Breakthrough CO2 adsorption in bio-based activated carbons

In this work, the effects of different methods of activation on CO₂ adsorption performance of activated carbon were studied. Activated carbons were prepared from biochar, obtained from fast pyrolysis of white wood, using three different activation methods of steam activation, CO₂ activation and Potassium hydroxide (KOH) activation. CO₂ adsorption behavior of the produced activated carbons was studied in a fixed-bed reactor set-up at atmospheric pressure, temperature range of 25–65°C and inlet CO₂ concentration range of 10–30 mol% in He to determine the effects of the surface area, porosity and surface chemistry on adsorption capacity of the samples. Characterization of the micropore and mesopore texture was carried out using N₂ and CO₂ adsorption at 77 and 273 K, respectively. Central composite design was used to evaluate the combined effects of temperature and concentration of CO₂ on the adsorption behavior of the adsorbents. The KOH activated carbon with a total micropore volume of 0.62 cm³/g and surface area of 1400 m²/g had the highest CO₂ adsorption capacity of 1.8 mol/kg due to its microporous structure and high surface area under the optimized experimental conditions of 30 mol% CO₂ and 25°C. The performance of the adsorbents in multi-cyclic adsorption process was also assessed and the adsorption capacity of KOH and CO₂ activated carbons remained remarkably stable after 50 cycles with low temperature (160°C) regeneration.     

Development of a field enhanced photocatalytic device for biocide of coliform bacteria

A field enhanced flow reactor using bias assisted photocatalysis was developed for bacterial disinfection in lab-synthesized and natural waters. The reactor provided complete inactivation of contaminated waters with flow rates of 50 m L/min. The device consisted of titanium dioxide nanotube arrays, with an externally applied bias of up to 6 V. Light intensity, applied voltage, background electrolytes and bacteria concentration were all found to impact the device performance. Complete inactivation of Escherichia coli W3110(~ 8 × 10~3CFU/m L) occurred in 15 sec in the reactor irradiated at 25 m W/cm~2 with an applied voltage of 4 V in a 100 ppm NaCl solution. Real world testing was conducted using source water from Emigration Creek in Salt Lake City, Utah. Disinfection of natural creek water proved more challenging, providing complete bacterial inactivation after 25 sec at 6 V. A reduction in bactericidal efficacy was attributed to the presence of inorganic and organic species, as well as the increase in robustness of natural bacteria.     

Zero-valent iron doped carbons readily developed from sewage sludge for lead removal from aqueous solution

Low-cost but high-efficiency composites of iron-containing porous carbons were prepared using sewage sludge and ferric salts as raw materials. Unlike previous time- and energy-consuming manufacturing procedures, this study shows that pyrolyzing a mixture of sludge and ferric salt can produce suitable composites for lead adsorption. The specific surface area, the total pore volume and the average pore width of the optimal composite were 321 m²/g, 0.25 cm³/g, and 3.17 nm, respectively. X-ray diffraction analysis indicated that ferric salt favored the formation of metallic iron, while Fourier transform infrared spectroscopy revealed the formation of hydroxyl and carboxylic groups. The result of batch tests indicated that the adsorption capacity of carbons activated with ferric salt could be as high as 128.9 mg/g, while that of carbons without activation was 79.1 mg/g. The new manufacturing procedure used in this study could save at least 19.5 kJ of energy per gram of activated carbon.     

Potential ammonia emission from flag leaves of paddy rice (Oryza sativa L. cv. Koshihikari)

The present study aimed to investigate the potential ammonia (NH₃) emission from flag leaves of paddy rice (Oryza sativa L. cv. Koshihikari). The study was conducted at a paddy field in central Japan that was designed as a free-air CO₂ enrichment (FACE) facility for paddy rice. A dynamic chamber method was used to measure the potential NH₃ emissions. The air concentrations of NH₃ at two heights (2 and 6 m from the ground surface) were measured using a filter-pack method, and the exchange fluxes of NH₃ of the whole paddy field were calculated using a gradient method. The flag leaves showed potential NH₃ emissions of 25-38 ng N cm⁻² h⁻¹ in the daytime from the heading to the maturity stages, and they showed potentials of approximately 22 ng N cm⁻² h⁻¹, even in the nighttime, at the heading and mid-ripening stages. The exchange fluxes of NH₃ of the whole paddy field in the daytime were net emissions of 0.9-3.9 g N ha⁻¹ h⁻¹ whereas the exchange fluxes of NH₃ in the nighttime were approximately zero.     

