Molecular Design and Spodumene Flotation-A Review.

Spodumene flotation stands as the most commonly used method to concentrate lithium minerals. However, it faces significant challenges related to low collector recoveries and similarity in the surface characteristics of the minerals, which make the effective separation of this valuable mineral difficult. For this reason, numerous researchers have conducted studies to address and confront this problem. In this work, an exhaustive bibliographic search was carried out using keywords and search queries, and the results were structured in three sections according to temporal, methodological, and thematic criteria. The first section covers the period from 1950 to 2004, focusing on experimental tests. The second section covers from 2004 to the present and focuses on flotation tests and measurement analysis. Simultaneously, the third section spans from 2011 to the present and is based on molecular dynamics simulations. Topics covered include spodumene surface properties, the influence of metal ions, pre-treatment techniques, and the use of collectors. Ultimately, molecular dynamics simulations are positioned as a tool that accurately represents experimental phenomena. In this context, specialized software such as Materials Studio or Gromacs prove to be reliable instruments that allow a detailed study of mineral surfaces and other elements to be carried out, which justifies their consideration for future research in this scientific field.

Organelle Genetics in Plants 2.0.

Most of the DNA of eukaryotes is located in the nucleus [...].

Experimental and Simulation Studies on Hematite Interaction with Na-Metasilicate Pentahydrate.

Iron ore is a fundamental pillar in construction globally, however, its process is highly polluting and deposits are becoming less concentrated, making reusing or reprocessing its sources a sustainable solution to the current industry. A rheological analysis was performed to understand the effect of sodium metasilicate on the flow curves of concentrated pulps. The study was carried out in an Anton Paar MCR 102 rheometer, showing that, in a wide range of dosages, the reagent can reduce the yield stress of the slurries, which would result in lower energy costs for transporting the pulps by pumping. To understand the behavior observed experimentally, computational simulation has been used by means of quantum calculations to represent the metasilicate molecule and the molecular dynamics to study the adsorption of metasilicate on the hematite surface. It has been possible to obtain that the adsorption is stable on the surface of hematite, where increasing the concentration of metasilicate increases its adsorption on the surface. The adsorption could be modeled by the Slips model where there is a delay in adsorption at low concentrations and then a saturated value is reached. It was found that metasilicate requires the presence of sodium ions to be adsorbed on the surface by means of a cation bridge-type interaction. It is also possible to identify that it is absorbed by means of hydrogen bridges, but to a lesser extent than the cation bridge. Finally, it is observed that the presence of metasilicate adsorbed on the surface modifies the net surface charge, increasing it and, thus, generating the effect of dispersion of hematite particles which experimentally is observed as a decrease in rheology.

Parental energy-sensing pathways control intergenerational offspring sex determination in the nematode Auanema freiburgensis.

BACKGROUND: Environmental stimuli experienced by the parental generation influence the phenotype of subsequent generations (Demoinet et al., Proc Natl Acad Sci U S A 114:E2689-E2698, 2017; Burton et al., Nat Cell Biol 19:252-257, 2017; Agrawal et al., Nature 401:60-63, 1999). The effects of these stimuli on the parental generation may be passed through the germline, but the mechanisms at the basis of this non-Mendelian type of inheritance, their level of conservation, how they lead to adaptive vs non-adaptive, and intergenerational vs transgenerational inheritance are poorly understood. Here we show that modulation of nutrient-sensing pathways in the parental generation of the nematode Auanema freiburgensis regulates phenotypic plasticity of its offspring. RESULTS: In response to con-specific pheromones indicative of stress, AMP-activated protein kinase (AMPK), mechanistic target of rapamycin complex 1 (mTORC1), and insulin signaling regulate stress resistance and sex determination across one generation, and these effects can be mimicked by pathway modulators. The effectors of these pathways are closely associated with the chromatin, and their regulation affects the chromatin acetylation status in the germline. CONCLUSION: These results suggest that highly conserved metabolic sensors regulate phenotypic plasticity through regulation of subcellular localization of their effectors, leading to changes in chromatin acetylation and epigenetic status of the germline.

Organelle Genetics in Plants.

