The Preparation and Dust Suppression Performance Evaluation of Iron Ore Tailing-Based Cementitious Composites.

In order to comprehensively utilize iron ore tailings (IOTs), the possibility of using IOTs as raw materials for the preparation of cementitious composites (IOTCCs) was investigated, and IOTCC was further applied to mine interface pollution control. The mechanical properties, hydration products, wind erosion resistance, and freeze-thaw (F-T) cycle resistance of IOTCCs were evaluated rigorously. The activity index of iron tailings increased from 42% to 78% after grinding for 20 s. The IOTCC was prepared by blending 86% IOT, 10% ground granulated blast-furnace slag (GGBS), and 4% cement clinker. Meanwhile, the hydration products mainly comprised ettringite, calcium hydroxide, and C-S-H gel, and they were characterized via XRD, IR, and SEM. It was observed that ettringite and C-S-H gel were principally responsible for the strength development of IOTCC mortars with an increase in curing time. The results show that the kaolinite of the tailings was decomposed largely after mechanical activation, which promoted the cementitious property of IOT.

A comprehensive review on the ultrasound-enhanced leaching recovery of valuable metals: Applications, mechanisms and prospects.

In recent two decades, ultrasound has been broadly applied to the hydrometallurgical leaching process to recover valuable metals within raw materials, aiming to solve the shortcomings of the conventional leaching process, including relatively low leaching recovery, long leaching duration, high reagent usage, high energy consumption and so on. The present work focuses on a comprehensive overview of the ultrasound-enhanced leaching of various metals, such as common nonferrous and ferrous metals, rare metals, rare earth elements, and precious metals, from raw metal ores and secondary resources. Moreover, the enhanced leaching mechanisms by ultrasound are discussed in detail and summarized based on the improvement of leaching kinetics, enhancement of the mass transfer and diffusion of lixiviants, and promotion of the oxidative conversion of metals from insoluble to soluble states. Lastly, the challenges and outlooks of future research on the leaching recovery for valuable metals with the assistance of ultrasound irradiation are proposed.

The molecular structure effects of starches and starch phosphates in the reverse flotation of quartz from hematite.

Native starches and their phosphates with various molecular structures was introduced as the depressant to realize the flotation of quartz from hematite in this study. The present starch phosphates (WSP, NSP, GSP) were modified by the reaction between phosphate and three different corn starches (WS, NS, G50). The synthesis and characterization of starch phosphates found that starch with high amylopectin content was easily modified into starch phosphates. Microflotation tests showed that starch phosphates exhibited stronger depressing abilities of hematite flotation than native starches. Zeta potential measurement showed that both starches and starch phosphates could positively shift the zeta potential of hematite, while starch phosphates had more effects than starches. XPS and MDS indicated that the chemisorption occurred between Fe of hematite surface and CO groups of starch-based depressants. In addition, starch phosphates could adsorb onto the hematite surface through PO groups. MDS also presented that the adsorption strength of starch phosphate was mainly determined by the type and number of generating chelating rings, and the molecular structure of starch significantly affected the formation of chelate rings. The proposed adsorption model insights will significantly promote the development of starch-based depressants for iron ore flotation and other mineral processing applications.

Flotation purification of waste high-silica phosphogypsum.

High-silica phosphogypsum (PG) is a kind of industrial by-product with great utilization potential. However, it is difficult to reuse PG directly due to the related gangue minerals (e.g., SiO2), and thus efficient purification is required to allow its further applications. Herein, a typical high-silica phosphogypsum waste was purified by a new "reverse-direct flotation" method. The organic matters and fine slimes were removed by reverse flotation, and then, the silica impurity was removed by direct flotation. Via the closed-circuit flotation process, the whiteness of the PG concentrate is improved from 33.23 to 63.42, and the purity of gypsum in the PG concentrate increases from 83.90% to 96.70%, with a gypsum recovery of 85%. Additionally, the content of SiO2 is significantly reduced from 11.11% to 0.07%. In-depth investigations suggest that the difference in the floatability of gypsum and quartz is prominently intensified by flotation reagents at pH = 2-2.5, and thus leads to good desilication performance. Further characteristics of the PG concentrate prove that impurities have been well removed, and the PG concentrate meets the requirement of related standards for gypsum building materials. The flotation method reported here paves the way for the purification of high-silica phosphogypsum, which can be extended to the purification and value-added reutilization of other industrial solid wastes.