The application of iron mesh double layer as anode for the electrochemical treatment of Reactive Black 5 dye

In this work a novel anode configuration consisting of an iron mesh double layer is proposed for the electrochemical treatment of wastewater. The removal of Reactive Black 5 dye(RB5) from synthetic contaminated water was used as a model system. At a constant anode surface area, identical process operating parameters and batch process mode, the iron mesh double layer electrode showed better performance compared to the conventional single layer iron mesh. The double layer electrode was characterized by RB5 and chemical oxygen demand(COD) removal efficiency of 98.2% and 97.7%, respectively, kinetic rate constant of 0.0385/min, diffusion coefficient of 4.9 × 10~(-5)cm~2/sec and electrical energy consumption of 20.53 kWh/kgdye removed. In the continuous flow system, the optimum conditions suggested by Response Surface Methodology(RSM) are: initial solution p H of 6.29,current density of 1.6 m A/cm~2, electrolyte dose of 0.15 g/L and flow rate of 11.47 m L/min which resulted in an RB5 removal efficiency of 81.62%.     

Physico-chemical characterization and source tracking of black carbon at a suburban site in Beijing

Particles from ambient air and combustion sources including vehicle emission, coal combustion and biomass burning were collected and chemically pretreated with the purpose of obtaining isolated BC (black carbon) samples. TEM (transmission electron microscopy) results indicate that BC from combustion sources shows various patterns, and airborne BC appears spherical and about 50 nm in diameter with a homogeneous surface and turbostratic structure. The BET (Barrett–Emmett–Teller) results suggest that the surface areas of these BC particles fall in the range of 3–23 m²/g, with a total pore volume of 0.03–0.05 cm³/g and a mean pore diameter of 7–53 nm. The nitrogen adsorption–desorption isotherms are indicative of the accumulation mode and uniform pore size. O₂-TPO (temperature programmed oxidation) profiles suggest that the airborne BC oxidation could be classified as the oxidation of amorphous carbon, which falls in the range of 406–490°C with peaks at 418, 423 and 475°C, respectively. Generally, the BC characteristics and source analysis suggest that airborne BC most likely comes from diesel vehicle emission at this site.     

Preparation and evaluation of aminopropyl-functionalized manganese-loaded SBA-15 for copper removal from aqueous solution

A novel material, aminopropyl-functionalized manganese-loaded SBA-15 (NH₂-Mn-SBA-15), was synthesized by bonding 3-aminopropyl trimethoxysilane (APTMS) onto manganese-loaded SBA-15 (Mn-SBA-15) and used as a Cu^2 + adsorbent in aqueous solution. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction spectra (XRD), N₂ adsorption/desorption isotherms, high resolution field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the NH₂-Mn-SBA-15. The ordered mesoporous structure of SBA-15 was remained after modification. The manganese oxides were mainly loaded on the internal surface of the pore channels while the aminopropyl groups were mainly anchored on the external surface of SBA-15. The adsorption of Cu^2 + on NH₂-Mn-SBA-15 was fitted well by the Langmuir equation and the maximum adsorption capacity of NH₂-Mn-SBA-15 for Cu^2 + was over two times higher than that of Mn-SBA-15 under the same conditions. The Elovich equation gave a good fit for the adsorption process of Cu^2 + by NH₂-Mn-SBA-15 and Mn-SBA-15. Both the loaded manganese oxides and the anchored aminopropyl groups were found to contribute to the uptake of Cu^2 +. The NH₂-Mn-SBA-15 showed high selectivity for copper ions. Consecutive adsorption–desorption experiments showed that the NH₂-Mn-SBA-15 could be regenerated by acid treatment without altering its properties.     

