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The graphene oxides (GOs) with various content of metallic ions impurities were prepared, and the adsorption performance of the GO before and after elution was evaluated. The prepared GOs were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, inductively coupled plasma and atomic force microscopy. The results indicated that the metallic ion impurities hardly affected the interlayer distance, microstructure and thickness of the prepared GOs. The adsorption isotherm and adsorption kinetic results showed that the metallic ions adsorbed on the GO surface had a negative influence on both the adsorption capacity and rate. After eluted by HNO3 or HCl, most of the metallic ions adsorbed on the GO-91 surface were ion-exchanged by the protons of the acid eluents, and the purified GO showed enhanced equilibrium capacities and improved adsorption rate. The elution efficiency of HCl was better than that of HNO3, and the adsorption capacity and rate of the GO eluted by HCl approximately reached to those of the GO prepared from the graphite with high purity. It indicated that HCl could efficiently remove the metallic ions adsorbed on the GO surface. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study investigated the preparation of graphene oxide from mildly oxidized graphite through ultrasonic exfoliation. Both the original and produced materials were analyzed by ultraviolet-visible spectrophotometer, X-ray diffraction and atomic force microscopy. The results indicated that the exfoliation yield of graphene oxide was proportional to the input ultrasonic energy. In addition, a two-stage exfoliation phenomenon was observed in the exfoliation of mildly oxidized graphite with both ultrasonic homogenizer and cleaner. It also was found that increasing the content of [] in a C-H2SO4-[] reaction system was the most simple and direct method to increase the oxidation degree of graphite oxide. [ABSTRACT FROM AUTHOR]

The relationship between the defects of reduced graphene oxide (RGO) and the oxidation degree of graphite in the preparation of graphene with chemical conversion method has been studied in this work. This study was performed on an artificial graphite through the measurements of X ray diffraction, Raman spectroscopy and particle size analysis. The experimental results have shown that there indeed was a close relationship between the defects and the oxidation degree, which appeared in the form of S-type curve. Also, it was found that a low KMnO 4 addition would lead to a partial oxidation of graphite, leaving defects mainly on the edges of RGO; with a high KMnO 4 addition, the defects on RGO mostly appeared on the surfaces. [ABSTRACT FROM AUTHOR]

The mechanisms of the formation of micropores in the thermal decomposition of goethite to hematite have been studied through the measurements of X-ray diffraction, Brunauer-Emmett-Teller adsorption and scanning electronic microscopy, as well as the estimation of crystal cell parameters in this work. The results have shown that the thermal decomposition led to the crystal cells of goethite to be contracted along the [010] and [001] directions and to be elongated along the [100] direction, forming nano-scale and rod-like hematite. It was the contractions along the two directions that led to the formation of the micropores in the hematite particles. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

pillared interlayered clays (-PILCs) were synthesized through a novel method, in which nanoparticles were formed in montmorillonite interlayers. In this method, silver ions were first exchanged into montmorillonite interlayers, and then reduced into nanoparticles by trisodium citrate at 100°C in aqueous solutions. The synthesized @montmorillonite nanocomposite was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and its surface area was evaluated by using Brunauer-Emmet-Teller (BET) method. Compared to traditional PILCs synthesized through ion exchange method, the formed -PILCs had better thermal stability and stronger structure because their pillars are nanoparticles. Furthermore, this method introduces a possibility to control the size of the pillars and thus the pore size of the PILCs, due to that the nanoparticle pillars can be modified on their forms and diameters in the synthesizing process. Also, it was found that the intercalating nanoparticle pillars were formed at restricted pH values and silver ion concentrations. The TEM image of the Ag@montmorillonite composite synthesized in montmorillonite dispersions showed that there were many nanoparticles, identified as Ag nanoparticles by EDX, with the size of 2 to 20 nm, are observed on montmorillonite. These Ag nanoparticles had an analogous globular shape, which indicates the growth of the silver nanoparticles was on the montmorillonite surface, or was restricted by the montmorillonite interlayer space alone. [ABSTRACT FROM AUTHOR]

