Monthly Archives: August 2015

Off-grid energy as a catalyst for site development

Posted on by
Reply

Force Crag Mine, one of the key case study sites for my PhD research is situated half way up a mountain in the English Lake District. It is several miles from the nearest service connection or road – one reason for the use of passive treatment for the polluted water leaving the mine.  But, the site is also host to historic mine buildings and mineral processing equipment owned by the National Trust which operates tours to the site, although these are limited to a few occasions during the warmer months.  Perhaps the site may be more attractive to visitors throughout the year if there was a cafe and other facilities, but what about electricity to boil the kettle and heat to warm the building?

Small scale hydropower was used at Force Crag Mine more than a century ago, and might offer a viable means of generating electricity at the site today.  Cascading waterCascading waters exist in both small watercourses and also flowing from the abandoned mine workings to the treatment system.  In addition, the water flowing from the mine is typically stable in temperature year-round, despite changes in air temperatures.  This might offer a means of providing space heating to visitor facilities – with the help of heat pumps coupled to a hydropower turbine – during the colder months.

These sources of energy are entirely renewable, and might offer a catalyst to improve the amenity value of such a remote yet historically interesting site.

 

 

Characterization of Passive Treatment System Substrates and Potential for Zinc Recovery

Posted on by
Reply

Here is the abstract to my paper presented at the 2015 ICARD conference:

Treatment of mine drainage, during operation and following abandonment, can represent a substantial cost to mine operators and governing authorities. Recovery of valuable metals from mine drainage as part of the treatment process may offset costs, yet this is rarely seen in practice. Industrial-scale metal recovery from mine waters are the preserve of active treatment systems, where reactor conditions are carefully controlled to ensure consistent quality of product. In many circumstances passive treatment is the preferred approach, but close process control is not feasible in these systems. Analysis of substrate from a pilot-scale compost-based passive treatment system, which operated for two years, has been conducted. The treatment system, which harnessed bacterial sulfate reduction to remove metals as their sulfides, showed that under UK regulations used substrate was within the worst-case ‘hazardous’ category due to accumulated zinc, and required pre-treatment due to high total organic carbon. Typical costs for disposal are estimated at 1104 US$/tonne, excluding removal and transport. The majority of zinc accumulates in the upper substrate layer. Greatest zinc concentration of 14,050mg/kg (1.4%w/w) was observed in the 0– 230mm depth layer; whereas in the corresponding lower layer, 230–460mm, zinc was 808mg/kg (0.08%w/w). This suggests that selective ‘harvesting’ of upper substrate layers may reduce waste volumes generated, and higher zinc concentrations may be more amenable to metal recovery. Batch-scale leaching tests have also been undertaken, demonstrating recovery in excess of 83 – 96% of zinc from the upper-layer substrate, depending on acid strength used (20; 100; 500mol/m3 sulfuric acid), within a 100 hour leach test. The results are discussed in the context of the possible economic benefits of metal recovery for passive treatment systems at larger scale.

 

the full paper can be accessed here