Concentrated Sulfuric Acid Research Articles

Characterizations of Fe2O3/TiO2 composites fabricated from titanium slag

In this study, Fe2O3/TiO2 composites were successfully fabricated by a simple approach for treating titanium slag with dilute sulfuric acid, followed by a ball-milling process and calcination at a temperature of 400-800 oC in air. The resultant Fe2O3/TiO2 composites were characterized by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), the N2 adsorption-desorption isotherm, and UV–vis diffuse reflectance spectroscopy. The effects of the concentration of sulfuric acid and the calcinated temperature on the formation of the Fe2O3/TiO2 composites were investigated in detail. The obtained Fe2O3/TiO2 composite has a BET surface area, energy bandgap, and pH point of zero charge of 76.65 m2/g, 2,09 eV, and 8,45, respectively. Therefore, this as-prepared Fe2O3/TiO2 composite could be a promising and cost-effective adsorbent for the effective removal of heavy metals and photodegradation of dyes from an aqueous environment.

Acid dissolution of LiF/(NH4)3AlF6 mixtures obtained in the fluorination of α-spodumene with NH4HF2: Modeling and optimization

Lithium is an essential element in the current energy paradigm shift. Therefore, Li extraction from mineral sources has become a scientific and technological priority. Industrially, the mineral α-spodumene is heated to 1100 °C to obtain phase β and then digested with concentrated sulfuric acid at 250 °C. As an alternative, the extraction of Li from α-spodumene with molten NH4HF2 has been proposed as an efficient alternative method at low temperature (∼160 °C). However, the LiF obtained requires an acid leaching step to be solubilized and to separate the Li from other products. This research presents the modeling and optimization of the acid leaching operating parameters of the LiF/(NH4)3AlF6 mixture. This mixture was obtained by processing α-spodumene with NH4HF2 at low temperatures. The solids were characterized by XRD, SEM/EDS, and the Rietveld method. The leaching operating parameters investigated were solid/liquid ratio, sulfuric acid concentration, and leaching time. (NH4)3AlF6 dissolution and Li extraction were analyzed and modeled separately using artificial neural networks and least squares, respectively. The optimization stage of the process leads to (NH4)3AlF6 dissolution of 99% and Li extractions of 93%, working with 6% (v/v) sulfuric acid solution and an S/L ratio of 30 g/L for 24 min

Evolution of the Bromate Electrolyte Composition in the Course of Its Electroreduction inside a Membrane-Electrode Assembly with a Proton-Exchange Membrane.

The passage of cathodic current through the acidized aqueous bromate solution (catholyte) leads to a negative shift of the average oxidation degree of Br atoms. It means a distribution of Br-containing species in various oxidation states between -1 and +5, which are mutually transformed via numerous protonation/deprotonation, chemical, and redox/electrochemical steps. This process is also accompanied by the change in the proton (H+) concentration, both due to the participation of H+ ions in these steps and due to the H+ flux through the cation-exchange membrane separating the cathodic and anodic compartments. Variations of the composition of the catholyte concentrations of all these components has been analyzed for various initial concentrations of sulfuric acid, cA0 (0.015-0.3 M), and two values of the total concentrations of Br atoms inside the system, ctot (0.1 or 1.0 M of Br atoms), as functions of the average Br-atom oxidation degree, x, under the condition of the thermodynamic equilibrium of the above transformations. It is shown that during the exhaustion of the redox capacity of the catholyte (x pass from 5 to -1), the pH value passes through a maximum. Its height and the corresponding average oxidation state of bromine atoms depend on the initial bromate/acid ratio. The constructed algorithm can be used to select the initial acid content in the bromate catholyte, which is optimal from the point of view of preventing the formation of liquid bromine at the maximum content of electroactive compounds.

