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Coltan Environmental Management

Sustainable restitution/recultivation of artisanal tantalum mining wasteland in Central Africa

Duration: August 2010 - July 2013 (3 years)
Funded by the Volkswagen Foundation, Hannover, Germany
Website of Project:
Pilote site: Gatumba, Ngororero, Western Rwanda

The project is planned for a duration of three years (2010-2013). A pilot phase in 2007/2008 has established a framework for targeted interdisciplinary field and laboratory work on the Gatumba mining district in western Rwanda which will serve as a test ground representative for many similar areas in Central Africa. The first two project years will establish a complete inventory on rocks, soil, water and vegetation, aiming at a thorough understanding of the present state, and of the various processes taking place in the study area, complemented by some specific studies in neighboring Uganda, Burundi and Congo. In year 3, various elements and scenarios will be developed, which can serve as a tool box for planning restitution/recultivation projects with a perspective on improvement of soil fertility in general. Field trials are currently carried out with the objective of an integrated crop management system, including economic evaluation. The local population and administration are actively involved. Regular project meetings take place annually. Workshops on specific research topics are combined with the project meetings and allowed all participants to link their specific knowledge to other disciplines.

Key results and research priorities

Human Health: There is no indication at Gatumba that (past) mining or the abandoned quarries affect public health. Health problems in coltan mining camps in the Kivu province, DR Congo, are not due to mining per se but due to societal disruption that can only be solved by better governance.

Toxic elements: Moderately elevated arsenic and uranium contents have been found in soil, stream sediments and tailing at Gatumba, but surface (stream) water is below WHO safety levels. Precise sources of arsenic and uranium (including its radioactive daughter elements such as radium) have yet to be determined. The pathways of these elements from primary anomalies, dispersion in soil and river sediments to food plants, animals and humans need investigation, as well as possible ways of mitigation.

Erosion: The current mining practice of artisanal ground sluicing destroys large areas of fertile soil. Abandoned quarries, tailings and waste rock in stream valleys are characterized by accelerated erosional processes. Investigations must find mitigation techniques to minimise erosion and large scale spread of mining waste downhill in both active and abandoned mines. Optimal water management must be designed and applied, as known from small-scale mining regions in other parts of the world.

Soil fertility: Agricultural research must develop best practices for rapidly improving the fertility of mine site soils (technosols) as well as of traditional arable land, and for controlling soil erosion. We will study the potentials for accumulation of nutrients through optimised crop rotations (including N2-fixing plant species), applying rock flour from nearby alkaline larvas to improve the soil K status, and incorporating rock phosphates to increase available P contents of soils. We conducted both farmer participatory trials and greenhouse experiments to examine the effect of soil amendments (nutrient-rich plant residues, amended rock fertilisers, compost, mineral fertilisers). A detailed investigation will quantify the availability of organic materials suitable for composting in situ and subsequent use as a substrate for tree nurseries and soil amendment for the recultivation of mining wasteland.

Pot trial with three legume shrubs (Tephrosia vogelii, Cajanus cajan and Leucaena diversifolia) grown on pegmatite dump, technosol and pegmatite dump developing into Gleysol amended with compost, cattle manure and the combination of compost+manure from the Ruhanga mines in Gatumba, western Rwanda

Natural habitat: Forestry and Botany have to develop methods to re-introduce valuable native tree and bush species to mine sites that are not suitable for cultivation. Can parts of the quarries be made islands of special ecological value?

People and sustainable mining: We are currently developing a georeferenced landuse map of selected areas in the Gatumba district which will integrate data from geological, soil, botanical, agricultural and socioeconomic surveys and will be complemented by information from the local population, and mining companies. The whole process will follow a farming systems' approach which will incorporate local capacity. The participation of the local population is central to the project, and we will identify ways of sustainable mining which reconcile the demands from all stakeholders with a long-term perspective. Cost-benefit analysis will be applied to all mitigation measures.