共查询到20条相似文献,搜索用时 46 毫秒
1.
Metallic phases in slags and their influence on the leaching characteristics were investigated. The proportions of metallic
phase in four slags were 0.028%, 0.24%, 1.87%, and 3.05% by weight. The lead content was 10–248 mg/kg in bulk slag after metal
removal, while in the metallic phase it was 579–7390 mg/kg. Lead concentrations in the metallic phase were more than ten times
higher than in slags after metal removal. Lead was distributed in the metallic phase at 2.0%, 8.3%, 10.3%, and 47.4%. The
concentrations of all metallic elements in metallic phases were much higher than in bulk slag. Iron, copper, and nickel had
accumulated in magnetic metals, while aluminum and zinc were found in nonmagnetic metals. As regards chromium, manganese,
lead, and tin, the proportion of metallic phases depended on the slag samples. By removing metallic phases, both water and
pH 4 leachable lead decreased. The basic principles of melting residues containing lead are the separation of lead as a metal
in reductive melting, and the containment of lead ions into uniform glassy particles in oxidization melting. Melting slag
can be seen to contribute to environmental preservation by facilitating the recycling of materials through the separation
of metals from melting slag.
Received: February 21, 2000 / Accepted: July 27, 2000 相似文献
2.
Hydrogarnet was synthesized hydrothermally below 200°C using molten slag obtained from municipal solid waste. For comparison,
it was also synthesized using pure-phase CaO–Al 2O 3–SiO 2–H 2O, as reported previously. The structural and textural properties of this material were investigated using various analytical
and spectroscopic techniques such as X-ray diffraction, X-ray fluorescence spectrometry, atomic absorption spectrometry (AAS),
thermogravimetry/differential thermal analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy.
The Cl − fixation ability of hydrogarnet was investigated in the temperature range 500–800°C in a fixed-bed flow reactor using a HCl
concentration (1000 p.p.m.v.) similar to that of incinerator exhaust gas. Under these experimental conditions, the hydrogarnet
was capable of reducing the HCl gas level to less than 1 p.p.m.v. Analysis of the spent catalyst revealed that the hydrogarnet
was being transformed into wadalite and CaCl 2 at high temperatures. The elution test for chromium ions in hydrogarnet obtained from slag was also used, and it was found
that chromium ions were not eluted from hydrogarnet.
Received: January 27, 2001 / Accepted: October 11, 2001 相似文献
3.
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 > Na 2CO 3. 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. 相似文献
4.
This work presents the first results of a study concerning on-road and in-vehicle exposure to particulate matter in the area
of Athens. PM 10 concentration measurements were conducted by TSI DustTrak, while driving along routes with different characteristics of traffic
density, during September 2003–March 2004. Concurrent measurements of the ultrafine particles (UFPs) number concentration
were also conducted, by condensation particle counter during part of the days. Pedestrian exposure to PM 10 and UFPs was also studied through stationary measurements on the kerbside of selected roads on November 2003 and February
2004. A major avenue, a heavy-trafficked road across a children hospital and two central roads, one in a residential and one
in a commercial area were selected for measurement. The results indicate that every day commuters are exposed to significant
concentration levels. Higher exposures were observed in heavy-trafficked areas and during rush hours. Mean PM 10 in-vehicle and on-road concentrations ranged from 30–320 μg/m 3 and 70–285 μg/m 3, respectively. The ultrafine particles number concentrations were in the range of 5.0 × 10 4–17.3 × 10 4 particles/cm 3 in-vehicle and 3.1 × 10 4–7.3 × 10 4 particles/cm 3 on the kerbside of a central residential road. Both PM 10 and UFPs concentrations presented repeated short-term peak exposures. The results clearly point out the importance of the
road microenvironment (in-vehicle and on kerbside) for population exposure in urban areas. 相似文献
5.
Polyvinyl chloride (–CH 2–CHCl–)
n
(PVC) was ground with a powdered inorganic material (CaO, CaCO 3, SiO 2, Al 2O 3, or slag) in a planetary ball mill under atmospheric conditions to investigate the effect of additions on its dechlorination.
