Synthesis of zeolite from waste fly ash for adsorption of CO2

Zeolitic sorbents for CO₂ adsorption were prepared from waste coal fly ash (FA) through hydrothermal treatment at various ratios of NaOH/FA and NaAlO₂/FA, including an initial alkali fusion step. The fusion step decomposed the fly ash into very small amorphous particulate zeolite forms. The fly ash was converted to Na-P1 type with a NaOH/FA ratio of 0.5 and Na-A type with a NaAlO₂/FA ratio of 0.53. The product properties were affected by the reaction temperature: Na-P1 and Na-A types were formed at 100°C. Temperatures above 140°C led to the formation of more sodalite because of the redissolving and recrystallization of zeolite crystals. Alkali metal and alkaline earth metal cations were impregnated in the synthesized Na-P1 and Na-A zeolite through an ion-exchange method. The completed zeolitic sorbents were applied to the adsorption of low-level CO₂. As a result of the experiments, calcium ions were found to be the best for CO₂ adsorption owing to their electrostatic behavior and acid-base interaction.     

Enhanced decomposition of (4-chloro-2-methylphenoxy) acetic acid by combined ultrasonic and oxidative treatment

Combined ultrasonic (US) irradiation and sodium peroxodisulfate (Na₂S₂O₈) treatment has been investigated for promotion of both decomposition of (4-chloro-2-methylphenoxy) acetic acid (MCPA) and mineralization of organic residues. This treatment is expected to accelerate both reactions, because the US cavitation effect promotes the production of radicals, such as SO ₄ ^? · and OH·, by the decomposition of Na₂S₂O₈ and water. In this study, decomposition experiments were performed on 100?ppm MCPA aqueous solutions in a sonoreactor at reaction temperatures of 298?C333?K with US irradiation alone, Na₂S₂O₈ treatment alone, and the combination of US and Na₂S₂O₈ treatment. It was found that the combined treatment achieved a higher MCPA decomposition rate and total organic carbon (TOC) removal ratio than either treatment alone. The decomposition ratios of both MCPA and TOC increased with reaction temperature, and especially steep increases were observed at 333?K due to a significant promotion of thermal decomposition of Na₂S₂O₈. The production of radical species was also promoted by the combined treatment. These results suggest that the higher MCPA decomposition rate and TOC removal ratio are due to the increased formation of sulfate and hydroxyl radicals via thermal and US decomposition of Na₂S₂O₈.     

Preparation of MgCr<Subscript>2</Subscript>O<Subscript>4</Subscript> from waste tannery solution and effect of sulfate,chloride, and calcium on leachability of chromium

This paper presents a study regarding the preparation of MgCr₂O₄ from waste tannery solution, and chromium leaching behavior is also investigated with varying amounts of sulfate, chloride and calcium. The phase transformation, crystallinity index and crystallite diameter were characterized using XRD, FT-IR and thermal analysis. A well-crystallized MgCr₂O₄ was successfully prepared at 1400 °C. The sintering temperature had a major impact on the formation of MgCr₂O₄ compared with sintering time. The MgCr₂O₄ phase was observed initially at 400 °C and its crystallite diameter increased with increasing temperature. The concentration of total chromium leached and Cr(VI) decreased gradually with increasing temperature. The considerable amount of Cr(VI) was found in the leachate at 300–500 °C caused by Cr(VI) intermediary products. Sulfate and chlorine could impact the transformation efficiency of chromium adversely, and chlorine has a more significant effect than sulfate. The presence of calcium disturbed the formation of MgCr₂O₄ and new chromium species (CaCrO₄) appeared, which resulted in a sharp increase in the concentration of leached Cr(VI). Incorporating Cr(III) into the MgCr₂O₄ spinel for reusable products reduced its mobility significantly. This was demonstrated to be a promising strategy for the disposal of chromium containing waste resource.     