Removal of Cs from water and soil by ammonium-pillared montmorillonite/Fe3O4 composite

To remove cesium ions from water and soil, a novel adsorbent was synthesized by following a one-step co-precipitation method and using non-toxic raw materials. By combining ammonium-pillared montmorillonite (MMT) and magnetic nanoparticles (Fe₃O₄), an MMT/Fe₃O₄ composite was prepared and characterized. The adsorbent exhibited high selectivity of Cs⁺ and could be rapidly separated from the mixed solution under an external magnetic field. Above all, the adsorbent had high removal efficiency in cesium-contaminated samples (water and soil) and also showed good recycling performance, indicating that the MMT/Fe₃O₄ composite could be widely applied to the remediation of cesium-contaminated environments. It was observed that the pH, solid/liquid ratio and initial concentration affected adsorption capacity. In the presence of coexisting ions, the adsorption capacity decreased in the order of Ca^2 + > Mg^2 + > K⁺ > Na⁺, which is consistent with our theoretical prediction. The adsorption behavior of this new adsorbent could be expressed by the pseudo-second-order model and Freundlich isotherm. In addition, the adsorption mechanism of Cs⁺ was NH₄⁺ ion exchange and surface hydroxyl group coordination, with the former being more predominant.     

A hydroxyl radical detection system using gas expansion and fast gating laser-induced fluorescence techniques

An OH radical measurement instrument based on Fluorescence Assay by Gas Expansion(FAGE)has been developed in our laboratory.Ambient air is introduced into a low-pressure fluorescence cell through a pinhole aperture and irradiated by a dye laser at a high repetition rate of 8.5 k Hz.The OH radical is both excited and detected at 308 nm using A-X(0,0)band.To satisfy the high efficiency needs of fluorescence collection and detection,a 4-lens optical system and a self-designed gated photomultiplier(PMT)is used,and gating is actualized by switching the voltage applied on the PMT dynodes.A micro channel photomultiplier(MCP)is also prepared for fluorescence detection.Then the weak signal is accumulated by a photon counter in a specific timing.The OH radical excitation spectrum range in the wavelength of 307.82–308.2 nm is detected and the excited line for OH detection is determined to be Q_1(2)line.The calibration of the FAGE system is researched by using simultaneous photolysis of H_2O and O_2.The minimum detection limit of the instrument using gated PMT is determined to be 9.4×10~5molecules/cm~3,and the sensitivity is 9.5×10~(-7)cps/(OH·cm~(-3)),with a signal-to-noise ratio of 2 and an integration time of 60 sec,while OH detection limit and the detection sensitivity using MCP is calculated to be 1.6×10~5molecules/cm~3and 2.3×10~(-6)cps/(OH·cm~(-3)).The laboratory OH radical measurement is carried out and results show that the proposed system can be used for atmospheric OH radical measurement.     

Characterization of particle number size distribution and new particle formation in Southern China

Knowledge of particle number size distribution(PND) and new particle formation(NPF)events in Southern China is essential for mitigation strategies related to submicron particles and their effects on regional air quality,haze,and human health.In this study,seven field measurement campaigns were conducted from December 2013 to May 2015 using a scanning mobility particle sizer(SMPS) at four sites in Southern China,including three urban sites and one background site.Particles were measured in the size range of15-515 nm,and the median particle number concentrations(PNCs) were found to vary in the range of 0.3× 10~4-2.2 × 10~4 cn~(-3) at the urban sites and were approximately 0.2 × 10~4 cm~(-3) at the background site.The peak diameters at the different sites varied largely from 22 to 102 nm.The PNCs in the Aitken mode(25-100 nm) at the urban sites were up to 10 times higher than they were at the background site,indicating large primary emissions from traffic at the urban sites.The diurnal variations of PNCs were significantly influenced by both rush hour traffic at the urban sites and NPF events.The frequencies of NPF events at the different sites were0%-30%,with the highest frequency occurring at an urban site during autumn.With higher SO_2 concentrations and higher ambient temperatures being necessary,NPF at the urban site was found to be more influenced by atmospheric oxidizing capability,while NPF at the background site was limited by the condensation sink.This study provides a unique dataset of particle number and size information in various environments in Southern China,which can help understand the sources,formation,and the climate forcing of aerosols in this quickly developing region,as well as help constrain and validate NPF modeling.     