The grinding causes a dehydrochlorinating reaction, forming a mixture of partially dechlorinated PVC and inorganic chloride,
depending on the grinding time. The dechlorination increases as the grinding progresses, and is improved with increasing amounts
of additives. The most effective additive is a mixture of CaO, SiO 2, and Al 2O 3, which has the same constituent components as blast furnace slag. CaO, a mixture of CaO, SiO 2, and blast furnace slag, are also effective, but CaCO 3 is the least effective additive tired.
Received: August 3, 2000 / Accepted: September 21, 2000 相似文献
6.
In Japan, melting-furnace fly ash (MFA) generated from ash melting and gasification/melting plants is considered an “urban
mine” due to its high metal content. This study aimed to develop a novel approach to pretreating MFA for metal recovery. Water
extraction with CO 2 bubbling was investigated because MFA mainly consists of water-soluble salts containing elements such as Cl, Ca, Na, and
K. Instead of acid addition, CO 2 bubbling was applied to maintain the optimal pH for minimizing the release of target metal elements and maximizing the removal
of undesirable elements during water extraction. The results revealed that CO 2 bubbling effectively decreased the release of Pb, Zn, and Cd into the treatment water. This was mainly due to coprecipitation
with CaCO 3, which was primarily formed by the reaction of Ca 2+ from the MFA with CO 3
2− from the CO 2 gas. The bubbling process also helped accelerate the removal of Cl from MFA. Furthermore, the study showed that it is possible
to lower the water-to-solid ratio to 5 with only a slight reduction in water extraction effect. Finally, approximately four
times the concentration of target metals (rare metals and Cu, Pb, and Zn) was achieved by removing 90% of Cl, 70%–90% of Na
and K, and 30%–40% of Ca through water extraction with CO 2 bubbling, resulting in a concentration of target metals that was nearly equal to that of ore. 相似文献
7.
This paper gives the results of partial oxidation experiments of polyethylene (PE) in supercritical water (SCW). The experiments
were carried out at a reaction temperature of 693K and a reaction time of 30 min using 6 cm 3 of a batch-type reactor. The loaded sample weight was 0.3 g and there was 2.52 g water (0.42 g/cm 3). The ratio of oxygen atoms to carbon atoms was 0.3. The results show a significant CO formation in O 2–SCW, and the 1-alkene/ n-alkane ratio in partial oxidation was higher than that in SCW pyrolysis. These results suggest the possibility of the hydrogenation
of hydrocarbon through partial oxidation followed by a water–gas shift reaction.
Received: July 19, 2000 / Accepted: September 28, 2000 相似文献
8.
With large quantity of flux (Na 2CO 3), lead can be recovered from the funnel glass of waste cathode-ray tubes via reduction–melting at 1000 °C. To reduce flux cost, a technique to recover added flux from the generated oxide phase is also important in order to recycle the flux recovered from the reduction–melting process. In this study, the phase separation of sodium and the crystallization of water-soluble sodium silicates were induced after the reduction–melting process to enhance the leachability of sodium in the oxide phase and to extract the sodium from the phase for the recovery of Na 2CO 3 as flux. A reductive atmosphere promoted the phase separation and crystallization, and the leachability of sodium from the oxide phase was enhanced. The optimum temperature and treatment time for increasing the leachability were 700 °C and 2 h, respectively. After treatment, more than 90% of the sodium in the oxide phase was extracted in water. NaHCO 3 can be recovered by carbonization of the solution containing sodium ions using carbon dioxide gas, decomposed to Na 2CO 3 at 50 °C and recycled for use in the reduction–melting process. 相似文献
9.
The long-term monitoring of precipitation and its chemical composition are important for identifying trends in rain quality
and for assessing the effectiveness of pollution control strategies. A statistical test has been used to the atmospheric concentrations
measured in the French rural monitoring network (MERA) in order to bring out spatio-temporal trends in precipitation quality
in France over the period 1990–2003. The non-parametric Mann–Kendall test which has been developed for detecting and estimating
monotonic trends in the time series was used and applied in our study at annual values of wet-only precipitation concentrations.
