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ZERO-VALENT IRON AS APPROPRIATE REACTIVE MATERIAL FOR SB AND AS REMOVAL - THE APPLICATION OF INSITU PERMEABLE REACTIVE BARRIER TECHNOLOGY

B. Lalinska, P. Sottnik

Abstract

Antimony mineralization has been intensively exploited at numerous deposits in Slovakia from 17th century until a while since. Weathering and dissolution processes in the environment of mine tailings and closed mines, mobilize elevated levels of toxic elements such as arsenic and antimony, which represent dangerous contaminants for the surrounding ecosystem. The problem of contaminated groundwater should be solved and one of the possible remediation method is the Permeable reactive barrier system (PRB). The choice of Fe0 as filling reactive material for PRB, was done on the base of publications, which have discussed suitability of this filling material for As adsorption. While arsenic and antimony are very common elements we have decided to test this filling material also for Sb removal. We have performed 3 batch and 4 column tests to study the usefulness of zerovalent iron for As and Sb removal from contaminated water. In all of the experiments, naturally contaminated water was used. In the first phase, batch tests were run with three different types of iron: iron powder (Lambda), Fe chip (Merck) and steel manufacturing byproducts in form of turnings. All pilot experiments were successful, best results were observed in case of laboratory Fe chips, but removal efficiency of iron turnings was also suitable and its advantage of low price is incomparable. In second phase we have focused on materials effectivity in column experiments. We have used various mixtures of filling material such as: iron powder mixed with sand in ratio 700g of sand/70g of iron powder; 700g of sand/140g of iron powder; pure iron powder in combination with pure sand; steel manufacturing by-products (in form of turnings); turnings mixed with sand. The best results were observed by using iron turnings as reactive material (Fig. 1). The thickness of turnings in column was 50cm, and the contaminated water was poured over the column 6 times. That means that the contaminated water passed the trajectory of 3 meters, while the water discharge speed was 1000l/h (24l/day). Water discharge speed in place where the barrier is planning to be built is 8 liters a day and the amount of contaminants under 1mg/l. So the three meters thick PRB will be surely adequate for the remediation proposes. The time sequence after which the reactive filling has to be replaced are tested in laboratory conditions, but the effectivity of such system decrease slowly, so the result will be known probably after long period of time.

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