RESUMEN
The depletion of valuable mineral reserves has rendered effluents generated from mining and industrial processing activities a promising resource for the production of precious elements. The synthesis and improvement of new adsorbents to extract valuable compounds from industrial wastes and pregnant leach solutions, besides increasing wealth, can play a significant role in reducing environmental concerns. In this work, a new and low-cost adsorbent for the selective extraction of rhenium (perrhenate ions, ReO4-) was synthesized by the free-radical polymerization (FRP) of a diallyl dimethylammonium chloride monomer (quaternary amine) in the presence of a crosslinker. Various methods were employed to characterize the polymeric adsorbent. The results revealed that the designed polymeric adsorbent had a high surface area and pores with nano-metric dimensions and a pore volume of 6.4 × 10-3 cm3/g. Four environments-single, binary, multicomponent, and real solutions-were applied to evaluate the adsorbent's performance in the selective separation of Re. Additionally, these environments were used to understand the behavior of molybdenum ions, the primary competitors of perrhenate ions in the ion exchange process. In competitive conditions, using variations in qe,mix/qe, an antagonism phenomenon (qe,mix/qe < 1) occurred due to the inhibitory effect of surface-adsorbed molybdenum ions on the binding of the perrhenate ions. However, across all conditions, the separation values for Re were higher than those for the other studied elements (Mo, Cu, Fe).
RESUMEN
Acid mine drainage (AMD) formation and toxic arsenic (As) pollution are serious environmental problems encountered worldwide. In this study, we investigated the crucial roles played by common secondary mineral phases formed during the natural weathering of pyrite-bearing wastes-soluble salts (melanterite, FeSO4·7H2O) and metal oxides (hematite, Fe2O3)-on AMD formation and As mobility under acidic conditions (pH 1.5-4) prevalent in historic tailings storage facilities, pyrite-bearing rock dumps and AMD-contaminated soils and sediments. Our results using a pyrite-rich natural geological material containing arsenopyrite (FeAsS) showed that melanterite and hematite both directly-by supplying H+ and/or oxidants (Fe3+)-and indirectly-via changes in the nature of oxidation layer formed on pyrite-influenced pyrite oxidation dynamics. Based on SEM-EDS, DRIFT spectroscopy and XPS results, the oxidation layer on pyrite was mainly composed of ferric arsenate and K-Jarosite when melanterite was abundant with/without hematite but changed to Fe-oxyhydroxide/oxide and scorodite when melanterite was low and hematite was present. This study also observed the formation of a mechanically 'strong' coating on pyrite that suppressed the mineral's oxidation. Finally, As mobility under acidic conditions was limited by its precipitation as ferric arsenate, scorodite, or a Fe/Al arsenate phase, including its strong adsorption to Fe-oxyhydroxides/oxides.
RESUMEN
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.