Mild Acid Leaching Research Articles

A Clean Process for the Recovery of Potash Fertilizer from Glauconitic Rock via Hydrogen Gas Pre-treatment and Mild Acid Leaching

A Clean Process for the Recovery of Potash Fertilizer from Glauconitic Rock via Hydrogen Gas Pre-treatment and Mild Acid Leaching

Sodium carbonate roasting and mild acid leaching of vanadium titanomagnetite concentrates: Vanadium extraction and residue sodium decrease

Vanadium titanomagnetite is a crucial resource for vanadium and titanium. The traditional process of treating vanadium titanomagnetite concentrates has shortcomings like low vanadium recovery rate and titanium recovery inability, resulting in resource wasting and solid waste discharging. Thus, a new process of Na2CO3 roasting and mild H2SO4 leaching has been proposed. In the concentrates, titanium occurs majorly in titanomagnetite (Fe3-xTixO4, 0≤x≤1) and ilmenite (FeTiO3), vanadium in titanomagnetite and sphene (CaTiSiO5), calcium in sphene, and silicon and aluminum in several minerals. Phases are tuned during Na2CO3 roasting, where V and impurities Al and Si transform into soluble sodium compounds, leachable phase sphene doesn't change, and Ti is enriched in insoluble phases. Then, leached by mild H2SO4, the soluble compounds are almost all leached, and the leaching rates of V, Ca, Al, and Si are 91%, 76%, 84%, and 82%, respectively. The Na2O content in the leaching residue decreases to 1.0 wt%, which enables the residue for Ti extraction. This process is expected to recover V and Ti comprehensively from the vanadium titanomagnetite concentrates. The roasting kinetics are also studied based on CO2 content in the off-gas for a deeper understanding of the mechanism.

Generation of mesoporosity in crystals of zeolite omega by post-synthesis treatments with surfactants

The large-pore zeolite omega (SiAl = 3.1) has been treated with solutions of the surfactant hexadecyltrimethylammonium (CTA) in aqueous ammonia in order to generate intracrystalline mesoporosity. For this purpose, the as-made sample was calcined, transformed in the acid form by ion exchange with ammonium chloride solution followed by calcination, and the resulting acid form subsequently treated with steam at 620 ºC to partially dealuminate the framework. The samples were characterized by XRD, N2 adsorption, TGA, SEM, 29Si and 27Al MAS NMR, pyridine adsorption for acidity determination, and tested in the isomerization/disproportionation of m-xylene. It has been found that partial dealumination of the framework (Si/Al ∼ 7.3) followed by mild acid leaching (HCl = 0.3 M) to remove only the extraframework aluminium species is required for CTA to generate intracrystalline mesopores with a narrow pore diameter of 4 nm. The CTA treatment is ineffective when applied to the acid form (Si/Al ∼ 5.7) or the steamed sample before acid leaching. The concentration of strong acid sites and the average acid strength of the CTA samples are lower than those of the steamed/acid leached sample, which suggests the presence of weak acid sites located at the mesopores. The mesopores greatly enhanced the catalytic activity in the m-xylene conversion by decreasing diffusional constraints. However, the selectivity to the bulky trimethylbenzenes is not improved by the CTA treatment, which suggests that the reaction mainly takes place at the strong acid sites located at the micropores.

The effects of submarine alteration and phosphatization on igneous rocks: Implications for Sr-, Nd-, Pb-isotope studies

