769 MINE TAILINGS RECLAMATION IN AUSTRALIA - AN OVERVIEW1 I by 2 3 4 5 L.C. Bell , S.C. Ward , E.D. Kabav and C.J. Jones Abstract. The paper briefly reviews legislative requirements for rehabilitation of mine tailings in Australia before consideration of case studies of r' - rehabilitation in bauxite, base metal, gOld and uranium mining operations. For particular mineral industries, comparisons are made of the limitations and approaches to tailings rehabilitation in markedly different geographic [ regions. Introduction The objective of this paper is to briefly review thG rehabilitation of tailings [ Mining and mineral processing makes a resulting from mining and mineral processing major contribution to the Australian economy in Australia. Some general comments about and, in 1987 /88, exports of minerals and the legislative requirements for primary mineral products were valued at rehabilitation will be made prior to a [ AS17 ,819 million representing 44% of the discussion of some case examples for a country's merchandise exports. Most of this number of the major mining industries where production was derived from the 264 mines tailings rehabilitation is a major concern [ extracting metallic materials (primarily (bauxite, base metals, gold and uranium), bauxite, gold, iron ore, copper, lead, zinc, nickel and uranium ores) and the 121 mines Legislative Requirements producing coal. The distribution of the [ major mining and mineral processing Most of the specific legislation related operations in Australia is shown in Fig. 1. to environmental matters including tailings containment and rehabilitation in Australia Most of the mines producing metallic has been produced by the individual State minerals and their associated mineral Governments as a result of the division of L processing plants produce tailings which must powers under the Australian Constitution. be contained to prevent on-site and off-site The Commonweal th Government does have the pollution during the mine life and which must opportunity to ensure that mining proposals [ be subsequently rehabilitated such that the are environmentally sound, however, through disposal site has long term stability against the Environment Protection (Impact of the erosive forces of wind and water, Proposals) Act of 1974 which requires that Tailings dams are also a c0111DOn feature of an environmental impact statement be [ the coal mining industry. The fine particle prepared for projects proposed by or on size coal tailings have the potential to be behalf of the Commonwealth, Where export of retreated to produce a marketable product, minerals is involved, the Commonwealth and thus few dams have been rehabilitated Government has the power to prevent export L with a vegetative cover to a condition where where the environmental impact of the they could be abandoned. proposed operation is adverse. In addition to this non-specific power, the Commonwealth [ 1 Paper presented at the 1989 symposium jointly sponsored by the Canadian Land Reclamation Association and the American Society for Surface Mining and Reclamation, Calgary, Alberta, August 27-31, 1989. L 2 Reader in Soil Science, University of Queensland, Brisbane, Q, 4067, Australia. [ 3 Research Scientist, Alcoa of Aust., Booragoon, W,A, 6154, Australia, 4 Senior Consultant-Environmental, Alcoa of Aust., Booragoon, W.A. 6154, Australia. 5 Environmental Scientist, Mt. Isa Mines, Mt. Isa, Q. 4825, Australia. L 770 Government does have the power to legislate Bauxite Residue Tailings with respect to specific details of environmental control of mining for In Australia. bauxite is mined in the territories such as the Australian Capital northern tropics at Weipa (Comalco A:-~inium Territory, the Australian Antartic Territory Ltd.) and Gove (Nabalco Pty. Ltd.) • In the and, to a lesser extent, the Northern temperate south-west, bauxite is mined at Territory (uranium) (Australian Envirorunental Jarrahdale, Huntly, Del Park and Willowdale Council 1984). (Alcoa of Australia Ltd.) and Mt. Saddleback (Worsley Alumina Pty. Ltd.). The bauxite At a State level, the legislative mined at Weipa is beneficiated and then requirements with respect to air and water shipped to Gladstone on the central quality around tailings dam during filling, Queensland coast for refining (Fig. 1). and to rehabilitation requirements once the There is a refinery at Gove, while in the dam is full, vary considerably from State to south-west, Alcoa of Australia has State. Even for a given State, the refineries at Kwinana, Pinjarra and Wagerup, stringency of requirement may vary depending and Worsley Alumina has a refinery at on the age of the mining operation; some old Worsley near Collie. These six refineries mines operate with requirements to protect produce 36% of the western world's alumina, the air and water quality of the mine Comalco Aluminium Ltd. operated a refinery surrounds but have no requirement for at Bell Bay in Tasmania between 1956 and rehabilitation of tailings dams. Most new 1972. mines have legislative requirements covering rehabilitation and may involve specific All these refineries use the Bayer reference to covering of the tailings with process and generate significant quantities soil and establishment of a self-sustaining of alkaline residue (2. 