Eleven published articles (4 reviews, 7 research papers) are collected in the Special Issue entitled "Organelle Genetics in Plants." This selection of papers covers a wide range of topics related to chloroplasts and plant mitochondria research: (i) organellar gene expression (OGE) and, more specifically, chloroplast RNA editing in soybean, mitochondria RNA editing, and intron splicing in soybean during nodulation, as well as the study of the roles of transcriptional and posttranscriptional regulation of OGE in plant adaptation to environmental stress; (ii) analysis of the nuclear integrants of mitochondrial DNA (NUMTs) or plastid DNA (NUPTs); (iii) sequencing and characterization of mitochondrial and chloroplast genomes; (iv) recent advances in plastid genome engineering. Here we summarize the main findings of these works, which represent the latest research on the genetics, genomics, and biotechnology of chloroplasts and mitochondria.

Transcriptional and Post-transcriptional Regulation of Organellar Gene Expression (OGE) and Its Roles in Plant Salt Tolerance.

Given their endosymbiotic origin, chloroplasts and mitochondria genomes harbor only between 100 and 200 genes that encode the proteins involved in organellar gene expression (OGE), photosynthesis, and the electron transport chain. However, as the activity of these organelles also needs a few thousand proteins encoded by the nuclear genome, a close coordination of the gene expression between the nucleus and organelles must exist. In line with this, OGE regulation is crucial for plant growth and development, and is achieved mainly through post-transcriptional mechanisms performed by nuclear genes. In this way, the nucleus controls the activity of organelles and these, in turn, transmit information about their functional state to the nucleus by modulating nuclear expression according to the organelles' physiological requirements. This adjusts organelle function to plant physiological, developmental, or growth demands. Therefore, OGE must appropriately respond to both the endogenous signals and exogenous environmental cues that can jeopardize plant survival. As sessile organisms, plants have to respond to adverse conditions to acclimate and adapt to them. Salinity is a major abiotic stress that negatively affects plant development and growth, disrupts chloroplast and mitochondria function, and leads to reduced yields. Information on the effects that the disturbance of the OGE function has on plant tolerance to salinity is still quite fragmented. Nonetheless, many plant mutants which display altered responses to salinity have been characterized in recent years, and interestingly, several are affected in nuclear genes encoding organelle-localized proteins that regulate the expression of organelle genes. These results strongly support a link between OGE and plant salt tolerance, likely through retrograde signaling. Our review analyzes recent findings on the OGE functions required by plants to respond and tolerate salinity, and highlights the fundamental role that chloroplast and mitochondrion homeostasis plays in plant adaptation to salt stress.

The Characterization of Arabidopsis mterf6 Mutants Reveals a New Role for mTERF6 in Tolerance to Abiotic Stress.

Exposure of plants to abiotic stresses, such as salinity, cold, heat, or drought, affects their growth and development, and can significantly reduce their productivity. Plants have developed adaptive strategies to deal with situations of abiotic stresses with guarantees of success, which have favoured the expansion and functional diversification of different gene families. The family of mitochondrial transcription termination factors (mTERFs), first identified in animals and more recently in plants, is likely a good example of this. In plants, mTERFs are located in chloroplasts and/or mitochondria, participate in the control of organellar gene expression (OGE), and, compared with animals, the mTERF family is expanded. Furthermore, the mutations in some of the hitherto characterised plant mTERFs result in altered responses to salt, high light, heat, or osmotic stress, which suggests a role for these genes in plant adaptation and tolerance to adverse environmental conditions. In this work, we investigated the effect of impaired mTERF6 function on the tolerance of Arabidopsis to salt, osmotic and moderate heat stresses, and on the response to the abscisic acid (ABA) hormone, required for plants to adapt to abiotic stresses. We found that the strong loss-of-function mterf6-2 and mterf6-5 mutants, mainly the former, were hypersensitive to NaCl, mannitol, and ABA during germination and seedling establishment. Additionally, mterf6-5 exhibited a higher sensitivity to moderate heat stress and a lower response to NaCl and ABA later in development. Our computational analysis revealed considerable changes in the mTERF6 transcript levels in plants exposed to different abiotic stresses. Together, our results pinpoint a function for Arabidopsis mTERF6 in the tolerance to adverse environmental conditions, and highlight the importance of plant mTERFs, and hence of OGE homeostasis, for proper acclimation to abiotic stress.