Characterization, Spatial Variation and Management Strategy of Sewer Sediments Collected from Combined Sewer System: A Case Study in Longgang District, Shenzhen.

In the urban drainage system, the formation of sewer sediments is inevitable, and the removal of sewer sediments is necessary for system maintenance. Disposal of arisings from sewer sediment removal is becoming a serious environmental issue. The current knowledge of sewer sediments is limited, which is restrained to sewer sediments management. To better understand this municipal waste, the sewer sediments of a combined sewer system in Longgang District, Shenzhen were collected and characterized, and the spatial distribution characteristics of contaminants were analyzed. Based on the bivariate correlation analysis, it is found that many contaminants in sewer sediments have a strong relationship with spatial variables. Compared to the sewer sediments in industrial areas, those in residential areas contain higher concentrations of Hg and phosphorus. The sediments in the sewage conduit also contain more organic matter (OM), phosphorus, Cu, and Ni, and the sediments in the rainwater conduit contain a higher concentration of Cd. Moreover, the sediments produced in different catchments also show huge differences in the content of contaminants. These spatial distribution characteristics may provide help for the further classification of sewer sediments, thereby making the disposal of sediments more targeted. According to the local standards of sludge disposal, land application and incineration are not suitable for managing sewer sediments due to the low OM content and poor lower heating value (LHV). Although sanitary landfill is feasible for sewer sediments disposal, the complicated composition of sewer sediments still poses the risk of polluting the surrounding environment. The management of sewer sediments via the production of building materials is a promising technical route that can avoid the migration of hazardous contaminants and produce valuable products. This study may improve our understanding of sewer sediments and provide a reliable recommendation for sewer sediment management.

Removal of cadmium and lead from aqueous solutions by thermal activated electrolytic manganese residues.

Electrolytic manganese residues (EMR) is produced from the electrolysis manganese industry. In this study, the thermal activated EMRs (T-EMR) were used to adsorb cadmium and lead from aqueous solution. X-ray diffractometer (XRD), scanning electron microscope-Energy Dispersive Spectrometer (SEM-EDS), X-ray photoelectron spectroscopy (XPS) were adopted to characterize EMR before and after the modification, and the performance and adsorption mechanisms of T-EMR for cadmium and lead were determined. Results show that the pH has a strong influence on the adsorption of cadmium and lead and the maximum adsorption capacity can be achieved at pH 6. The adsorption of Cd(II) can be better fitted by the Lagergren pseudo-first-order dynamic model, while that of Pb(II) fits the pseudo-second-order kinetic model better. The Freundlich isotherm model fits the adsorption of two metals better than Langmuir model. The thermodynamic results demonstrate that the adsorption of Cd(II) or Pb(II) on T-EMR is endothermic and spontaneous. As the nitric acid with pH 0.5 was used, nearly all of the adsorbed Cd(II) and 75% Pb(II) can be desorbed from the loaded T-EMR. It is concluded that the adsorption of Cd(II) and Pb(II) on T-EMR is in virtue of electrostatic attraction, ion-exchange and surface precipitation. The heavy metals are mainly adsorbed on ferric and manganese oxides and silicate minerals in T-EMR by electrostatic attraction. In addition, cadmium and lead also can be adsorbed via the ion exchange reaction. Moreover, some Pb(II) are adsorbed by forming lead sulfate. Thus, T-EMR may be an environmentally-friendly, effective adsorbent for the removal of heavy metals from aqueous solution.

Evaluating toxicity impacts of environmental exposed chromium on small Indian mongoose (Urva auropunctatus) hematological, biochemical and histopathological functioning.