The emission data suggest that SO 2 and NO
x
emissions decreased (−3.3 and −2.0% year −1, respectively) contrary to NH 3 emissions that increased slightly (+0.2% year −1) over the period 1990–2002 in France. On the national scale, the pH values have a significant decreasing trend of −0.025 ± 0.02
unit pH year −1. and concentrations in precipitation have a significant decreasing trend, −3.0 ± 1.6 and −3.3 ± 0.6% year −1, respectively, corresponding with the downward trends in SO 2 emissions in France (−3.3% year −1). A good correlation ( R
2 = 0.84) between SO 2 emissions and concentrations was obtained. The decreasing trend of was more significant (−5.4 ± 5.2% year −1) than that of (−1.3 ± 2.4% year −1). Globally, the concentration of the major ions showed a clear downward trend including marine and alkaline ions. In addition,
the relative contribution of HNO 3 to acidity precipitation increased by 51% over the studied period. 相似文献
10.
In the process of lead production from lead-bearing materials generated in copper metallurgy, a large amount of hazardous waste in the form of slag is produced. To assess the effect of the slag on the environment, its physicochemical properties were determined. In this study, the following methods were used: wavelength dispersive X-ray fluorescence (WD XRF), X-ray diffraction (XRD), and Bunte-Baum-Reerink method to determine softening and melting points, as well as viscosity examination and leaching tests. The measurements were performed on the slag produced with two different amounts of iron addition to the lead smelting process. The resulting slags, an oxide rich phase slag and a sulfide rich phase slag have different compositions and physicochemical properties. It was found that the increase in iron addition causes an increase in the softening melting point of the oxide rich phase slag by about 100 °C, and a twofold increase in the viscosity of both slag phases. The increase in iron addition also results in the decrease in As leachability and increase in Zn, Fe, and Cu leachability from the slags. Slag produced with increased iron addition has a greater impact on the environment. 相似文献
11.
Polychlorinated biphenyl (PCB) residues from the sodium dispersion (SD) process were employed as the raw materials for the
production of activated carbon using KOH activation. The pore properties, such as the specific surface area and pore size
distribution, were characterized using the Barrett–Joyner–Halenda method and the Horvath–Kawazoe method based on the N 2 adsorption isotherm at 77 K. The activated carbon produced showed similar adsorption capacities and specific surface areas
to the commercially available product. The effects of the activation conditions on the porosity of the activated carbon produced
were studied. The most significant factor affecting the specific surface proved to be the activation temperature. The activated
carbon produced from PCB residues from the high-temperature (423–443 K) SD process had a binary pore size distribution well
developed in the 4 nm region and in the micropore region. The pore structure of the carbon produced from PCB residues from
the low-temperature (333–393 K) SD process had a wide range of micropores and mesopores. 相似文献
12.
The amounts of harmful gas emissions from the process of composting swine waste were determined using an experimental composting
apparatus. Forced aeration (19.2–96.1 l/m 3/min) was carried out continuously, and exhaust gases were collected and analyzed periodically. With weekly turning and the
addition of a bulking agent in order to decrease the moisture content and increase air permeability, the temperature of most
of the contents rose to 70°C and composting was complete within 3–5 weeks. NH 3, CH 4, and N 2O emissions were high in the early stage of composting. About 10%–25% of the nitrogen in the raw material was lost as NH 3 gas during composting. The emission rate of NH 3 mainly depended on the aeration rate, so that as the aeration rate rose, the level of NH 3 emissions increased. The CH 4 and N 2O emissions could be kept lower with adequate treatment at more than 40 l/m 3/min aeration. N 2O may be mainly the result of the denitrification of NO
x
-N in the additional matured compost used as a composting accelerator.
Received: September 11, 1998 / Accepted: November 8, 1999 相似文献
13.
We studied an entrained-flow gasification process which efficiently converts waste plastics to energy at a high energy recovery
rate. Waste plastics, after being shredded to <8 mm or <14 mm, were fed into an entrained-flow gasifier with air and oxygen.
In the gasifier, organic substances were pyrolyzed, partially combusted, and then converted into synthetic gas (CO, H 2) at a high temperature (over 1600 K). The clarified gasification characteristics were that the lower heat value (LHV) of
the product gas was over 4.2 MJ/Nm 3 and the cold gas efficiency was approximately 60%. Other inert substances in the wastes such as ashes and metals were melted
into slag and condensed on bag filters. The bag filters and a water scrubber removed impurities such as dusts, heavy metals,
and hydrogen halides from the product gases. Solid hydrocarbons, which include char and soot, were removed at a hot cyclone
and on the bag filters.
Received: July 19, 2000 / Accepted: October 3, 2000 相似文献
14.
