Mineral Particles in Foliar Fertilizer Formulations Can Improve the Rate of Foliar Uptake

The application of foliar sprays of suspensions of relatively insoluble essential element salts is gradually becoming common, chiefly with the introduction of nano-technology approaches in agriculture. However, there is controversy about the effectiveness of such sparingly soluble nutrient sources as foliar fertilizers. In this work, we focussed on analysing the effect of adding Ca-carbonate (calcite, CaCO3) micro- and nano-particles as model sparingly soluble mineral compounds to foliar fertilizer formulations in terms of increasing the rate of foliar absorption. For these purposes, we carried out short-term foliar application experiments by treating leaves of species with variable surface features and wettability rates. The leaf absorption efficacy of foliar formulations containing a surfactant and model soluble nutrient sources, namely Ca-chloride (CaCl2), magnesium sulphate (MgSO4), potassium nitrate (KNO3), or zinc sulphate (ZnSO4), was evaluated alone or after addition of calcite particles. In general, the combination of the Ca-carbonate particles with an essential element salt had a synergistic effect and improved the absorption of Ca and the nutrient element provided. In light of the positive effects of using calcite particles as foliar formulation adjuvants, dolomite nano- and micro-particles were also tested as foliar formulation additives, and the results were also positive in terms of increasing foliar uptake. The observed nutrient element foliar absorption efficacy can be partially explained by geochemical modelling, which enabled us to predict how these formulations will perform at least in chemical terms. Our results show the major potential of adding mineral particles as foliar formulation additives, but the associated mechanisms of action and possible additional benefits to plants should be characterised in future investigations.

Membrane Distillation-Crystallization for Sustainable Carbon Utilization and Storage

Anthropogenic greenhouse gas emissions from power plants can be limited using postcombustion carbon dioxide capture by amine-based solvents. However, sustainable strategies for the simultaneous utilization and storage of carbon dioxide are limited. In this study, membrane distillation-crystallization is used to facilitate the controllable production of carbonate minerals directly from carbon dioxide-loaded amine solutions and waste materials such as fly ash residues and waste brines from desalination. To identify the most suitable conditions for carbon mineralization, we vary the membrane type, operating conditions, and system configuration. Feed solutions with 30 wt % monoethanolamine are loaded with 5-15% CO2 and heated to 40-50 °C before being dosed with 0.18 M Ca2+ and Mg2+. Membranes with lower surface energy and greater roughness are found to more rapidly promote mineralization due to up to 20% greater vapor flux. Lower operating temperature improves membrane wetting tolerance by 96.2% but simultaneously reduces crystal growth rate by 48.3%. Sweeping gas membrane distillation demonstrates a 71.6% reduction in the mineralization rate and a marginal improvement (37.5%) on membrane wetting tolerance. Mineral identity and growth characteristics are presented, and the analysis is extended to explore the potential improvements for carbon mineralization as well as the feasibility of future implementation.

Minerals Determined a Special Ecological Niche and Selectively Enriched Microbial Species from Bulk Water Communities in Hot Springs

Minerals provide physical niches and supply nutrients or serve as electron donors/acceptors for microorganism survival and growth, and thus minerals and microbes co-evolved. Yet, little is known about how sediment minerals impact microbial community assembly in hot springs and to what extent mineralogical composition influences microbial community composition and diversity. Here the influences of minerals on thermophiles in Tengchong hot springs were revealed by network analysis of field samples, as well as in-situ microcosm experiments with minerals. A molecular ecological network was constructed based on high throughput sequencing data of 16S rRNA gene, with a combination of water geochemistry and sedimentary mineralogical compositions. Six modules were identified and this highly modular network structure represents the microbial preference to different abiotic factors, consequently resulting in niche partitioning in sedimentary communities in hot springs. Diverse mineralogical compositions generated special niches for microbial species. Subsequently, the in-situ microcosm experiments with four minerals (aragonite, albite, K-feldspar, and quartz) and spring water were conducted in a silicate-hosted alkaline spring (i.e., Gmq) and a carbonate-hosted neutral hot spring (i.e., Gxs) for 70 days. Different microbial preferences were observed among different mineral types (carbonate versus silicate). Aragonite microcosms in Gmq spring enriched archaeal genera Sulfophobococcus and Aeropyrum within the order Desulfurococcales by comparison with both in-situ water and silicate microcosms. Sulfophobococcus was also accumulated in Gxs aragonite microcosms, but the contribution to overall dissimilarity is much lower than that in Gmq spring. Besides, Caldimicrobium was a bacterial genus enriched in Gxs aragonite microcosms, in contrast to in-situ water and silicate microcosms, whereas Candidatus Kryptobacter and Thermus were more abundant in silicate microcosms. The differences in microbial accumulations among different mineral types in the same spring implied that mineral chemistry may exert extra deterministic selective pressure in drawing certain species from the bulk water communities, in addition to stochastic absorption on mineral surface. Taken together, our results highlight the special niche partitioning determined by mineralogical compositions and further confirm that minerals could be used as “fishing bait” to enrich certain rare microbial species.

Cadmium removal by bioclastic granules (Lithothamnium calcareum): batch and fixed-bed column systems sorption studies

The potential of Bioclastic Granules - BG (calcium-carbonate-based material) using the algae Lithothamnium calcareum as sorbent for the removal of Cd(II) from aqueous solutions by sorption was evaluated through batch and continuous systems tests using a fixed-bed column. Sorption process variables, in particular pH (2-7), particle size (<38-300 μm), initial BG concentration (0.1-1.0 g L^-1), initial Cd(II) concentrations (5-400 mg L^-1) and contact time (5-240 min), were evaluated. Adsorption isotherm profiles of Cd(II) per BG were similar to an L-type, or Langmuir type, with the adsorption forming a monolayer of approximately 0.61 μm, with a q_max of 188.74 mg g^-1 and k_L of 0.710 L mg^-1. Thomas's model considers that sorption is not limited to a chemical reaction but is controlled by mass transfer at the interface. In the present study, the obtained value of k_Th was 0.895 mL h^-1 mg^-1, reaching a sorption capacity q_o of 124.4 mg g^-1. For the Yoon-Nelson model, it was possible to obtain two important parameters to describe the behavior of the column, the rate constant (k_YN), obtaining a value of 0.09 h^-1 and an τ of 82.12 h corresponding to the time required for sorption to occur of 50% of the solute in the rupture curve. X-ray diffraction and scanning electron microscopy analyses coupled to the X-ray dispersive energy system (SEM/EDS) of the BG after the Cd(II) ion sorption tests evidenced the formation of crystals with the prevalence of a new mineral phase (otavite).