"Bubble bath" removes heavy metals
Jan Erik Kaarø
As much as 90% of the heavy metals in badly contaminated soil disappeared when it was exposed to research assistant Aina Sandvik's "bubble bath".
The purpose of this project at NTH's Dept. of Geology and Mineral Resources Engineering was to identify a practical method of cleaning up soil.
So far, the method has functioned well in the laboratory. Professor Knut Lyng Sandvik, who is leading the project, is pretty certain that the method can also be used on a larger scale, but the price is likely to determine whether anyone will be willing to go in for the concept. It could cost around NOK 200 to clean up a ton of soil.
Simple principle
The soil samples used in the tests were taken from an old mine dump in Trondheim, and tailings discarded in the sea. The tests, which have recently come to an end, were simple. Aina Sandvik poured the earth into an apparatus resembling a food mixer, added water, chemicals blew in air and started up the machine. After a short while, a slurry froth containing the heavy metals appeared on top of the slurry. The results of the cleaning process turned out to be best for the samples that had come from the dump, and not quite as good for samples taken from the seabed. As much as 90% of the lead and 70% of the copper and zinc could be removed from the onshore samples. In her best tests of seabed sediments, Sandvik managed to remove 65% of the copper, zinc and lead, but there were large quantities of "contaminated products." The results of these tests were probably poorer because the seabed samples were more fine-grained and the heavy metals were present in higher concentrations than in the dump material.Expensive
The procedure involved in chemical cleansing of soils has been known for a long time. It is used, for instance, by the mining industry to separate ore minerals. The trick is to find the best combination of chemicals. The NTH experiments used a brew of copper sulphate, sodium sulphide and a surface active reagent.Professor Lyng Sandvik believes that the method can be employed in most places with contaminated soil, e.g. on former industrial sites. Germany already has plants that can chemically cleanse several tons of soil per hour. The biggest problem is the cost of the process. Cleaning up 1000 square metres of a contaminated site means treating at least 10,000 tons of soil. This would mean a bill of as much as NOK 2 million for whoever has to pay.
NTH's "bubble bath project" was carried out in collaboration with the City of Trondheim and was financed by the State Pollution Control Authority.