Potential of major by-products from non-ferrous metal industries for CO2 emission reduction by mineral carbonation: a review.

By-products from the non-ferrous industry are an environmental problem; however, their economic value is high if utilized elsewhere. For example, by-products that contain alkaline compounds can potentially sequestrate CO2 through the mineral carbonation process. This review discusses the potential of these by-products for CO2 reduction through mineral carbonation. The main by-products that are discussed are red mud from the alumina/aluminum industry and metallurgical slag from the copper, zinc, lead, and ferronickel industries. This review summarizes the CO2 equivalent emissions generated by non-ferrous industries and various data about by-products from non-ferrous industries, such as their production quantities, mineralogy, and chemical composition. In terms of production quantities, by-products of non-ferrous industries are often more abundant than the main products (metals). In terms of mineralogy, by-products from the non-ferrous industry are silicate minerals. Nevertheless, non-ferrous industrial by-products have a relatively high content of alkaline compounds, which makes them potential feedstock for mineral carbonation. Theoretically, considering their maximum sequestration capacities (based on their oxide compositions and estimated masses), these by-products could be used in mineral carbonation to reduce CO2 emissions. In addition, this review attempts to identify the difficulties encountered during the use of by-products from non-ferrous industries for mineral carbonation. This review estimated that the total CO2 emissions from the non-ferrous industries could be reduced by up to 9-25%. This study will serve as an important reference, guiding future studies related to the mineral carbonation of by-products from non-ferrous industries.

Utilization of low-calcium fly ash via direct aqueous carbonation with a low-energy input: Determination of carbonation reaction and evaluation of the potential for CO2 sequestration and utilization.

Environmental impacts from coal-fired power generation that produces large amounts of CO2 and fly ash are of great interest. To reduce negative environmental impacts, fly ash utilization was investigated via a direct aqueous carbonation with a low-energy input in which the alkali calcium content in the fly ash reacted with CO2 to form carbonate. Raw fly ash was characterized to understand the potential for direct aqueous carbonation of fly ash. The performance of the fly ash as a calcium source for direct aqueous carbonation at atmospheric pressure was investigated for different solid-liquid ratios and introduced CO2 concentrations. Variations in fly ash elemental composition, reaction solution pH, CO2 concentration in the reactor outlet, CO2 uptake efficiency, CaCO3 content and degree of carbonation were used to illustrate this process reaction. The maximum CO2 uptake efficiency was ~0.016 g-CO2/g-fly ash. This value was compared with previous studies, and the CO2 uptake efficiency was comparable despite the use of a low-energy input method, i.e., direct aqueous carbonation with atmospheric pressure and unconcentrated CO2. The calculated maximum degree of carbonation was 31.0%, which corresponds to 0.0063 g-CO2/g-fly ash. Carbonated product characterization confirmed the carbonation reaction mechanism and safety for further utilization. A comparison of CO2 uptake efficiency in this work with previous work, and considering the energy input and reactive species content, is provided. An assessment of the CO2 reduction potential is provided.

CO2 Utilization via Direct Aqueous Carbonation of Synthesized Concrete Fines under Atmospheric Pressure.

Mineral carbonation using alkaline wastes is an attractive approach to CO2 utilization. Owing to the difference between waste CO2 and feedstock CO2, developing CO2 utilization technologies without CO2 purification and pressurization is a promising concept. This study investigated a potential method for CO2 utilization via direct aqueous carbonation of synthesized concrete fines under atmospheric pressure and low CO2 concentration. The carbonation reaction with different solid-liquid ratios and different concentrations of introduced CO2 was examined in detail. Under basic conditions, a CO2 uptake of 0.19 g-CO2/g-concrete fines demonstrated that direct aqueous carbonation of concrete fines under atmospheric pressure and low CO2 concentration is effective. The CaCO3 concentration, degree of carbonation, and reaction mechanism were clarified. Furthermore, characterization of the carbonated products was used to evaluate ways of utilizing the carbonated products.

Non-electrolytic synthesis of copper oxide/carbon nanocomposite by surface plasma in super-dehydrated ethanol.

