Heavy metal, soft rock

Over the last five years, the Belgian based DEME (Dredging, Environmental and Marine Engineering) Group has been focusing on the need for more successful removal of heavy metals from soil and groundwater, especially where a variety of contaminants are contained. This effort has resulted in two new technologies, which, although entirely different, are complimentary in application. The first is a mineralogical approach that uses metasorb, Soils¹ new granular adsorbent, while the second is an electrochemical treatment using bipolar electrolysis.


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Metasorb is a low-cost solution to the problem of large scale contamination

by heavy metals. Developed bt DEME remediation specialist Soils NV, in

association with the University of Ghent¹s Faculty of Agriculture, it is now

a patented product available commercially, in bulk. The adsorbent is a

coarse, granular product combining aluminosilicates and a number of

additives, providing extremely high porosity and the capability of fixing

all heavy metals. Metasorb is available in two formulations: finer-grained

product for soil treatment and a coarser grained version for treatment of

contaminated groundwater and wastewaters.

Pilot project

The coarser grained metasorb-Water can be applied as an end-of-pipe

treatment of process waters or pumping and treatment of polluted

groundwater. It is typically used in percolation filters, often set up in

series for larger scale products. Metasorb-Water has an average metal

adsorption capacity of up to 15%, and can reduce most heavy metals to below

100 microgrammes per litre.

Bipolar electrolysis works by passing an electric current through water as

it is pumped through a cell containing two poles. Pollutants are then

oxidised or otherwise transformed into chemicals capable of extraction by

decantation and filtration.

As a result of successful laboratory studies, Soils were asked by Union

Minière, one of the world¹s largest non-ferrous production groups, to carry

out a pilot project near their zinc plant in Belgium, where leaching of

various metals has caused widespread, low-level contamination of

groundwater.

In the first stage of the pilot, Soils designed, engineered and constructed

a mobile treatment plant, with a capacity of 20m3/hour, housed within a

single standard freight container.

‘This project presented a double challenge,’ says Stany Pensaert, Soils NV’s

project manager in electrolysis systems R&D. ‘A plant of this kind had never

been biult before, and the biploar electrolysis process had never been

tested beyond laboratory scale.’

The pilot also provided data for economic analysis. Results confirmed the

laboratory findings: all metals could be removed to below legislative

standards and operational costs were as low as E0.4-0.5/m3.

‘The process can be even more cost-effective when treating higher levels of

pollution,’ says Pensaert. ‘Because high metal concentrations often create

high water conductivity, correspondingly less electricity is requires to

power the operation.’

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