Over the last 20 years, mining companies throughout Australia have increasingly adopted an objective of establishing sustainable native ecosystems following mining. A significant area of risk associated with mine closure is the question of completion criteria for native ecosystem rehabilitationwhat standards will regulators and the community accept as part of an overall mine closure plan, which if met, will result in lease relinquishment? Two examples from mines located in forest and woodland habitat in different parts of Australia illustrate how companies have adopted an innovative approach to the development of ecological completion criteria. Alcoa World Alumina Australia mines bauxite in the jarrah forest of southwestern Australia. Shallow mining (~4 m) occurs in isolated pods averaging 10 ha in size. The overall objective of rehabilitation is 'to restore a self-sustaining jarrah forest ecosystem, planned to enhance or maintain water, timber, recreation and conservation values'. Completion criteria were developed after extensive liaison with stakeholders. The criteria are assessed at five different stages, ranging from planning (prior to mining) to late (10-15 years). More than 25 years of research data enabled Alcoa to set criteria that include a range of biodiversity and ecosystem function measures. Wesfarmers Curragh Mine in central Queensland is located in a woodland environment. The open-cut coal mine produces large spoil areas that are reshaped and planted to an open woodland/grassland community. A recent study recommended completion criteria which state (in part) that 'The objective of rehabilitation following mining at Curragh is to establish a stable, self-sustaining native ecosystem that fulfils designated land uses including protection of water resources and nature conservation, and which…is similar in composition and function to that occurring in representative unmined reference sites'. Compared to those of Alcoa, the Curragh criteria reflect differences in the pre-mining environment, climate, and the mining operation. This paper describes the similar approach used to develop completion criteria at the two mines, and illustrates how the issue is being addressed in Australia.
The kinetics of exchange of 32P and 45Ca in aqueous solution with synthetic, stoichiometric hydroxyapatitie was followed up to 200 hours. Seventy percent of the total exchange occurred in 1 hour, and isotopic equilibrium was reached at approximately 40 hours. Using McKay (13) plots, the exchange reaction was shown to be heterogeneous. Diffusion of isotope through solution “compartments” was considered to be rapid in relation to exchange occurring at the solid surface. The nature of the exchange curve was explained by the differing energies of activation of exchange for surface atoms located at different positions on the crystal landscape. The use of well‐crystallized, stoichiometric hydroxyapatite resulted in the establishment of a well‐defined isotopic equilibrium (11) with little evidence of loss of isotope through intracrystalline diffusion or recrystallization.
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