Did Salts in Seawater Play an Important Role in the Adsorption of Molecules on Minerals in the Prebiotic Earth? The Case of the Adsorption of Thiocyanate onto Forsterite-91

Thiocyanate may have played as important a role as cyanide in the synthesis of several molecules. However, its concentration in the seas of the prebiotic Earth could have been very low. Thiocyanate was dissolved in two different seawaters: a) a composition that comes close to the seawater of the prebiotic Earth (seawater-B, Ca2+ and Cl-) and b) a seawater (seawater-A, Mg2+ and SO42-) that could be related to the seas of Mars and other moons in the solar system. In addition, forsterite-91 was a very common mineral on the prebiotic Earth and Mars. Two important results are reported in this work: 1) thiocyanate adsorbed onto forsterite-91 and 2) the amount of thiocyanate adsorbed, adsorption thermodynamic, and adsorption kinetic depend on the composition of the artificial seawater. For all experiments, the adsorption was thermodynamically favorable (ΔG < 0). The adsorption data fitted well in the Freundlich and Langmuir-Freundlich models. When dissolving thiocyanate in seawater 4.0-A-Gy and seawater 4.0-B-Gy, the adsorption of thiocyanate onto forsterite-91 was ruled by enthalpy and entropy, respectively. As shown by n values, the thiocyanate/foraterite-91 system is heterogeneous. For all kinetic data, the pseudo-first-order model presented the best fit. The constant rate for thiocyanate dissolved in seawater 4.0-A-Gy was twice that compared to thiocyanate dissolved in seawater 4.0-B-Gy or ultrapure-water. The interaction between thiocyanate and Fe2+ of forsterite-91 was with the nitrogen atom of thiocyanate. In the presence of thiocyanate, sulfate interacts with forsterite-91 as an inner-sphere surface complex, and without thiocyanate as an outer-sphere surface complex.

Main group cyanides: from hydrogen cyanide to cyanido-complexes

Homoleptic cyanide compounds exist of almost all main group elements. While the alkali metals and alkaline earth metals form cyanide salts, the cyanides of the lighter main group elements occur mainly as covalent compounds. This review gives an overview of the status quo of main group element cyanides and cyanido complexes. Information about syntheses are included as well as applications, special substance properties, bond lengths, spectroscopic characteristics and computations. Cyanide chemistry is presented mainly from the field of inorganic chemistry, but aspects of chemical biology and astrophysics are also discussed in relation to cyano compounds.

Potentialities of a mesoporous activated carbon as virus detection probe in aquatic systems

Enteric viruses are widely spread in water environments, some being harmful for human communities. Regular epidemics highlight the usefulness of analysing such viruses in wastewaters as a tool for epidemiologists to monitor the extent of their dissemination among populations. In this context, CNovel™ Powdered Activated Carbon (PAC) was chosen for its high porosity and high adsorption capacity to investigate sorbent ability to be used as part of of virus detection probes. Self-supported PAC Foils (PAC-F), PAC coated Brushes (PAC-B) and PAC Sampler (PAC-S) were used to prospect PAC efficacy in virus adsorption and above all, the feasibility of virus retrieval from them, allowing to further analysis such as molecular analysis quantification. Aiming at the development of a field-operational tool, PAC saturation and reusability were also investigated, as well as PAC-polarisation effect on its adsorption capacity. Our results pointed out that sorbent-based probes exhibited a high adsorption efficacy of spiked Murine Norovirus (MNV-1) in bare 0.1 M NaCl solution (>90 % for PAC-B and >86 % for PAC-F at ≈10⁷ genome unit virus concentration), with no saturation within our experimental framework. On the other hand, polarisation assays using PAC-F as electrode, did not demonstrate any adsorption improvement. Experiments on PAC probes reusability suggested that they should be used three times at the most for a maximum efficiency. Values of virus retrieval were low (up to 11 % with PAC-B and up to 14 % with PAC-F in 0.1 M NaCl virus suspensions), illustrating the need for the techniques to be improved. A preliminary field assay using PAC-S, demonstrated that our catch-and-retrieve protocol yielded to the detection of autochthonous human Norovirus Genogroup I (NoV GI) and Adenovirus (AdV), in wastewaters suggesting its promising application as virus detection tool in such high loaded and complex waters.