Sub-lethal toxic impacts of chromium on hematological, biochemical and histological parameters were analyzed in the female small Indian mongoose (Urva auropuctatus) residing contaminated environment of tannery industry. Chromium bioaccumulation in the blood, liver and kidney tissue of the exposed mongooses was found elevated compared to the control mongooses' tissues. Total body weight (75.7%), liver weight (83.6%) as well as HSI (68.1%), RSI (86.2%) and the platelets counts (59.7%) were found significantly elevated, with significantly reduced RBCs (59.6%), and WBCs (64%). LFT and RFT were also found abnormal, moreover, the histopathological injuries had been distinct inside the kidney (>75%) and hepatic (>75%) tissues of exposed animals. Shrinkage and vacuolization (>75%) inside the hepatocyte expanded sinusoidal spaces and nuclear pyknosis (>75%) was evident within the hepatic tissue. Hypertrophy of epithelial cells of renal tubules and inter-renal cells of the head kidney with a reduction in tubular lumens (>75%) and vacuolization of tubules were witnessed within the kidney section. Atrophy inside the kidney inter-renal cells, glomeruli compression within the Bowman's capsules (>75%) following the necrosis in hematopoietic tissues were found in exposed animals. The present findings indicate that chronic exposure to chromium induces severe anemia, decreased serum protein concentration, hepatic and renal tissue histopathology, impairing the vital capabilities of liver, metabolic regulation, excretion, and stress homeostasis maintenance of which within the long-run may posture a severe risk to animal well-being then distress their inhabitants.

Utilization of carbonate-based tailings to remove Pb(II) from wastewater through mechanical activation.

The removal of lead in water and disposal of tailings are important environmental issues that need to be addressed urgently. This work explored the feasibility of utilizing the carbonate-based tailings (CBT) for removing lead from the simulated wastewater with the aid of wet stirred ball milling (mechanical activation). Batch experiments were performed to evaluate the influences of various experimental parameters like dosage of CBT, milling balls addition and initial concentration of lead. Under the action of mechanical activated CBT, the lead removal in the solution could reach more than 99% in 2 h, and the lead removal capacity reached 832 mg/g. The results of X-Ray Diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR) and Scanning Electron Microscope-Energy Dispersive Spectra (SEM-EDS) revealed that the calcite (CaCO3) in CBT played a major role in removing lead and the lead in the solution was transferred to the precipitate as cerussite (PbCO3). The mechanical activation promoted the dissolution of calcite, reduced the particle size of CBT and peeled off the lead carbonate precipitation on the surface of calcite, thereby enabling the reaction to be efficiently and thoroughly completed. The lead content in the precipitate after the reaction reached 38.4 wt%, which made it possible for lead recovery.

Removal of Cu(II) from wastewater by using mechanochemically activated carbonate-based tailings through chemical precipitation.

This work explored the feasibility of utilizing the copper tailings (CT) for removing copper from the waste mine water based on the mechanochemical activation. Batch experiments were performed to evaluate the influences of various experimental parameters like the dosage of CT, reaction time, initial concentration of Cu, and anion species. By cogriding copper solution with CT in the stirred mill (mechanochemical activation), over 99.5% of copper was removed and the residual copper concentration in the solution was less than 0.5 mg/L, reaching the discharge limit. This reaction was a chemical precipitation process. The calcite of CT played a major role in precipitating copper and had a better removal effect on copper in the copper sulfate solution than copper nitrate solution. For copper sulfate solution, the copper deposit was mainly posnjakite (Cu4(SO4)(OH)6·H2O). In the copper nitrate solution, the copper sediment might consist mainly of basic copper nitrate. The stability of the two reaction products was measured by leaching test. The result showed that the sediment obtained by this method was relatively stable and was not hazardous wastes.

Eco-friendly synthesis of VO2 with stripped pentavalent vanadium solution extracted from vanadium-bearing shale by hydrothermal process in high conversion rate.

VO2(B) has shown excellent cathode performance in lithium batteries and become a hot research topic in recent years. A stripped vanadium solution extracted from vanadium-bearing shale containing a high concentration of vanadium and certain amounts of impurities was used as a vanadium source to synthesize VO2(B) by hydrothermal process. The VO2 conversion rate can reach as high as 99.47% in a reaction time of 8 h, and this is the highest result reported. The crystalline structure and morphology of the synthesized products were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Furthermore, the electrochemical properties of VO2(B) in lithium-ion batteries were investigated. The results indicated that the VO2(B) has the initial specific discharge capacity of 192.0 mAh g-1. Stripped vanadium solution is a raw material for producing V2O5 and NH4VO3, which are indispensable vanadium sources in VO2 synthesis. Therefore, synthesis of VO2 via hydrothermal reduction by oxalic acid using stripped vanadium solution extracted from vanadium-bearing shale as a direct vanadium source is an eco-friendly, innovative and efficient method, and will have a great impact on VO2 synthesis.