One Pot Synthesis of Calcium Sulfate Hemihydrate from Fishbone-derived Carbon

Calcium Sulfate Hemihydrate (CSH) with uniform morphology and high crystallinity were successfully prepared by a precipitation-hydrolysis method in a concentrated sulfuric acid solution containing fishbone-derived carbon. The CSH was produced by carbonization of fishbone powder at 500 °C for 2 h, followed by sulfonation with concentrated sulfuric acid for 3 h. The solid mixture was washed until the pH of 2, then left at room temperature for 3 days. Physical properties of synthesized CSH were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), wavelength dispersive X-ray fluorescence (WDXRF), Scanning Electron Microscope (SEM), nitrogen adsorption-desorption isotherm, and melting point test. It is concluded that the CSH were formed due to hydrolysis of fishbone-derived carbon in a moderately concentrated sulfuric acid solution of carbon-derived fishbone and crystallization into a fibrous octa calcium phosphate (OCP) form. In this research, effect of crystal growth time, effect of pH during the crystal growth, and effect of volume of the solution were also investigated. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Synthesis and performance of plant-based ionic liquids in water-based drilling fluids

In this paper, the ionic liquids Met-1, Met-2, Asp-1 and Asp-2 were prepared by acid-base neutralization reactions with different molar ratios of amino acids (methionine and aspartic acid) and concentrated sulfuric acid as raw materials. Four ionic liquids were formulated into different concentrations of inhibitors, and their hydration inhibition and inhibition mechanism were investigated by anti-expansion experiment, linear swelling experiment and flocculation experiment. The results showed that when the molar ratio of aspartic acid to concentrated sulfuric acid was 1:1.5, which was named Asp-2, and the concentration of Asp-2 was 1.0%, the inhibitor achieved the best hydration inhibition performance on clay with 91.95% anti-swelling rate and 21.37% linear swelling rate. Infrared spectra (FT-IR) analysis, thermogravimetric analysis (TGA), and laser particle size analysis were used to investigate the inhibition mechanism of Asp-2. The results showed that the average particle size of the hydrated soil samples increased by 0.282 μm and the median particle size increased by 2.101 μm after the addition of Asp-2 inhibitor, indicating that Asp-2 inhibitor played a good inhibitory role in the drilling fluid.

Study on the effect of structural sodium dissolution on the physical properties of red mud treated by sulfuric acid

Red mud is a strong alkaline solid waste produced by the alumina industry. Although it has found frequent use in building applications, its sodium content causes unwanted effects like “Frost”, demanding the removal of Na+ from red mud. Effective removal of Na+ can result in improving the performance of red mud as a material and increase its applicability. However, the removal of Na+ remains a key problem that needs to be addressed. In this paper, a comprehensive and systematic study has been carried out on the commonly used method of sulfuric acid dealkalization and its influence on the physical properties of red mud has been investigated. The variation of mineral phase content species in red mud and the mechanism of Na+ removal during acid leaching has been studied by regulating the sulfuric acid concentration. The red mud residues have been characterized using a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and Brunauer Emmett Teller (BET) based on nitrogen adsorption–desorption. The results show that the Na+ leaching yield gradually increases with the increase in sulfuric acid concentration. Further, the Na-H, Na-O, Si-O, and Ca-O bonds in the main Na+ assigned mineral phase cancrinite are broken in a certain order based on the differences of bond energies at different acid concentrations. The results of this study can help to successfully address the issue of treatment of Na+ in bauxite slag and lessen the environmental contamination brought on by the subsequent discharge of waste liquid. Additionally, after treatment, the discharged waste liquid might be converted into usable products. The findings of this work have crucial implications for future-focused research in addition to offering a plausible pathway for ion alterations throughout the red mud dealkalization process.

