Modelling the Environmental and Economic Trade-offs of Gangue Management at Nigerian Columbite Processing Plants

Columbite processing in Nigeria generates large volumes of mineral processing gangue containing residual heavy metals and processing chemicals, imposing environmental costs that are rarely internalised by operators. This study models the environmental and economic trade-offs of alternative gangue management strategies at columbite processing plants in Plateau and Nassarawa states. Life cycle assessment methodology was applied to quantify the environmental impacts of three gangue management scenarios: unlined tailings impoundment, engineered lined impoundment with leachate collection, and gangue co-processing for aggregate production. Full cost accounting was used to monetise environmental and remediation liabilities alongside operational costs for each scenario. Data were collected from three processing plants through mass balance surveys, operational cost records, and environmental monitoring programmes. Results demonstrate that unlined tailings impoundment, despite its lowest immediate cost, accumulates environmental liabilities estimated at 2.3 times the capital investment in engineered containment when remediation costs are modelled over a 20-year horizon. Gangue co-processing for aggregate production achieves the highest net present value when aggregate market prices are factored, converting a waste liability into a revenue stream. The study also demonstrates that current gangue management practices result in cumulative heavy metal loading to receiving streams exceeding regulatory thresholds in two of three cases. Policy recommendations include mandatory environmental liability disclosure in mining company financial statements and economic incentives for gangue valorisation. Keywords: gangue management, columbite processing, life cycle assessment, Nigeria, environmental liability.