A suite of fresh and variably phosphatized submarine volcanic rock samples from NW Pacific seamounts from the Mid Cretaceous were subject of a detailed trace element and isotopic leaching study to examine the effect of phosphate alteration on the use of Sr-, Nd-, and Pb- radiogenic isotope systems. The study particularly focuses on the behavior of the respective parent/daughter element pairs during phosphatization and leaching in order to evaluate the impact on radiogenic ingrowth correction (“age correction”) for old seafloor samples and their use in geochemical studies. For this purpose, variably intense leaching procedures (no leaching; 2 M HCl at 70 °C for 1 h; 6 M HCl at 130 °C for 3 h) were applied to diverse sample materials (rock powder, rock chips and fresh volcanic glass chips).Phosphatization causes significant modification of isotope ratios and elemental proportions of most trace elements including the rare earth elements. As opposed to common seafloor weathering, Rb/Sr decreases in the lavas with increasing phosphatization, while U/Pb enrichment appears slightly amplified. Mild acid leaching of rock chips, however, generally yields Sr, Nd and Pb isotope ratios largely in accordance with values from fresh glass fractions of the same samples and comparable with the results for similarly leached rock powders. Applying original (non-leached) elemental concentration ratios for the radiogenic age correction of mildly leached sample chips produces mixed results for 87Sr/86Srin but generally agrees with expected 143Nd/144Ndin, 206Pb/204Pbin, 207Pb/204Pbin, and 208Pb/204Pbin values.All residua of strongly leached powders yield significantly more radiogenic 206Pb/204Pbm, 143Nd/144Ndm and higher U/Pb than mildly leached rock chips or powders or even non-leached powder of the respective samples, opposite to what is expected when removing seawater-derived secondary phases by stronger acid leaching. We suggest that this enrichment, after removal of most of the magmatic Pb and Nd, reflects minor refractory components that formed in association with the phosphatization and developed high 206Pb/204Pb ratios by radiogenic ingrowth since the eruption of these lavas in the Mid Cretaceous due to high U/Pb.Utilizing modeled parent/daughter ratios based on magma evolution systematics of associated fresh glass yields no satisfying initial isotopic compositions for the strongly leached samples despite supposed removal of secondary isotopic signals upon leaching. Applying the modeled parent/daughter ratios to age correct mildly leached sample chips and powder otherwise slightly improves the accordance with their respective fresh glass fractions for 208Pb/204Pbin but yields similar results as if using the actual parent/daughter ratios for 143Nd/144Ndin, 86Sr/87Srin, 206Pb/204Pbin, and 207Pb/204Pbin.

Clean production technology for effective recovery of vanadium from shale: Interaction between activators and vanadium-loaded minerals

The vanadium in shale is embedded in the muscovite crystal phase, hindering its solubility in leaching process. In this study, a pre-decarburization activated roasting and mild acid leaching process was developed for the recovery of vanadium from shale. The results showed that NaCO3 and K2SO4 were the most effective composite additives to break muscovite into microcline and promote the production of water-soluble vanadate. Thermodynamic analysis exhibited that the pre-decarbonization before roasting was beneficial to the full oxidation of vanadium, and confirmed that the addition of K2SO4 in roasting prevented the formation of insoluble calcium vanadate, but produced anhydrite instead. XRD and SEM-EDS analysis verified that the formations of microcline and anhydrite hindered those of anorthite and calcium vanadate, and it enhanced the leaching efficiency of vanadium to 92% under the condition of mild acid leaching (2% v/v H2SO4 only). This process significantly promoted the amount of water-soluble vanadium so as to reduce the acid consumption in leaching and the content of impurities (i.e., Fe3+, Fe2+). Finally, V2O5 with purity of 99.5% was obtained after ion exchange with resin D201, precipitation by acid ammonium salt and calcination.

Investigation of mechanical and thermal activation on metal extraction from red mud