A simple, low-cost method for suppression of dioxins/furans (hereinafter referred to as dioxins) is required because many
middle- and, especially, small-scale incinerators have fallen into disuse or have been dismantled because of the high running
and system costs of measures for the suppression of dioxins. Therefore, the purpose of the present study was to develop a
simple removal method for dioxins from combustion gas and to evaluate the basic removal rate of dioxins. The removal method
for suspended matter in a gas mixture (cold model) and dioxins in exhaust gases (hot model) has been investigated by means
of gas injection into water, the mechanism of which is that the suspended matter in the gas gathers at the gas–liquid interface.
In the cold model, the removal ratio of fine particles (R P) by gas injection into water was reproduced well by the following equation: R P (%) = 100 × {1−exp(−0.8 · S S · t C)}, where S S (cm 2/cm 3) is the specific surface area of bubbles and t C (s) is the residence time of bubbles in water. The removal ratio of fine particles increased as the product S s · t C increased. In a hot model using the exhaust gas from combustion experiments of polyvinyl chloride, the removal ratio of dioxins
(R D) by injecting the exhaust gas into water was estimated by the following equation: R D (%) = 100 × {1−exp(−0.8 · S S · t C · C D0
0.07)}, where C D0 [ng/cm 3 (at standard temperature and pressure)] is the dioxins concentration in the exhaust gas before injection into water. R D depends greatly on the specific surface area of bubbles and the residence time of the bubbles in water, and only weakly on
the dioxins concentration in the exhaust gas. Injection of the exhaust gas into water has been shown to be effective and was
evaluated as a simple method for the removal of dioxins from exhaust gas. 相似文献
15.
Flame-retardant plastics, such as desktop and laptop personal computer bodies, could be completely liquefied by carbon materials-catalyzed
hydroliquefaction in tetralin without using H 2 as a hydrogen source. Active carbons with larger surface areas (1450–3450 m 2/g) acted as superior catalysts in transferring tetralin hydrogens to plastics. On the other hand, carbon blacks and fullerene-rich
soot were less active catalysts. Graphite and mesocarbon microbeads did not show any catalytic effects. Benzene, toluene,
and ethylbenzene were obtained as recyclable hydrocarbons; their total amounts varied from 4 wt% to 12 wt% depending on the
types of plastics and the carbon materials used. Organic bromides such as polybromodioxins were not contained in the gases
and oils of the product.
Received: July 19, 2000 / Accepted: September 17, 2000 相似文献
16.
Three industrial by-products (fly ash, phosphogypsum and blast furnace slag), were evaluated for their potential re-use as soil amendments to reduce methane (CH 4) emission resulting from rice cultivation. In laboratory incubations, CH 4 production rates from anoxic soil slurries were significantly reduced at amendment levels of 0.5%, 1%, 2% and 5% (wt wt −1), while observed CO 2 production rates were enhanced. The level of suppression in methane production was the highest for phosphogypsum, followed by blast slag and then fly ash. In the greenhouse experiment, CH 4 emission rates from the rice planted potted soils significantly decreased with the increasing levels (2–20 Mg ha −1) of the selected amendments applied, while rice yield simultaneously increased compared to the control treatment. At 10 Mg ha −1 application level of the amendments, total seasonal CH 4 emissions were reduced by 20%, 27% and 25%, while rice grain yields were increased by 17%, 15% and 23% over the control with fly ash, phosphogypsum, and blast slag amendments, respectively. The suppression of CH 4 production rates as well as total seasonal CH 4 flux could be due to the increased concentrations of active iron, free iron, manganese oxides, and sulfate in the amended soil, which acted as electron acceptors and controlled methanogens’ activity by limiting substrates availability. Among the amendments, blast furnace slag and fly ash contributed mainly to improve the soil nutrients balance and increased the soil pH level towards neutral point, but soil acidity was developed with phosphogypsum application. Conclusively, blast slag among the selected amendments would be a suitable soil amendment for reducing CH 4 emissions as well as sustaining rice productivity. 相似文献
17.
