Novel Ion Exchange Materials for Heavy Metals Removal
INVENTION: The novel ion exchange materials are metal sulfide based materials. They are made of inexpensive, non-toxic elements. They can be prepared by solid state or hydrothermal synthesis and are chemically and thermally stable. The current production scale is on the order of grams, however the cost effective manufacturing process is easily scaleable to large quantities. One form of the material is very stable under strongly acidic conditions and can be regenerated by 12M HCl without modifying its ion-exchange capacity.
Mercury and other heavy metal ions like lead and cadmium are present in many aquatic environments and waste streams. Traditional adsorbents like zeolites and clay and activated carbons have low selectivity and weak binding affinity for soft metal ions. Newer heavy metal adsorbents have been synthesized by thiol-group functionalization of clays and resins and have high capacities, but they have very high cost and are relatively unstable due to the thiol groups. The novel materials described here display distinct advantages over the thiol-functionalized adsorbents such as lower preparation cost and better chemical and thermal stability with high exchange capacity for Hg, Pb and Cd.
The materials selectivity for heavy metal ions is unique. The affinity for Hg or Pb remains almost unaffected in presence of hard ions like Na or Ca due to the materials soft sulfide ligands. It is highly selective for Cs and Sr, which are major contaminants in the fission products of nuclear waste. Of particular notability is the high selectivity and remediation capacity for Mercury with a Kd up to 1.1x107 compared to 5x105 for commercial resins. The ion exchange material works excellent not only for high initial concentrations of Hg, Pb and Cd, but it is also effective for elimination of these metal ions at ppb levels. It can remove Hg2+ from water down to concentrations of 0.2 ppb, and works over a wide pH range (3-9). The material is also capable for reduction of Cd concentrations down to ~ 2 ppb.
Potential applications for the materials are; silver recovery from photographic effluents; purification of process water from industries producing electrical lamps, gauges, batteries, chemicals and thermometers; Hg removal from mine waste; ion exchangers in nuclear waste management facilities.
ADVANTAGES: The materials promise very high capacity for removal of heavy metals that are not normally easily removed from water. The environmentally friendly manufacturing process is easily scaleable and cost effective. The ion exchange materials can operate under demanding conditions of temperature and pH.
Mercouri Kanatzidis, Emmanouil Manos and Nan Ding
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