Hydroxyl-rich porous carbons from sulfated sucrose for supercapacitors

Using sucrose as a precursor, hydroxyl-rich porous carbons are synthesized by concentrated sulfuric acid pre‑carbonization and further thermochemical activation. The activating agents have significant effects on the physicochemical and electrochemical properties of the resultant porous carbons. Compared with NaOH and K2CO3, KOH delivers the strongest pore etching ability, resulting in a specific surface area of the microporous-dominated carbon (C-PH) as high as 2097 m2 g−1 with a pore volume of 1.62 m3 g−1. In a three-electrode system in a basic aqueous electrolyte, when the mass loading of C-PH is 3 and 5 mg, the specific capacitance of 313 and 295 F g−1 is harvested at 1 A g−1, respectively. In a symmetrical-electrode system, when the mass loading is 3, 5, and 7 mg, the simulated device enclosed C-PH achieves the specific capacitance of 281, 265, and 249 F g−1 at 1 A g−1, respectively. In the case of the corresponding loading mass, the device achieves the energy density of 9.7, 9.3, and 8.6 Wh kg−1 at the power density of 253, 240, and 224 W kg−1, respectively. Results demonstrate KOH has the strongest thermochemical pore-making ability and the resultant hydroxyl-rich porous carbon delivers promising potential in constructing high-performance carbon-based supercapacitors.

CuI-catalyzed ligand-free synthesis of 2-aryloxazolo[5,4-b]-5,10,15,20-tetraarylporphyrins

A convenient ligand-free synthetic procedure has been developed to synthesize novel nickel(II) and copper(II) 2-aryloxazolo[5,4-b]-5,10,15,20-tetraarylporphyrins in 60–72% yields by a CuI-catalyzed intramolecular debrominative cyclization of 2-aroylamino-3-bromo-5,10,15,20-tetraarylporphyrins in dimethylsulfoxide containing potassium carbonate as a base. Subsequently, the copper(II) 2-(4-iodophenyl)oxazolo[5,4-b]-5,10,15,20-tetraphenylporphyrin underwent demetallation in the presence of concentrated sulfuric acid and afforded 2-(4-iodophenyl)oxazolo[5,4-b]-5,10,15,20-tetraphenylporphyrin in 75% yield which on zinc insertion using zinc(II) acetate in chloroform-methanol mixture provided zinc(II) 2-(4-iodophenyl)oxazolo[5,4-b]-5,10,15,20-tetraphenylporphyrin in 78% yield. The structures of newly constructed 2-aryloxazolo[5,4-b]-5,10,15,20-tetraarylporphyrins were assigned on the basis of spectral data and single crystal X-ray analysis. On photophysical investigation, these porphyrin analogues exhibit similar electronic properties as reported in the case of β-imidazole/thiazole-fused meso-tetraarylporphyrins.

Evaluation of steam explosion pretreatment on the cellulose nanocrystals (CNCs) yield from poplar wood

The high sulfuric acid concentration used in the hydrolysis of cellulose to isolate cellulose nanocrystals (CNCs) leads to low yields due to the dissolution of both amorphous and semi-crystalline cellulose. The present study explored the use of steam explosion pretreatment before acid hydrolysis to enhance the crystallization of semi-crystalline/ non-crystalline cellulose and generating new CNC precursors with poplar wood as feedstock. The crystallinity of steam exploded poplar wood increased 1.3-fold compared to untreated poplar wood. Consequently, the overall yield of CNCs of steam exploded poplar wood increased 2.5-fold compared to untreated poplar wood. Moreover, the steam explosion pretreatment did not affect the quality of the CNCs with regard to the crystal size, crystallinity, and colloidal stability. Whereas the thermal stability of the CNCs increased due to the steam explosion pretreatment. This study demonstrates a simple and scalable pretreatment step that can significantly improve the CNCs yield from the acid hydrolysis step thereby improving the overall economics and commercial viability.

