Example – joint production of zinc and heavy metals

Generic product activity or name
Zinc, cadmium, lead, sulphur.

Heavy metals.

Context and background
Zinc, cadmium, lead, copper and sometimes sulphur occur as outputs from the same base metal ores. While zinc is predominating in many ores, cadmium often occurs as the minor component. But even so, most primary cadmium is actually extracted from the zinc ores (Butterman and Plachy 2002). However, due to other (secondary) sources of cadmium, this example shows that zinc is the only co-product without an alternative production route.

Presentation of example
The demand for zinc is increasing moderately, while the demands for the heavy metals lead and cadmium are stagnating mainly due to environmental regulations such as the European RoHS-directive (Restriction of Hazardous Substances Directive). The environmental restrictions have lead to a falling price and a decline in market trend for cadmium and lead (USGS 2016a and b). The supply of cadmium from compulsory take-back and recycling of cadmium containing products means that some primary cadmium is currently deposited. If the markets for cadmium continue to decline the byproduct cadmium will have to be stockpiled and managed (USGS 2016a). The same situation can be expected in the future for the other heavy metals. Sulphur is increasingly produced from desulphurisation of flue gases from refineries, power plants etc. and in Europe there is no longer demand for primary production of sulphur. When seeing these developments together it is clear that zinc is the only product that has no alternative production and furthermore the only product with a substantial demand able to drive the primary extraction. Zinc is thus the determining product of these joint productions.

Information sources used
The USGS Commodity Statistics and Information is a good source for statistics and information on the worldwide supply of and demand for of minerals and materials. 

Butterman WC and Plachy J (2002). Mineral Commodity Profiles: Cadmium. https://pubs.usgs.gov/of/2002/of02-238/ (accessed 2017-01-13)

USGS (2016a). Mineral Commodity Summary – Cadmium.
http://minerals.usgs.gov/minerals/pubs/commodity/cadmium/ (accessed 2016-03-17)

USGS (2016b). Mineral Commodity Summary – Lead. http://minerals.usgs.gov/minerals/pubs/commodity/lead/mcs-2016-lead.pdf (accessed 2016-03-17) 

Weidema B P (2004). Geographical, technological and temporal delimitation in LCA. UMIP 2003 method. København: Miljøstyrelsen. (Environmental News 74) http://lca-net.com/p/1046

Author of this example
Bo Weidema


How to reference this
Weidema B P (2017), Example – Joint production of zinc and heavy metals. www.consequential-lca.org