Adsorption characteristics of vanadium on different resin-active carbon composite electrodes in capacitive deionization.

Three kinds of anion exchange resins (AERs) (D201, D301, D314) and one kind of cation exchange resin (D860) were used with activated carbon (AC) to fabricated the ion exchange resin-AC (IER/AC) composite electrodes in capacitive deionization (CDI) for selective adsorption of V(V). The characteristics of four kinds of composite electrodes, such as wettability, pore distribution and electrochemical properties, indicates IER/AC composite has great potential as electrode materials for the electro-adsorption in CDI. The pH of solution has apparent influence on the adsorption capacity of the composite electrodes for V(V) because of the various V(V) species in the solution with different pH. The reduction rate of V(V) on IER/AC electrodes mainly relates to the amount of VO2+ in solution. The adsorption capacity of AER/AC electrodes for V(V) is slightly affected by the applied voltage may be due to that the adsorption of V(V) is mainly dependent on ion exchange with AERs and only a minority of V(V) is adsorbed by electrostatic adsorption. The adsorbed V(V) on D860/AC electrode decreases with the rising applied voltage because the pH increases with the increase of voltage. The separation of V(V) from V(V), Al and P indicates that the selective adsorption capability of IER/AC composite electrode is related to the migration rate of V(V), Al, P at different voltages and the selectivity of resins. This study may provide reference for recovering and separating metal ions from aqueous solution with CDI.

Recovery of V(V) from complex vanadium solution using capacitive deionization (CDI) with resin/carbon composite electrode.

The resin-activated carbon composite (RAC) electrodes were fabricated and applied in capacitive deionization for recovery of V(V) from complex vanadium solution. The adsorption capacity of the RAC electrode for V(V) is extremely low and the reduction of V(V) is significant in low pH solution, but the adsorbed V(V) on the electrode increases obviously and the reduction of V(V) gradually diminishes with the rise of pH. However, as the pH is increased to 10, the adsorbed V(V) on the RAC electrode declines. The higher applied potential is beneficial to the adsorption of V(V) and 1.0 V is appropriate for the adsorption. The impurities ions (Al, P and Si) are mainly adsorbed in the electric double layers on the RAC electrode and V(V) is dominantly adsorbed by the resins in the electrode. The adsorbed impurity ions can be easily removed by diluted H2SO4 and V(V) can be effectively eluted by 10% NaOH solution. The vanadium-bearing eluent can be recycled to recover and enrich vanadium from the complex solution. The performance of the RAC electrode keeps stable during the cyclic operation. This study may provide a promising and novel method for the recovery and separation of metals from aqueous solution.

Ultrasound-assisted synthesis of N235-impregnated resins for vanadium (V) adsorption.

N235-impregnated resins were prepared using XAD-16HP macroporous adsorption resins as support with and without ultrasonic irradiation to evaluate the effects of ultrasound impregnation (UI) on the preparation and adsorption characteristics of the resins. The results show that the impregnation ratio of the solvent-impregnated resins (SIRs) prepared by ultrasound impregnation method (SIRs-UI) increases obviously but their adsorption capacity for V(V) just slightly increases and the utilization rate of the extractant decreases with the augmentation of ultrasound power. This may be caused by the fact that more extractant can enter into the deeper pores of the resins under high ultrasound intensity, but these extractants cannot effectively react with V(V). The impregnation equilibrium time of SIRs-UI can be obviously shortened in comparison to that of the SIRs prepared by conventional impregnation method (SIRs-CI) (3 min versus 240 min) due to the cavitation effect evoked by ultrasound. Ultrasonic irradiation may cause more N235 desorbed from the pores of the resin at low N235 content, resulting in lower adsorption capacity for V(V) than that of SIRs-CI, but the adsorption capacity is inverse at higher N235 content. N235 may be distributed more homogeneously in the pores of XAD-16HP with ultrasonic irradiation, thus, SIRs-UI presents higher adsorption capacity and stronger stability than SIRs-CI. This study manifests that ultrasound-assistant impregnation method may be a potential and promising technique for the preparation of SIRs.