Enhanced photoelectrocatalytic degradation of ammonia by in situ photoelectrogenerated active chlorine on TiO2 nanotube electrodes

TiO_2 nanotube(Ti NT) electrodes anodized in fluorinated organic solutions were successfully prepared on Ti sheets. Field-emission scanning electron microscopy(FE-SEM) and X-ray diffraction(XRD) were performed to characterize the TiNT electrodes. The linear voltammetry results under irradiation showed that the TiNT electrode annealed at 450°C presented the highest photoelectrochemical activity. By combining photocatalytic with electrochemical process, a significantly synergetic effect on ammonia degradation was observed with Na_2SO_4 as supporting electrolyte at pH 10.7. Furthermore, the photoelectrocatalytic efficiency on the ammonia degradation was greatly enhanced in presence of chloride ions without the limitation of pH. The degradation rate was improved by 14.8 times reaching 4.98 × 10~(-2) min~(-1) at pH 10.7 and a faster degradation rate of 6.34 × 10~(-2) min~(-1)was obtained at pH 3.01. The in situ photoelectrocatalytic generated active chlorine was proposed to be responsible for the improved efficiency. On the other hand, an enhanced degradation of ammonia using TiNT electrode fabricated in fluorinated organic solution was also confirmed compared to TiNT electrode anodized in fluorinated water solution and TiO_2 film electrode fabricated by sol–gel method. Finally, the effect of chloride concentration was also discussed.     

UV light tolerance and reactivation potential of tetracycline-resistant bacteria from secondary effluents of a wastewater treatment plant

Tetracycline-resistant bacteria (TRB) are of concern as emerging microbial contaminants in reclaimed water. To understand the effects of UV disinfection on TRB, both inactivation and reactivation profiles of TRB, as well as 16 tetracycline-resistant isolates from secondary effluent, were characterized in this study. The inactivation ratio of TRB was significantly lower (3.0-log) than that of heterotrophic bacteria (> 4.0-log) in the secondary effluent. Additionally, the proportion of TRB significantly increased from 1.65% to 15.51% under 20 mJ/cm² ultraviolet (UV) exposure. The inactivation rates of tetracycline-resistant isolates ranged from 0.57/s to 1.04/s, of which tetracycline-resistant Enterobacter-1 was the most tolerant to UV light. The reactivation of TRB, tetracycline-resistant isolated strains, as well as heterotrophic bacteria commonly occurred in the secondary effluent even after 20 mJ/cm² UV exposure. The colony forming ability of TRB and heterotrophic bacteria reached 3.2-log and 3.0-log under 20 mJ/cm² UV exposure after 22 hr incubation. The final inactivation ratio of tetracycline-resistant Enterobacter-1 was 1.18-log under 20 mJ/cm² UV exposure after 22 hr incubation, which is similar to those of TRB (1.18-log) and heterotrophic bacteria (1.19-log). The increased proportion of TRB and the reactivation of tetracycline-resistant enterobacteria in reclaimed water could induce a microbial health risk during wastewater reuse.     