Electrolytic processes are widely used to synthesize different nanomaterials and it does not depend on what kind of the method has been applied (wet-chemistry, sonochemistry, plasma chemistry, electrolysis and so on). Generally, the reactions in the electrolyte are considered to be reduction/oxidation (REDOX) reactions between chemical reagents or the deposition of matter on the electrodes, in line with Faraday's law. Due to the presence of electroconductive additives in any electrolyte, the polarization effect of polar molecules conducting an electrical current disappears, when external high-strength electric field is induced. Because initially of the charge transfer always belongs of electroconductive additive and it does not depend on applied voltage. The polarization of ethanol molecules has been applied to conduct an electric current by surface plasma interaction for the synthesis of a copper oxide/carbon nanocomposite material.

Study on simultaneous recycling of EAF dust and plastic waste containing TBBPA.

In the present work we investigated the fates of zinc, lead, and iron present in electric arc furnace dust during thermal treatment of the dust with tetrabromobisphenol A (TBBPA) and tetrabromobisphenol A diglycidyl ether (TBBPADGE). Mixtures of these materials were compressed into pellets and heated in a laboratory-scale furnace at 550 °C for 80 min, under oxidizing and inert conditions. The solid, condensed, and gaseous-phase products were characterized using an array of analytical methods: scanning electron microscopy, X-ray diffraction, electron probe microscopy, inductively coupled plasma, ion chromatography, and gas chromatography. The results indicated that heating the mixtures under specific conditions enabled high separation of zinc and lead from iron-rich residues, by a bromination-evaporation process. In the case of TBBPADGE, a maximum of 85% of zinc and 81% of lead were effectively separated under the above conditions. The process is based on the reaction between the highly reactive HBr gas evolved during thermal degradation of the flame-retarded materials with zinc (ZnO and ZnFe2O4) and lead in the dust, followed by complete evaporation of the formed metallic bromides from the solid residue.

Fate of lead oxide during thermal treatment with tetrabromobisphenol A.

In this paper, the bromination reaction between lead oxide and hydrogen bromide originating from the thermal decomposition of tetrabromobisphenol A (TBBPA), under inert and oxidizing atmospheres, was investigated, using a laboratory-scale furnace. The results obtained under inert conditions indicated that bromination of PbO proceeded simultaneously with debromination of TBBPA, with an average effectiveness of 69% (max. 80%). Volatilization of the formed PbBr2 began at 315°C, intensified at 750°C, and reached 98% at 850°C. The formed organic char served as a source of carbon for reduction of the unreacted lead oxide to metallic lead in the range 315-750°C. Additional experiments conducted at selected temperatures under slightly oxidizing (5 vol% O2) and quasi-atmospheric (20 vol% O2) conditions showed no significant effects on bromination-evaporation of lead in the studied mixture. However, in isothermal treatment under quasi-atmospheric oxygen levels, complete vaporization of the formed lead bromide was obtained at a temperature of only 650°C.

Distribution of copper, silver and gold during thermal treatment with brominated flame retardants.

The growing consumption of electric and electronic equipment results in creating an increasing amount of electronic waste. The most economically and environmentally advantageous methods for the treatment and recycling of waste electric and electronic equipment (WEEE) are the thermal techniques such as direct combustion, co-combustion with plastic wastes, pyrolysis and gasification. Nowadays, this kind of waste is mainly thermally treated in incinerators (e.g. rotary kilns) to decompose the plastics present, and to concentrate metals in bottom ash. The concentrated metals (e.g. copper, precious metals) can be supplied as a secondary raw material to metal smelters, while the pyrolysis of plastics allows the recovery of fuel gases, volatilising agents and, eventually, energy. Indeed, WEEE, such as a printed circuit boards (PCBs) usually contains brominated flame retardants (BFRs). From these materials, hydrobromic acid (HBr) is formed as a product of their thermal decomposition. In the present work, the bromination was studied of copper, silver and gold by HBr, originating from BFRs, such as Tetrabromobisphenol A (TBBPA) and Tetrabromobisphenol A-Tetrabromobisophenol A diglycidyl ether (TTDE) polymer; possible volatilization of the bromides formed was monitored using a thermo-gravimetric analyzer (TGA) and a laboratory-scale furnace for treating samples of metals and BFRs under an inert atmosphere and at a wide range of temperatures. The results obtained indicate that up to about 50% of copper and silver can evolve from sample residues in the form of volatile CuBr and AgBr above 600 and 1000°C, respectively. The reactions occur in the molten resin phase simultaneously with the decomposition of the brominated resin. Gold is resistant to HBr and remains unchanged in the residue.