Towards Photothermal Acid Catalysts Using Eco-Sustainable Sulfonated Carbon Nanoparticles—Part I: Synthesis, Characterization and Catalytic Activity towards Fischer Esterification

The development of photothermal catalysts for biodiesel synthesis reaction (transesterification) requires the production of light-absorbing nanoparticles functionalized with catalytic (acid) groups. Using Stöber method, it is possible to produce resorcinol/formaldehyde resin (RF) nanoparticles, which can be carbonized (pyrolysis in an inert atmosphere) and sulfonated. In this work, vegetable tannins are used as a replacement for synthetic resorcinol in the Stöber synthesis of resin (TF) nanoparticles. The nanoparticles are characterized using DLS, FESEM, TEM and N2 adsorption-desorption isotherms. Both resin and carbon nanoparticles are sulfonated by reaction with concentrated sulfuric acid. The attachment of sulfonic groups is verified by FTIR and EDX. The number of sulfonic groups is measured by acid/base titration and TGA. All sulfonated nanoparticles show catalytic activities towards Fischer esterification of ethanoic acid with ethanol, and high (up to 70%) conversion is obtained. The conversion is lower with TF-based nanoparticles, but the turnover numbers are similar in the RF- and TF-based materials. Sulfonated carbon and resin nanoparticles show higher catalytic activity compared to commercial acidic catalysts (e.g., Nafion®). Photothermal heating of carbon nanoparticles is observed. In Part II, sunflower oil transesterification, catalyzed by sulfonated nanoparticles, is observed. Photothermal catalysis of acetic acid esterification and sunflower oil transesterification is demonstrated.

Effects and mechanism of Fe loading and sulfuric acid concentration on selective catalytic activity of SO42−-CeCO3F-CePO4

BackgroundA denitration catalyst with superior performance was prepared by loading Fe and sulfuric acid treatment, and its reaction mechanism was studied. MethodsThe transition metal Fe was loaded on SO42−-CeCO3F-CePO4 to prepare NH3-SCR denitration catalyst by impregnation. The best performing catalyst was explored by varying the loading ratio of Fe and the concentration of sulphuric acid. Significant findingsIn the range of 300∼400 ℃, the denitration rate reaches more than 90 %. The denitrification activity reaches 91.3 % at 350 ℃, and it has close to 100 % N2 selectivity at 100∼400℃. Appropriate concentrations of Fe and sulfuric acid can promote the full functioning of Ce on the surface of the support, exposing more strongly acid sites. The active substances such as Ce oxide, Fe oxide and Fe sulfate produced on the surface are better dispersed, which can provide more active sites and increase the reaction rate. Brønsted acid site generated by the P-O bond of phosphate in CePO4 was the main active site. At 350 ℃, the catalyst surface followes both the E-R mechanism and the L-H mechanism, and the two mechanisms participated in the denitration reaction.

Flexible Puncture-Resistant Composites for Antistabbing Applications: Silica and Silicon Carbide Nanoparticle-/TPU-Coated Aramid Fabrics.

In harsh environments, it is crucial to design personal protective materials that possess both puncture/cut resistance and chemical resistance. In order to fulfill these requirements, this study introduces an innovative approach that combines hydrophobically modified rigid nanoparticles with thermoplastic polyurethane elastomers. These materials are then laminated with high-performance aramid fabrics through a scraping process, resulting in a multifunctional composite with puncture/cut resistance, superhydrophobicity, self-cleaning properties, and acid/alkali resistance. The quasi-static puncture tests conducted reveal the remarkable performance of the composite. The maximum spike puncture resistance reaches 267.62 N, which is 17.14 times higher than that of the pure fabric (15.61 N). Similarly, the maximum knife puncture resistance reaches 115.02 N, exhibiting a 5.01 times increase compared to that of the pure aramid fabric (22.97 N). Furthermore, the results obtained from the yarn pull-out, fabric burst strength, and tearing experiments demonstrate that the incorporation of rigid nanoparticles significantly enhances the friction between the yarns, enabling a greater number of yarns to participate in the dissipation of impact energy. As a result, the puncture resistance of the fabric is greatly improved. Significantly, the composite exhibits sustained superhydrophobicity even after exposure to harsh chemicals such as concentrated sulfuric acid and sodium hydroxide as well as undergoing cyclic mechanical wear. These findings highlight the composite's exceptional durability and resistance to corrosion. Overall, this study offers insights and methods for the development of multifunctional flexible puncture-resistant equipment for individuals.