Red mud is an inevitable and under-utilized byproduct of the aluminium industry. The current study evaluates the effect of mechanical and thermal activation on the acid leaching of red mud. The acid leaching of the pretreated product is followed by acid-base treatment to precipitate the dissolved aluminium values from solution and enrich the residue with Fe and Ti values. Mild acid leaching yielded ~76% aluminium dissolution with 81% silicon removal. The direct acid leaching resulted in dissociation of sodium aluminosilicate; meanwhile, gibbsite phase remains in the residue. The mechanical milling for 1 h enhanced the aluminium dissolution to 89.5% with silicon and iron dissolution of 98.5 and 9.6%, respectively. The silica and iron oxide values were separated before HCl leaching by thermal pretreatment step using microwave heating with NaOH and carbon additives respectively. The sodium silicate and sodium aluminate phases formed during alkali thermal treatment resulted in ~33% silicon and ~ 27% aluminium removal by water washing. Meanwhile, HCl leaching of the water wash residue resulted in 82% aluminium dissolution with 70% recovery and residue containing ~52% Fe2O3, and 28% TiO2 is obtained. The carbothermal reduction yielded iron-rich magnetic concentrate having 48% iron grade with 20% metallic iron, and ~ 83% iron recovery. Leaching of the non-magnetic fraction containing hercynite and fayalite as the major aluminium and silicon bearing phases resulted in 81% aluminium dissolution with overall aluminium recovery of only 37%. Mullite formation is also observed in the precipitate with a high Al/Si molar ratio. The carbothermal route was found as an energy-efficient route, whereas the mechanical milling route yielded maximum Al extraction of ~90% with Fe and Ti content of 41.1% and 16.8% in the residue.

Recovery of TiO2-enriched material from vanadium titano-magnetite concentrates by partial carbon reduction and mild acid leaching

Vanadium-titano magnetite (VTM) is a typical resource in China. The typical method used to recover valuable elements from VTM concentrates is by the blast furnace smelting method. However, titanium is nearly all wasted in the form of blast furnace slag. A new pathway towards obtaining TiO2-enriched material for titanium extraction was designed in this study. The main means is the combination of partial carbon reduction and mild acid leaching. After reduction and leaching, most of the iron and other elements are transferred into solution, leaving a TiO2-enriched residue. Iron and vanadium are reclaimed from the leaching liquid later. In this study, the reduction and leaching parameters were optimized, which included reducing at 1000 °C for 3 h with a carbon addition of 6% by mass of VTM and leaching at 80 °C for 3–4 h by using a 0.2 mol/L H2SO4 solution with a liquid-to-solid ratio of 100:1. The dehydrated residue was mainly rutile containing 72.2 wt% TiO2, which is a satisfactory material for Ti extraction. In addition, upon determining the phase composition and the mass loss after reduction with different dosages of carbon, the reduction route for iron in the magnetite phase and the main gas byproduct during reduction were analyzed. This study provides a new idea for extracting titanium from VTM concentrates.

Core-Shell Magnetic Structure of La1–xSrxMnO $_{3+\delta }$ Nanocrystallites

Magnetic La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+δ</sub> particles of composition x = 0.36 and average size of 40 nm have been prepared from the oxidizing flux of sodium nitrite at ≈500 °C. Detailed magnetic and neutron diffraction measurements have been performed on raw nanoparticles and particles subjected to mild acid leaching. Based on these experiments and X-ray fluorescence analysis of the respective products, we conclude on the core-shell magnetic structure of the molten-salt-prepared particles, consisting of ferromagnetic (FM) ordering in the interior and A-type antiferromagnetic (AFM) ordering in the intermediate shell just below the outermost, magnetically disordered layer. The reason for such complex arrangement, unprecedented in sol-gel-prepared manganite nanoparticles of the same composition, is in a certain radial distribution of La, Sr cations, and an increased oxygen stoichiometry related to the presence of extra oxygen atoms covalently bound at the particle surface. The acid leaching, performed by consecutive treatments with ice-cold solutions of dilute nitric acid and citric acid, removes the overoxidized surface and some outer Sr-richer layers, decreasing the composition to x = 0.32. As a result, the AFM ordering is almost completely suppressed while FM ordering is preserved in the leached nanoparticles.

Beneficial changes in coke properties with alkaline treatment on aluminum-rich mordenite

The impact of the textural properties of mordenite zeolites on the growth and toxicity of coke formed at 350°C during propene transformation is investigated. The addition of intracrystal mesopores by alkaline treatment to a unidimensional zeolite is a simple tool for changing its classical deactivation mode, pore blocking, to a mode more usual on zeolites with a three-dimensional framework, poisoning. This change requires that the zeolite possess a high hierarchy factor, as a result of severe alkaline conditions generating a lot of intracrystal mesopores. Desilication treatment removes part of the Brønsted acid sites and generates extra-framework aluminum species that can block access to the protonic sites and/or enhance their strength, which increases the coking rate. A mild acid leaching is enough to dissolve them. The presence of a few mesopores is sufficient to enhance the access of oxygen to coke, which favor its combustion.

