Storage capacity optimisation of tailing ponds by means of mechanical dewatering
Type:
Presented during:
CEDA Dredging Days 2009 - Dredging Tools for the Future, Rotterdam
Authors:
Pensaert S and Van de Velde K - DEC, Belgium
Abstract: Up till now it is common practice for mining and metallurgical companies to store mineral residues, such as tailings, in large ponds without any (pre)treatment. As most of these residues are pumped to the ponds hydraulically this has resulted in huge dumpsites with a high volume of water. Nowadays this procedure is no longer considered as environmentally sustainable. Lack of space, difficulties in permitting additional storage capacity, lixiviation of pollutants, stability issues etc. demonstrate the need for more efficient storage. The same problem applies for dredged sediment storage ponds. Efforts towards optimisation of storage capacity and minimisation of disposal costs are the key elements of the development schemes for new technology. New developments in combined dredging and mechanical dewatering offer a cost-efficient solution to reduce the mass and volume of the mineral residues or dredged sediments in existing ponds. Dewatering followed by controlled backfill of the ponds can increase the storage capacity of the pond seriously.
DEC (DEME Environmental Contractor) is currently carrying out a full scale dewatering of two metallurgical tailing ponds in the Belgium. The largest pond is pond contains about 1,500,000 m³ gypsum precipitate residue from the neutralisation of spent hydrosulphuric acid of zinc leaching. The smaller pond contains 500,000 m³ of goethite, a residue from hydrometallurgical zinc refining. The goethite is extremely corrosive which required special attention in the design of the whole treatment process.
A full scale dewatering plant was being designed, built, and is nowadays being operated, based on two large membrane filter presses. Residues dredged from the ponds as well as freshly generated residues from the metallurgical plant are pumped to the dewatering installation, which has a total capacity of 150,000 tons of dry matter per year. The stable filter cakes are backfilled in a controlled way in the already dredged areas of the ponds. The project has started in 2006 and will take 10 years.
With this project a volume gain of about 100 % (50 % volume reduction) will be achieved, enabling a new storage capacity of another 40 years.
Keywords: mechanical dewatering, sediment, tailings