Sulfide Tails Management within the Framework of Sustainable Development in Mineral Sand Mines-The Case Study of Sierra Rutile Ltd

Article excerpt

Introduction

Background

Mining contributes to the economic development of many countries in the world (Yilmaz, Kesimal, & Ercjkdi, 2004). Sierra Leone has exceptional geological reserves of mineral sand ore, principally rutile and ilmunite, and mining of the deposits offers significant prospects for generating the much-needed foreign exchange required to revitalize the country's economy. As good as their impact is on the economy, however, mining activities in general have also been a target of environmental criticism.

Mineral sand mining is associated with a variety of environmental and social problems that require sound management strategies to mitigate. This article focuses on the management of sulfide tails as one of the key environmental challenges in mineral sand mining operations. It assesses the impact that the management of sulfide tails resulting from the processing operations of the Sierra Rutile Ltd. (SRL), Sierra Leone's largest mineral processing operation, has on the quality of tailings effluent and the adjacent domestic water pond, from which the company and nearby communities source their domestic water needs. We also reviewed the challenges in sulfide tails management and environmental health risk analysis of sulfide tails management options.

Environmental Health Challenges Resulting from Sulfide Tails Management

Mine tailings containing metal sulfides could have serious environmental impacts if control strategies that prevent the oxidation of sulfide exposed to weathering conditions are not established. Natural oxidation of metal sulfides may generate acid rock drainage (ARD). Mine tailings that are affected by ARD processes are normally characterized by high concentrations of trace metals and sulfates ions in solution and by generally low pH values (pH = 2-4) (Mendez-Ortiz, Carillo-Chavez, & Monroy-Fernandez, 2007). Pyrite oxidizes to produce very acidic waters, which can solubilize heavy metals and other toxic elements and cause them to be transported downstream, eventually ending up in the water systems (Jenkins, Johnson, & Freeman, 2000; Pentreath, 1994). Although acid streams can occur naturally, most are a result of mining activities giving rise to acid mine drainage (Jenkins et al., 2000).

ARD solutions can potentially contaminate surface water and groundwater as well as soils. The extreme acidity is harmful to most aquatic life, and even after neutralization, the precipitates formed by it continue to affect aquatic organisms. Toxic elements, such as copper, cadmium, and zinc are often associated with acidic mine drainage (AMD), contributing substantially to its devastating ecological effects (Cotter & Brigden, 2006).

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Environmental Health Risk Analysis of Sulfide Tails Management Options

Soil cover protection of sulfide tails can achieve an 80% reduction in sulfide oxidation with a single 1.0 m (3.3 ft.) till cover; reduction efficiency increases to 90% with 1.5 m (9.8 ft.) of till cover and to 99% reduction with advance multiple layer covers including an effective low-permeability cover (Swedish Environmental Protection Agency [SEPA], 2000). The major drawback to this method, however, is that at locations with greater depth to the groundwater table there is an obvious risk that the cover will be drained and the transport of oxygen will increase during long dry periods consequently increasing groundwater acidity (Mitigating the Environmental Impact of Mining, 2004).

To evaluate the effectiveness of oxygen-consuming barriers, Tremblay (1994) investigated a 2 m (6.6 ft.) cover of organic waste (85% bark, 10% pulp wood, and 5% sawdust) and reported a decrease in oxygen content with depth of the cover, increase in pH, and decreasing metal release in leachate from the covered areas. Some organic concentration of phenol and tanning, however, was reported that could pose another environmental health challenge. …