scholarly journals A Highly Selective Reagent Scheme for Scheelite Flotation: Polyaspartic Acid and Pb–BHA Complexes

Minerals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 561
Author(s):  
Zhao Wei ◽  
Junhao Fu ◽  
Haisheng Han ◽  
Wei Sun ◽  
Tong Yue ◽  
...  
Keyword(s):  
Crystal Chemistry ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
High Selectivity ◽  
Selective Adsorption ◽  
Mineral Surfaces ◽  
Polyaspartic Acid ◽  
Benzohydroxamic Acid ◽  
Successful Separation ◽  
Selective Reagent

Previous studies have proved that the lead complexes of benzohydroxamic acid (Pb–BHA) are effective collectors of scheelite flotations; however, the separation of scheelite from calcite needs depressants with high selectivity. In this study, we reported a novel depressant for calcite minerals, and Pb–BHA served as the collector of scheelite. The flotation behavior of polyaspartic acid (PASP) in a scheelite and calcite flotation that uses Pb–BHA was determined via flotation experiments. Furthermore, the selective adsorption of PASP on the mineral surfaces and the effect of PASP on the adsorption of Pb–BHA on the mineral surfaces were investigated through zeta potential measurements, X-ray photoelectron spectroscopy (XPS), crystal chemistry calculations, and Fourier transform infrared spectroscopy (FTIR) measurements. Thus, PASP demonstrated high selectivity in both scheelite and calcite and contributed to the successful separation of scheelite from calcite. PASP exhibited a higher adsorption capacity and stronger chemisorption with the active sites of calcium atoms on the calcite surface. The crystal chemistry calculations indicated that the distance of the PASP functional groups matched with the calcium distance of a calcite mineral surface, which can be attributed to the selectivity of PASP. Furthermore, the adsorption of PASP impeded the adsorption of Pb–BHA on the calcite surfaces, whereas the opposite was the case for scheelite. The mutually reinforcing selectivity of PASP and Pb–BHA considerably contributes to the efficient flotation separation of scheelite from calcite.

scholarly journals Activation Mechanism of Lead(II) to Ilmenite Flotation Using Salicylhydroxamic Acid as Collector

Minerals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 567
Author(s):  
Hang Liu ◽  
Wenqing Zhao ◽  
Jihua Zhai ◽  
Xiaolong Lu ◽  
Pan Chen ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Adsorption Mechanism ◽  
Lead Ions ◽  
Activation Mechanism ◽  
Salicylhydroxamic Acid ◽  
Benzohydroxamic Acid ◽  
Adsorption Analysis ◽  
Potential Shifts ◽  
Lead Species

In this study, salicylhydroxamic acid (SHA), which exhibits superior flotation performance to conventional collector benzohydroxamic acid (BHA), was first introduced in ilmenite flotation. The addition of lead(II) can significantly increase the recovery of ilmenite using SHA as collector. Thus, the adsorption mechanism of SHA on lead(II)-activated ilmenite surface was systematically studied using micro-flotation tests, adsorption analysis, zeta potential measurements, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Micro-flotation results revealed that SHA had stronger collecting ability than BHA, and ilmenite floatability could be activated by lead ions with either SHA or BHA as collector. Ilmenite showed good floatability at pH 6–8 (over 90% recovery) in the presence of Pb2+ and SHA. In such conditions, the main lead species of Pb(OH)+ and Pb2+ acted as active sites and caused positive surface potential shifts, thereby increasing the adsorbed amounts of negatively charged SHA on the surface of the mineral. FTIR and XPS analyses suggested that the lead species was chemically adsorbed on the surface of ilmenite to form active sites chelated by SHA. Moreover, the free lead ions in solution might form the Pb–SHA complexes to adsorb on the mineral surface, thereby increasing the floatability of ilmenite.

