Future aspects of mine water treatment
Elina Merta, VTT Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 VTT, Finland, elina.merta(at)vtt.fi
According to Haanpää (2013), in the future different mine water streams will be more and more treated separately which enables more tailored solutions based on water quality, quantity and further water utilization. Treatment solutions are also expected to evolve towards combinations of several unit processes and more controlled process configurations. The selection of technologies available will grow, and continuous on-line monitoring of different water streams will improve the requisites for the optimization of treatment processes.
Simate & Ndlovu (2014) have comprehensively reviewed literature on novel solutions for mine water treatment. Their main message is that neither active nor passive treatment approach alone is suitable as a long term solution and the treatment solutions should be more directed to the recovery of resources from mine water or from the treatment residues. These resources may include metals or other saleable chemicals, electricity, alkali, construction materials, agricultural commodities, adsorbents for industrial wastewater treatment and pigments. Also in their opinion, combinations of two or more technologies, either existing or completely new, are probably needed to build up viable solutions for mine water treatment in the future.
Selective precipitation of metals can be carried out by sulphide precipitation technique or ion exchange. Other options for metal recovery include selective metal precipitating agents, such as dithiocarbamate, Thio-Red and dipropyl dithiophosphate, which have been developed to remove uni- or divalent heavy metals from water. Selective metal precipitating agents produce precipitates having very low solubility and the amount of metallic sludge is low compared to e.g. lime or NaOH alkalinisation. However, the cost of such agents is still relatively high. (Simate & Ndlovu 2014)
A novel Finnish invention CH Collector is based on solid chelating precipitants containing functional groups with replaceable hydrogen atoms together with groups of basic character. The material is able to collect heavy metals present in very low concentrations directly from the solution without pH adjustment or any auxiliary substances. The method has been proven with uranium and scandium. (UEF 2013, Simate & Ndlovu 2014)
Adsorption by nanomaterials is a novel method for selective metal removal and recovery. Nanomaterials, such as magnetic iron nanoparticles and carbon nanotubes (CNT) can be used to separate heavy metals. CNT’s can be treated in different ways depending on the target contaminant. (Simate & Ndlovu 2014)
Membrane distillation is a thermally driven process. Its utilization in water recovery as well as acid and metal concentration has been recently demonstrated for mining wastewater. Sulphuric acid as well as clean water from mine water with high sulphate concentration can be recovered also by electrodialysis. However, this process has not been demonstrated on a large scale. (Simate & Ndlovu 2014)
Mine water treatment can be coupled with electricity production by microbial fuel cells. Yet in research phase, the AMD fuel cell technology could efficiently remove dissolved iron while simultaneously generating electricity. (Simate & Ndlovu 2014)
Recovery of products from alkaline treatment residues is one option to improve the sustainability of this conventional treatment approach.
Haanpää, K. 2013. Pöyry Finland Oy. Kaivosvesien hallinta ja käsittelymenetelmät. Kestävä kaivostoiminta –tutkimusseminaari 21.11.2013, Mutku ry
Simate, G.S. & Ndlovu, S. 2014. Acid mine drainage: Challenges and opportunities. Journal of Environmental Chemical Engineering, 2:1785-1803.
UEF 2013. New method for efficient removal of uranium and other heavy metals from water. University of Eastern Finland. Available: http://www.uef.fi/en/uef/-/new-method-for-efficient-removal-of-uranium-and-other-heavy-metals-from-water