Preparation of rare earth modified clay-based solid acid catalysts and their application for biodiesel production from soybean oil

ABSTRACT In this study, catalysts of SO4 2-/ZrO2-La2O3-Hangjin 2# clay (SZLa-HJ) and SO4 2-/ZrO2-CeO2-Hangjin 2# clay (SZCe-HJ) were prepared with La and Ce as cocatalysts respectively. The activity of the catalysts was evaluated based on the conversion of biodiesel, while examining the effects of rare earth doping, sulfuric acid concentration, and calcination temperature. Central composite design optimized the preparation procedure for SZLa-HJ and SZCe-HJ. NH3-TPD, Py-FTIR, EDS, TG, DAT, SEM, XRD and XPS techniques were employed to describe it. The results showed that adding La or Ce to SO4 2-/ZrO2 Hangjin 2# clay effectively controlled the distribution of acid sites by increasing both Bronsted and Lewis acid sites in a way that maintained more Lewis acid sites in the catalyst; this was favorable for transesterification reaction.

Effect of concentration sulfuric acid on alumina extraction from napa soil

West Sumatra is one of Indonesia's provinces with abundant and diverse natural potential. Based on data from the Department of Energy and Mineral Resources, West Sumatra province has a rich potential for metal and non-metallic minerals. Some types of minerals include gold lead (Au), zinc (Zn), manganese (Mn), coal, ironstone, and others. In iron ore, metal minerals contained iron minerals and gangue minerals such as silica and alumina. Napa soil is one of the materials found in West Sumatra containing aluminosilicate with a SiO2/ Al2O3 ratio of 63.20 %/ 16.55 %. It also contains TiO2, CaO, and K2O. Extraction of alumina generally using HCl or H2SO4 solvent. In previous research, HCl has been used as a solvent in extracting alumina from napa soil. Based on the literature search, no one has used H2SO4 as a solvent in the extraction of alumina from napa soil; therefore, it is necessary to conduct research as a material for further study. Therefore, this study will be conducted on variations in the concentration of acid solvents to determine the optimum amount of alumina products in the extraction of alumina in napa soil. In this study, the optimum results obtained alumina extraction with variations in the sulfuric acid concentration at a concentration of 6.0 M, with a % yield of 26.73%. The XRF analysis of alumina extraction showed that the Al2O3 content increased by 72.89%. Characterization of Alumina by FTIR indicated the presence of Al-O, Al-OH.

Processing of Grape Bagasse and Potato Wastes for the Co-Production of Bacterial Cellulose and Gluconic Acid in an Airlift Bioreactor.

The feasibility of using Garnacha Tintorera bagasse and potato wastes as substrate for the co-production of bacterial cellulose (BC) and gluconic acid by Komagataibacter xylinus fermentation was studied. Firstly, the sulfuric acid hydrolysis of bagasse was evaluated depending on the sulfuric acid concentration (2-4%), temperature (105-125 °C), and time (60-180 min). The bagasse hydrolysates showed a low monosaccharide concentration profile: glucose 3.24-5.40 g/L; cellobiose 0.00-0.48 g/L; arabinose 0.66-1.64 g/L and xylose 3.24-5.40 g/L. However, the hydrolysis treatment enhanced the total phenolic content of the bagasse extract (from 4.39 up to 12.72 mg GAE/g dried bagasse). The monosaccharide profile of the culture medium was improved by the addition of potato residues. From a medium containing bagasse-potato powder (50:50 w/w) and optimal hydrolysate conditions (125 °C for 60 min and 2% H2SO4), the composition of glucose increased up to 30.14 g/L. After 8 days of fermentation in an airlift bioreactor by Komagataibacter xylinus, 4 g dried BC/L and 26.41 g gluconic acid/L were obtained with a BC productivity of 0.021 g/L·h, an efficiency of 0.37 g/g and yield of 0.47 g/g. The productivity of gluconic acid was 0.14 g/L·h with an efficiency of 0.93 g/g and yield of 0.72 g/g. This research demonstrates the promising potential of utilizing waste materials, specifically Garnacha Tintorera bagasse and potato residues, as sustainable substrates for the co-production of valuable bioproducts, such as bacterial cellulose and gluconic acid.