X-ray emission spectra of graphene nanosheets.

Investigations of the electronic structure of graphene nanosheets synthesized by the reduction of oxidized graphene nanosheets were carried out using ultra-soft X-ray emission spectroscopy (USXES). Oxidized graphene nanosheets were produced from carbon nanofiber starting material using a modified Hummers method. X-ray diffraction, and scanning and transmission electron microscopy investigations were used in addition to USXES to study the electronic structure evolution from carbon nanofibers to graphene nanosheets. The effect of the degree of corrugation of the graphene nanosheets on the fine structure of the CK(alpha)-emission bands was revealed by USXES. It was found that corrugation of the graphene nanosheets is caused by overlapping of the pi-orbitals and formation of mixed (sigma + pi)-states.

Vaporization of zinc during thermal treatment of ZnO with tetrabromobisphenol A (TBBPA).

In the present work we investigate the vaporization of zinc or its compounds during thermal treatment of ZnO with tetrabromobisphenol A. Samples of 2g of ZnO:TBBPA (3.34:1) were isothermally heated in a laboratory-scale furnace at temperatures from 490 °C to 950 °C, and the solid, condensed and gaseous products formed were analyzed by X-ray diffraction analysis, electron probe microanalysis, inductively coupled plasma analysis, ion chromatography, and gas chromatography coupled with mass spectrometry. The results obtained indicate that the vaporization of ZnBr(2) formed strongly depends on heating time and temperature, yet is restrained by char, if formed with sufficient yield (above 15 wt%). Starting from 850 °C, this char commences carbothermic reduction of any remaining ZnO, which from then begins to evaporate as zinc metal vapor. Volatilization of zinc is completed at 950 °C. The presence of 5 vol.% of oxygen has no significant effect on the vaporization of formed ZnBr(2), the carbothermic reduction or the volatilization of metallic zinc. Strongly oxidizing conditions (20 vol.% of oxygen), however, boost the oxidation of char and thus the vaporization of ZnBr(2), but prevent carbothermic reduction of any un-reacted ZnO by depleting this char.

Influence of temperature and heating time on bromination of zinc oxide during thermal treatment with tetrabromobisphenol A.

Our prior research indicates that hydrogen bromide (HBr) evolved during thermal decomposition of tetrabromobisphenol A (TBBPA) can be utilized as a reagent for selective bromination and evaporation of zinc oxide. The present work investigated dependency of the bromination reaction on time at selected temperatures using a laboratory-scale furnace. The formed solid, condensed, and gaseous products were analyzed by X-ray diffraction analysis, electron probe microanalysis, inductively coupled plasma analysis, ion chromatography, and gas chromatography coupled with mass spectrometry. Results indicate that the bromination rate is strongly dependent on heating time. This dependency is a direct consequence of progress in the decomposition of TBBPA, which provides inorganic bromine suitable for the reaction. The bromination rate increases with time until the bromine source is depleted. The process is shorter at higher applied temperatures and appears instantaneous at 310 degrees C and above. However, the maximum bromination yield is independent of the applied conditions and ranges from 64 to 70%. Additionally, the influence of oxidizing conditions on the bromination reaction and the effect of ZnO on decomposition of TBBPA were investigated in this study.

Studies on bromination and evaporation of zinc oxide during thermal treatment with TBBPA.

Thermodynamic considerations indicate that base metal oxides such as ZnO, PbO, Cu2O, etc. should easily react with HBr, the main gaseous product from the thermal decomposition of tetrabromobisphenol A (TBBPA), to form low boiling point metallic bromides suitable for volatile separation. In this work a differential scanning calorimeter and laboratory-scale furnace was used to investigate the scope and conditions for the bromination of ZnO by the thermal decomposition of TBBPA. The formed solid, condensed, and gaseous products were analyzed by X-ray diffraction analysis, electron probe microanalysis, inductively coupled plasma analysis, ion chromatography, and gas chromatography coupled with mass spectrometry. The results obtained in this study indicate that the bromination of ZnO occurred at 272 degrees C (DSC) and above 290 degrees C (furnace) with an effectiveness of 41, 64, and 81% dependent on the experimental conditions. Volatilization of the formed ZnBr2 began at 340 degrees C and had a 45% yield at 650 degrees C. This yield corresponded to 28-36% of the original zinc content in the mixture under the present experimental conditions.

