Investigation of Heavy Metal Levels in Tin Mine Wastes and the Implication to Mine Closure Plan: A Case Study of Rutongo Mine, Rwanda

Abstract

Rwanda has not experienced any mine closure since mining operations started in the 1930s. To date, there is no information on good practice mine closure procedures despite the presence of old mining operations. Therefore, this study is the first of its kind to scrutinise the closure plan for Rutongo, a tin mine that has existed for over 80 years and is approaching its mine life. The study seeks to quantify heavy metal levels in mine wastes and suggests a closure plan for waste rock dumps (WRDs) and tailings storage facility (TSF) so as to reduce contamination effects during and after cessation of operations. Geochemical characterization using X-Ray Fluorescence (XRF) and Inductive-Coupled Plasma Mass Spectroscopy (ICP-MS) was conducted. Results indicated the presence of pyrite and arsenopyrite, the deleterious elemental concentration ranging from 120 mg/kg to 710 mg/kg As, 10.32 mg/kg to 22.35 mg/kg Co, and 8.6 mg/kg to 128 mg/kg Cr. When these results are benchmarked against various soil quality standards, it is evident that the mine wastes are contaminated by As and a critical concentration of Cr and Co. A mine closure plan with remediation and containment strategies for bio-accumulation of As, Cr, and Co and use of covers that have a capillary barrier to minimise water percolation, and a top soil that supports vegetation backed by hyper-accumulators was recommended.