Environmental aspects of coal mine drainage: a regional study of Moatize in Mozambique

Sammanfattning: Mozambique is one of the largest coal producers in Africa. Extraction of the coal is carried out in the Moatize district of the Tete province in the center of the country. A surface mining technique is used to extract the coal below ground level. During mining activities, sulfide minerals, which are commonly associated with coal, are exposed to oxygen and water, leading to the generation of acid mine drainage (AMD). AMD is high in acidity and has a high content of metals, metalloids and sulfate that can cause severe damage to the environment. Moatize is inside the lower Zambezi River basin, the pollution that occurs there due to mining activities constituting a risk both for public health and for the water resources. The standard guidelines in Mozambique for wastewater from coal mining are very weak, allowing the coal mining companies to pollute considerably. The prevention, containment and remediation of polluted mine water are measures that should be carried out to avoid the spread of pollution. Prevention is the least expensive strategy, but it cannot always prevent the generation of polluted mine water. Thus containment and treatment need to be put into practice. Both active and passive treatment are used to treat polluted mine water. Since Moatize is a largely unstudied area, both static and leaching tests were carried out to investigate the possibility of AMD being generated. The geochemical processes that could impact on the quality of mine drainage stemming from the waste rock there were assessed. Use of cost-effective methods for the treatment of mine water by use of bioremediation coupled with adsorption, using cassava peels that are readily available in the country as a carbon source and as an adsorbent is proposed. Since climate changes and climate variability can exacerbate the negative impact of surface mining, the possibility of this was assessed. It was found that the production of AMD was likely in at least one of the coal mines in Moatize. The mine water from coal mines in Moatize was found to have a high content of sulfate, calcium, magnesium and manganese. A set of guidelines for coal mine effluents that was developed, based on different guidelines obtained from around the world, was proposed for Mozambique. Sulfate reducing bacteria coupled with adsorption appeared to be appropriate for removing these pollutants. Cassava peels used as adsorbents appeared to be effective in removing calcium, magnesium and manganese. Based on climate data, the period from November on through February was found to be the period in which the pollution load in Moatize was greatest. Since the flow rate in the Revúbué River, which is close to the coal mines, is highly dependent upon the precipitation that occurs during the rainy season, the discharge of polluted mine water should be avoided. To achieve sustainable mining in Moatize, the coal mining companies, the regulators and the stakeholders from water sector there need to work together. A framework for integrating efforts to satisfy the needs of the different stakeholders involved in the water sector in Moatize was proposed.