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Industry  Environment


of surface waters and ground waters long after a mine has closed. Compared to heavy industry, compound semiconductor fabrication uses relatively small amounts of toxic materials and has a good track record of managing hazardous waste. A recent inspection report by the UK Health and Safety Executive on the control of hazardous materials within semiconductor Fabs reported satisfactory arrangements, but did highlight some poor handling of GaAs wafer waste during lapping operations [1].


The behaviour of metals in the environment has been much studied as the link between anthropogenic discharges of lead, cadmium, arsenic and chromium and public health have been more clearly defined. Following incidents such as Love Canal, NY and Times Beach, MO, legislation was introduced in both the United States and the European Union to address the legacy of past industrial activity and promote the remediation of contaminated brownfield sites, especially CERCLA “Superfund” legislation in the United States.


Figure 1. Part of the periodic table showing the main constituent compound semiconductor elements.Elements considered toxic are in red,with US EPA maximum contaminant levels (MCL) for drinking water given,where available


recent years, the relationship between geology and public health has been investigated. Geochemical maps have been compiled for most of Europe, showing the concentrations of selected toxic metals in soils and stream sediments; the UK has already been mapped in detail. Anomalies or hot spots may be related to localized mineralization; for example, lead and zinc ore veins in Derbyshire or to past industrial use (see Figure 2). Lead and antimony distribution in soils can often be correlated with traffic density as a result of the legacy of ethyl lead additives in petrol before their use was restricted.


Elements such as mercury, arsenic, cadmium and antimony can be derived from both natural and anthropogenic sources and are of concern in the environment because of their toxicity. Metal mining and smelting of metallic sulphide ores are the primary sources of mercury, arsenic and cadmium in the environment. Exposed sulphide minerals in mine waste spoil heaps, such as pyrite (Fe2


S), quickly oxidise to


soluble sulphates, resulting in acid mine drainage from run-off, with characteristic ‘yellow boy’ precipitation (see Figure 3).


The low pH of mine waters can mobilise arsenic and zinc, among other metals, leading to on-going pollution


48 www.compoundsemiconductor.net January/February 2012


Although heavy industries such as steel manufacture, chemical production and ore processing account for the overwhelming instances of contaminated land, legislation to limit the use of potentially hazardous metals can still impact the semiconductor industry. The ROHS legislation [2] introduced in the EU in 2002 to restrict certain metals, such as lead, mercury and cadmium, in electronics is a good example of this.


Semiconductor substrates such as GaAs, InP and CdTe are stable, insoluble in wafer-form and resistant to oxidation under normal pH and temperature. It is likely that packaged devices will remain intact for many years in electronic waste consigned to landfills; incineration presents a more direct pathway to the atmosphere and the environment.


However, GaAs wafer processing generates large volumes of solid and liquid waste[4] that exceeds regulatory discharge levels and must be treated in the fab or disposed of as hazardous waste to landfill at significant cost. Another consideration is the end-of-life management of electronics and PV and the fate of toxic elements they contain. The behaviour of metals in soil is complex, as the form of the metal (element, inorganic compound or organic compound), oxidation state, pH of the soil and reduction/oxidation potential all influence toxicity and mobility.


Exposure pathways must be present before a contaminant represents a potential health risk; sophisticated models estimate exposure and determine whether a metal in a contaminated soil poses a risk and whether a brownfield site can be developed safely.


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