PROJECT DESCRIPTION
BACKGROUND
The LIFE project concerned the UM zinc refining business unit, UM Zinc. UM Zinc produces some 500,000 tons/year of refined cathodic zinc. The 2 major technologies used for zinc refining are the Imperial Smelt Furnace technology (ISF) and the Roast-Leach-Electrowinning process (RLE). The most important environmental disadvantage of the RLE process is the production of an Iron (Fe) waste residue (also the ISF technology produces an Iron waste in the form of a slag). UM uses the Goethite process for iron removal while most of the competitors use the Jarosite process. This iron waste is stockpiled in so-called mono-deposits or ponds. UM has developed a process for the inertisation and solidification of Goethite on a laboratory scale during 1995 and 1996. This process consists in mixing goethite with basic slag from the steel industry. This slag contains an excess of free and reactive CaO and is also a waste problem for the steel industry. During mixing and further curing pozzolanic reactions take place between the acidic Goethite and the basic slag and the product cures into a hard and inert kind of rock. This rock, patented as Graveliet, has been thoroughly evaluated for its ecotechnical and constructional properties by external laboratories. The rock which is completely inert can replace gravel in concrete. By the year 2005, Flanders will have a shortage of natural gravel because the gravel mining in the valley of the river Meuse will come to an end. The Graveliet process is a low cost and low energy consuming process and can be regarded as a unique solution for the Iron waste problem in the zinc industry. Other more expensive, more energy consuming solutions exist but most of these solutions do not solve the stockpiling problem of the iron waste.
OBJECTIVES
The aim of this project was to further develop the technology for Graveliet production on a pilot scale. These pilot experiments were designed to optimise the mixing-extrusion-curing technology and to prepare a sufficient amount of samples for construction and eco-technical evaluations. The pilot plant was designed to handle about 10 metric tons per day.
RESULTS
The evaluation of clay and concrete technology led to a pilot installation that was suitable for Graveliet production. The different unit operations within the flow sheet were evaluated and modifications that would be necessary for an industrial plant were identified and discussed with the manufacturer. Several operating parameters that would have an important influence on the final Graveliet properties were also investigated and an estimate of the operating cost of an industrial plant, based on comparable technology, was made. The leaching properties of Graveliet are such that it conforms with the regulations of the Flemish authorities for use as a secondary construction material, albeit with some restrictions. The construction properties of Graveliet are such that it can be used as a replacement for gravel in concrete. The cost of the Graveliet process on a pilot scale, which was estimated at about EUR 55/ton of Graveliet, or nearly EUR 20/ton of zinc, is only partially relevant to an eventual industrial process, where much lower costs would be expected. Overall, the Graveliet process was demonstrated to be a viable solution to the iron resiue problem in the zinc industry. The evaluation of clay and concrete technology led to a pilot installation that was suitable for Graveliet production. The different unit operations within the flow sheet were evaluated and modifications that would be necessary for an industrial plant were identified and discussed with the manufacturer. Several operating parameters that would have an important influence on the final Graveliet properties were also investigated and an estimate of the operating cost of an industrial plant, based on comparable technology, was made. The leaching properties of Graveliet are such that it conforms with the regulations of the Flemish authorities for use as a secondary construction material, albeit with some restrictions. The construction properties of Graveliet are such that it can be used as a replacement for gravel in concrete. The cost of the Graveliet process on a pilot scale, which was estimated at about EUR 55/ton of Graveliet, or nearly EUR 20/ton of zinc, is only partially relevant to an eventual industrial process, where much lower costs would be expected. Overall, the Graveliet process was demonstrated to be a viable solution to the iron resiue problem in the zinc industry.