Leaching of rare earths from Abu Tartur (Egypt) phosphate rock with phosphoric acid

The leaching of rare earth elements (REEs) from Egyptian Abu Tartur phosphate rock using phosphoric acid has been examined and was subsequently optimized to better understand if such an approach could be industrially feasible. Preliminary experiments were performed to properly define the design of experiments. Afterward, 2⁴ full factorial design was implemented to optimize the leaching process. Optimum REEs leaching efficiency (96.7 ± 0.9%) was reached with the following conditions: phosphoric acid concentration of 30 wt.-% P₂O₅, liquid/solid ratio, mL/g, of 5:1, at 20 °C, and 120 min of leaching time. The apparent activation energy of the dissolution of REEs from phosphate rock using the phosphoric acid solution was -19.6 kJ/mol. D2EHPA was subsequently applied as an organic solvent for REEs separation from the acquired leach liquor. REEs stripping and precipitation were conducted, and finally, rare earth oxides with a purity of 88.4% were obtained. The leach liquor was further treated with concentrated sulfuric acid to recover the used phosphoric acid and produce gypsum with a purity of >95% at the same time. A flow diagram for this innovative cleaner production process was developed, and larger-scale experiments are proposed to further understand this promising approach to comprehensive phosphate rock processing.

     

Laboratory studies on the remediation of mercury contaminated soils

Mercury, in contrast to other toxic metals, cycles between the atmosphere, land, and water. During this cycle, it undergoes a series of complex chemical and physical transformations. Because of these transformations, it is found in the environment not only as simple inorganic and organic compounds, but also as complex compounds. As a result, it is difficult to remediate mercury contaminated materials. Laboratory studies were conducted with a mercury contaminated complex waste from an industrial site to evaluate the ability of extractants such as H₂O₂, H₂SO₄ and Na₂S₂O₃ to decontaminate the waste. Up to 87 percent of the total mercury present in the waste was extracted. Mercury was recovered as insoluble mercury sulfide by adding Na₂S solution to the combined filtrates from the H₂O₂ + H₂SO₄ and Na₂S₂O₃ treatment steps. The technique described in this article is capable of recovering mercury in a usable form and can be used as a pretreatment to remediate mercury contaminated waste before laud disposal.     

Study of nitrogen oxide absorption in the calcium sulfite slurry

Experiments were conducted using a bubbling reactor to investigate nitrogen oxide absorption in the calcium sulfite slurry. The effects of CaSO₃ concentration, NO₂/NO mole ratio and O₂ concentrations on NO₂ and SO₂ absorption efficiencies were investigated. Five types of additives, including MgSO₄, Na₂SO₄, FeSO₄, MgSO₄/Na₂SO₄ and FeSO₄/Na₂SO₄, had been evaluated for enhancing NO₂ absorption in CaSO₃ slurry. Results showed that CaSO₃ concentration had significant impact on NO₂ and SO₂ absorption efficiencies, and the highest absorption efficiencies of SO₂ and NO₂ could reach about 99.5 and 75.0 %, respectively. Furthermore, the NO₂ absorption was closely related to the NO₂/NO mole ratio, and the existence of NO₂ in flue gas may promote NO absorption. The presence of O₂ in simulated flue gas was disadvantage for NO _x removal because it can oxidize sulfite to sulfate. It was worth pointing out that FeSO₄/Na₂SO₄ was the best additive among those investigated additives, as the NO₂ removal efficiency was significantly increased from 74.8 to 95.0 %. IC and in situ FTIR results suggest that the main products were NO₃ ^? and NO₂ ^? in liquid phase and N₂O, N₂O₅ and HNO₃ in gas phase during the CaSO₃ absorption process.     

Recovery of Nd and Dy from rare earth magnetic waste sludge by hydrometallurgical process

This paper describes a hydrometallurgical process for recovering neodymium (Nd) and dysprosium (Dy) from a magnetic waste sludge generated from the Nd–Fe–B(–Dy) manufacturing process. Phase analysis by XRD study revealed Nd(OH)₃ and Fe₂O₃ as main mineral phases, and chemical analysis by ICP showed the contents of 35.1 wt% Nd, 29.5 wt% Fe, 1.1 wt% Dy and 0.5 wt% B. A solution of 1 M HNO₃ + 0.3 M H₂O₂ was used to dissolve up to 98 % Nd and 81 % Dy, while keeping Fe dissolution below 15 % within 10 min. Fe dissolved in solution was completely removed as Fe(OH)₃ at pH 3 followed by precipitation of Nd and Dy with oxalic acid (H₂C₂O₄) and recovered 91.5 % of Nd and 81.8 % of Dy from solution. The precipitate containing Nd and Dy was calcined at 800 °C to obtain Nd₂O₃ as final product with 68 % purity, and final recovery of 69.7 % Nd and 51 % of Dy was reported in this process.     