Determination of physicochemical properties of tetrabromobisphenol A.

Aqueous solubility (Sw), 1-octanol/water partition coefficient (Kow), and vapor pressure of the nonionic form of 2,2',6,6'-tetrabromo-4,4'-isopropylidenediphenol (tetrabromobisphenol A or TBBP-A) were measured. From this, enthalpies of solution and vaporization were estimated. Furthermore, enthalpy of fusion and melting point were measured to estimate subcooled liquid vapor pressure, the infinite dilution activity coefficient, and Henry's law constant. Since TBBP-A is expected to exit in both ionic and nonionic forms at near neutral pH, pH effects on physicochemical properties were also examined. Because of the ionization of TBBP-A, Sw increased by five orders of magnitude, while Kow decreased by eight orders of magnitude. Furthermore, an analytical model based on mass balance and dissociation of TBBP-A was applied to represent the pH dependence.

Measurement of temperature dependence for the vapor pressures of twenty-six polychlorinated biphenyl congeners in commercial Kanechlor mixtures by the Knudsen effusion method.

The vapor pressures of the major congeners in commercial polychlorinated biphenyl (PCB) mixtures (Kanechlors; Kanebuchi Chemical Industry, Tokyo, Japan) have been experimentally determined by Knudsen mass loss effusion. We obtained vapor pressures for the individual PCBs in the crystalline solid, liquid, and subcooled liquid forms as a function of temperature. We derived the thermodynamic parameters, such as the enthalpies of sublimation and vaporization, from the temperature dependence of the vapor pressure by the Clausius-Clapeyron equation. To decide whether the commercial PCB mixtures were ideal solutions, we obtained the activity coefficients by comparing our experimental vapor pressures for pure PCB congeners with those calculated from Kanechlor molar compositional data and vapor pressure values. In many cases, we found that, at 298 K, the values of the activity coefficients of major PCBs in Kanechlor 300 and 500 ranged from 1 to 2. Thus, we suggested that the commercial PCB mixtures show slight positive deviations from ideal solution (Raoult's Law) behavior at ambient temperatures.

Synthesis of amorphous carbon nanoparticles and carbon encapsulated metal nanoparticles in liquid benzene by an electric plasma discharge in ultrasonic cavitation field.

A newly-developed method permits an electric plasma discharge to occur with relatively low electric power in insulating organic solutions due to the presence of an ultrasonic cavitation. A stable electric plasma could be generated in an ultrasonic cavitation field containing a thousand tiny activated bubbles, in which the electric conductivity could be improved due to formed radicals and free electrons, using copper electrodes and a titanium ultrasonic horn. This method allowed us to synthesize pyrolytic amorphous carbon nanoparticles smaller than about 30 nm in diameter from benzene liquid. In addition, we synthesized TiC nanoparticles about 50-150 nm in size, and copper nanoparticles smaller than 10 nm, which were encapsulated in multilayered graphite cages. Finally, we used GC-MS and MALDI-TOF-MS to observe and analyze the polymerized compounds and the degree of polymerization of the benzene liquid after the plasma treatment.

Thermodynamic prediction of vapor pressures for polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and polybrominated dibenzo-p-dioxins.

The vapor pressures and thermal properties of nonmeasured polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and seven polybrominated dibenzo-p-dioxins (PBDDs) were predicted using a correlation method based on the experimental vapor pressures for 22 PCDD/Fs and octabrominated dibenzo-p-dioxin obtained by the Knudsen effusion method. The vapor pressures of all 59 PCDDs and 131 PCDFs predicted in the present study were more or less higher than the data predicted by Rordorf, although the calculation method was the same. For the most toxic 2,3,7,8-tetrachlorinated dibenzo-p-dioxin, the vapor pressure at 298 K predicted in the present study was 6.2 x 10(-6) Pa, which was 31-fold higher than the value provided by Rordorf (2.0 x 10(-7) Pa). The predicted vapor pressures for low-brominated PBDDs agreed with the data estimated by Rordorf. For 2,3,7,8-tetrabrominated dibenzo-p-dioxin, the vapor pressure predicted in the present study was 1.8 x 10(-8) Pa, obviously lower than those predicted by Rordorf.

