Nitrogen compounds at mines and quarries:Sources, behaviour and removal from mine and quarry waters - Literature study

Mining wastewaters can contain nitrogen from incomplete detonation of nitrogen rich explosives and from nitrogen containing chemicals used in enrichment processes. Nitrogen released to the wastewaters is a potential environmental risk. Nitrogen can be dangerous for aquatic organisms or more prominently cause eutrophication in receiving waterways. Nitrogen chemistry is complex, allowing numerous chemical and biological reaction paths and compounds. Various techniques have been investigated for nitrogen removal from aqueous solutions, such as industrial and municipal wastewaters. Many of the technologies currently available are not suited for the treatment of mine wastewaters containing low levels of nitrogenous compounds, due to treatment costs or stringent operating parameters. Although biological methods potentially offer an effective and inexpensive option for the removal of nitrogen from wastewaters, in mine applications these techniques may be limited by the temperature dependence, especially in cold regions. Zero-valent metals can be utilised for passive reduction of nitrate in aqueous solution. However, whilst no external energy is required to facilitate N reduction using zero-valent metals, pH buffering or extremely low pH conditions are required to supply adequate protons for the reduction reaction to proceed. Evaporation and aeration techniques are often used for ammonia removal from industrial wastewaters but their use in mine applications is limited by low concentrations, large volumes and requirement for pH control. Membrane technologies are similarly poorly-suited to the treatment of large volumes of mine wastewater. Due to their high cost and substantial operational requirements, membrane technologies are generally employed for the production of high-quality water. Sorption techniques have been thoroughly examined for the removal of nitrogenous contaminants from aqueous solution and they offer an attractive alternative. Sorption technologies offer benefits including the relative simplicity of sorption methods, their economy in application and operation, and the low temperature dependence of sorption reactions. Electrochemical methods can be used to convert nitrogenous compounds to a desired form facilitating nitrogen removal as nitrogen gas or as pure ammonia. Thus, these methods offer a temperature-independent alternative for biological nitrogen removal techniques. In addition, electrochemical processes can be run periodically as necessary and no chemical addition is required. Based on a literature review, a combination of sorption and electrochemical techniques is potentially most promising method for the treatment of large volumes of wastewater containing multiple nitrogenous compounds. The performance of both sorption techniques and electrochemistry enhanced ammonia stripping will be further experimentally studied for the attenuation of multiple nitrogenous compounds in mine wastewater