A porous-nanostructured material made of short-chain eskolaite (α-Cr2O3) nanoparticles has been synthesized from Cr2O3-loaded activated carbon. The size of the nanoparticles in the chain ranges from 2 to 100 nm. The Cr2O3-loaded activated carbon was prepared by adsorption of dichromate () ions from aqueous solutions on ultrafine activated carbon (less than 12 µm in size) in a batch-glass-stirred reactor at 28°C. After a filtration step, the Cr2O3-loaded activated carbon was processed at high temperature under an oxidizing atmosphere to remove the carbon as CO2(g) and obtain a product high in Cr2O3. This thermal process was carried out in a tube furnace using air as the oxidant. At 1100°C, a product with 98% Cr2O3was produced. The synthesized material is highly porous and is composed by agglomerates of short chains of eskolaite nanoparticles. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected area (electron) diffraction (SAED) microscopy were used to determine the chemical composition, texture, crystal structure, and size of the product components. [ABSTRACT FROM AUTHOR]

In this work, the thermal decomposition of a goethite concentrate from an iron ore concentration plant was studied in order to develop an economic process of preparing porous hematite as an effective adsorbent for the treatment of wastewater containing heavy metals. This study was performed by means of the measurements of X-ray diffraction (XRD), physical adsorption, and thermal gravimetric analyzer (TGA) for the decomposition process and the characterization of the prepared porous hematite. The experimental results showed that the prepared porous hematite mainly consisted of micropores, and considerably increased the specific surface area and pore volume. The mechanism might be attributed to the dehydration and dehydroxylation of goethite in the thermal treatment. It has been found that calcinating temperature was the predominant factor in the preparation of the porous hematite. Also, residence time in the calcinations greatly affected the pore characterization of the porous hematite. [ABSTRACT FROM AUTHOR]

The decomposition of goethite and goethite/siderite concentrates into hematite with thermal modification was studied through the measurements of X-ray diffraction (XRD), scanning electronic microscope (SEM) and thermal gravimetric analysis (TGA). The experimental results showed that goethite decomposed into hematite directly at around 300°C without any intermediate phase and the decomposition of siderite completed at 500°C. Nanoscale granular structures were observed in the thermally treated products. It deserves highlighting that the decomposition processes proceeded from surfaces into bulks. [ABSTRACT FROM AUTHOR]

The present work studies the immobilization forms of lead in alkali-activated cementitious binders (AACBs) based on mine tailings. Through deconvolution of Pb 4f XPS spectra of the mine tailings-based binders, the immobilization forms of lead in network, and lead in silicate glass of PbO·3SiO 2 and PbO·7SiO 2 were first quantitatively presented. The 29 Si NMR spectra of the binders synthesized with Pb(NO 3 ) 2 additions from 0 to 6% give the ratios of silicates involved in the formation of lead silicate glass, ranging from 0 to 10.56%. In addition, images of scanning electron microscope (SEM) equipped with X-ray microanalytical mapping and results of zeta potential measurements confirmed the immobilization forms in the mine tailings-based binders. It not only gives fundamentals for the solidification/stabilization (S/S) of mine tailings through alkaline activation process, but also enriches the understanding on the immobilization of heavy metals in AACBs. [ABSTRACT FROM AUTHOR]

Although quartz sand is widely used as filler material in construction, a few studies investigated the incorporation of quartz sand in geopolymers. To study the incorporation of quartz sand in the reinforcement of metakaolin geopolymer not only fills this gap, but also gives a clue on using non-calcinated aluminosilicates (e.g., mine tailings) in the synthesis of geopolymers. In the presence of sodium silicate, metakaolin geopolymers were synthesized with quartz sand of various size ranges as filler material. XRD, FTIR, SEM and NMR characterizations on the geopolymers indicate the dissolution, precipitation, and the formation of combination on quartz particles that associates them into the geopolymeric gel, so as to reinforce the mechanical strength of geopolymers. The compressive strength of metakaolin geopolymers with only silicate, silicate plus quartz sand and silicate plus rutile sand is 31.2, 52.2 and 41.5 MPa, respectively. In geopolymer with silicate and quartz sand, a decreasing Si/Al ratio as increasing distance from the quartz particle is observed through an energy dispersive X-ray (EDX) mapping. The SEM images and NMR spectra suggest that the formed combination is of several micrometers with main species of polysialates (-Si-O-) such as Q 4 (2Al) , Q 4 (1Al) . [ABSTRACT FROM AUTHOR]