Emerging Roles of Mitochondrial Ribosomal Proteins in Plant Development.

Mitochondria are the powerhouse of eukaryotic cells because they are responsible for energy production through the aerobic respiration required for growth and development. These organelles harbour their own genomes and translational apparatus: mitochondrial ribosomes or mitoribosomes. Deficient mitochondrial translation would impair the activity of this organelle, and is expected to severely perturb different biological processes of eukaryotic organisms. In plants, mitoribosomes consist of three rRNA molecules, encoded by the mitochondrial genome, and an undefined set of ribosomal proteins (mitoRPs), encoded by nuclear and organelle genomes. A detailed functional and structural characterisation of the mitochondrial translation apparatus in plants is currently lacking. In some plant species, presence of small gene families of mitoRPs whose members have functionally diverged has led to the proposal of the heterogeneity of the mitoribosomes. This hypothesis supports a dynamic composition of the mitoribosomes. Information on the effects of the impaired function of mitoRPs on plant development is extremely scarce. Nonetheless, several works have recently reported the phenotypic and molecular characterisation of plant mutants affected in mitoRPs that exhibit alterations in specific development aspects, such as embryogenesis, leaf morphogenesis or the formation of reproductive tissues. Some of these results would be in line with the ribosomal filter hypothesis, which proposes that ribosomes, besides being the machinery responsible for performing translation, are also able to regulate gene expression. This review describes the phenotypic effects on plant development displayed by the mutants characterised to date that are defective in genes which encode mitoRPs. The elucidation of plant mitoRPs functions will provide a better understanding of the mechanisms that control organelle gene expression and their contribution to plant growth and morphogenesis.

Mutations in the plant-conserved MTERF9 alter chloroplast gene expression, development and tolerance to abiotic stress in Arabidopsis thaliana.

The control of organelle gene expression in plants is far from fully understood. The characterization of mutants in Arabidopsis thaliana is assigning an increasingly prominent role to the mitochondrial transcription termination factors (mTERFs) in this process. To gain insight into the function of mTERF genes in plants, we took a reverse genetics approach to identify and characterize A. thaliana mTERF-defective mutants. Here we report the characterization of the mterf9 mutant, affected in an mTERF protein functionally conserved in plants and targeted to chloroplasts. Loss of MTERF9 results in defective chloroplast development, which is likely to cause paleness, stunted growth and reduced mesophyll cell numbers. Expression analysis of different plastid genes revealed reduced levels of plastid-encoded polymerase (PEP)-dependent transcripts and increased levels of transcripts dependent of nucleus-encoded polymerase. mterf9 plants exhibited altered responses to sugars, abscisic acid (ABA), salt and osmotic stresses, and the microarray data analysis showed modifications in MTERF9 expression after salt or mannitol treatments. Our genetic interactions results indicate a functional relationship between MTERF9 and the previously characterized MDA1 gene, and between MDA1 and some plastid ribosomal genes. MDA1 and MTERF9 were upregulated in the mterf9 and mda1 mutants, respectively. Moreover, 21 of 50 genes were commonly co-expressed with MDA1 and MTERF9. The analysis of the MDA1 and MTERF9 promoters showed that both were rich in stress-related cis-regulatory elements. Our results highlight the role of the MTERF9 gene in plant biology and deepens the understanding of the functional relationship of plant mTERF genes.

A regulated auxin minimum is required for seed dispersal in Arabidopsis.

Local hormone maxima are essential for the development of multicellular structures and organs. For example, steroid hormones accumulate in specific cell types of the animal fetus to induce sexual differentiation and concentration peaks of the plant hormone auxin direct organ initiation and mediate tissue patterning. Here we provide an example of a regulated local hormone minimum required during organogenesis. Our results demonstrate that formation of a local auxin minimum is necessary for specification of the valve margin separation layer where Arabidopsis fruit opening takes place. Consequently, ectopic production of auxin, specifically in valve margin cells, leads to a complete loss of proper cell fate determination. The valve margin identity factor INDEHISCENT (IND) is responsible for forming the auxin minimum by coordinating auxin efflux in separation-layer cells. We propose that the simplicity of formation and maintenance make local hormone minima particularly well suited to specify a small number of cells such as the stripes at the valve margins.