Strategies towards a green solvent biorefinery: Efficient delignification of lignocellulosic biomass residues by gamma-valerolactone/water catalyzed system

Biorefineries promote the integral use of lignocellulosic biomass by separating lignin, cellulose, and hemicelluloses, so environmentally friendly solvents with good efficiency in lignin removal at mild conditions (low temperatures and pressures) are under thorough research. This study evaluates the optimization of γ-Valerolactone (GVL) systems using a solvent complying with the principles of green chemistry as an efficient delignification strategy for lignocellulosic biomass residues such as sugarcane bagasse and pine sawdust. First, depithed sugarcane bagasse was delignified by a solvent system composed of GVL/water and a low concentration of sulfuric acid (SA), considering temperature, reaction time, GVL, and SA concentration in the liquor as variables, organized following a 4-factor Draper-Lin Central Composite Design (CCD). Milder treatments compared with literature were applied, with extreme points at 130–180 °C, 40–140 min, 43–77 wt% GVL, and 0–0.01 M SA, respectively. The experimental conditions involving pine sawdust were assessed at the highest delignification point of sugarcane bagasse. Delignification from 75% to 96% was obtained for sugarcane bagasse. In the same conditions, pine sawdust delignification was slightly lower. The solid fraction characterization involved yield, ISO brightness, crystallinity index, intrinsic viscosity in cupriethylenediamine, structural carbohydrates, and lignin content, whereas sugars, byproducts, and degradation products were analyzed in the liquid fraction. The study compares different properties combined into one single combined severity factor. The evaluation also involved optical properties relevant to some uses, such as dissolving pulps or nanocellulose.

Exploring Modified Rice Straw Biochar as a Sustainable Solution for Simultaneous Cr(VI) and Pb(II) Removal from Wastewater: Characterization, Mechanism Insights, and Application Feasibility.

This study aimed to investigate the efficacy of a rice straw biosorbent in batch adsorption for the removal of chromium (Cr(VI)) and lead (Pb(II)) heavy-metal ions from wastewater. The biosorbent was chemically synthesized and activated by using concentrated sulfuric acid. The produced biosorbent was then characterized by using Fourier transform infrared (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analyses, which provided insights into surface morphology and functional groups. The study examined the effects of pH, rice straw dose, ion concentration, and contact time on metal ion adsorption. Optimal conditions for efficient removal (95.57% for Cr(VI) and 85.68% for Pb(II)) were achieved at a pH of 2.0, a biosorbent dose of 2 g/L, an initial concentration of 20 mg/L, and a contact time of 50 min in synthetic solutions. The isotherms and kinetics model fitting results found that both metal ion adsorption processes were multilayer on the hetero surface of rice straw biosorbent via rate diffusion kinetics. Thermodynamic investigations were conducted, and the results strongly indicate that the adsorption process is endothermic and spontaneous. Notably, the results indicated that the highest desorption rate was achieved by adding 0.3 N HCl to the system.

Synthesis, Surface Morphology, Gas Sensor, DSC Technique and Third-Order Behavior of Conducting Polymer.