Physical separation,mechanical enrichment and recycling-oriented characterization of spent NiMH batteries

Nickel–metal hydride (NiMH) batteries contain high amount of industrial metals, especially iron, nickel, cobalt and rare earth elements. Although the battery waste is a considerable secondary source for metal and chemical industries, a recycling process requires a suitable pretreatment method before proceeding with recovery step to reclaim all valuable elements. In this study, AA- and AAA-type spent NiMH batteries were ground and then sieved for size measurement and classification. Chemical composition of the ground battery black mass and sorted six different size fractions were determined by an analytical technique. Crystal structures of the samples were analyzed by X-ray diffraction. Results show that after mechanical treatment, almost 87 wt% of the spent NiMH batteries are suitable for further recycling steps. Size classification by sieving enriched the iron content of the samples in the coarse fraction which is bigger than 0.25 mm. On the other hand, the amounts of nickel and rare earth elements increased by decreasing sample size, and concentrated in the finer fractions. Anode and cathode active materials that are hydrogen storage alloy and nickel hydroxide were mainly collected in finer size fraction of the battery black mass.     

Photo-Stabilisation and UV Blocking Efficacy of Coated Macro and Nano-Rutile Titanium Dioxide Particles in Paints and Coatings

Surface treated macro and nanoparticle TiO₂ samples have been prepared, characterised and their efficiency as UV blockers evaluated in clear coatings and paints. The particle size of the ‘base’ TiO₂ has been optimised to block UV radiation and the surface treatment developed to deactivate the photocatalytic activity of the surface of the TiO₂ particles. The resultant UV blockers have been evaluated in both solvent and water-based clear coatings. Nanoparticle TiO₂ has been prepared from ‘seed’ and the particle size was controlled by calcination. It was found that the choice of particle size is a compromise between UVA absorption, UVB absorption, visible transmission and photoactivity. It has been demonstrated that TiO₂ with a crystallite size of 25 nm yields a product with the optimum properties. A range of dispersants was successfully used to disperse and mill the TiO₂. Both organic and inorganic dispersants were used; 2-amino-2-methyl-1-propanol and 1-amino-2-propanol (MIPA) and P₂O₅ and Na₂SiO₃ respectively. The surface of the nano-TiO₂ was coated with mixed oxides of silicon, aluminium, zirconium and phosphorous. Addition of the resultant coated nano-rutiles to an Isocyanate Acrylic clear coating prolonged the lifetime of that coating compared to the blank. Generally, a surface treatment based on SiO₂, Al₂O₃ and P₂O₅ was more successful than one based on ZrO₂, Al₂O₃ and P₂O₅. Higher addition levels of the surface treatment were beneficial for protecting the polymeric coating. The UV blocker products were also evaluated in a water-based acrylic, first a water-based dispersion of the UV blocker was prepared before addition to the acrylic. The dispersions and resultant acrylic thin films were evaluated using UV/Vis spectroscopy and durability assessed. The ratio of absorbance at 300:500 nm for the water-based dispersion was shown to be a good predictor of both the transparency of the resultant acrylic thin film and the durability of that film, in terms of weight loss. Macro grade titanium dioxide pigments were also prepared and coated with treatments of silica, alumina and siloxane and their photo-stabilising activity in alkyd paint film assessed and found to be directly related to the electron–hole pair mobility and trapping as determined by micro-wave spectroscopy.     