Quantitative structure–mesothelioma potency model optimization for complex mixtures of elongated particles in rat pleura: A retrospective study

ABSTRACTCancer potencies of mineral and synthetic elongated particle mixtures, including asbestos fibers, are influenced by changes in fiber dose composition, bioavailability, and biodurability in combination with relevant cytotoxic dose-response relationships. An extensive rat intrapleural dose characterization data set with a wide variety of elongated particles physicochemical properties facilitated statistical analyses of pleural mesothelioma response data combined from several studies for evaluation of alternative dose-response models. Utilizing logistic regression of individual elongated particle dimensional variations within each test sample, four major findings emerged: (1) Mild acid leaching provides superior prediction of tumor incidence compared to samples that were not leached; (2) sum of the elongated particle surface areas from mildly acid-leached samples provides the optimum holistic dose-response model; (3) progressive removal of dose associated with very short and/or thin elongated particles significantly degrades the resultant particle count and surface area dose-based predictive model fits; and (4) alternative biologically plausible model adjustments provide evidence for reduced potency of elongated particles with aspect ratios less than 8 and lengths greater than 80 µm. Regardless of these adjustments, the optimum predictive models strongly incorporate potency attributable to abundant short elongated particles in proportion to their surface area. Transmission electron microscopy analyses of low-temperature-ashed pleural membrane and lung tissues 5.5 mo post intrapleural exposures do not support hypotheses that short elongated particles that reach the pleural space are rapidly eliminated. Low-aspect-ratio elongated particles were still abundant in pleural membrane tissues but may have reduced potencies due to aggregation tendencies and therefore lower potential for intracellular presence.

Influence of steam-calcination and acid leaching treatment on the VGO hydrocracking performance of faujasite zeolite

The effect of hydrothermal treatment and mild acid leaching on the physico-chemical properties of zeolite Y and its vacuum gas oil hydrocracking performance was investigated. Ultra-stabilized Y (USY) zeolites were obtained by steam-calcination at 500, 600 and 700°C. Steam-treated zeolites were further subjected to a mild acid leaching treatment. The zeolite samples were characterized by XRD, elemental analysis, XPS, N2 adsorption, 29Si and 27Al NMR and FTIR spectroscopy of adsorbed pyridine. Steam-calcination resulted in dealumination and with increasing severity the micropore surface area and the framework Al content decreased. At the same time, the Al content at the zeolite crystal surface increased. Acid leaching improved the pore accessibility and acid properties due to the extraction of extraframework Al species (EFAl). NiMoP-based hydrocracking catalysts were prepared from the modified USY zeolites with alumina as binder. Hydrocracking activities correlated with the acidity of the zeolites. Too severe steam treatment led to depopulation of acid sites and lowered the hydrocracking performance. Hydrocracking catalysts based on the acid leached zeolites were more active than the ones based on the corresponding steam-treated zeolites. It is based on the removal of agglomerated extraframework Al species that block the access to some of the micro- and mesopores. This study points out that, aside from the acidity, also other parameters such as pore accessibility and the presence of EFAl have considerable influence on the hydrocracking of the heavy molecules in a gas oil feed.