Clay Tailings Flocculated in Seawater and Industrial Water: Analysis of Aggregates, Sedimentation, and Supernatant Quality.

High-molecular-weight anionic polyacrylamide was used to analyze the effect of kaolin on the structure of particle aggregates formed in freshwater and seawater. Batch flocculation experiments were performed to determine the size of the flocculated aggregates over time by using focused beam reflectance measurements. Sedimentation tests were performed to analyze the settling rate of the solid-liquid interface and the turbidity of the supernatant. Subsequently, a model that relates the hindered settling rate to the aggregate size was used to determine the mass fractal dimension (Df). Flocculation kinetics revealed that greater amounts of kaolin generated larger aggregates because of its lamellar morphology. The maximum size was between 10 and 20 s of flocculation under all conditions. However, the presence of kaolin reduced the settling rate. The fractal dimension decreased with the increase in the kaolin content, resulting in the formation of irregular and porous aggregates. By contrast, factors such as the flocculation time, water quality, and quartz size had limited influences on the fractal dimension. Seawater produced a clearer supernatant because of its higher ionic strength and precoagulation of particles. Notably, the harmful effect of clays in seawater was reduced.

Compressive Yield Stress of Flocculated Kaolin Suspensions in Seawater.

The mining industry has resorted to using seawater while trying to find a solution to the water shortage, which is severe in some regions. Today, the industry looks to tailings dams to recover more water and, thus, increase recirculation. The migration of interstitial water due to the consolidation of particle networks can give rise to large water mirrors in different dam areas. These pools can contain enough water to be recovered and recirculated if the external stress caused by the weight of the pulp exceeds the compressive yield stress. The density and rheological properties of the discarded pulps determine the feasibility of water expulsion during tailings consolidation. As these conditions are largely established in the thickening stage, it is necessary to revisit operations, looking at the dam as a water source. Thus, a thorough understanding of the compressive properties that determine the level of consolidation of typical pulps and their relationships to aggregate properties, such as size and fractal dimension, is crucial. Here, the effect of two types of water, industrial water and synthetic seawater, on kaolin flocculation, sedimentation rate, yield stress, and compressive yield stress were studied. In addition, the relationship of these properties with the flocculant dose and the resulting aggregate size and fractal dimension was examined. One promising finding to practitioners was that salt and small doses of high molecular weight flocculant improved the consolidation of kaolin slurries under compression. These conditions generated low compressive yield stress compared to fresh water and water with low salt content, favoring the consolidation of the pulps and the release of water.

Bioleaching Modeling-A Review.

The leaching of minerals is one of the main unit operations in the metal dissolution process, and in turn it is a process that generates fewer environmental liabilities compared to pyrometallurgical processes. As an alternative to conventional leaching methods, the use of microorganisms in mineral treatment processes has become widespread in recent decades, due to advantages such as the non-production of emissions or pollution, energy savings, low process costs, products compatible with the environment, and increases in the benefit of low-grade mining deposits. The purpose of this work is to introduce the theoretical foundations associated with modeling the process of bioleaching, mainly the modeling of mineral recovery rates. The different models are collected from models based on conventional leaching dynamics modeling, based on the shrinking core model, where the oxidation process is controlled by diffusion, chemically, or by film diffusion until bioleaching models based on statistical analysis are presented, such as the surface response methodology or the application of machine learning algorithms. Although bioleaching modeling (independent of modeling techniques) of industrial (or large-scale mined) minerals is a fairly developed area, bioleaching modeling applied to rare earth elements is a field with great growth potential in the coming years, as in general bioleaching has the potential to be a more sustainable and environmentally friendly mining method than traditional mining methods.

Differential contributions of ribosomal protein genes to Arabidopsis thaliana leaf development.

