Virotec has developed uniquely tailored treatment solutions for the treatment of contaminated soil, industrial and municipal wastewater, waste solids and other environmental remediation applications, and its technology, based on a range of reagents, with unique physical and chemical attributes, has had proven success across a wide range of industries.

In the ViroSoil technology, a reagent known as ViroBind is central to the process. Its application effectively neutralises acidity long term and any metals present are bound tightly in a non-leachable form. The treatment solution also adds nutrients to the soil or spoil, creating an improved soil profile capable of supporting vegetative growth without the risk of metal uptake or acid generation in the future. This allows the potential for the creation of useable soils from previously barren and contaminated materials.

ViroBind is fine grained (up to 80% being less than 10µm) and has highly charged reactive surfaces resulting in high surface area-to-mass and charge-to-mass ratios. Consequently, ViroBind has an excellent binding capacity (approximately 1,500 meq/kg), acid neutralisation capacity (up to 14moles/kg) and is highly insoluble (<2 per cent of the constituent minerals can be leached by rainwater).

Its application also allows the safe processing of sediments previously held long term in holding lagoons or the treatment of sediments previously stockpiled on land and now leaching acid waters to the surrounding environment. Work carried out by Virotec on one such spoil has shown, for example, that the treated material can be converted into a reusable, commercialgrade top or subsoil material, eliminating the need for disposal to landfill.

At the Port of Gladstone in North Queensland, Australia, the Port Authority had problems with dredged acid sulphate soils which had an average pH of 4.0, an EC of >6.35 mS/cm (with >15.0 mS/cm representing completely saline soil), and a significantly high exchangeable sodium percentage (ESP), meaning that any re-vegetation capacity of the soil was extremely low and leaching of contaminants into the surrounding environment might be a significant problem.

To counteract these pollution problems, the Port Authority applied ViroSoil to 30,000m3 of contaminated soils, and within 24 hours acidity was reduced to 0.02 mole/kg, resulting in stable pH conditions and the vegetation of the treated soils.

Virotec notes that Gladstone Port Authority has been very pleased with the initial and long term outcomes and note that in addition to the vegetation of the soil, the leachate and runoff from the site have been of good quality since the application of ViroSoil.

In addition to acid sulphate remediation, the ViroBind reagent binds metals as part of the formation of new chemically and physically stable mineral phases with very low solubilities. This results in the permanent binding of the metals to the ViroBindTM reagent, which has an increasing capacity to tightly bind trace metals over time.Results have demonstrated that an increase in metal binding capacity of 40 to 50% is likely after just six months.Therefore, metals are bound in a non-leachable and non-bioavailable form.

As Virotec points out, in addition to the remediation of various environmental contaminants, treated soil and sediment can produce a valuable by-product. By altering the physical and chemical composition of dredged sediment, a conditioned soil mix can be produced which has commercial resale value.

The resultant soil can be produced with the safe knowledge that, in the long-term, the metals are immobilised and acidity reduced to pH of 6.5-7.5.Subsequently, the treated soil and sediment can be removed and its previous storage area can be redeveloped or further utilised for the processing of more dredged materials.

In one such application, a marine dredging company is utilising the technology to process 7,000m3 of stored, unusable dredgings to convert to a ‘conditioned’ soil mix for resale to residential and commercial traders, and the production of the ‘garden mix’ from an otherwise waste material has resulted in commercial success for the marine dredging company.

By DAVID FOXWELL