Metakaolin-based geopolymers were synthesized at Si/Al ratios of 1:1, 1.5:1, 2:1, 3:1, 4:1, and 5:1 by using silica fume as silica corrector to alter Si ratios. The microstructure and strength of these geopolymers were characterized through XRD, SEM, NMR and compressive strength measurements. The dissolving rates of Al and Si species in geopolymerization were measured, and freeze-dried N-A-S-H gel was characterized by FTIR spectra. Modelling and simulation were employed to calculate the binding energy of one Si atom and the total energy of geopolymers formed at various Si/Al ratios. At Si/Al ratio of 2:1, high concentrations of Si and Al species are dissolved from precursors, high contents of Si-O-T linkages are formed and the geopolymer is of high compressive strength. The mechanical strength of geopolymers at various Si/Al ratios is dependent on the formation of N-A-S-H gel, rather than the zeolitic nuclei or silicate derivatives. This study might provide fundamentals for the geopolymerization of mine tailings, which usually possess high Si/Al ratios. [ABSTRACT FROM AUTHOR]

[Display omitted] • Surface iso -transformation mechanisms between calcite and fluorite was revealed. • F− ions increased calcite recovery, but CO 3 2− ions decreased fluorite recovery. • F− bonded with Ca2+ on calcite surface, but CO 3 2− did not bond with Ca2+ on fluorite. • Adsorption heat and rate of NaOL on iso -transformed calcite increased, approaching to fluorite. Fluorite (CaF 2) and calcite (CaCO 3), both minerals containing calcium and owning similar surface properties, which is unfavorable to the selective separation. This study revealed the mechanisms of surface homogeneity transformation between them. Flotation results showed that F− ions increased the recovery of calcite, but CO 3 2− decreased the recovery of fluorite, due possibly to the surface homogenization of these two minerals. In addition, the surface evolution changed the adsorption of collector (i.e. , sodium oleate). SEM tests further showed the formation and adsorption of scattered cubic CaCO 3 crystals on the surface of fluorite. Differently, a significant quantity of spherical CaF 2 crystals uniformly coated the calcite surface. Moreover, apparent dissolution occurred on calcite surface. Furthermore, XPS tests showed that Ca-F bonds were formed on calcite surface while Ca-CO 3 bonds were formed on fluorite surface, but the content of former was higher than the latter. XRD tests further showed the formation of fluorite on calcite surface. The DFT calculation exhibited that the adsorption energy of F− and Ca2+ on calcite (1 0 4) surface was −20.78 kJ/mol, more negative than that of CO 3 2− and Ca2+ on fluorite (1 1 1) surface (−6.57 kJ/mol). Moreover, the higher affinity of sodium oleate towards the surface of fluorite-converted calcite was demonstrated by the increased reaction heat and rate, leading to difficult flotation separation of them. This study exhibits the iso -transformation mechanisms of calcite and fluorite, shedding lights on the surface evolution of these two minerals, thereby providing scientific evidence in promoting their flotation separation efficiency. [ABSTRACT FROM AUTHOR]

[Display omitted] • Controlled crystallization method was firstly proposed for improved sylvite flotation. • Cubic, hopper-like and needle-like structure were obtained under mild growth, high supersaturation and fast crystallization, respectively. • Flotation recovery of needle-like structure obtained 96.19%, which was higher than that of cubic and hopper-like structure. • Strong interaction between needle-like structure and bubble facilitated the flotation. By understanding minerals as crystals, a crystallization-controlled methodology was performed to enhance the floatability of soluble minerals. Here, aimed strategies were applied to modulate the crystallization of KCl salt to grow crystals with various shapes as cubic-, hopper- and needle-like structure. Stereoscope and scanning electronic microscopy (SEM) helped to unveil the morphologies where X ray diffraction (XRD) characterized their high crystallinities. Afterwards, Atomic Force Microscope (AFM) was performed to research the crystallizing behaviors that cubic-like structure was obtained by turbid fast growth, while hopper-like structure formation was due to the constant high supersaturation and needle-like crystal occurred under still fast crystallization. Flotation tests with octadecylamine hydrochloride (ODA) as collector demonstrated the floatability of samples obeyed the order as needle-like (96.19 %) > hopper-like (81.59 %) > cubic-like (80.08 %) KCl samples. The mechanism was studied by surface area and related interaction tests. BET result demonstrated the highest surface area of needle-like structure than that of hopper-like and cubic-like structure. Besides, induction time combined with adhesion & desorption force tests further explained the better interaction of needle-like sample with bubble than cubic-like sample. While the special structure of hopper-like structure with lower weight but inner filled solution resulted in its near equivalent floatability with cubic-like sample. In conclusion, a new strategy for promoting flotation behavior by designing the crystallization of soluble KCl was proposed, shedding some light on further application on other soluble or semi-soluble minerals. [ABSTRACT FROM AUTHOR]