The compound polyaniline (Poly-ANI) with different concentrations of (H2SO4) sulfuric acid has been synthesized by the chemical polymerization method. The prepared compounds have been characterized using number of techniques including FTIR, FE-SEM, EDS and DSC. Additionally, UV-Vis spectroscopy employed for studying the linear optical properties of polymer with different acid concentrations. Third order optical nonlinearity was characterized using Z-scan at 532nm. The results showed that the nonlinear refractive index has a negative sign. It was observed that the nonlinear refractive index changes in different ratios of H2SO4. The high value of nonlinear refractive index ( ) obtained along Z-axis is cm2/W, and the corresponding is 21.5 × 10-5 esu. Also, the Poly-ANI film shows the response to NH3 gas sensing in the range 20ppm-250ppm and can be used for NH3 sensing application.

Pressure leach of β-spodumene with carbonic acid: Weak acid process for extraction of lithium

This contribution develops a process for recovering lithium from β-spodumene by sequential pressure leach with solutions of carbonic acid, as a replacement for digestion of β-spodumene with concentrated sulfuric acid. Six sequential steps, each operated at 200 °C and 100 bar for 1 h, retrieve 75 % of lithium from the initial feed material. This compares with a 12.6 % Li recovery from a single-stage (batch) operation. We develop both the thermodynamic and mass-transfer models of the leach process and argue that the lithium extraction is mass-transfer controlled. The underlying mechanism involves: (i) near-instantaneous ion exchange between H+ for Li+ at the onset of the digestion; (ii) direct formation of amorphous Li-depleted rinds; (iii) precipitation of secondary minerals, boehmite (AlO(OH)) and skin-forming amorphous silica (SiO2), the latter only in the batch operation; (iv) counter-current diffusion of H+ and Li+ through the surface layer (surface layer = depleted sublayer + precipitation sublayer); (v) dissolution of the surface layer at the solid-solution interface, through the reactions with water. The evidence comes from the near-proportionality between the lithium recovery and mass of dissolved β-spodumene, no detection of keatite-HAlSi2O6, particle morphology, precipitation of amorphous skins of SiO2 decorated with boehmite specks observed by electron microscopy and predicted from thermodynamic modelling as well as from a mass-transfer analysis of the Li-recovery rates. Direct observations confirm the existence of a three-phase reacting system, as predicted from thermodynamic calculations, with the absence of a supercritical fluid phase. Lithium recoveries, of at least 28 % in a single step, are attainable, but only for long contact time of 48 h. Digestion lasting hundreds of hours is needed for the batch process to reach Li extraction corresponding to that of the sequential leach. The challenges for industrial implementation of the process comprise recycling of large amounts of water, avoiding the precipitation of silica that forms rinds, accelerating the hydrolysis of Li-depleted sublayer, concentrating the dilute solutions of Li+ and overcoming hesitance of industry to consider high-pressure treatment.

Nutritional diagnosis of nitrogen and phosphorus in Ocimum basilicum L. plants grown under macronutrient applications

The objective of this work was to assess the nutritional status of basil (Ocimum basilicum L.) plants grown under application of macronutrients, in a Typic Hapludult. The experiment was conducted in Cruz das Almas, BA, Brazil, in a greenhouse. The treatments were based on a Baconian matrix statistical arrangement, in which one of the nutrients is supplied in different quantities, whereas the other nutrients are maintained at the reference rates. Six nutrients, nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S) were evaluated at three different rates. Two additional treatments were used (reference rates; and without nutrient applications), totaling 20 treatments. A completely randomized experimental design with five replications was used, totaling 100 experimental units. Plant material was collected 50 days after treatment applications and dried in an oven for 72 hours. Approximately 0.1 g of dry weight of leaves, stems, and roots were subjected to acid digestion in a mixture of concentrated sulfuric acid and hydrogen peroxide. The digested material was diluted in 100 mL of distilled water to obtain the extract for nutritional diagnosis. The optimal maximum N and P accumulations in basil leaves for high plant performances were 51 and 3.0 g kg-1, respectively. The estimated rates for each nutrient to provide the optimal total N accumulation in basil plants were: N = 235.61, P =91.27, K = 175, S = 41.98 (mg dm-3), Ca = 0.97, and Mg = 0.36 (cmolc dm-3).