Separation Technologies for Inorganic Compounds Contained in Industrial Wastewaters Including Metal Ions, Metalloids, Thiosalts, Cyanide, Ammonia and Nitrate

Industrial wastewaters such as mining effluents and landfill leachate may contain metal ions in higher concentrations than those for which the regulatory standards require a treatment for their removal/reduction. Chemical precipitation/settling is the most common method used for removal/reduction of metal ions (e.g. iron, lead, copper, nickel, zinc, aluminum, manganese, etc.). Separation of metalloids (e.g. arsenic, selenium, molybdenum, antimony, etc.) can be achieved by co-adsorption onto iron or aluminum. Thiosalts, incomplete anoxysulphur compounds and cyanide often require the addition of a strong oxidation reagent. Biological nitrification and denitrification are conventional methods for removal of ammonia and nitrate. Respectively as industry accepts and often prefers to use conventional methods as proven and best available technology economically achievable (BATEA), depending on the site conditions and requirements. Emerging technologies such as membrane technologies (e.g. nanofiltration, reverse osmosis, etc.) have only been recently applied to many sites. Innovative approaches, such as snow making, are also used to separate ammonia and metal ions from wastewaters. Innovations have progressed on developing either new technologies or new approaches for mode of application of known technologies. Mode of application could vary from active methods, where pumps and pipes are used and the process takes place in reactors under controlled conditions, or passive methods, where the use of pipes and pumps is eliminated or limited. Wetlands (natural or engineered) and peat filters are often considered as passive methods. Conventional, emerging and innovative separation technologies and application of passive and active methods as well as capabilities and limitation of processes are discussed.

Keywords: Heavy metals, Metalloids, Ammonia-nitrate removal, Cyanide destruction, Thiosalts, Landfill leachate treatment, Mining effluents, Acid mine drainage, High density sludge process, BATEA, Chemical precipitation, Lime neutralization, Passive treatment, Biological treatment, Sulphate reducing bacteria, Wetland, Peat filter, Waste management, Ion exchange, Membrane technologies.