During zinc production a residual product 'goethite' is released. Nyrstar (formerly known as Umicore) used to store this goethite sludge in basins at its premises in Balen. However, the company no longer had any capacity to store the sludge, therefore another solution had to be found.
At a production level of 260,000 tonnes of zinc a year, Nyrstar Balen produces some 75,000 tonnes of goethite per year. The process also yields 40,000 tonnes of neutralised flotation sludge a year. Based on a Build, Own, Operate, Transfer (BOOT) contract, Nyrstar wanted to tackle this problem.
After an extensive selection procedure, DEC in a joint venture partnership, was awarded the contract for the outsourcing of the investment and the operation of a system for the compact stocking of goethite and the neutralisation of the sludge.
DEC built a new dewatering system, where both residual flows are compacted. The solid filter cakes are then disposed of in the landfill on the site. To make maximum use of the existing dump capacity, historic sludge was also excavated and compacted in the dewatering system.