How Relevant Is It to Use Mineral Proxies to Mimic the Atmospheric Reactivity of Natural Dust Samples? A Reactivity Study Using SO2 as Probe Molecule

The experimental investigation of heterogeneous atmospheric processes involving mineral aerosols is extensively performed in the literature using proxy materials. In this work we questioned the validity of using proxies such as Fe2O3, FeOOH, Al2O3, MgO, CaO, TiO2, MnO2, SiO2, and CaCO3 to represent the behavior of complex mixtures of minerals, such as natural desert and volcanic dusts. Five volcanic dusts and three desert dusts were compared to a number of metal oxides, commonly used in the literature to mimic the behavior of desert dusts in the ability to form sulfites and sulfates on the surface exposed to SO2 gas. First, all samples were aged at room temperature, atmospheric pressure, under controlled experimental conditions of 175 ppm SO2 for 1 h under 30% of relative humidity. Second, they were extracted with 1% formalin and analyzed by High-Performance Liquid Chromatography (HPLC) to quantify and compare the amount of sulfites and sulfates formed on their surfaces. It was evidenced that under the experimental conditions of this study neither one selected pure oxide nor a mixture of oxides can adequately typify the behavior of complex mixtures of natural minerals. Therefore, to evaluate the real-life impact of natural dust on atmospheric processes it is of vital importance to work directly with the natural samples, both to observe the real effects of desert and volcanic dusts and to evaluate the relevancy of proposed proxies.

Advances in Methods for Recovery of Ferrous, Alumina, and Silica Nanoparticles from Fly Ash Waste

Fly ash or coal fly ash causes major global pollution in the form of solid waste and is classified as a “hazardous waste”, which is a by-product of thermal power plants produced during electricity production. Si, Al, Fe Ca, and Mg alone form more than 85% of the chemical compounds and glasses of most fly ashes. Fly ash has a chemical composition of 70–90%, as well as glasses of ferrous, alumina, silica, and CaO. Therefore, fly ash could act as a reliable and alternative source for ferrous, alumina, and silica. The ferrous fractions can be recovered by a simple magnetic separation method, while alumina and silica can be extracted by chemical or biological approaches. Alumina extraction is possible using both alkali- and acid-based methods, while silica is extracted by strong alkali, such as NaOH. Chemical extraction has a higher yield than the biological approaches, but the bio-based approaches are more environmentally friendly. Fly ash can also be used for the synthesis of zeolites by NaOH treatment of variable types, as fly ash is rich in alumino-silicates. The present review work deals with the recent advances in the field of the recovery and synthesis of ferrous, alumina, and silica micro and nanoparticles from fly ash.

Bubbles and Dust: Experimental Results of Dissolution Rates of Metal Salts and Glasses From Volcanic Ash Deposits in Terms of Surface Area, Chemistry, and Human Health Impacts

Explosive volcanic eruptions lead to ash deposition and subsequent leaching of contaminants into soils or surface water, impacting flora and fauna, including human health. This study determined the control of ash surface area and chemical composition on ash dissolution rates. Fresh, unhydrated ash samples from four contrasting volcanoes were analyzed in the laboratory. Column leachate tests were used to compare leaching rates over a range of basaltic to andesitic ashes as a function of time and surface area, to analyze the effects of ash deposition. It was found that surface area, measured both geometrically and by multipoint Brunauer-Emmett-Teller analysis, generally increases for a short time, gradually decreases, then increases over the rest of the leaching experiment, due to area to mass ratio fluctuations. After the column leachate tests, postleaching water analyses for elemental compositions were conducted by inductively coupled plasma-mass spectrometry and ion chromatography. Steady state dissolution rates initially decayed rapidly due to the smallest size fraction of ash (dust), which provides a large area of fresh leachable surfaces as well as the rapid dissolution of highly soluble metal salts. Some of the dissolved concentrations of elements relevant to human and ecosystem health such as F, Cd, Se, As, and Cr rose above World Health Organization (WHO) drinking water standards within an hour of experimental leaching. In nature, however, safe consumption standards are further dependent upon bioaccumulation and chronic exposure. As such, individual and recurring ash deposition events have applications to emergency response and preparedness in volcanic regions.

Dynamics of volcanic ash remobilisation by wind through the Patagonian steppe after the eruption of Cordón Caulle, 2011

Wind erosion of freshly-deposited volcanic ash causes persistent storms, strongly affecting ecosystems and human activity. Wind erosion of the volcanic ash was measured up to 17 months after the ash deposition, at 7 sites located within the ash-deposition area. The mass flux was measured up to 1.5 m above ground level. Mass transport rates were over 125 times the soil wind-erosion rates observed before the ash deposition, reaching up to 6.3 kg m^-1 day^-1. Total mass transport of ash during the 17 months ranged between 113.6 and 969.9 kg m^-1 depending on topographic location and wind exposure. The vertical distribution of the mass flux at sites with higher vegetation cover was generally inverted as compared to sites with lower vegetation cover. This situation lasted 7 months and then a shift towards a more uniform vertical distribution was observed, in coincidence with the beginning of the decline of the mass transport rates. Decay rates differed between sites. Despite changes over time, an inverse linear correlation between the mass transports and the mass-flux gradients was found. Both the mass-flux gradients and the average mass-transport rates were not linked with shear-stress partition parameters, but with the ratio: ash-fall thickness to total vegetation cover.