Rehabilitation of highly erodible smectite bearing kimberlitic tailings facilities in South Africa: a case study
|
Authors: van Wyk, SJ; Haagner, ASH Open access courtesy of:
|
DOI https://doi.org/10.36487/ACG_repo/2215_66
Cite As:
van Wyk, SJ & Haagner, ASH 2022, 'Rehabilitation of highly erodible smectite bearing kimberlitic tailings facilities in South Africa: a case study', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 907-926, https://doi.org/10.36487/ACG_repo/2215_66
Abstract:
This paper presents a case study of rehabilitation status quo of kimberlite tailings facilities dating back more than 100 years. Since there was no specific environmental legislation, the tailings materials were deposited by means of downhill tipping and later by open-end pipe distribution on the toe of a foothill and semicontained in a makeshift trench and paddock system. Erosive forces have since decimated the highly erodible tailings surfaces and evidence of downstream impacts on receiving water bodies have emerged which necessitate urgent and sustainable rehabilitation interventions. The study site presents a realistic case for caution for the broader rehabilitation and closure risks for the mine’s much larger tailings operations. Literature studies revealed that the kimberlitic tailings present a cocktail of challenging properties for conventional rehabilitation methods – to the extent that it is practically uncontainable without serious civil interventions. The smectite clay mineral in the kimberlite rock present the tailings with unique secondary type pedo-physical and geochemical properties. Extreme Exchangeable Sodium Percentage (ESP) presents soil surface stability challenges through chemical dispersiveness, hard crust formation, lack of water infiltration, extreme erodibility and limiting soil moisture as well as potassium metabolism in plants and soil organisms. Furthermore, the tailings have extreme alkaline pH values (9.7–10.2) which present unsuitable conditions for vegetation establishment for various reasons whilst high Cation Exchange Capacity (CEC) values present substantial buffer capacity against pH, inhibiting soil amelioration potential. Considering the compounding effect of steep tailings geometry, harsh climate and intense rainfall events, direct revegetation cannot be regarded as a sustainable cover for closure. The Revised and Modified Universal Soil Loss Equation (RUSLE/MUSLE) was used to evaluate various geometrical and cover combinations for the kimberlitic substrates, considering the existing contamination status, availability of cover materials (topsoil, rock and geofabrics) and space around the facilities. The modelling incorporated long-term erosion loss, as well as single event recurring erosion loss for 2-, 5-, 10-, 20, 50- and 100-year rainfall data. The results showed that the only scenario to achieve less than 10tonne/ha/annum erosion loss would be complete rock encapsulation. The only topsoil store-and-release cover system that would restrict high erosion rates would be for a geometry of 25 m and 14° and a minimum of 350 mm thick cover for the specific sandy cover material available in the region. However, considering the coarse nature of the cover soils available, cover failure can be expected from sub-surface chemical sealing that will interface with low shear strength of the cover on the topsoil/tailings interface. Tunnel erosion and slope failure will desiccate the cover during high intensity rain events leading to seepage and consistent gully and donga erosion irrespective of any geometric design, rendering complete (imported) rock encapsulation the only sustainable cover option. This case study revealed that smectite bearing kimberlite tailings closure require an urgent re-evaluation and an alternative view on design, costing and operation is required to meet closure commitments.
Keywords: kimberlite, erosion, tailings, smectite clay, closure design, covers, rock cladding
References:
Acocks, JPH 1988, ‘Veld Types of South Africa Memoirs of the Botanical Survey of South Africa’, 57: vol. 1, no. 46.
Defferrard, PL, Rohde, TK & Lord, M 2016, 'Leading practice store and release cover trials for a tailings storage facility at Century mine', in AB Fourie & M Tibbett (eds), Mine Closure 2016: Proceedings 11th International Conference on Mine Closure.
Dixon, JB 1989, ‘Minerals in Soil Environments’, Soil Science Society of America, vol. 1, no. 2, pp. 675–727.
Foy, CD, Chaney, RL & White, MC 1978, ‘The physiology of metal toxicity in plants’, Annual Review Plant Physiology, vol. 29,
pp. 511–566.
Furnas, CC 1931, ‘Grading Aggregates - I. - Mathematical Relations for Beds of Broken Solids of Maximum Density’, Industrial and Engineering Chemistry, vol. 23, no. 9, pp. 1052–1058.
Hattingh, JM & van Deventer, P & van Wyk, SJ 2002, ‘ERGO Mine: A reconnaissance investigation to determine long-term stability and future behaviour of rock armour used on the walls of Brakpan tailings dam’, ISCW Report number: GW/A/2002/126.
Hattingh, JM & van Deventer, PW 2003, ‘Utilisation of water for rehabilitation of gold tailings’, WRC No K5/899, Water Research Commission, Pretoria.