7 mt/a of residue vegetative cover. from the two northern refineries and around A"_ _._,,. • 6.. ••-- _:e_ ()0 .............. ·-·- _.. ,__ _... 0 9loo-l" f: c: .......... c: ......... ... Cl -·- ., - ...... c: ..... ·--** • ·- ** •---....·-- ,__ _ L ·- • '"" )( * ·--·.. ,.... o •• •----•••19"11 " ... ., ... I .... ei *[ ..........····- . L........ I •,••• -- ..... ......... •o• T •• -----· ...1 ·1·- ....--- ... f'19 v,T•• __ ..I•" ..... 1-., ....,.,,.,"0,1111- ........ ~ ·-10-- 0 •••c-•.,.•·- ••••• - ,..,... C •• P'-c••-• - .- Fig. 1. Major mineral and mineral processing operations.. in Australia. 771 12 mt/a at the four south-western residue ge7ierated by the refinery between r refineries). In the Bayer process, alwnina 1956 and 1972 is contained in an unlined 40 I is extracted from bauxite by digesting the ha pond where it was depositied as a crushed ore in sodium hydroxide at elevated conventional wet slurry. ,- temperature and pressure. The solid residue from the refining process is often separated At Alcoa's refineries at Kwinana and 1 into two size fractions during refining, viz. Pinjarra, disposal was originally of a the coarse fraction known as residue sand mixture of both red mud and residue sand. (>150 µm) and a fine fraction known as red Since 1982, mud/sand separation plants have mud (<150 µm). been opera ting at the disposal areas at [ these sites, and the two fractions can now Properties of the Tailings be disposed of separately. At Wagerup, the two fractions have always been disposed of Red mud consists primarily of iron, separately. [ alwninium and silica minerals, the dominant minerals being quartz, haematite- and Alcoa's impoundments are up to 160 ha in goethite. Alkaline substances such as sodium area and around 20m deep with the total area aluminium silicates (desilication product) of tailings at its three refineries now [ are formed during the Bayer process and also exceeding 720 ha. Leakage of caustic is form part of the red mud. Residue sand prevented by a clay seal and, in one case, a consists primarily of quartz with iron oxides synthetic membrane provides an additional such as haematite and goethite. The red mud seal. All impoundments built since 1983 [ fraction of the bauxite residues is dominated have gravity under drains to aid residue by silt and clay particles, whereas the consolidation, improve caustic recovery and residual sand contains little or none of reduce the potential for leakage. these sized particles. The available water [ capacities of the mud and sand are moderately Approximately 50% of the red mud at high and low respectively. Kwinana and Pinj arr a is currently being disposed of by dry disposal which involves Most of the caustic soda associated with separating the mud and sand fractions using [ the residue is removed by washing, but a cyclones. The red mud is then dewatered to solution of sodium hydroxide, carbonate and about 50% solids then pumped into an aluminate remains entrained with the solids. impoundment and solar-dried to around 70%- [ At Gladstone, the bauxite residue is slurried 75% solids, at which time it has a strength in seawater after washing. At Gove, the similar to naturally occurring soils. The residue is slurried with return liquor from sand fraction of the residue is used to the residue disposal areas, and at the other build dykes and to top-off filled disposal refineries fresh water is used. The tailings areas before they are reclaimed. The L materials are all extremely alkaline, saline impoundments originally designed for wet- and sodic, and, when freshly produced, are slurry disposal are being converted to dry incapable of supporting plant growth. In disposal after appropriate drainage. addition, both the red mud and sand are Worsley Alumina Ltd. uses a dry disposal extremely deficient in nitrogen and technique which involves dewatering. A phosphorus and, in many cases, the combined red mud/red sand mixture is availability of manganese and zinc is also dewatered to about 55%-65% solids and then [ low. pumped into clay-sealed and underdrained storage areas developed in natural valleys Method of Tailings Disposal adjacent to the refinery, where it is solar- dried. Bauxite residue in Australia is usually L disposed of by pumping it as a wet-slurry of Rehabilitation of Tailings 15-25% solids into natural depressions or lined or unlined artificial impoundments. Plants are grown on or around residue [ 'Dry disposal' of residue has recently been disposal areas to control dust on operating introduced into a number of the refineries. areas, to prevent wind and water erosion on filled areas, to blend the areas in with At Gladstone, red mud and residue sand their surroundings, to reclaim filled areas L are pumped to separate unlined ponds in a to a productive use and to stabilise the slurry of seawater. At Gove, a red batters of the dykes surrounding the mud/residue sand slurry is pumped to unlined impoundments.