Fate of PCDD/PCDF during mechanical-biological sludge treatment.

In this preliminary study the seventeen 2,3,7,8-substituted congeners of PCDD/PCDF were analyzed at the inlet and outlet water and for three sewage sludge samples taken from different treatment stages to check behaviours of PCDD/PCDF at a municipal wastewater treatment plant (MWTP) in Poland. At the inlet (untreated sewage) water dominated PCDD congeners, whereas in the outlet (treated water) dominated the PCDF congeners. The octaCDD, 1,2,3,4,6,7,8-heptaCDD/CDF and octaCDF congeners dominated in all of the sludge samples. The total toxicity load gradually increased in the series excess, digested and dewatered sludge and amounted to 12.2, 14.4 and 16.9ngI-TEQkg(-1).

Application of the conductor-like screening model for real solvents for prediction of the aqueous solubility of chlorobenzenes depending on temperature and salinity.

The conductor-like screening model for real solvents (COSMO-RS) is applied to the prediction of the aqueous solubility of chlorobenzenes (CBZs) in a liquid-liquid and liquid-solid equilibrium. The solubilities of CBZs at temperatures ranging from 5 to 60 degrees C are reported, and the enthalpies of solution are derived from van't Hoff plots. The salting effect of 12 chlorobenzenes is determined for sodium, potassium, and calcium solutions at concentrations ranging from 0.01 to 3.5 mol/L. A new experimental aqueous solubility value is given for the isotopic labeled 1,2,4-trichlorobenzene determined at 25 degrees C by the generator column procedure. The COSMO-RS method presented in this study can be useful to estimate the magnitude of the salt effect and temperature influence on the behavior of any chlorobezene under environmental conditions.

Vapor pressure of ten polychlorinated biphenyl congeners and two commercial fluids as a function of temperature.

The Knudsen mass-loss effusion technique was used to measure the vapor pressures of commercial Kanechlor fluids (Kanechlor 300 and Kanechlor 500) and 10 major individual polychlorinated biphenyls (PCBs) in Kanechlors as a function of temperature and ortho-chlorine substitution. From the temperature dependence of vapor pressure, the thermodynamic parameters, such as enthalpies and entropies of sublimation and vaporization, were derived using the Clausius-Clapeyron equation. The results were compared with both experimental and calculated literature values. The ortho-chlorine substitution effects on the vapor pressure of major PCB congeners in Kanechlor mixtures were studied on the same homologous series. Within this series, the greater the number of chlorine substitutions in the ortho-positions, the higher the vapor pressure, because of the ortho-effect.

Vapor pressures and enthalpies of sublimation of 17 polychlorinated dibenzo-p-dioxins and five polychlorinated dibenzofurans.

An apparatus for vapor pressure measurement with a very small cell by the mass-loss Knudsen effusion technique was tested with solid benzoic acid and anthracene. The vapor pressure and enthalpy of sublimation results of the two reference compounds were in good agreement with accepted literature data. The vapor pressures at different temperatures of 17 polychlorinated dibenzo-p-dioxins (including dibenzo-p-dioxin) and five polychlorinated dibenzofurans (including dibenzofuran) were measured with the apparatus, and the enthalpies of sublimation of the 22 dioxins and furans were derived from the temperature dependence of vapor pressure. The results were systematically compared with the literature data.

Formation behavior of PCDD/Fs in PVC pyrolysis with copper oxide.

Formation and decomposition behaviors of PCDD/Fs during pyrolysis of polyvinyl chloride (PVC) with CuO have been investigated. These reactions proceed simultaneously, and the rate of decomposition exceeds that of formation with further retention. More 2,3,7,8-TCDD is formed when the dechlorination of PCDD/Fs proceeds significantly. Homologue profile patterns of PCDD/Fs show that the fractions of O8CDD and H6CDFs are relatively larger within PCDDs and PCDFs, respectively. Extremely large amounts of PCDD/Fs are obtained with the long retention time at 200 degrees C. The formation of PCDD/Fs decreases drastically with increase in the molar ratio of CuO/PVC. The acceptability of thermodynamic calculations on the formation of PCDD/Fs is also investigated. The thermodynamic calculated tendency of the effect of oxygen on the formation of PCDD/Fs agrees well with the experimental results, although absolute values of the amount of PCDD/Fs are much different.