Chemical looping combustion (CLC) of municipal solid waste (MSW)

Chemical Looping Combustion (CLC) has been found to be a better alternative in converting Municipal Solid Waste (MSW) to energy and has the potential to reduce the generation of dioxins due to the inhibition of the de-novo synthesis of dioxins. This study comprehensively reviews the experimental studies of CLC of MSW, the oxygen carriers, reactor types, performance evaluation, and ash interaction studies. Modeling and simulation studies of CLC of MSW were also critically presented. Plastic waste is MSW’s most studied non-biomass component in MSW under CLC conditions. This is because CLC has been shown to reduce the emission of dioxins and furans, which are normally emitted during the conventional combustion of plastics. From the several oxygen carriers tested with MSW’s CLC, alkaline earth metals (AEM) modified iron ore was the most effective for reducing dioxin emissions, improving combustion efficiency and carbon conversion. Also, oxygen carriers with supports were more reactive than single carriers and CaSO₄/Fe₂O₃ and CaSO₄ in silica sol had the highest oxygen transport ability. Though XRD analysis and thermodynamic calculations of the reacted oxygen carriers yielded diverse results due to software computation constraints, modified iron ore produced less HCl and heavy metal chlorides compared to iron ore and ilmenite. However, alkali silicates, a significant cause of fouling, were observed instead. The best reactor configuration for the CLC of MSW is the fluidized bed reactor, because it is easy to obtain high and homogeneous solid–gas mass transfer. Future research should focus on the development of improved oxygen carriers that can sustain reactivity after several cycles, as well as the system’s techno-economic feasibility.

     

Evaluation of gold and silver leaching from printed circuit board of cellphones

Electronic waste has been increasing proportionally with the technology. So, nowadays, it is necessary to consider the useful life, recycling, and final disposal of these equipment. Metals, such as Au, Ag, Cu, Sn and Ni can be found in the printed circuit boards (PCB). According to this, the aims of this work is to characterize the PCBs of mobile phones with aqua regia; obtaining “reference” values of leaching, to gold and silver, with cyanide and nitric acid, respectively; and study the process of leaching of these metals in alternative leaching with sodium thiosulfate and ammonium thiosulfate. The metals were characterized by digesting the sample with aqua regia for 1 and 2 h at 60 °C and 80 °C. The leaching of Au with a commercial reagent (cyanide) and the Ag with HNO₃were made. The leaching of Au and Ag with alternative reagents: Na₂S₂O_3, and (NH₄)₂S₂O₃ in 0.1 M concentration with the addition of CuSO₄, NH₄OH, and H₂O₂, was also studied. The results show that the digestion with aqua regia was efficient to characterize the metals present in the PCBs of mobile phones. However, the best method to solubilize silver was by digesting the sample with nitric acid. The leaching process using sodium thiosulfate was more efficient when an additional concentration of 0.015 and 0.030 M of the CuSO₄ was added.     

Production of hydrogen by steam gasification of dehydrochlorinated poly(vinyl chloride) or activated carbon in the presence of various alkali compounds

Steam gasification of dehydrochlorinated poly(vinyl chloride) (PVC) or activated carbon was carried out in the presence of various alkali compounds at 3.0 MPa and 560°C–660°C in a batch reactor or in a semi-batch reactor with a flow of nitrogen and steam. Hydrogen and sodium carbonate were the main products, and methane and carbon dioxide were the minor products. Yields of hydrogen were high in the presence of sodium hydroxide and potassium hydroxide. The acceleration effect of the alkali compounds on the gasification reaction was as follows: KOH > NaOH > Ca(OH)₂ > Na₂CO₃. The rate of gasification increased with increasing partial steam pressure and NaOH/C molar ratio. However, the rate became saturated at a molar ratio of NaOH/C greater than 2.0.     

Dechlorination and decomposition of Aroclor 1242 in real waste transformer oil using a nucleophilic material with a modified domestic microwave oven

This research was done to assess the dechlorination and decomposition of polychlorinated biphenyls (PCBs) in real waste transformer oil through a modified domestic microwave oven (MDMW). The influence of microwave power (200–1000 W), reaction time (30–600 s), polyethylene glycol (PEG) (1.5–7.5 g), iron powder (0.3–1.5 g), NaOH (0.3–1.5 g), and H₂O (0.4–2 ml) were investigated on the decomposition efficiency of PCBs existing in real waste transformer oil with MDMW. Obtained data indicate that PEG and NaOH have the greatest influence on decomposition of PCBs; while, iron did not influence, and H₂O decreased, the decomposition efficiency of PCBs. Experimental data also indicated that with the optimum amount of variables through a central composites design method (PEG = 5.34 g, NaOH = 1.17 g, Fe = 0.6 g, H₂O = 0.8 ml and microwave power 800 W), 78 % of PCBs was degraded at a reaction time of about 6 min. In addition, the PCBs decomposition without using water increased up to 100 % in the reactor with the MDMW at 6 min. Accordingly, results showed that MDMW was a very efficient factor for PCBs decomposition from waste transformer oil. Also, using microwave irradiation, availability and inexpensive materials (PEG, NaOH), and iron suggest this method as a fast, effective, and cheap method for PCB decomposition of waste oils.     

