Mercury recycling using air borne nanoparticles, sea salt electrochemistry operated by sunlight

Mercury despite its key uses in various field poses certain toxic global pollutants to health and environment. One of the recommendation for reduction of mercury (Hg) is that of mercury containing lamps. Elemental gaseous mercury exist in atmosphere through anthropogenic activities which later undergoes photochemical transformation leading to its deposition on earth and aquatic surface. Important sources of mercury include mercury-containing lamps such as fluorescent lamps, high –intensity discharge lamps and compact fluorescent lamps.

Existing compact fluorescent lamps recycling processes are aimed at reducing human exposure and recycling of all components of lamps from glass to mercury safely. These conventional recycling processes include; physical separation, thermal-desorption of mercury, heterogeneous photo catalytic techniques. Such processes are however energy intensive, time consuming, and produce several undesired waste including some toxic compounds. .

McGill University researchers led by Professor Parisa A. Ariya in Montreal-Canada developed an innovative two-step green technique to remove and recycle mercury from spent compact fluorescent lamps, using a near zero-energy system. The new findings by Hu et al. (2016) appear in the journal of ACS Sustainable Chemistry & Engineering.

The Canadian scientists developed this green technology using naturally occurring air borne particles, which removes and recycles mercury containing lamps with minimal usage of energy. This involves two processes; adsorption of gaseous elemental mercury on iron oxides nanoparticles and electrochemical recovery of elemental mercury. This already low energy operated technology, was further tested to be near energy neutral by using solar lights.

Study results showed magnetite nanoparticles are efficient to removal mercury vapour. Approximately 60 µg mercury vapor can be removed up to 90% by 1.0 g of magnetite nanoparticles, within a time scale of minutes.  The smaller size and bigger BET surface area of synthesized magnetite nanoparticles demonstrate more elevated adsorption capacity. Aged nanoparticles were observed to show better adsorption activity than freshly prepared nanoparticles suggesting partially oxidized surface may elevate adsorption activity.  Both nanoparticles and mercury were recycles using green electrochemical techniques, including sea-salt.

Adsorption capacities of iron oxides are relatively lower than some other adsorbents, however, it is high enough to be a viable efficient interface for industrial usage. Moreover, naturally occurring and strong magnetic properties show great advantages for reduction of waste and waste management.  Investigations on recovery of elemental mercury captured from broken compact fluorescent lamps after electrochemical system showed mercury absorbed by magnetite and maghemite are were recovered from the cathode respectively accounting for 85% and 35% recoveries respectively.  It is also shown that multiple adsorption-recycling steps can be undertaken to increase the recycling efficiency, while the usage of solar energy renders the technique nearly energy neutral.

Regeneration efficiencies of the magnetite nanoparticles ranged from 94% to 112% over 3 regeneration cycles with surface area without lost its adsorption capacity The authors’ results propose that supported iron oxides nanoparticles have great potential for the removal of mercury pollutant in large scale.