The well-established toxic effects of mercury (Hg) compounds on both the environment and human health have led US regulatory agencies to set stringent guidelines for Hg levels in waste effluents; with targeted action limits as low as 12 ng Hg/L for wastewater effluents. Unfortunately, such low levels are not met by any of the water treatment methods currently available. With the emergence of nanotechnology, nano-zerovalent (nZVI) iron particles (characterized by high specific surface area (SSA = 30.5 m2/g) and reactivity) offer the opportunity to improve the previously reported ability of bulk zerovalent iron (ZVI, average (SSA = 0.116 m2/g)) particles to remove Hg from aqueous effluents. Comparative laboratory experiments were therefore conducted to assess the effect of iron particle size on the removal of Hg from aqueous effluents with different solution chemistries. Results obtained from laboratory experiments showed the following: 1)  nZVI show faster oxidation rates resulting in particle coating with hydr(oxide) layers, and therefore, a faster removal of Hg from solution by adsorption rather than by reduction/volatilization. The latter,being dominant initially in the presence of bulk ZVI particles. 2) Differences in major water quality parameters (e.g., pH, ionic strength, and DOC levels) as well as the presence or absence of light affected Hg removal efficiencies by both ZVI and nZVI. 3) Finally, in addition to differences in maximum adsorption capacities determined by batch experiments (96,140 ng/g and 239,020 ng/g for ZVI and nZVI, respectively), nZVI in flow-through sand-packed columns show great promises towards the above-mentioned sub-ppb action limits.

Mercury removal from aqueous effluents using zerovalent iron: Effect of particle size and implications for wastewater treatment

240th National Meeting (2010)

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