Kinetic and products study of the gas-phase reaction of Lewisite with ozone under atmospheric conditions

The rate constant for the gas-phase reaction of O_3 and Lewisite was studied in air using the smog chamber technique. The experiments were carried out under pseudo-first-order reaction conditions with [O_3] [Lewisite]. The observed rate constant of O_3 with Lewisite was(7.83 ± 0.38) × 10~(-19)cm~3/(molecule·sec) at 298 ± 2 K. Lewisite was discussed in terms of reactivity with O_3 and its relationship with the ionization potential. Our results show that the rate constant for the gas-phase reaction of O_3 with Lewisite is in line with the trend of the rate constants of O_3 with haloalkenes.     

Effect of AlCl3 concentration on nanoparticle removal by coagulation

In recent years, engineered nanoparticles, as a new group of contaminants emerging in natural water, have been given more attention. In order to understand the behavior of nanoparticles in the conventional water treatment process, three kinds of nanoparticle suspensions, namely multi-walled carbon nanotube-humic acid (MWCNT-HA), multi-walled carbon nanotube-N,N-dimethylformamide (MWCNT-DMF) and nanoTiO₂-humic acid (TiO₂-HA) were employed to investigate their coagulation removal efficiencies with varying aluminum chloride (AlCl₃) concentrations. Results showed that nanoparticle removal rate curves had a reverse “U” shape with increasing concentration of aluminum ion (Al^3 +). More than 90% of nanoparticles could be effectively removed by an appropriate Al^3 + concentration. At higher Al^3 + concentration, nanoparticles would be restabilized. The hydrodynamic particle size of nanoparticles was found to be the crucial factor influencing the effective concentration range (ECR) of Al^3 + for nanoparticle removal. The ECR of Al^3 + followed the order MWCNT-DMF > MWCNT-HA > TiO₂-HA, which is the reverse of the nanoparticle size trend. At a given concentration, smaller nanoparticles carry more surface charges, and thus consume more coagulants for neutralization. Therefore, over-saturation occurred at relatively higher Al^3 + concentration and a wider ECR was obtained. The ECR became broader with increasing pH because of the smaller hydrodynamic particle size of nanoparticles at higher pH values. A high ionic strength of NaCl can also widen the ECR due to its strong potential to compress the electric double layer. It was concluded that it is important to adjust the dose of Al^3 + in the ECR for nanoparticle removal in water treatment.     

Denitrification and biofilm growth in a pilot-scale biofilter packed with suspended carriers for biological nitrogen removal from secondary effluent

Tertiary denitrification is an effective method for nitrogen removal from wastewater. A pilot-scale biofilter packed with suspended carriers was operated for tertiary denitrification with ethanol as the organic carbon source. Long-term performance, biokinetics of denitrification and biofilm growth were evaluated under filtration velocities of 6, 10 and 14 m/hr. The pilot-scale biofilter removed nitrate from the secondary effluent effectively, and the nitrate nitrogen (NO₃-N) removal percentage was 82%, 78% and 55% at the filtration velocities of 6, 10 and 14 m/hr, respectively. At the filtration velocities of 6 and 10 m/hr, the nitrate removal loading rate increased with increasing influent nitrate loading rates, while at the filtration velocity of 14 m/hr, the removal loading rate and the influent loading rate were uncorrelated. During denitrification, the ratio of consumed chemical oxygen demand to removed NO₃-N was 3.99–4.52 mg/mg. Under the filtration velocities of 6, 10 and 14 m/hr, the maximum denitrification rate was 3.12, 4.86 and 4.42 g N/(m²·day), the half-saturation constant was 2.61, 1.05 and 1.17 mg/L, and the half-order coefficient was 0.22, 0.32 and 0.24 (mg/L)^1/2/min, respectively. The biofilm biomass increased with increasing filtration velocity and was 2845, 5124 and 7324 mg VSS/m² at filtration velocities of 6, 10 and 14 m/hr, respectively. The highest biofilm density was 44 mg/cm³ at the filtration velocity of 14 m/hr. Due to the low influent loading rate, biofilm biomass and thickness were lowest at the filtration velocity of 6 m/hr.     