Biodegradation of thiocyanate by a native groundwater microbial consortium

Gold ore processing typically generates large amounts of thiocyanate (SCN⁻)-contaminated effluent. When this effluent is stored in unlined tailings dams, contamination of the underlying aquifer can occur. The potential for bioremediation of SCN⁻-contaminated groundwater, either in situ or ex situ, remains largely unexplored. This study aimed to enrich and characterise SCN⁻-degrading microorganisms from mining-contaminated groundwater under a range of culturing conditions. Mildly acidic and suboxic groundwater, containing ∼135 mg L⁻¹ SCN⁻, was collected from an aquifer below an unlined tailings dam. An SCN⁻-degrading consortium was enriched from contaminated groundwater using combinatory amendments of air, glucose and phosphate. Biodegradation occurred in all oxic cultures, except with the sole addition of glucose, but was inhibited by NH₄⁺ and did not occur under anoxic conditions. The SCN⁻-degrading consortium was characterised using 16S and 18S rRNA gene sequencing, identifying a variety of heterotrophic taxa in addition to sulphur-oxidising bacteria. Interestingly, few recognised SCN⁻-degrading taxa were identified in significant abundance. These results provide both proof-of-concept and the required conditions for biostimulation of SCN⁻ degradation in groundwater by native aquifer microorganisms.

Thiocyanate adsorption on ferrihydrite and its fate during ferrihydrite transformation to hematite and goethite

Thiocyanate (SCN(-)) is a toxic contaminant produced by industrial processes such as gold ore cyanidation and coal coking. The potential for remediation by adsorption of SCN(-) on ferrihydrite, the influence of sulfate (SO4(2-)) on SCN(-) adsorption, and the fate of adsorbed SCN(-) during ferrihydrite aging were studied using macroscopic techniques complemented with attenuated total reflectance-Fourier transform infrared analysis (ATR-FTIR), X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Results showed that adsorption of SCN(-) was strongly affected by the concentration of electrolyte (NaNO3) and pH, with decreases in concentration of NaNO3 and pH leading to increased SCN(-) adsorption. The adsorption isotherms can be described by the Langmuir model. While at lower concentrations (0.52-1.04 mM), the presence of SO4(2-) had little impact on SCN(-) adsorption, at a higher concentration (2.08 mM), SCN(-) adsorption was significantly inhibited. ATR-FTIR data confirmed that SCN(-) was bound as an outer-sphere complex on ferrihydrite, and this mechanism was not influenced by changes in pH or electrolyte concentration. XRD data showed that ferrihydrite transformed to a mixture of hematite and goethite at 75 °C and pH 5 in the presence and absence of SCN(-). Partitioning data revealed that during ferrihydrite transformation, all adsorbed SCN(-) was released into solution.

Linz-Donawitz steel slag for the removal of hydrogen sulfide at room temperature

Slags collected from the basic oxygen furnaces of two Linz-Donawitz steel making plants were tested as adsorbents for H(2)S removal at room temperature (298 K). Two different particle size fractions, namely <212 and 212-500 μm, were selected from the original slag samples. Dynamic adsorption tests were carried out using a column-bed configuration and retention capacities were calculated after bed exhaustion. Retention capacities as high as 180 mg of H(2)S g(-1) of slag were attained, in spite of the very low specific surface area of the steel slags. As expected, humidity played a crucial role in the removal of H(2)S. Particle size had also an important effect on the capacity of the adsorption beds. Analysis of the exhausted slags revealed considerable amounts of elemental sulfur on the surface of the particles. Sulfates were also found on the exhausted slags, especially on the 212-500 μm size fractions. The characterization of the slags prior and after the H(2)S adsorption experiments allowed us to postulate plausible mechanisms to understand the outstanding capacity of these steel byproduct for H(2)S adsorption.