In Arabidopsis thaliana, mutations in genes encoding ribosomal proteins (r-proteins) perturb various developmental processes. Whether these perturbations are caused by overall ribosome insufficiency or partial dysfunction of the ribosome caused by deficiency of a particular ribosomal protein is not known. To distinguish these possibilities, a comparative study using several r-protein mutants was required. Here, we identified mutations in 11 r-protein genes from previously isolated denticulata and pointed-leaves mutants. Most of these mutations were associated with pointed leaves, with reduced growth due to a decrease in the number or size of palisade mesophyll and pavement cells. In addition, leaf abaxialization was usually observed when these r-protein mutations were combined with asymmetric leaves1 (as1) and as2 mutations. These results suggest that the establishment of leaf polarity is highly sensitive to ribosome functionality in general. However, several r-protein mutants showed a preference towards a specific developmental defect. For example, rpl4d mutations did not affect cell proliferation but caused strong abaxialization of leaves in the as1 and as2 backgrounds. On the other hand, rps28b enhanced leaf abaxialization of as2 to a weaker extent than expected on the basis of its negative effect on cell proliferation. In addition, hypomorphic rps6a alleles had the strongest effects on most of the phenotypes examined. These findings suggest that deficiencies in these three r-protein genes lead to production of dysfunctional ribosomes. Depending on their structural abnormalities, dysfunctional ribosomes may affect translation of specific transcripts involved in the regulation of some leaf developmental processes.

Analysis of ven3 and ven6 reticulate mutants reveals the importance of arginine biosynthesis in Arabidopsis leaf development.

Arabidopsis thaliana reticulate mutants exhibit differential pigmentation of the veinal and interveinal leaf regions, a visible phenotype that often indicates impaired mesophyll development. We performed a metabolomic analysis of one ven6 (venosa6) and three ven3 reticulate mutants that revealed altered levels of arginine precursors, namely increased ornithine and reduced citrulline levels. In addition, the mutants were more sensitive than the wild-type to exogenous ornithine, and leaf reticulation and mesophyll defects of these mutants were completely rescued by exogenous citrulline. Taken together, these results indicate that ven3 and ven6 mutants experience a blockage of the conversion of ornithine into citrulline in the arginine pathway. Consistent with the participation of VEN3 and VEN6 in the same pathway, the morphological phenotype of ven3 ven6 double mutants was synergistic. Map-based cloning showed that the VEN3 and VEN6 genes encode subunits of Arabidopsis carbamoyl phosphate synthetase (CPS), which is assumed to be required for the conversion of ornithine into citrulline in arginine biosynthesis. Heterologous expression of the Arabidopsis VEN3 and VEN6 genes in a CPS-deficient Escherichia coli strain fully restored bacterial growth in minimal medium, demonstrating the enzymatic activity of the VEN3 and VEN6 proteins, and indicating a conserved role for CPS in these distinct and distant species. Detailed study of the reticulate leaf phenotype in the ven3 and ven6 mutants revealed that mesophyll development is highly sensitive to impaired arginine biosynthesis.

The microRNA pathway genes AGO1, HEN1 and HYL1 participate in leaf proximal-distal, venation and stomatal patterning in Arabidopsis.

We isolated Arabidopsis thaliana mutants with incurved vegetative leaves. Positional cloning of incurvata8 (icu8), icu9 and icu15 has identified them as new loss-of-function alleles of the HYPONASTIC LEAVES1 (HYL1), ARGONAUTE1 (AGO1) and HUA ENHANCER1 (HEN1) genes, respectively, which encode known components of the microRNA pathway. The morphological and histological characterization of these mutants and of dicer-like1-9 indicates that small RNAs participate in the proximal-distal and adaxial-abaxial patterning of leaves, as well as in stomatal number establishment. The abnormal vasculature of ago1 and hyl1 leaves also suggests a role for AGO1 and HYL1 in venation patterning. Our mutants expand the allelic series of AGO1, HYL1 and HEN1, and might help to understand the developmental and cellular significance of miRNA-mediated posttranscriptional regulation.

Unveiling the functions of plastid ribosomal proteins in plant development and abiotic stress tolerance.

