primary zinc production from concentrate, UPR, ecoinvent 3.6, Allocation, cut-off
Reference product: copper cake [kg]
Location: CA-QC - Canada, Québec
This dataset represents the production of high grade (SHG-Special High Grade) primary zinc by hydrometallurgical processes. Specific data were collected from the only producer in the Québec region, for the years 2011-2012.
Primary zinc is produced in the form of ingots and shot, respectively used as coating in steel work/die cast and for electroplating. About 25% of the produced zinc is in the form of an aluminium alloy.
The zinc concentrate, coming from all around the world (e.g. Canada (Québec and Ontario), Australia), is transported to the site by train or by ship and truck and mixed on site. The site is able to treate zinc concentrate contaminated with mercury and selenium but cannot recover silver and lead. Contrary to the GLO dataset, this dataset does not include waste contaning indium ("indium rich leaching residues, from zinc production" by-product flow).
[This dataset has been generated using the system model "Allocation, cut-off by classification". A system model describes how activity datasets are linked to form product systems. The allocation cut-off system model subdivides multi-product activities by allocation, based on a physical properties, economic, mass or other properties. By-products of waste treatment processes are cut-off, as are all by-products classified as recyclable. Markets in this model include all activities in proportion to their current production volume.
Version 3 of the ecoinvent database offers three system models to choose from. For more information, please visit: https://www.ecoinvent.org/database/system-models-in-ecoinvent-3/system-models-in-ecoinvent-3.html)]
Sulphide concentrates are roasted first in fluidized bed roasters to produce zinc oxide (calcine) and sulphur dioxide. Roasting is an exothermic process and no additional fuel is used to sustain the reaction, the heat generated is recovered to produce steam. Calcine is then sent to the leaching step. Roaster gases are treated in hot electrostatics precipitators to remove dust. The remaining dust and volatile metals such as mercury and selenium are removed in the wet section of the acid plant through a cooling tour, a mist precipitator and a mercury tower (Boliden mercury removal processs). The sulphur dioxide is then converted to sulphuric acid in a conventional recovery system (converted and absorbing tower).
Leaching of the calcine is carried out in a number of successive stages using a gradually increasing strength of hot sulphuric acid. The initial stages dissolve the major part of the zinc oxide and the other stages dissolve the zinc ferrite (ZnO.Fe2O3) and convert iron into Jarosite (sodium Jarosite). Zinc sulfate (ZnSO4) entering the electrolysis stage produce electrolyte (H2SO4) that is returned to leaching plant. Other metals are also dissolved during the process and are removed after leaching. Iron is the major impurity, which is precipitated in the form of Jarosite.
Overall waste: The production of metals is related to the generation of several by-products, residues and wastes. Relatively large quantities of iron based solids, depending on the iron content, are generated by the leaching process (6.14E-1 kg Jarosite/kg zinc). Cement is added to the Jarosite to produce Jarofix (an inert waste). Solid residues also arise as the result of the liquid effluents treatment. The main waste stream is gypsum (CaSO4) and metal hydroxides that are produced at the wastewater neutralization plant. Mercury and selenium residues arise from the weak acid bleed treatment from the acid plant. Selenium can be recovered from these residues depending on the market demand for this metal.
Overall emissions: The emissions to air can either be stack emissions or fugitive emissions. Stack emissions are normally monitored continuously (SO2) or periodically (other emissions) and reported. The main emissions to air from zinc production are sulphur dioxide (SO2) and particulate matters including metals. Main emissions to water are metals and their compounds. The monitored metals are zinc, cadmium, lead, mercury, selenium, copper and arsenic.