Reducing life-cycle costs of passive mine water treatment by recovery of metals from treatment wastes

摘要

In compost bioreactor systems, a commonly deployed technology at passive mine water treatment sites, metals accumulate in the treatment system substrate. Ultimately, this substrate becomes exhausted and requires disposal. An assessment was undertaken using a case study site in northern England, investigating how metal recovery might be used to reduce the whole life-cycle cost of treatment. The large-scale system at Force Crag mine harnesses bacterial sulphate reduction, primarily to remove zinc within a compost substrate.Calculations of the rate of accumulation of zinc within the treatment system suggest that the value of zinc (as a pure metal) may amount to approximately ?7600 after 10 years of operation, at current market prices. More significantly, the compost would be classified under UK legislation as hazardous waste because of the elevated zinc concentration. The cost of disposal of the 840 m3 of compost in the treatment system would consequently be in excess of ?0.8M. Such a high waste disposal cost would have a major influence on whole life-cycle cost of the treatment system, irrespective of exactly how long the system operates before the substrate becomes exhausted. The cost of removal of the zinc from the treatment substrate by washing has been calculated at approximately ?155,000. This would reduce the volume, and therefore cost, of disposal by more than 10 times. Furthermore, it may be possible to re-use the decontaminated compost substrate, although this is an area of further investigation.Data presented in this paper suggest that recovery of metals from treatment system substrates might offer substantial passive treatment system life-cycle cost reductions. At Force Crag, it is estimated that discounted life-cycle costs can be reduced from ?1.63M to ?1.12M over 10 years. Allowances for substrate decontamination processes should therefore be considered by treatment system operators from project inception, in order that these savings can be realised.