Waste and tailings management
Xstrata's Product Stewardship Standard requires that all operations eliminate, reduce, reuse, recycle or properly dispose of waste generated. In addition, our Biodiversity and Land Management Standard requires the progressive rehabilitation of disturbed land and effective management of waste generated to a planned post closure land use.
Waste from our mining and metals processes consists predominantly of overburden stripped in open cut mines, fine tailings, waste slurry from washing, concentration, or treatment of ground ore, coarse stone or dirt discarded from a coal preparation plant, and slag from smelters.
One of our most significant environmental risks is the storage of minerals processing waste. Our 65 sites manage more than 60 surface tailings storage facilities, slimes dams and mineral waste ponds. The walls of these structures range in height from five metres to 102 metres and cover a combined area of more than 3,800 hectares. Associated risks include water management for these storage facilities.
Programmes for managing these risks include the HSEC Assurance Programme, specialist risk assessments, annual engineering reviews, divisional and site audits, inspections and routine monitoring of the structural stability of the storage facility to prevent catastrophic failures and potential losses of containment through seepage.
A particular water management issue is acid rock drainage (ARD). ARD is a natural phenomenon that can occur in dumps and tailings dams where sulphuric acid is formed when sulphide-bearing minerals such as pyrite are exposed to air and water during mining. If not effectively managed, the resulting acid can dissolve heavy metals such as lead, zinc, copper, arsenic, selenium, mercury and cadmium into ground and surface water.
Our risk assessment processes have identified this as an issue at our Alumbrera open cut copper mine in Argentina and at Collinsville coal mine in north Queensland (see case study). Alumbrera mine in Argentina generates three categories of waste – benign material which is used as a final cap, intermediate material, which is used in an intermediate cap on the slopes of the waste rock dump, and potential ARD rock. The closure plan for the mine, currently expected to close in approximately 10 years' time, requires potentially acid-generating material to be capped with a combination of intermediate and benign material. The key challenge is stopping water infiltration into the dumps and developing a strategy to ensure that any acidic water remains within the tailings material. Capping trials have been ongoing since 2002 covering a six hectare area. The tailings dam currently occupies 480 hectares with a final design of 850 hectares.
Significant improvements in the management of wastes across the Group in 2005 have resulted in an enhanced understanding of our waste streams and reporting that is in accordance with the Global Reporting Initiative (GRI). The 2005 HSEC assurance audits showed all sites have implemented waste management plans in line with our Product Stewardship Standard launched in 2004, bringing into compliance recent acquisitions and a number of smaller operations.
Our operations generated 638 million tonnes of waste in 2005 a 6.3% reduction from 681 million tonnes generated in 2004. The main sources of wastes generated were 549 million tonnes of excavated materials and overburden, 66 million tonnes of tailings and processing wastes, 20 million tonnes of coarse rejects and 2 million tonnes of slag.
Tailings, coarse reject and slag accounted for 88 million tonnes of waste in 2005, of which 3.6 million tonnes were recycled. One million tonnes of hazardous waste, as defined by the Basel Convention 1992, (including hydrocarbons, heavy metal contaminated sludges, medical waste and vehicle batteries) were generated in 2005, down slightly from 1.1 million tonnes the previous year. Over 27% or 272,000 tonnes of hazardous waste generated were reused or recycled, an increase of 26,000 tonnes from 2004, and 6,400 kilolitres of waste oil were reused in blasting or recycled through off-site facilities. A small proportion of waste (46,000 tonnes) was disposed of in off-site regulated facilities and the remainder (692,000 tonnes) was disposed of in regulated on-site facilities.
A major waste management issue for the zinc industry is the generation of high iron content waste. In Xstrata Zinc's operations, iron is removed as iron sulphate (jarosite), classified as a hazardous waste. At San Juan de Nieva in Spain, jarosite is transformed into jarofix, a solidified, stabilised, inert material, which is being used to rehabilitate a nearby quarry. Xstrata Zinc was the first European zinc producer to adopt this new technology, allowing it to achieve two main objectives: resolution of the waste problem and land rehabilitation.