The effect of acid activation and calcination of halloysite on the efficiency and selectivity of Pb(II), Cd(II), Zn(II) and As(V) uptake

Clay Minerals ◽  
2016 ◽  
Vol 51 (3) ◽  
pp. 385-394 ◽  
Author(s):  
Paulina Maziarz ◽  
Jakub Matusik
Keyword(s):  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Structural Changes ◽  
Selective Adsorption ◽  
Temperature Treatment ◽  
High Temperature Treatment ◽  
Acid Activation ◽  
Subsequent Formation ◽  
X Ray ◽  
Mineral Structure

AbstractThe present study investigated the efficiency and mechanisms of aqueous Pb(II), Cd(II), Zn(II) and As(V) adsorption on natural (H), calcined (HC), and acid-activated halloysite (HA). The XRD and FTIR measurements indicated that the aluminosilicate framework was not affected by high-temperature treatment, in contrast to acid activation, which led to structural changes mainly in the tetrahedral sheet. The sorption of cations on H sample was low, though it was most effective for As(V). The X-ray photoelectron spectroscopy results suggested that removal of As(V) might be related to its reduction to As(III) involving oxidation of Fe(II) present in the mineral structure and/or iron minerals. The calcination enhanced halloysite sorption capacity for cations, while the As(V) sorption decreased. This was due to partial dehydroxylation and the subsequent formation of additional active sites. The acid treatment induced selective adsorption of Pb(II).

The Selective Oxidation of Hydrocarbons on Isolated Iron Active Sites under Ambient Conditions

2019 ◽  
Vol 41 (6) ◽  
pp. 946-946
Author(s):  
Zhengliang Qi Zhengliang Qi ◽  
Junmei Liu Junmei Liu ◽  
Wanwan Guo and Jun Huang Wanwan Guo and Jun Huang
Keyword(s):  
Ionic Liquid ◽  
Activated Carbon ◽  
Carbon Material ◽  
Active Sites ◽  
High Selectivity ◽  
Good Activity ◽  
Ambient Conditions ◽  
Oxidation Of Hydrocarbons ◽  
Fe Catalysts ◽  
Iron Active Sites

The N-doped carbon material supported Fe catalysts were developed for the oxidation of C-H bond of hydrocarbons to ketones and alcohols. The supported Fe catalysts were prepared by pyrolysis of [CMIM]3Fe(CN)6 ionic liquid in activated carbon. And the Fe(Ⅲ)@CN-600 showed good activity and high selectivity for the oxidation of alfa C-H bond of alkylbenzenes. The isolated Fe(Ⅲ) iron active sites should be responsible for the high activity and selectivity for the oxidation of hydrocarbons to ketones. Several ketones were obtained in good to excellent yields. Moreover, cyclohexanone can also be obtained through the oxidation of cyclohexane.

Adsorption of PtCl62− from Hydrochloric Acid Solution by Chemically Modified Lignin Based on Rice Straw

2018 ◽  
Vol 71 (12) ◽  
pp. 931 ◽  
Author(s):  
Baoping Zhang ◽  
Bowen Shen ◽  
Meichen Guo ◽  
Yun Liu
Keyword(s):  
Hydrochloric Acid ◽  
Acid Solution ◽  
Rice Straw ◽  
Hydrochloric Acid Solution ◽  
Photoelectron Spectroscopy ◽  
Selective Adsorption ◽  
Adsorption Time ◽  
Langmuir Isotherm Model ◽  
Pseudo Second Order ◽  
Modified Lignin

A novel adsorbent with the properties of selective adsorption based on rice straw was used to adsorb PtCl62− from hydrochloric acid solution by batch sorption. Many influencing factors for PtCl62− adsorption, such as initial concentration of PtCl62−, adsorption time, and concentration of hydrochloric acid, were optimized. The results suggested that the saturation adsorption capacity of PtCl62− was 218.8mgg−1 and the equilibrium adsorption time was 120min. The adsorbent had excellent selectivity on PtCl62− when the concentration of hydrochloric acid was lower than 0.5molL−1. The adsorption fitted well with the Langmuir isotherm model and pseudo-second-order kinetics model. The adsorption mechanism was investigated by FT-IR and X-ray photoelectron spectroscopy analyses and it indicated that PtIV was reduced to PtII by hydroxy groups and then coordinated with N through ion exchange between Cl− and PtCl42−.

scholarly journals Multiplicity of Active-Site in Heterogeneous Ziegler-Natta Catalyst and Its Correlation with Polymer Microstructure

1970 ◽  
Vol 46 (4) ◽  
pp. 487-494
Author(s):  
ATM Kamrul Hasan
Keyword(s):  
Molecular Weight ◽  
Computer Simulation ◽  
Active Site ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Chain Structure ◽  
Surface Complexes ◽  
Polymer Microstructure ◽  
Natta Catalyst ◽  
Ziegler Natta Catalyst