Levy GJ & van der Watt HVH 1988, Effects of clay mineralogy and soil sodicity on soil infiltration rate’, South African Journal of Plant and Soil, vol. 5, pp. 92–96.
Low, AB & Rebelo, AG (eds.) 1996, ‘Vegetation of South Africa, Lesotho and Swaziland’, Department of Environmental Affairs, Pretoria.
MacVicar, CN, 1986, ‘Land Types of South Africa’, Memoirs of the National Agricultural Resources of South Africa, no.7, Pretoria, Department of Agriculture and Water Supply, pp. 45.
McPhee, PJ, Smitten, AA, Venter, CJ, Hartman, MO & Crosby, CT 1983, ‘The South African rainfall simulation programme for assessing soil loss and runoff’, in H Maaren (ed), Proceedings of the South African National Hydrology Symposium, Department of Environmental Affairs, Pretoria, Technical Report TR119, pp. 350–368.
Renard, KG, Foster, GR, Weesies, GA & McCool, DK 1991, ‘Predicting soil erosion by water’, A guide to conservation planning with the Revised Soil Loss Equation (RUSLE), USDA Agricultural Research Service, Tucson.
South Africa 1998a, GNR 632, ‘Planning & Management of Residue Stockpiles’, National Environmental Management Water Act 36 of 1998, Government Printer, Pretoria.
South Africa 2008, National Environmental Management Waste Act 59 of 2008, ‘Regulations Regarding the Planning and Management of Residue stockpiles and Residue Deposits’, Government Printer, Pretoria.
South Africa 1998b, GNR 926, ‘National Norms and Standards for the Storage of Waste’, National Environmental Management Water Act.
South Africa 2006, ‘South African National Standard No. 10286, Code of practice of Mine Residue Facilities’, Minerals and Petroleum Resources Development Act, Government Printer.
Shainberg I & Singer JJ 1988, ‘Drop impact energy – soil exchangeable sodium percentage (ESP) interaction in seal formation’, Soil Science Society of America Journal, vol. 52, pp. 1449–1452.
Small, RJ & Clark, MJ 1982, Slopes and Weathering, Cambridge University Press, London.
Smith HJC 1990, ‘The crusting of soils as affected by parent material, rainfall, cultivation and sodicity’, MSc agric thesis, University of Pretoria.
Smit, H 2008, ‘Project Report on a Field Survey of the Historic Kimberlite Slime Dams at the mine’s game park’, 41 p.
Stern R 1990, ‘Effects of soil properties and chemical ameliorants on seal formation, run-off and erosion’, DSc agric thesis, University of Pretoria.
US Department of Energy 1997, ‘Toxicological benchmarks for screening contaminants of potential concern for effects on terrestrial plants’, 1997 revision.
van Deventer, PW 2000, ‘Influence of Exchangeable sodium and clay mineralogy on the infiltration capacity of soils’, WRC
No. 499/1/00, Water Research Commission, Pretoria, South Africa.
van Deventer, PW, Bennie, ATP & Hattingh JM 2002, ‘Hydraulic properties of stony soils’, WRC No 725/1/02, Water Research Commission, Pretoria, South Africa.
van Deventer, PW 1997, ‘Physical properties of disturbed stony soils’, International Conference on Problems of Anthropogenic Soil Formations, Moscow, Russia.
van Deventer, PW & Hattingh, JM 2003, ‘Soil quality as a key function in sustainable land management of revegetated mine residue’, Soil Science Society of South Africa Congress, Stellenbosch, South Africa.
van Deventer, PW, Bloem, AA & Hattingh JM 2008, ‘Soil quality as a key success factor in sustainable rehabilitation of kimberlite mine waste’, Journal of the Southern African Institute of Mining and Metallurgy, vol. 108, no. 3, pp. 131–137.
van der Merwe, F 2007 Aquasim Project Report on the Hydrology and Surface Water Quality of the Upper Pienaars River Catchment.
Weiersbye, IM & Witkowski, ETF 1998, ‘The structure, diversity and persistence of naturally colonizing and introduced vegetation on gold tailings dams’, Plant Ecology and Conservation Series, no. 8, University of Witwatersrand.
Williams, JR 1975, ‘Sediment-yield prediction with universal equation using runoff energy factor’, Present and Prospective Technology for Predicting Sediment Yield and Sources, US Department of Agriculture, Agricultural Research Service, Brooksville,
pp. 244–252.
Young, RA, & Mutchler, CK 1977, ‘Erodibility of some Minnesota soils’, Journal of Soil and Water Conservation, vol. 32, no. 4,
pp. 180–182.
© Copyright 2024, Australian Centre for Geomechanics (ACG), The University of Western Australia. All rights reserved.
View copyright/legal information
Please direct any queries or error reports to repository-acg@uwa.edu.au
View copyright/legal information
Please direct any queries or error reports to repository-acg@uwa.edu.au