The Origin, Physicochemical Properties, and Removal Technology of Metallic Porphyrins from Crude Oils

Crude oil is an indispensable energy feedstock for daily activities, although some amounts of metallic porphyrins components with undesired characteristics have been identified. These constituents are assumed to originate from the geochemical process of chlorophyll and heme derivatives. In addition, their chemical structures have been thoroughly characterized using spectroscopy techniques, while several analytical methods were adopted in the detection and concentration quantification in the crude oils. The metallic porphyrins have several demerits, including the deactivation of used catalysts, contamination of the treated petrochemical products, and corrosion of the industrial equipment. Also, the removal process is considered challenging due to the strong interaction with the asphaltene fraction of crude oil. This review article, therefore, provides brief information on the origin, physicochemical properties, and possible removal technology of metallic porphyrins from crude oil samples. Besides, a better understanding of chemistry contributes a useful insight towards the development and establishment of better futuristic processing technology.

Biophysical and geochemical processes control antagonistically the soil-atmosphere CO2 exchange during biocrust ecological succession in the Tabernas Desert

<p>Biological soil crusts (biocrusts) have been reported to play a considerable role in the global carbon budget through CO<sub>2</sub> uptake by photosynthesis. However, it is still unclear if ecosystems dominated by biocrusts are net carbon sinks. That is mainly because so far, most research have focused on characterizing photosynthesis <em>ex-situ</em>, neglecting the underlying soil component, and particularly the <em>in-situ</em> spatio-temporal variability of soil CO<sub>2</sub> fluxes, which can be substantial. Moreover, it is still unknown how those CO<sub>2</sub> fluxes evolve during the ecological succession of biocrusts and which are the biophysical and geochemical factors that control them. Therefore, this research aimed to (1) identify those factors and (2) describe and explain the evolution of annual cumulative soil CO<sub>2</sub> fluxes over ecological succession in a dryland.</p><p>To this end, we conducted continuous measurements over 2 years of the topsoil CO<sub>2</sub> molar fraction (<em>χ</em><sub>s</sub>) in association with below- and aboveground microclimatic variables in 21 locations representative of the ecological succession of biocrusts, characterized by 5 stages: (1) physical depositional crust; (2) incipient cyanobacteria; (3) mature cyanobacteria; (4) lichen community dominated by <em>Squamarina lentigera</em> and <em>Diploschistes diacapsis</em> and (5) lichen community of <em>Lepraria isidiata</em>. Those measurements were also conducted under plants (<em>Macrochloa tenacissima</em>, <em>Salsola genistoides</em>, and <em>Lygeum spartum</em>). Using spatio-temporal statistics, an explanatory model of <em>χ</em><sub>s </sub>dynamics was calibrated on the first year of data and cross-validated to test prediction on the second year. An explanatory model of annual cumulative fluxes was also developed.</p><p>The biocrust type, soil water content (<em>ϑ</em>) and temperature (<em>T</em><sub>s</sub>) and interactions between those variables explained and predicted efficiently the <em>χ</em><sub>s </sub>dynamics. Among those factors, the effect of <em>ϑ</em> was preponderant and dependent on <em>T</em><sub>s</sub> and antecedent soil moisture conditions. The magnitude of the <em>ϑ</em> effect tended to increase in late successional stages, producing greater CO<sub>2</sub> emissions, most likely as a result of progressive soil organic carbon accumulation resulting in greater substrate availability for microbial respiration, and higher porosity enhancing CO<sub>2</sub> diffusion. The calcite content (and potentially indirectly the pH through a buffering effect of CaCO<sub>3</sub>) also played a role in explaining annual cumulative CO<sub>2 </sub>fluxes. Those fluxes were particularly mitigated where CaCO<sub>3</sub> was abundant, apparently due to a substantial nocturnal uptake of atmospheric CO<sub>2 </sub>by soil (influx) throughout the study. The cumulative annual influx represented up to 115% of the cumulative annual efflux, generating a net annual carbon uptake by soil in some locations. Influxes have been increasingly reported recently from drylands soils, which are now regarded as potential carbon sinks. Those influxes have been attributed to different abiotic processes which are still debated. In this ecosystem, in the light of our observations, we assume that a geochemical process of CO<sub>2</sub> dissolution in soil water followed by CaCO<sub>3 </sub>dissolution that consumes CO<sub>2 </sub>might be involved. If this assumption could be verified, this geochemical process consuming CO<sub>2</sub> would need to be separated from biocrust photosynthesis and respiration, when measuring soil surface CO<sub>2</sub> fluxes, to not overestimate and underestimate respectively the biotic contribution to the global carbon budget.</p>

Jarosite formation in deep Antarctic ice provides a window into acidic, water-limited weathering on Mars

Many interpretations have been proposed to explain the presence of jarosite within Martian surficial sediments, including the possibility that it precipitated within paleo-ice deposits owing to englacial weathering of dust. However, until now a similar geochemical process was not observed on Earth nor in other planetary settings. We report a multi-analytical indication of jarosite formation within deep ice. Below 1000 m depth, jarosite crystals adhering on residual silica-rich particles have been identified in the Talos Dome ice core (East Antarctica) and interpreted as products of weathering involving aeolian dust and acidic atmospheric aerosols. The progressive increase of ice metamorphism and re-crystallization with depth, favours the relocation and concentration of dust and the formation of acidic brines in isolated environments, allowing chemical reactions and mineral neo-formation to occur. This is the first described englacial diagenetic mechanism occurring in deep Antarctic ice and supports the ice-weathering model for jarosite formation on Mars, highlighting the geologic importance of paleo ice-related processes on this planet. Additional implications concern the preservation of dust-related signals in deep ice cores with respect to paleoclimatic reconstructions and the englacial history of meteorites from Antarctic blue ice fields.

Removal of Arsenate and Arsenite in Equimolar Ferrous and Ferric Sulfate Solutions through Mineral Coprecipitation: Formation of Sulfate Green Rust, Goethite, and Lepidocrocite

An improved understanding of in situ mineralization in the presence of dissolved arsenic and both ferrous and ferric iron is necessary because it is an important geochemical process in the fate and transformation of arsenic and iron in groundwater systems. This work aimed at evaluating mineral phases that could form and the related transformation of arsenic species during coprecipitation. We conducted batch tests to precipitate ferrous (133 mM) and ferric (133 mM) ions in sulfate (533 mM) solutions spiked with As (0–100 mM As(V) or As(III)) and titrated with solid NaOH (400 mM). Goethite and lepidocrocite were formed at 0.5–5 mM As(V) or As(III). Only lepidocrocite formed at 10 mM As(III). Only goethite formed in the absence of added As(V) or As(III). Iron (II, III) hydroxysulfate green rust (sulfate green rust or SGR) was formed at 50 mM As(III) at an equilibrium pH of 6.34. X-ray analysis indicated that amorphous solid products were formed at 10–100 mM As(V) or 100 mM As(III). The batch tests showed that As removal ranged from 98.65–100%. Total arsenic concentrations in the formed solid phases increased with the initial solution arsenic concentrations ranging from 1.85–20.7 g kg−1. Substantial oxidation of initially added As(III) to As(V) occurred, whereas As(V) reduction did not occur. This study demonstrates that concentrations and species of arsenic in the parent solution influence the mineralogy of coprecipitated solid phases, which in turn affects As redox transformations.