Preparation of activated carbons from polycarbonate with chemical activation using response surface methodology

The disposal of waste plastics is a major environmental issue all over the world. As an alternative to disposal that also adds value to the waste product, polycarbonate particles were used as model waste plastic material, mixed with sodium hydroxide and then pyrolyzed at 773 K to produce activated carbon. Activated carbon has numerous industrial applications, including use as adsorbents in adsorption heat pumps and several environmental applications. Activated carbon obtained upon pyrolysis was characterized by determining its adsorption capacity for liquid nitrogen and water vapor. The effects of the key process variables, i.e., chemical ratio and activation time, on micropore development and water adsorptivity were evaluated by response surface methodology. The quadratic models were found to be satisfactory in describing their performance. Based on the contour plots, activated carbon with a maxima of surface area and micropore volumes can be produced at an optimal level of chemical ratio along with longer activation time. The water adsorptivity generally has less difference at low relative pressures, but inflexion of water adsorptivity occurs at a relative pressure of P/P ₀ ≈ 0.4. The optimized water adsorptivity in the operating pressure range of adsorption heat pumps (P/P ₀ = 0.11–0.38) can exceed 0.24 kg/kg.     

Preparation and characterization of high surface area activated carbon from pine wood sawdust by fast activation with H<Subscript>3</Subscript>PO<Subscript>4</Subscript> in a spouted bed

Activated carbons were produced from waste pine wood sawdust using fast activation with H₃PO₄ in a spouted bed. In this study, activation temperature was set as 800 °C, and activation time ranged from 1 to 15 min. Experimental results show that sawdust impregnated with higher mass ratio of H₃PO₄ would be agglomerated in spouted bed, and difficult to fluidize. Therefore, an amount of quartz sand was added to assist for good fluidization. Fluidization of particle can improve the BET surface area or micropore volume of activated carbons. High BET surface area activated carbons can be obtained with activation time of only 1–5 min by combining the fluidization and H₃PO₄ fast activation. The obtained activated carbons contained developed pore structure and abundant surface functional groups (carboxyl, carbonyl and P-containing groups) by SEM–EDS, FTIR and XPS techniques. The particles of impregnation ratio of 1:1 can achieve fluidization without adding the quartz sand, which was convenient for experimental operation and even industrial production, and the BET surface area can reach more than 1000 m²/g in activation time of only 5 min.     

Greenhouse gases emissions from solid waste: an analysis of Expo 2010 Shanghai,China

The management of greenhouse gases (GHGs) emissions is currently a very important environmental issue. Mega-event organizers and host cities have attached great importance to GHGs emissions associated with event-related activities. However, GHGs emissions from event solid waste have never been thoroughly discussed. This study investigated GHGs emissions of major event’s solid waste using life cycle assessment, based on Shanghai Expo case. The results showed that GHGs from collecting and sorting, transportation and landfill treatment amount to 9790 t CO₂e. And the emission intensity is estimated to be 134 g CO₂e per event service. GHGs reduction from recycling amounts to 48 kt CO₂e, with 78 % of these the result of construction waste recycle. It illustrates that waste recycle plays a vital role in GHGs mitigation. Finally, the study suggests that the concept of waste avoidance, waste reuse and waste recycle is an effective waste management to mitigate climate change and should be implemented in major event to achieve the goal of green event.     

