Gold Ore Column Studies with a New Mercury Precipitant

A review on current practices and emerging technologies for sustainable management, sequestration and stabilization of mercury from gold processing streams

This paper presents an overview of unit processes that lead to potential mercury contamination during gold processing, which can pose serious health, environmental and technical concerns. Mercury release in gold processing streams is attributed to its dissolution from mercury bearing gold ores during cyanide leaching, and its mobile nature in the subsequent stages (e.g., carbon adsorption, elution, Zn precipitation/electrowinning, and smelting) and tailing storage facilities. Although retorting prior to smelting and sulphur-impregnated carbon filters have been developed to ensure minimal mercury contamination, these methods deal with gaseous mercury which is highly toxic and still a serious threat for both the environment and workers. Moreover, spent carbon filters containing high mercury concentrations introduce a new environmental issue. Therefore, there is a demonstrated need for safer and more efficient removal and sequestration techniques. Thus, this work includes a review of mercury removal from activated carbon as well as current mercury treatment and stabilization practices including precipitation, adsorption, cementation, ion exchange and solvent extraction. In addition, emerging mercury remediation materials such as nanomaterials and bimetals with a promising potential in sustainable management, sequestration, and stabilization of mercury from aqueous media will be highlighted. In summary, the results show a high mercury removal capacity of the outlined materials and techniques (between 70 to around 100% removal). However, one of the issues that emerges from these studies is the lack of selectivity of reagents for mercury capture from aqueous solutions containing precious metals. In this regard, future studies with more focus on the selective mercury removal from activated carbon, and then its precipitation from solutions using substances with a greater adsorption capacity to mass ratio (suitable for safe disposal), are therefore recommended.

Mesoporous hydroxylapatite/activated carbon bead-on-string nanofibers and their sorption towards Co(ii)

We fabricated mesoporous hydroxylapatite/activated carbon bead-on-string nanofibers from electrospun nanofibers by a hydrothermal method and evaluated their sorption towards Co(ii)viasorption kinetics and isotherms.

Removal of selenite from water using a synthetic dithiolate: an experimental and quantum chemical investigation

Combination of the dithiol N,N'-bis(2-mercaptoethyl)isophthalamide, abbreviated as BDTH2 and as 1, with excess H2SeO3 in aqueous acidic (pH ≈ 1) conditions resulted in precipitation of BDT(S-Se-S) (6), with a (77)Se NMR chemical shift of δ = 675 ppm, and oxidized BDT. When the reaction is conducted under basic conditions Se(IV) is reduced to red Se(0) and oxidized 1. No reaction takes place between 1 and selenate (Se(VI)) under acidic or basic conditions. Compound 6 is stable in air but decomposes to red Se(0) and the disulfide BDT(S-S) (9) with heating and in basic solutions. Mechanisms and energetics of the reactions leading to 6 in aqueous solution were unraveled by extensive calculations at the ωB97X-D/aug-cc-pVTZ-PP level of theory. NMR chemical shift calculations with the gauge-independent atomic orbital (GIAO) method for dimethyl sulfoxide as solvent confirm the generation of 6 (calculated δ value = 677 ppm). These results define the conditions and limitations of using 1 for the removal of selenite from wastewaters. Compound 6 is a rare example of a bidentate selenium dithiolate and provides insight into biological selenium toxicity.

Novel chelating resin with cyanoguanidine group: useful recyclable materials for Hg(II) removal in aqueous environment

A novel chelating resin containing cyanoguanidine moiety has been successfully prepared by the functionalizing reaction of a macroporous bead based on chloromethylated copolymer of styrene-divinylbenzene (CMPS) with dicyandiamide (DCDA) in the presence of phase transfer catalyst. The Fourier transform-infrared spectra (FT-IR) and scanning electron microscopy (SEM) were employed in the characterization of the resulting chelating resin, meanwhile, the adsorption properties of the resin for Hg(II) were investigated by batch and column methods. The results indicated that the resin displayed a marked advantage in Hg(II) binding capacity, and the saturated adsorption capacity estimated from the Langmuir model was dramatically up to 1077 mg g(-1) at 45 °C. Furthermore, it was found that the resin was able to selectively separate Hg(II) from multicomponent solutions with Zn(II), Cu(II), Pb(II) and Mg(II). The desorption process of Hg(II) was tested with different eluents and the ratio of the highest recovery reached to 96% under eluting condition of 1M HCl+10% thiourea. Consequently, the resulting chelating resin would provide a potential application for treatment process of Hg(II) containing wastewater.

Adsorption of Hg2+ from aqueous solution onto polyacrylamide/attapulgite

Polyacrylamide/attapulgite (PAM/ATP) was prepared by the solution polymerization of acrylamide (AM) onto gamma-methacryloxypropyl trimethoxy silane (KH-570)-modified attapulgite (ATP). PAM/ATP was characterized using Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The effects of contact time, adsorbent dosage, and pH of the initial solution on the adsorption capacities for Hg(2+) were investigated. The adsorption process was rapid; 88% of adsorption occurred within 5 min and equilibrium was achieved at around 40 min. The equilibrium data fitted the Langmuir sorption isotherms well, and the maximum adsorption capacity of Hg(2+) onto PAM/ATP was found to be 192.5 mg g(-1). The adsorption kinetics of PAM/ATP fitted a pseudo-second-order kinetic model. Our results suggest that chemisorption processes could be the rate-limiting steps in the process of Hg(2+) adsorption. Hg(2+) adsorbed onto PAM/ATP could be effectively desorbed in hot acetic acid solution, and the adsorption capacity of the regenerated adsorbents could still be maintained at 95% by the sixth cycle.

Low-level mercury removal from groundwater using a synthetic chelating ligand

Mercury is present in many industrial processes at low concentrations and is a cause for concern due to the propensity for mercury to bioaccumulate. As a cumulative toxin, introduction of mercury into the environment at any level has the potential to adversely affect ecologic systems. To date, no commercial precipitants are available that can irreversibly and permanently bind mercury. In the current work, selected commercial reagents were compared alongside the dianionic ligand 1,3-benzenediamidoethanethiolate (BDET(2-)) to test the feasibility of low-level (parts-per-billion, ppb) mercury treatment for groundwater near a chloralkali plant. Of all the reagents examined, only K(2)BDET was capable of reducing mercury concentrations to below instrumental detection limits of 0.05 ppb with the added benefit of producing a stable precipitate.

Cd, Hg, and Pb Compounds of Benzene-1,3-diamidoethanethiol (BDETH(2))

Benzene-1,3-diamidoethanethiol (BDETH2) is an exceptional precipitant for removing soft heavy metals from water. The present work will detail the bonding arrangement of BDETH2 to the metals Cd, Hg, and Pb, along with the full characterization data of the BDET-M compounds. It was found that the Hg compound has a linear S-M-S geometry. The characterization data consisted of Mp, EA, IR, Raman, MS, XANES, EXAFS, and solid-state multinuclear NMR.