was observed between the magnetic pr operties of soils and the magnetic properties of hematite which is a s trong indication for the importance of iron in removing heavy metals f rom contaminated soil. The Jones P40 experiments showed a similar remo val efficiency as the FIS for iron but not for the heavy metals. Soils treated with wet HIMS, however, showed considerably lower heavy metal contents than soils only treated with conventional washing techniques , indicating the usefulness of HIMS in cleaning heavy-metal-contaminat ed soils. Plant-scale treatment of three polluted soils showed that th e Jones separator is a feasible technique for soil washing and treatme nt of heavy metals. (C) 1998 Elsevier Science B.V. All rights reserved .