Potential of biogas production from mixed leaf and food waste in anaerobic reactors

Anaerobic digestion of mixed leaf (MLW) and food wastes (FW) was used to explore the potential use of MLW as an accelerator for FW digestion in two parts for biogas production and as a waste management option in a university community. The effects of the single substrate of FW, co-digestion, ratio of MLW and FW (3:2 and 2:3) and ratio of waste feed to inoculum: F/I (0.1 and 0.4), and feeding frequency (every other day and every 2 days) were evaluated in two neutralized anaerobic reactors. The results showed that different mixture ratios with the same F/I ratio were the major factor on biogas (39.87 m³/kg VS_added) and CH₄ yield (25.99 m³/kg VS_added), including %COD removal (84.50%). Co-digestion had the same effect as F/I on biogas production. Only FW provided the lowest biogas and CH₄ yield. The use of a MLW:FW 2:3, F/I 0.4 mixture with every 2 days feeding provided higher biogas production and %COD removal than with every other day feeding. Two neutralized anaerobic reactors were suitable for digestion with a high F/I, and a wider interval feeding. This finding affirms the possibility of biogas production using MLW as the co-substrate with FW, as opposed to using FW alone.     

Preparation and characterization of mesoporous γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> recovered from aluminum cans waste and its use in the dehydration of methanol to dimethyl ether

The present study includes synthesis of two γ-Al₂O₃ samples from waste aluminum cans using a simple precipitation method. Precipitation was carried out using two different precipitating agents (i.e. NaOH and NH₄OH). The two prepared alumina samples were characterized by means of X-ray diffraction (XRD) and N₂ adsorption–desorption techniques. Surface acidity of γ-Al₂O₃ samples was measured by adsorption of two different probe molecules (i.e. pyridine and dimethyl pyridine) followed by desorption measurements using thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. Catalytic activity of the two prepared alumina samples towards the dehydration of methanol (to dimethyl ether) was studied in a fixed bed reactor at 300 °C. For comparison reasons, commercial γ-Al₂O₃ sample was, also, tested for the same catalytic reaction under the same conditions. Results showed that the alumina sample prepared using NaOH as a precipitating agent exhibited a better catalytic activity and stability compared with that prepared using NH₄OH and showed a similar activity as the commercial γ-Al₂O₃ sample.     

Extraction of polybrominated diphenyl ethers contained in waste high impact polystyrene by supercritical carbon dioxide

A new recycling process for the supercritical CO₂ (sc-CO₂) extraction of polybrominated diphenyl ethers from waste high impact polystyrene (HIPS) was developed in this paper. HIPS was first dissolved in d-limonene. The remaining decabromo diphenyl ether (decaBDE) particles in solution were then removed by centrifugation, and the PBDEs in the centrifugate solution were further extracted by sc-CO₂. The influence of temperature and pressure, the volume ratio of sc-CO₂ to plastic solution, and the concentration of decaBDE in the solution on the separating efficiency were investigated. The decaBDE particles in 20 % of the HIPS solution can be removed by centrifugation at a speed of 10,000 r/min at 30 °C. The suitable sc-CO₂ fluid conditions were 65 °C and 20 MPa, and the optimum volume ratio of the sc-CO₂ to the HIPS solution was 2:1. More than 97 % of the PBDEs were successfully removed, and the concentration of PBDE residues in the recycled HIPS was reduced to lower than 0.1 % (dry) by this recycling process.     

Determination of total chlorine and bromine in solid wastes by sintering and inductively coupled plasma-sector field mass spectrometry

A sample preparation method based on sintering, followed by analysis by inductively coupled plasma-sector field mass spectrometry (ICP-SFMS) for the simultaneous determination of chloride and bromide in diverse and mixed solid wastes, has been evaluated. Samples and reference materials of known composition were mixed with a sintering agent containing Na₂CO₃ and ZnO and placed in an oven at 560 °C for 1 h. After cooling, the residues were leached with water prior to a cation-exchange assisted clean-up. Alternatively, a simple microwave-assisted digestion using only nitric acid was applied for comparison. Thereafter the samples were prepared for quantitative analysis by ICP-SFMS. The sintering method was evaluated by analysis of certified reference materials (CRMs) and by comparison with US EPA Method 5050 and ion chromatography with good agreement. Median RSDs for the sintering method were determined to 10% for both chlorine and bromine, and median recovery to 96% and 97%, respectively. Limits of detection (LODs) were 200 mg/kg for chlorine and 20 mg/kg for bromine. It was concluded that the sintering method is suitable for chlorine and bromine determination in several matrices like sewage sludge, plastics, and edible waste, as well as for waste mixtures. The sintering method was also applied for determination of other elements present in anionic forms, such as sulfur, arsenic, selenium and iodine.