Optimization of CO2 adsorption capacity and cyclical adsorption/desorption on tetraethylenepentamine-supported surface-modified hydrotalcite

The objective of this research was to investigate CO_2adsorption capacity of tetraethylenepentamine-functionalized basic-modified calcined hydrotalcite(TEPA/b-c HT)sorbents at atmospheric pressure formed under varying TEPA loading levels,temperatures,sorbent weight to total gaseous flow rate(W/F)ratios and CO_2concentrations in the influent gas.The TEPA/b-c HT sorbents were characterized by means of X-ray diffraction(XRD),Fourier transform infrared spectrometry(FT–IR),thermal gravimetric analysis(TGA),Brunauer–Emmet–Teller(BET)analysis of nitrogen(N_2)adsorption/desorption and carbon–hydrogen–nitrogen(CHN)elemental analysis.Moreover,a full 2~4factorial design with three central points at a 95%confidence interval was used to screen important factor(s)on the CO_2adsorption capacity.It revealed that85.0%variation in the capacity came from the influence of four main factors and the15.0%one was from their interactions.A face-centered central composite design response surface method(FCCCD–RSM)was then employed to optimize the condition,the maximal capacity of 5.5–6.1 mmol/g was achieved when operating with a TEPA loading level of 39%–49%(W/W),temperature of 76–90°C,W/F ratio of 1.7–2.60(g·sec)/cm~3and CO_2concentration of 27%–41%(V/V).The model fitted sufficiently the experimental data with an error range of±1.5%.From cyclical adsorption/desorption and selectivity at the optimal condition,the 40%TEPA/b-c HT still expressed its effective performance after eight cycles.     

Carbon balance of an intensively grazed temperate pasture in two climatically contrasting years

Grazed grasslands occupy 26% of the earth's ice free land surface and are therefore an important component of the global C balance. In New Zealand, pastoral agriculture is the dominant land use and recent research has shown that soils under intensive dairy pastures have lost large amounts of carbon (∼1000 kg C ha⁻¹ y⁻¹) during the past few decades. The objective of this research was to determine the net ecosystem carbon balance (NECB) of an intensively grazed dairy pasture in New Zealand. Net ecosystem CO₂ exchange (NEE) was measured using an eddy covariance (EC) system from 1 January 2008 to 31 December 2009. Other C imports (feed) and exports (milk, methane, leaching, and harvested biomass) were calculated from farm production data and literature values. During 2008 there was a one in 100 year drought during summer/autumn, which was followed by a very wet winter. There were no prolonged periods of above or below average rainfall or soil moisture in 2009, but temperatures were consistently lower than 2008. The severe summer/autumn drought during 2008 caused a loss of CO₂ to the atmosphere, but annual NEE remained negative (a CO₂ sink, −1610 ± 500 kg C ha⁻¹), because CO₂ lost during the drought was regained during the winter and spring. The site was also a net CO₂ sink during 2009 despite the colder than usual conditions (−2290 ± 500 kg C ha⁻¹). Including C imports and exports in addition to CO₂ exchange revealed that the site was a C sink in both years, with a NECB of 590 ± 560 kg C ha⁻¹ in 2008, and 900 ± 560 kg C ha⁻¹ in 2009. The C sequestration found in this study is in agreement with most other Northern Hemisphere EC studies of grazed pastures on mineral soils, but is not consistent with the large C losses reported for soils under dairy pastures throughout New Zealand. In the current study (like many other EC studies) the influence of climatic conditions and management practices on the annual C balance was only semi-quantitatively assessed. An extended period of EC measurements combined with modelling is required to more accurately quantify the effect of different climatic conditions on the annual C balance, and the influence of different management practices needs to be quantified using specifically designed studies (such as paired EC towers), so that practices which minimise C losses and maximise C sequestration can be identified.     

