CEDA Dredging Days 2009

Rotterdam

November 5th 2009

STORAGE CAPACITY OPTIMISATION OF TAILING PONDS BY MEANS OF

MECHANICAL DEWATERING

Stany Pensaert - Head of R&D Department

• Various fine mineral residues are produced in large quantities and often handled in a hydraulic way:

• Sediments are dredged and pumped into large storage lagoons ashore.

• Mineral residues such as tailings from mining and metallurgy are pumped into tailing dams.

Problems with storing large

quantities of sediment or alike…

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• The natural consolidation of many of these minerals in the storage lagoons is poor: low amount of dry matter stored per unit of volume…

• Nowadays: lack of space, problems with planning permissions,… in countries where space is a problem:

• Existing lagoons: redevelop new storage volume in existing lagoon.

• New lagoons: dewatering prior to storage.

• Final goal is storing dry matter, not water.

• This means storing the minerals at the highest dry matter content or highest density.

How to increase the storage

capacity of sediment lagoons or

tailing ponds ?

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• Solution: mechanical dewatering of minerals

• Prior to storage.

• Existing lagoons: dredge from the lagoons and dewater.

• But: volume reduction is function of various steps.

How to increase the storage

capacity of sediment lagoons or

tailing ponds ?

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• Nyrstar (former Umicore) produces about 260,000 tons zinc each year.

• This generates residues:

• Goethite (FeOOH): 75,000 tons dry matter a year.

• Gypsum (neutralisation sludge): 30,000 tons dry matter a year.

The tailing ponds at a zinc smelter

in Belgium (Nyrstar Balen)

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• Gypsum (neutralisation sludge): 30,000 tons dry matter a year.

• Historical residues:

• Goethite: large pond, already capped.

• Goethite: new pond of 360,000 m³ to be dewatered.

• Gypsum & flotation residue: old pond of 1,500,000 m³ to be dewatered.

• Expansion of the lagoons for another 40 years of production was not permitted !

• Nyrstar awarded DEC (DEME Environmental Contractor) a BOOT contract for:

• Design and build a fixed dewatering plant for 150,000 tons of dry matter per year.

• Temporary dewatering of the goethite by means of mobile filter presses.

• Operation of the the fixed dewatering plant for a period of 10 years.

The tailing ponds at a zinc smelter

in Belgium (Nyrstar Balen)

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• Operation of the the fixed dewatering plant for a period of 10 years.

• All logistics: dredging of sludges, transport of cakes, recompaction,…!!!

• Planning of the project:

• Lab- and pilot scale dewatering tests: 2005

• Temporary mobile dewatering during construction of fixed plant: 2006-2007

• Construction fixed plant: 2006-2007

• Operation fixed plant: 2007 – 2017 (?)

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2003-2005: Old goethite lagoon was capped (18 ha)

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2001: Construction new lagoon for goethite (4,5 ha)

Current situation

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Gypsum lagoon (25 ha)

Current situation

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Goethite lagoon (4,5 ha)

Current situation

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Mechanical dewatering plant

Scope of the project

Old goethite Buffer tank Filter pressesStorage 4.5 ha

lagoon

Fresh

goethite

Buffer lagoon

made of filter

Filter pressesStorage 25 ha

lagoon

dredge

dredge

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goethite made of filter

cakes

Old gypsum Buffer tank Filter pressesStorage 25 ha

lagoondredge

Fresh

gypsum

Buffer lagoon

made of filter

cakes

Filter pressesStorage 25 ha

lagoon dredge

Heart of the process

• Two membrane filter presses of 20 m³ volume each.

• Normal production: one filter press per type of material

• Goethite: very acid and corrosive medium, high density.

• Gypsum: alkaline nature

• However presses have to be versatile for each product.

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• However presses have to be versatile for each product.

Dewatering existing goethite pond and cap

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Construction of buffer lagoons with goethite filter cakes.

- lagoon for fresh goethite receipt- water buffer- lagoon for fresh gypsum

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- lagoon for fresh gypsum

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Gypsum lagoon� dredge� store compacted filter cakes (18m in height)

Laboratory and pilot scale tests

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Mobile dewatering plants

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Intermediate full scale…

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Construction fixed plant

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Construction fixed plant

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Operation - dredging

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Operation - dewatering

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Operation – filter cake storage

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Situation summer 2009

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Final result

100 % of volume reduction

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Thanks for your attention