Translation of mRNAs into proteins is a universal process and ribosomes are the molecular machinery that carries it out. In eukaryotic cells, ribosomes can be found in the cytoplasm, mitochondria, and also in the chloroplasts of photosynthetic organisms. A number of genetic studies have been performed to determine the function of plastid ribosomal proteins (PRPs). Tobacco has been frequently used as a system to study the ribosomal proteins encoded by the chloroplast genome. In contrast, Arabidopsis thaliana and rice are preferentially used models to study the function of nuclear-encoded PRPs by using direct or reverse genetics approaches. The results of these works have provided a relatively comprehensive catalogue of the roles of PRPs in different plant biology aspects, which highlight that some PRPs are essential, while others are not. The latter ones are involved in chloroplast biogenesis, lateral root formation, leaf morphogenesis, plant growth, photosynthesis or chlorophyll synthesis. Furthermore, small gene families encode some PRPs. In the last few years, an increasing number of findings have revealed a close association between PRPs and tolerance to adverse environmental conditions. Sometimes, the same PRP can be involved in both developmental processes and the response to abiotic stress. The aim of this review is to compile and update the findings hitherto published on the functional analysis of PRPs. The study of the phenotypic effects caused by the disruption of PRPs from different species reveals the involvement of PRPs in different biological processes and highlights the significant impact of plastid translation on plant biology.

Copper Mineral Leaching Mathematical Models-A Review.

Mineral leaching is the key unit operation in metallurgical processes and corresponds to the dissolution of metals. The study of leaching is carried out in many areas, such as geology, agriculture and metallurgy. This paper provides an introduction to the theoretical background regarding the mathematical modelling of the leaching process of copper minerals, establishing an overall picture of the scientific literature on technological developments and the generation of representative mathematical and theoretical models, and indicating the challenges and potential contributions of comprehensive models representing the dynamics of copper mineral leaching.

Reducing Magnesium within Seawater Used in Mineral Processing to Improve Water Recovery and Rheological Properties When Dewatering Clay-Based Tailings.

In areas where access to water for mineral processing is limited, the direct use of seawater in processing has been considered as an alternative to the expense of its desalination. However, efficient flotation of copper sulfides from non-valuable phases is best achieved at a pH > 10.5, and raising the pH of seawater leads to magnesium precipitates that adversely affect subsequent tailings dewatering. Seawater pre-treatment with lime can precipitate the majority of magnesium present, with these solids then being removed by filtration. To understand how such treatment may aid tailings dewatering, treated seawater (TSw) was mixed with raw seawater (Rsw) at different ratios, analyzing the impact on the flocculated settling rate, aggregate size as measured by focused beam reflectance measurement (FBRM), and vane yield stress for two synthetic clay-based tailings. A higher proportion of Tsw (10 mg/L Mg2+) led to larger aggregates and higher settling rates at a fixed dosage, with FBRM suggesting that higher calcium concentrations in Tsw may also favor fines coagulation. The yield stress of concentrated suspensions formed after flocculation decreased with higher proportions of Tsw, a consequence of lower flocculant demand and the reduced presence of precipitates; while the latter is a minor phase by mass, their high impact on rheology reflects a small particle size. Reducing magnesium concentrations in seawater in advance of use in processing offers advantages in the water return from thickening and subsequent underflow transport. However, this may not require complete removal, with blending Tsw and Rsw an option to obtain acceptable industrial performance.

Flocculation of Clay-Based Tailings: Differences of Kaolin and Sodium Montmorillonite in Salt Medium.

Complex gangues and low-quality waters are a concern for the mining industries, particularly in water shortage areas, where the closure of hydric circuits and reduction in water use are essential to maintain the economic and environmental sustainability of mineral processing. This study analyzes the phenomena involved in the water recovery stage, such as sedimentation of clay-based tailings flocculated with anionic polyelectrolyte in industrial water and seawater. Flocculation-sedimentation batch tests were performed to ascertain the aggregate size distribution, the hindered settling rate, and the structure of flocs expressed through their fractal dimension and density. The aggregates' properties were characterized by the Focused Beam Reflectance Measurement (FBRM) and Particle Vision Microscope (PVM) techniques. The impact of the type of water depends on the type of clay that constitutes the suspension. For quartz/kaolin, the highest performance was obtained in industrial water, with bigger aggregates and faster settling rates. However, the tailings composed of quartz/Na-montmorillonite reversed this trend. The type of water impacted the efficiency of primary-particle aggregation. The trials in industrial water generated a portion of non-flocculated particles, which was observed through a bimodal distribution in the unweighted chord-length distribution. This behavior was not observed in seawater, where a perceptible fraction of non-flocculated particles was not found. The additional cationic bonds that offer seawater favor finer primary-particle agglomeration for all tailings types.