Management of Mine Tailings Stabilized by Adding Lime and Cement at Canadian Electrolytic Zinc in Valleyfield, Quebec
Symposium Rouyn-Noranda 2002
When processing zinc concentrate, the Valleyfield CEZinc plant generates a mine waste called “jarosite”. Up until 1998, jarosite was transported hydraulically into clay basins. Settled jarosite has a very low consistency (it is impossible to walk on the consolidated tailings) and a high metal content in the interstitial water. These particular jarosite characteristics made construction and closing of tailings ponds very expensive.
In 1998, CEZinc implanted a new process developed at Noranda; its main objective was to stabilize the jarosite chemically and physically. A new settling concept was developed for the new tailings, called “jarofix”. The main characteristics of the new process and settling concept are:
Jarosite is washed and dehydrated at the plant using a filter system;
Lime, cement and water are added to form jarofix;
Jarofix is transported by truck to the stocking area;
At the stocking site, the tailings are managed according to a stacking concept.
Elaboration of the piling concept and the staking area had to take into account the jarofix settling characteristics, its resistance to water and wind erosion, management of runoff water, feasibility of building retaining dams using hardened jarofix and the need to rehabilitate the storage area progressively.
Jarofix is unloaded from a ramp built up to develop a higher and higher unloading front. The height of the jarofix pile will reach 30 m at the centre. The initial 1998 layout plan included a 3-m high starter embankment, an 8-m high unloading ramp and a pond to manage the runoff water.
Properties of the consolidated jarofix in the stocking area are determined annually. Hardened jarofix has the consistency and strength of very stiff clay. Its hydraulic conductivity is similar to that of silt and it resists well to wind erosion. Three years after the beginning of deposition, the temperature in the centre of the jarofix pile remains high. Hardened jarofix is easy to excavate and compact, making it an excellent material with which to build retaining dams around the site.