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The fluid-driven transformation of chalcopyrite (CuFeS2) into Cu-rich sulfides (e.g., digenite, Cu1.8S; covellite, CuS; and chalcocite, Cu2S) is a complex mineral replacement reaction where the reaction pathway is controlled by the interplay between evolving mineral make-up, texture/porosity, and solution chemistry. This transformation was investigated in CuCl2 + H2SO4 solutions under mild hydrothermal conditions (180 to 300 °C); the reaction kinetics, nature of minerals formed, and oxidation states of aqueous Fe and Cu were followed in-situ in real-time using synchrotron powder X-ray diffraction (PXRD) and X-ray absorption spectroscopy (XAS). These results are corroborated by an analysis of the textures of reaction products from comparative ex-situ quench experiments. The in-situ and ex-situ experiments revealed that: (i) aqueous Cu2+ quickly reduced to Cu+ during chalcopyrite replacement in all experiments, and Fe dissolved as Fe2+; (ii) covellite was the first mineral to form, followed by digenite-high with delayed nucleation; and (iii) a non-quenchable hydrated Fe sulfate mineral (szomolnokite, FeSO4.H2O) formed at 240 °C at relatively low concentrations of added CuCl2, which supressed the formation of digenite-high. The quantitative mineral phase evolution retrieved using in-situ PXRD was modelled using a novel dual power law (dual Avrami approach). Avrami exponents revealed that chalcopyrite replacement proceeded initially via a 3-dimensional growth mechanism, followed by diffusion-controlled growth. This is consistent with initial formation of a porous covellite rim around chalcopyrite, confirmed by the observation of the ex-situ reaction products, followed by a second reaction stage where the transport properties of aqueous Fe (released from the chalcopyrite) and aqueous Cu (added from the initial solution) to and from the reaction front become the rate-limiting step; and these two kinetic stages exist even where covellite was the only replacement product. T

Dissolved organic matter (DOM) plays an important role in soil structure and biogeochemical function development, which are fundamental for the eco-engineering of tailings-soil formation to underpin sustainable tailings rehabilitation. In the present study, we have characterized the DOM composition and its molecular changes in an alkaline Fe ore tailing primed with organic matter (OM) amendment and plant colonization. The results demonstrated that microbial OM decomposition dramatically increased DOM richness and average molecular weight, as well as its degree of unsaturation, aromaticity, and oxidation in the tailings. Plant colonization drove molecular shifts of DOM by depleting the unsaturated compounds with a high value of nominal oxidation state of carbon (NOSC), such as tannin-like and carboxyl-rich polycyclic-like compounds. This may be partially related to their sequestration by secondary Fe–Si minerals formed from rhizosphere-driven mineral weathering. Furthermore, the molecular shifts of DOM may have also resulted from plant-regulated microbial community changes, which further influenced DOM molecules through microbial–DOM interactions. These findings contribute to the understanding of DOM biogeochemistry and ecofunctionality in the tailings during early pedogenesis driven by OM input and pioneer plant/microbial colonization, providing an important basis for the development of strategies and technologies toward the eco-engineering of tailings-soil formation.

Recently, particular attention has been given to metallic waveguides supporting surface plasmons as promising components for integrated optical devices. However, the use of conventional numerical optimization tools for their design is hindered by the intensive computational effort associated with meshing down to the resolution of the thin metallic layer. In this study, the previous three-point second order accurate finite-difference formula suitable for correctly placing thin dielectric layers within coarse grids is extended to fourth order accuracy by using the generalized Douglas scheme, including the case when thin metallic layers supporting surface plasmons lie wholly between sample points. The improved formulation, combined with an imaginary distance procedure, is used to analyze the eigenmodes of both 2D and 3D thin metal films located upon dielectric substrates. Accurate calculation with coarser meshes than those required by the other standard differencing schemes is demonstrated, thus providing both a significant saving in computational resource and an extra degree of freedom in meshing such structures.

The possibility that the cell cytoplasm contains enzymes catalysing RNA biosynthesis was investigated in Landschutz ascites tumour cells. Enzyme fractions were obtained by differential centrifugation of disrupted cell homogenates. The incorporation of (alpha32p) UTP into polyribonucleotides catalysed by such fractions was investigated in reaction mixtures containing primer RNA, ATP, GTP and CTP to stimulate conditions for synthesis of RNA. The microsomal fraction was most active in incorporating (alpha32p) UTP into polyribonucleotides. Experiments in which the microsomal fraction was analysed by sucrose density gradient centrifugation confirmed the particulate nature of the enzyme. An acetone dried powder of the microsomal fraction was prepared and its properties further investigated. The incorporation of (alpha32p) UTP was stimulated by an ATP regenerating system but not by ATP, GTP and CTP in the presence of the latter. The incorporation of (alpha32p) UTP showed a requirement for RNA as a primer and an absolute requirement for Mg2+ ions while Mn2+ ions, spermine and putrescene inhibited the reaction. Alkaline hydrolysis of the reaction products after(alpha32p)UTP incorporation showed mainly UMP residues to be labelled irrespective of whether ATP, GTP and CTP were present in the reaction mixture indicating synthesis of polu U chains. 3H ATP, GTP and CTP were found to be incorporated into polyribonucleotides under the same conditions as (alpha32p) UTP, though individual nucleotides were 3H ATP at increasing substrate concentrations of GTP, CTP and UTP added to the reaction mixtures over the range of concentrations tested. These experiments indicate homopolyribonucleotide synthesis rather than the synthesis of RNA. Extraction of RNA from the reaction mixtures after 3H ribonucleoside 5'-triphosphate incorporation and analysis by sucrose density gradient centrifugation showed no labelling of the ribosomal RNA. The incorporated radioactivity appeared between the 4S regi