Influence of sulfuric acid baking on leaching of spent Ni–Mo/Al 2O 3 hydro-processing catalyst

A low temperature sulfuric acid baking and mild acid leaching process was explored for maximum dissolution of metal values from a spent Ni–Mo/Al 2O 3 hydro-processing catalyst obtained from a Korean refinery. The spent catalyst was found to be a matrix of γ-Al 2O 3. containing 27.1% Al, 11.6% Mo, 2.5% Ni, 9.7% S, 4.8% C, 1.9% P, 0.4% Si and trace amounts of Co and Fe. Various baking parameters such as baking temperature, sulfuric acid concentration and baking duration were optimized according to 2 3 full factorial method for maximum dissolutions of Mo, Al and Ni during leaching. Under optimum baking conditions (400 °C; 1.28 stoichiometric H 2SO 4; 1 h), > 96% Mo, 99% Al and 95% Ni were readily dissolved from the spent catalyst by 2% v/v H 2SO 4 at 80 °C. Carbon and sulfur analyses of the baked samples and leaching residues indicated only 10–15% of residual hydrocarbons reacted during acid baking, while most of the sulfur (assumed to be metal sulfides) was converted into soluble sulfates/oxy-sulfates. By comparison, direct sulfuric acid leaching of the catalyst resulted in poor dissolution of Mo and Al, even with large excess of acid, thus demonstrating the beneficial effect of sulfuric acid baking.

Formation of Zirconium Diboride (ZrB2) by Room Temperature Mechanochemical Reaction Between ZrO2, B2O3 and Mg.

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Formation of zirconium diboride (ZrB 2) by room temperature mechanochemical reaction between ZrO 2, B 2O 3 and Mg

A mixture of magnesium, boric oxide and zirconium dioxide were mechanically milled under argon for up to 15 h in a laboratory scale ball mill. X-ray diffraction showed that there was an increasing conversion of ZrO 2 to ZrB 2 with milling time with >98% reaction after 15 h. Differential thermal analysis revealed there were multiple, overlapping reactions all of which seemed to be formation of ZrB 2. The energy evolved decreased with milling time and the sample after 15 h milling showed no thermal reaction. After milling, separation of the ZrB 2 from the coproduct MgO was easily achieved by a mild acid leaching leaving essentially pure ZrB 2 with a crystallite size of ∼75 nm.

Final remarks

The impact of the textural properties of mordenite zeolites on the growth and toxicity of coke formed at 350 °C during propene transformation is investigated. The addition of intracrystal mesopores by alkaline treatment to a unidimensional zeolite is a simple tool for changing its classical deactivation mode, pore blocking, to a mode more usual on zeolites with a three-dimensional framework, poisoning. This change requires that the zeolite possess a high hierarchy factor, as a result of severe alkaline conditions generating a lot of intracrystal mesopores. Desilication treatment removes part of the Brønsted acid sites and generates extra-framework aluminum species that can block access to the protonic sites and/or enhance their strength, which increases the coking rate. A mild acid leaching is enough to dissolve them. The presence of a few mesopores is sufficient to enhance the access of oxygen to coke, which favor its combustion.

Production of porous materials by dealumination of Ca-A zeolite

Three conventional methods of dealumination were tested on the alumina-rich Ca-A zeolite. The mild acid leaching and the hydrothermal treatment led to mesoporous materials with a sharp distribution of pore size in the 4 nm region. On the other hand, treatment with ammonium hexafluorosilicate resulted in materials with mesopores of 12 nm in size. The latter technique produced the best thermally resistant materials which exhibited also the largest void volume and the highest cation exchange capacity.

The structure of pumice: An XPS and 27Al MAS NMR study

AbstractIn order to investigate the surface structure of pumice, an amorphous aluminosilicate, samples of pumice and of standards of silica and alumina have been studied by x‐ray photoelectron spectroscopy (XPS). The effect of a mild acid leaching was also considered. The analysis of the Si 2p, Al 2p and O 1s photoelectron peaks and the Si KLL and O KLL Auger peaks indicated that pumice is formed by tetrahedral silica with some units being replaced by aluminate, AlO2−. The acid treatment decreases the alkali and the aluminate ions. X‐ray photoelectron spectra of the valence band of pumices and of standards of Al2O3 and SiO2 agree with the core‐level results. To support the conclusions from the XPS study, magic angle spinning (MAS) 27Al nuclear magnetic resonance (NMR) of pumice was used. The spectrum is indicative of tetrahedrally coordinated aluminium.