Amphiphilic Thiol Polymer Nanogel Removes Environmentally Relevant Mercury Species from Both Produced Water and Hydrocarbons.

Technologies for removal of mercury from produced water and hydrocarbon phases are desired by oil and gas production facilities, oil refineries, and petrochemical plants. Herein, we synthesize and demonstrate the efficacy of an amphiphilic, thiol-abundant (11.8 wt % S, as thiol) polymer nanogel that can remove environmentally relevant mercury species from both produced water and the liquid hydrocarbon. The nanogel disperses in both aqueous and hydrocarbon phases. It has a high sorption affinity for dissolved Hg(II) complexes and Hg-dissolved organic matter complexes found in produced water and elemental (Hg0) and soluble Hg-alkyl thiol species found in hydrocarbons. X-ray absorption spectroscopy analysis indicates that the sorbed mercury is transformed to a surface-bound Hg(SR)2 species in both water and hydrocarbon regardless of its initial speciation. The nanogel had high affinity to native mercury species present in real produced water (>99.5% removal) and in natural gas condensate (>85% removal) samples, removing majority of the mercury species using only a 50 mg L-1 applied dose. This thiolated amphiphilic polymeric nanogel has significant potential to remove environmentally relevant mercury species from both water and hydrocarbon at low applied doses, outperforming reported sorbents like sulfur-impregnated activated carbons because of the mass of accessible thiol groups in the nanogel.

Mercury Removal from Wastewater Using Cysteamine Functionalized Membranes.

This study demonstrates a three-step process consisting of primary pre-filtration followed by ultrafiltration (UF) and adsorption with thiol-functionalized microfiltration membranes (thiol membranes) to effectively remove mercury sulfide nanoparticles (HgS NPs) and dissolved mercury (Hg2+) from wastewater. Thiol membranes were synthesized by incorporating either cysteine (Cys) or cysteamine (CysM) precursors onto polyacrylic acid (PAA)-functionalized polyvinylidene fluoride membranes. Carbodiimide chemistry was used to cross-link thiol (-SH) groups on membranes for metal adsorption. The thiol membranes and intermediates of the synthesis were tested for permeability and long-term mercury removal using synthetic waters and industrial wastewater spiked with HgS NPs and a Hg2+ salt. Results show that treatment of the spiked wastewater with a UF membrane removed HgS NPs to below the method detection level (<2 ppb) for up to 12.5 h of operation. Flux reductions that occurred during the experiment were reversible by washing with water, suggesting negligible permanent fouling. Dissolved Hg2+ species were removed to non-detection levels by passing the UF-treated wastewater through a CysM thiol membrane. The adsorption efficiency in this long-term study (>20 h) was approximately 97%. Addition of Ca2+ cations reduced the adsorption efficiencies to 82% for the CysM membrane and to 40% for the Cys membrane. The inferior performance of Cys membranes may be explained by the presence of a carboxyl (-COOH) functional group in Cys, which may interfere in the adsorption process in the presence of multiple cations because of multication absorption. CysM membranes may therefore be more effective for treatment of wastewater than Cys membranes. Focused ion beam characterization of a CysM membrane cross section demonstrates that the adsorption of heavy metals is not limited to the membrane surface but takes place across the entire pore length. Experimental results for adsorptions of selected heavy metals on thiol membranes over a wide range of operating conditions could be predicted with modeling. These results show promising potential industrial applications of thiol-functionalized membranes.

Impact of mercury speciation on its removal from water by activated carbon and organoclay.

Mercury (Hg) speciation can affect its removal efficiency by adsorbents. This study assessed the removal of dissolved inorganic Hg(II) species (Hg(II)*), ß-HgS nanoparticles (HgS NP), and Hg complexed with dissolved organic matter (Hg-DOM) by three sorbents: activated carbon (AC), sulfur-impregnated activated carbon (SAC), and organoclay (OC). The effect of ionic composition, solution ionic strength, and natural organic matter (NOM) concentration on the removal of each Hg species was also evaluated. The three adsorbents were all effective in removing Hg(II)*, Hg-DOM, and HgS NPs. Increasing ionic strength decreased the removal of Hg(II)* species due to the formation of ionic Hg species with lower affinity for the sorbents. Added NOM decreased the removal of Hg(II)* and HgS NPs by all sorbents with the OC sorbent being most susceptible to NOM fouling. On a surface area-normalized basis, the OC removed all types of Hg species better than the AC and SAC samples. Moreover, adsorbed Hg-DOM transformed to a ß-HgS phase on the OC, but not for AC and SAC. These studies indicate that both Hg speciation and the water quality parameters need to be considered when designing sorbent-based emission controls to meet Hg removal targets.