Multiplicity of active-site in heterogeneous Ziegler-Natta catalysts and its correlation with polymer microstructure was studied through the surface structure analysis of catalyst by computer simulation of X-ray Photoelectron Spectroscopy (XPS) data and microstructure investigation of polypropylene chains based on the deconvolution of the molecular weight distribution curves by multiple Flory most probable distributions using Gel Permeation Chromatography (GPC) method. The number and relative intensities of these peaks were found correlated to the distribution of multiple active sites. In this investigation, four individual categories of active sites were identified, each of which yields polypropylene with unique properties of molecular weight and chain structure different from other active sites. The reason of the multiplicity of active sites was determined by the presence of different locations of surface titanium species coordinated with other surface atoms or molecules. These different surface complexes of active species determine the multiple active site nature of catalyst which replicates the microtacticity, molecular weight and chain microstructure distribution of polymer. Keywords: Ziegler-Natta catalyst; Multiple active sites; Flory components; Computer simulation; Deconvolution; MWD. DOI: http://dx.doi.org/10.3329/bjsir.v46i4.9596 BJSIR 2011; 46(4): 487-494

Conversion of methane to ethylene

1997 ◽  
Vol 75 (4) ◽  
pp. 465-468
Author(s):  
B.K. Miremadi ◽  
K. Colbow ◽  
S. Roy Morrison
Keyword(s):  
Ethylene Production ◽  
Active Sites ◽  
High Selectivity ◽  
Oxidation Catalyst ◽  
Ethylene Oxidation ◽  
Lithium Aluminate ◽  
Co Catalyst ◽  
Conversion Of Methane ◽  
Ethylene Selectivity ◽  
Intermediate Value

A lithium aluminate – MgO catalyst has been found to convert methane to ethylene with a high selectivity. The rate of conversion increased when a MoO3 co-catalyst was used to remove the poisoning products. It is shown that for optimum conversion and selectivity to ethylene, the oxygen pressure should be at an intermediate value, high enough to provide active sites but low enough to avoid ethylene oxidation. Thus the oxygen should be "bled-in" along the catalyst bed. In demonstration of these concepts we have shown a 28.6% CH4 conversion with 63.2% ethylene selectivity and 9.8% ethane, producing a C2 yield of about 21.4%. Keywords: methane oxidation, methane conversion, ethylene production, oxidation catalyst, aluminate catalyst.

scholarly journals A microporous Ce-based MOF with the octahedron cage for highly selective adsorption towards xenon over krypton

RSC Advances ◽  
2021 ◽  
Vol 11 (49) ◽  
pp. 30918-30924
Author(s):  
Xiaoling Wu ◽  
Zi-Jian Li ◽  
He Zhou ◽  
Lin Li ◽  
Zhenghua Qian ◽  
...  
Keyword(s):  
Thermal Stability ◽  
High Selectivity ◽  
Selective Adsorption ◽  
Inert Gases ◽  
Geometric Features ◽  
Promising Candidate ◽  
Organic Framework

A high selectivity of Xe over Kr at 293 K was achieved by a 3D Ce-based organic framework due to the geometric features. Favorable thermal stability and ionizing radio-resistance render it a promising candidate for radioactive inert gases treatment.

scholarly journals Mechanisms of Two-Electron and Four-Electron Electrochemical Oxygen Reduction Reactions at Nitrogen-Doped Reduced Graphene Oxide

2019 ◽  
Author(s):  
Hyo Won Kim ◽  
Vanessa Jane Bukas ◽  
Hun Park ◽  
Sojung Park ◽  
Kyle M. Diederichsen ◽  
...  
Keyword(s):  
Oxygen Reduction ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Isotope Effects ◽  
Underlying Mechanism ◽  
Reduction Reaction ◽  
Graphene Oxides ◽  
Nitrogen Doped ◽  
General Chemical ◽  
Reduced Graphene

Doped carbon-based systems have been extensively studied over the past decade as active electrocatalysts for both the two-electron (2e-) and four-electron (4e-) oxygen reduction reaction (ORR). However, the mechanisms for ORR are generally poorly understood. Here we report an extensive experimental and first-principles theoretical study of the ORR at nitrogen-doped reduced graphene oxides (NrGO). We synthesize three distinct NrGO catalysts and investigate their chemical and structural properties in detail via X-ray photoelectron spectroscopy, infrared and Raman spectroscopy, high-resolution transmission electron microscopy and thin-film electrical conductivity. ORR experiments include the pH dependences of 2e- versus 4e- ORR selectivity, ORR onset potentials, Tafel slopes and H/D kinetic isotope effects. These experiments show very different ORR behavior for the three catalysts, both in terms of selectivity and the underlying mechanism which proceeds either via coupled proton-electron transfers (CPETs) or non-CPETs. Reasonable structural models developed from DFT rationalize this behavior. The key determinant between CPET vs. non-CPET mechanisms is the electron density at the Fermi level under operating ORR conditions. Regardless of the reaction mechanism or electrolyte pH, however, we identify the ORR active sites as sp2 carbons that are located next to oxide regions. This assignment highlights the importance of oxygen functional groups, while details of (modest) N-doping may still affect the overall catalytic activity, and likely also the selectivity, by modifying the general chemical environment around the active site.