A novel granular adsorbent material containing zero-valent iron (ZVI-GAM) was prepared with fly ash as skeletal material, bentonite as binder and Enteromorpha prolifera as pore former. ZVI was synthesized by direct reduction of iron ore tailings powder with the coke as reductant in high temperature reducing atmosphere and embedded in the fly ash-based porous adsorbent, which could reduce the agglomeration and oxidation of ZVI. The structure of ZVI-GAM was characterized by SEM, EDX, XRD, FTIR and BET. The removal amount of crystal violet (CV) and methylene blue (MB) was evaluated at different contact time, initial dye concentration, pH values and temperature. The adsorption isotherms of CV and MB fitted well to the Langmuir model. The maximum removal capacity of ZVI-GAM for CV and MB was found to be 172.41 mg/g and 151.52 mg/g, respectively. The adsorption processes of CV and MB could be described by a pseudo-second-order kinetic model. The reduction kinetics of CV by ZVI-GAM fitted to pseudo-first-order kinetics model. The results indicated that chemisorption and reduction controlled the removal process of CV while chemisorption only controlled the removal process of MB. The thermodynamic study indicated that the adsorption processes of CV and MB were found to be endothermic and spontaneous. Therefore, ZVI-GAM was an effective, low-cost and recyclable material for dye removal. [ABSTRACT FROM AUTHOR]

In this work, high temperature in situ X-ray diffraction and in situ analysis of energy dispersive spectrometer were used to find the essence of the roasting of vanadium-bearing stone coal. In the process of roasting, vanadium-bearing muscovite with quartz was converted to feldspar group minerals (albite, orthoclase and anorthite), during which Al(V) O bonds in muscovite were broken. Meanwhile, vanadium was liberated from muscovite, which was the precondition that vanadium can be recovered. These findings were useful for proposing some measures, such as adding quartz, to recover the vanadium from stone coal more efficiently in practice. [ABSTRACT FROM AUTHOR]

The characterisation of reduced graphene oxides (rGOs) prepared from natural flaky, lumpy, and amorphous graphites using Hummers method was investigated. The prepared graphite oxides (GrOs) and rGOs were characterised by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, UV–vis spectroscopy, atomic force microscopy and electrochemical performance. The results showed that amorphous graphite was much easier to oxidise than lumpy and flaky graphites and was preferable for preparing single or double layer graphene because low graphitisation degree, high defect degree, high specific surface area and small crystal size were beneficial for (1) the oxidants to attack the exposed carbon atoms, (2) the intercalation of oxidants, and (3) the diffusion of oxidants between graphitic layers. In addition, rGO synthesised from amorphous graphite had the most defects and the smallest size of the in-plane sp 2 domains compared to those obtained from the other two nature graphites. [ABSTRACT FROM AUTHOR]

Comparative study has been performed on the adsorption of Pb(II) on graphene oxides (GOs) prepared from flaky, lump and amorphous graphites with the Hummers method in this work. The GOs were characterized by X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, Chemical analysis, Raman spectroscopy and Atomic force microscope. The results indicated that GO prepared from amorphous graphite had lower C/O ratio and more thin layers (less than 2 nm in thickness) than those prepared from the other two natural graphites. The adsorption process was well described by the pseudo-second-order kinetics model, and the equilibrium data agreed precisely with the Langmuir model. The hydroxyl and carboxyl located at the edges of GO sheets mainly participated in the complexation of Pb(II), and different GO sheets were bridged by Pb(II) through simultaneously bonding the marginal oxygenous groups. [ABSTRACT FROM AUTHOR]

In this study, we introduced a solvent-free mechanochemical route to synthesize Li–Al layered double hydroxide through a two-step grinding of LiOH and Al(OH) 3 , in which the mixture powder with Li/Al molar ratio at 1/2 was first dry ground for 2 h and then wet ground for another 1 h with water addition without any heating operation. The as-prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TG), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The products possessed highly crystalline of Li–Al LDH phase with no evident impure phases, presenting an easy and effective preparation of Li–Al LDH by using solvent-free mechanochemical approach. [ABSTRACT FROM AUTHOR]