This work investigated the chemical and mineralogical properties of CaO–SiO 2–Cr 2O 3–CaF 2–MgO slags. Synthetic slags were prepared and the effect of the slag basicity (mass ratio CaO/SiO 2) and MgO contents on the stability of the mineralogical species formed was analyzed. The morphology and composition of the slags were analyzed by X-ray powder diffraction (XRD) and scanning electron microscope-energy dispersive spectroscopy (SEM–EDS), whilst their chemical stability was evaluated by leaching with an aqueous acetic acid solution. It was found that in slags with CaO/SiO 2?=?1, the main Cr-compound was MgCr 2O 4 spinel, which forms octahedron crystals. Small amounts of CaCr 2O 4 and CaCrO 4 were also observed. It was found that with increasing the slag basicity from 1 to 2 the compounds MgCr 2O 4 and CaCr 2O 4 were formed together with the Cr(V)-containing compound complex Ca 5(CrO 4) 3F which forms hexagonal crystals. The results showed that the highest Cr concentration levels in the leaching liquors corresponded to slags with CaO/SiO 2?=?2, probably owing to the formation of CaCrO 4 and Ca 5(CrO 4) 3F, whilst the lowest chromium concentration levels corresponded to MgO-based slags owing to the stable binding of chromium in spinel with MgO. Additionally, potential–pH diagrams for the Ca–Cr–H 2O and Mg–Cr–H 2O systems at 25?°C were calculated. 相似文献
18.
A method of determining the chlorine (Cl) and sulfur (S) in municipal solid waste (MSW) was studied. The quartz furnace method
was improved in two ways: recovery from ash by hot extraction with dilute nitric acid, and avoidance of the volatilization
of alkali (earth) metal chlorides by setting the sample combustion temperature at 600°C. In a comparison with the bomb method,
using nine sets of kitchen garbage and waste plastics, the bomb method yielded a 15%–25% lower value than the improved quartz
furnace method. Combustion in the bomb was frequently incomplete, resulting in recovery losses of Cl and S. The average kitchen
garbage involved 5.2 mg Cl/g, of which at least 24.1% would be converted to HCl. Plastics contained 23 mg Cl/g generating
88.1% HCl on average. In the same way, kitchen garbage contained 3.0 mg S/g, generating 52.3% SO
x
, whereas plastics contained 1.1 mg S/g with 55.1% SO
x
formation.
Received: March 20, 2002 / Accepted: October 13, 2002 相似文献
19.
Lead can be recovered from funnel glass of waste cathode ray tubes via reduction melting. While low-temperature melting is necessary for reduced energy consumption, previously proposed methods required high melting temperatures (1400 °C) for the reduction melting. In this study, the reduction melting of the funnel glass was performed at 900–1000 °C using a lab-scale reactor with varying concentrations of Na 2CO 3 at different melting temperatures and melting times. The optimum Na 2CO 3 dosage and melting temperature for efficient lead recovery was 0.5 g per 1 g of the funnel glass and 1000 °C respectively. By the reduction melting with the mentioned conditions, 92% of the lead in the funnel glass was recovered in 60 min. However, further lead recovery was difficult because the rate of the lead recovery decreased as with the recovery of increasing quantity of the lead from the glass. Thus, the lead remaining in the glass after the reduction melting was extracted with 1 M HCl, and the lead recovery improved to 98%. 相似文献
20.
From the point of view of a sustainable and environment-friendly society based on the recycling of material resources, it
is preferable to utilize waste gypsum as a substitute for lime, which is currently produced by the calcination of limestone.
In the present work, the reductive decomposition of CaSO 4 was investigated under an atmosphere of CO: 2 vol%, CO 2: 30 vol%, with N 2 as a carrier gas without and with the addition of SiO 2, Al 2O 3, or Fe 2O 3. It was found that the decomposition temperature of CaSO 4 was significantly reduced from 1673 K to 1223 K when only 5 wt% Fe 2O 3 was added to CaSO 4. In the case of the addition of SiO 2 or Al 2O 3 to CaSO 4, the decomposition temperature was reduced from 1673 K to 1623 K. This was due to the formation of composite oxides (calcium
ferrite, calcium silicate, or calcium aluminate) during the reaction of CaSO 4 with the additives at a lower temperature. In addition, the formation of unfavorable product CaS was inhibited in the presence
of 5 wt% Fe 2O 3, and this inhibition effect further increased as the addition of Fe 2O 3 was increased. In contrast, no significant effect on the inhibition of CaS formation was observed on the addition of SiO 2 or Al 2O 3. 相似文献
|