Electrodialytic soil remediation in a small pilot plant (Part II): Extractions, IR, XRD, TEM and SEM investigations on untreated and EDR treated Cu contaminated soil

Observations were made of copper-polluted soil to see, if any changes in the bonding type of copper in the soil were made during electrodialytic soil remediation. Three different fractions of the copper-polluted soil were used for investigation with infrared spectroscopy (IR), X-ray diffraction (XRD), transmission electron microscope (TEM) and observations with scanning electron microscope (SEM), the last two combined with an EDX analysis unit. The three soil fractions were extracted with am-monia for observa-tion of the copper removal when copper forms copper-tetra-ammine complexes with am-monia. Ammonia was chosen because it forms strong complexes with copper and to keep the soil basic, so that the carbonates were not dissolved. The bulk soil was treated by electrodialytic reme-dia-tion, and soil treated for seven months was investigated with XRD, TEM and SEM.Malachite was found by use of XRD measurements in one of the untreated soil samples. These measurements were supported by EDX measurements (combined with either SEM or TEM), where almost pure copper particles were found. The EDX measurements do not include hydrogen, carbon and oxygen, which make the figures of all other elements higher than it should be. Two other groups of copper-containing particles were found in the soil by EDX. One group was a mineral also containing magnesium, aluminium, silicon, potassium, calcium and iron. This was probably a copper and iron-containing clay mineral, and the other group had a high content of calcium (approximately 30%). Some particles from this latter group also had a high content of iron (approximately 10%).Extraction experiments with ammonia showed that some of the copper was highly soluble in ammo-nia. This means that it would be advantageous to treat the soil fractions separately because of the big difference in the degree of pollution and the way copper is bound within the soil.The speciation of copper in the soil from a small pilot plant did not show any measurable change during the first seven months of operation. It seems that the number of particles with very a high concentration of copper, approximately 90%, decreased and the number of particles with copper in the same range as iron increased. No group of copper-containing particles was seen to disappear or to change into a different type.