scholarly journals Highly Selective Au/ZnO via Colloidal Deposition for CO2 Hydrogenation to Methanol: Evidence of AuZn Role

2021 ◽  
Vol 16 (1) ◽  
pp. 44-51
Author(s):  
Hasliza Bahruji ◽  
Mshaal Almalki ◽  
Norli Abdullah
Keyword(s):  
Active Sites ◽  
Au Nanoparticles ◽  
High Selectivity ◽  
Average Diameter ◽  
Co2 Hydrogenation ◽  
Impregnation Method ◽  
Co2 Conversion ◽  
Methanol Production ◽  
Surface Oxygen Vacancy ◽  
Colloidal Method

Gold, Au nanoparticles were deposited on ZnO, Al2O3, and Ga2O3 via colloidal method in order to investigate the role of support for CO2 hydrogenation to methanol. Au/ZnO was also produced using impregnation method to investigate the effect of colloidal method to improve methanol selectivity. Au/ZnO produced via sol immobilization showed high selectivity towards methanol meanwhile impregnation method produced Au/ZnO catalyst with high selectivity towards CO. The CO2 conversion was also influenced by the amount of Au weight loading. Au nanoparticles with average diameter of 3.5 nm exhibited 4% of CO2 conversion with 72% of methanol selectivity at 250 °C and 20 bar. The formation of AuZn alloy was identified as active sites for selective CO2 hydrogenation to methanol. Segregation of Zn from ZnO to form AuZn alloy increased the number of surface oxygen vacancy for CO2 adsorption to form formate intermediates. The formate was stabilized on AuZn alloy for further hydrogenation to form methanol.  The use of Al2O3 and Ga2O3 inhibited the formation of Au alloy, and therefore reduced methanol production. Au/Al2O3 showed 77% selectivity to methane, meanwhile Au/Ga2O3 produced 100% selectivity towards CO. Copyright © 2021 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). 

scholarly journals Synthesis of a magnetic C@Co material via the design of a MOF precursor for efficient and selective adsorption of water pollutants

2021 ◽  
Author(s):  
Yu Liu ◽  
Yan Wang ◽  
Xiao-Sa Zhang ◽  
Wen-Ze Li ◽  
Ai-Ai Yang ◽  
...  
Keyword(s):  
Active Sites ◽  
Organic Dyes ◽  
Selective Adsorption ◽  
Catalytic Performance ◽  
Adsorption Processes ◽  
Carbon Coated ◽  
Adsorption Of Water ◽  
Metal Organic ◽  
Cobalt Nanoparticle ◽  
Fast Acting

Abstract 3D metal-organic frameworks (MOFs) can be appropriate templates for the fabrication of nanomaterials due to they have active sites exposed on the channel or surface, which thus provide them with improved catalytic performance. In this study, a 3D cobalt-based MOF [Co(H2bpta)]n (Co-MOF), where H4bpta denotes 2,2′,4,4′-biphenyltetracarboxylic acid, has been constructed with the use of a ligand with a high carbon content. On this basis, a 2D magnetic carbon-coated cobalt nanoparticle composite (C@Co) was prepared by using the title MOF. Magnetic C@Co can readily absorb dye from the solution and can thus act as an inexpensive and fast-acting adsorbent. Moreover, we have explored the adsorption isotherms, kinetics and thermodynamics of the anion dyes in detail. The adsorption capacity of the C@Co for investigated methyl orange (MO) and congo red (CR) dyes were 773.48 and 495.66 mg g− 1, respectively. It is noteworthy that MO adsorption is higher in existing materials. Thermodynamic studies suggest that the adsorption processes are spontaneous and exothermic. This study opens a new insight into the synthesis and application of carbon-based materials that enable the selective removal of organic dyes.

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