Positively charged microporous ceramic membrane for the removal of Titan Yellow through electrostatic adsorption

To develop a depth filter based on the electrostatic adsorption principle, positively charged microporous ceramic membrane was prepared from a diatomaceous earth ceramic membrane.The internal surface of the highly porous ceramic membrane was coated with uniformly distributed electropositive nano-Y_2O_3 coating. The dye removal performance was evaluated through pressurized filtration tests using Titan Yellow aqueous solution. It showed that positively charged microporous ceramic membrane exhibited a flow rate of 421 L/(m~2·hr) under the trans-membrane pressure of 0.03 bar. Moreover it could effectively remove Titan Yellow with feed concentration of 10 mg/L between pH 3 to 8. The removal rate increased with the enhancement of the surface charge properties with a maximum rejection of 99.6%. This study provides a new and feasible method of removing organic dyes in wastewater. It is convinced that there will be a broad market for the application of charged ceramic membrane in the field of dye removal or recovery from industry wastewater.     

CO2 sequestration utilizing basic-oxygen furnace slag: Controlling factors, reaction mechanisms and V–Cr concerns

Basic-oxygen furnace slag(BOF-slag) contains 35%CaO,a potential component for CO_2sequestration.In this study,slag-water-CO_2 reaction experiments were conducted with the longest reaction duration extending to 96 hr under high CO_2 pressures of 100-300 kg/cm2 to optimize BOF-slag carbonation conditions,to address carbonation mechanisms,and to evaluate the extents of V and Cr release from slag carbonation.The slag carbonation degree generally reached the maximum values after 24 hr slag-water-CO_2 reaction and was controlled by slag particle size and reaction temperature.The maximum carbonation degree of 71%was produced from the experiment using fine slag of0.5 mm under 100℃and a CO_2 pressure of 250 kg/cm~2 with a water/slag ratio of 5.Vanadium release from the slag to water was significantly enhanced(generally 2 orders) by slag carbonation.In contrast,slag carbonation did not promote chromium release until the reaction duration exceeded 24 hr.However,the water chromium content was generally at least an order lower than the vanadium concentration,which decreased when the reaction duration exceeded 24 hr.Therefore,long reaction durations of 48-96 hr are proposed to reduce environmental impacts while keeping high carbonation degrees.Mineral textures and water compositions indicated that Mg-wustite,in addition to CaO-containing minerals,can also be carbonated.Consequently,the conventional expression that only considered carbonation of the CaO-containing minerals undervalued the CO_2 sequestration capability of the BOF-slag by~20%.Therefore,the BOF-slag is a better CO_2 storage medium than that previously recognized.     

Mechanism of Methylene Blue adsorption on hybrid laponite-multi-walled carbon nanotube particles

The kinetics of adsorption and parameters of equilibrium adsorption of Methylene Blue(MB)on hybrid laponite-multi-walled carbon nanotube(NT)particles in aqueous suspensions were determined.The laponite platelets were used in order to facilitate disaggregation of NTs in aqueous suspensions and enhance the adsorption capacity of hybrid particles for MB.Experiments were performed at room temperature(298 K),and the laponite/NT ratio(X_l)was varied in the range of 0–0.5.For elucidation of the mechanism of MB adsorption on hybrid particles,the electrical conductivity of the system as well as the electrokinetic potential of laponite-NT hybrid particles were measured.Three different stages in the kinetics of adsorption of MB on the surface of NTs or hybrid laponite-NT particles were discovered to be a fast initial stage Ⅰ(adsorption time t=0–10 min),a slower intermediate stage Ⅱ(up to t=120 min)and a long-lasting final stage Ⅲ(up to t=24 hr).The presence of these stages was explained accounting for different types of interactions between MB and adsorbent particles,as well as for the changes in the structure of aggregates of NT particles and the long-range processes of restructuring of laponite platelets on the surface of NTs.The analysis of experimental data on specific surface area versus the value of X_l evidenced in favor of the model with linear contacts between rigid laponite platelets and NTs.It was also concluded that electrostatic interactions control the first stage of adsorption at low MB concentrations.