Metal stabilization mechanism of incorporating lead-bearing sludge in kaolinite-based ceramics

The feasibility and mechanism of incorporating simulated lead-laden sludge into low-cost ceramic products was investigated by observing the reaction of lead with two kaolinite-based precursors under sintering conditions. To investigate the phase transformation process of lead, lead oxide (PbO) mixed with a kaolinite or mullite precursor were fired at 500-950 °C for 3 h. Detailed X-ray diffraction analysis of sintered products revealed that both precursors had crystallochemically incorporated lead into the lead feldspar (PbAl₂Si₂O₈) crystalline structure. By mixing lead oxide with kaolinite, lead feldspar begins to crystallize at 700 °C; maximum incorporation of lead into this structure occurred at 950 °C. However, two intermediate phases, Pb₄Al₄Si₃O₁₆ and a polymorph of lead feldspar, were detected at temperatures between 700 and 900 °C. By sintering lead oxide with the mullite precursor, lead feldspar was detected at temperatures above 750 °C, and an intermediate phase of Pb₄Al₄Si₃O₁₆ was observed in the temperature range of 750-900 °C. This study compared the lead leachabilities of PbO and lead feldspar using a prolonged leaching test (at pH 2.9 for 23 d) modified from the toxicity characteristic leaching procedure. The results indicate the superiority of lead feldspar in stabilizing lead and suggest a promising and reliable strategy to stabilize lead in ceramic products.     

Phosphate-induced lead immobilization from different lead minerals in soils under varying pH conditions

This study investigated phosphate-induced lead immobilization from different Pb minerals in soils under varying pHs. Four soils were used, including one Pb-contaminated soil (NC-Soil) and three soils spiked with litharge (PbO), cerrusite (PbCO3), or anglesite (PbSO4), referred to as PbO-soil, PbCO3-soil, and PbSO4-soil, respectively. The soils were equilibrated with KCl and Ca(H2PO4)(2).H2O under pH of 3-7. At low pH (3 and 5), Pb solubility followed PbO-soil>PbCO3-soil>PbSO4-soil; while at pH=7, it was PbSO4-soil>PbO-soil>PbCO3-soil. Phosphate decreased Pb dissolution time from >180 to <60 min and reduced soluble Pb by 67-100%. This was mostly via transformation of Pb minerals into chloropyromorphite [Pb(5)(PO(4))(3)Cl]. Our results indicated that P addition can effectively transform various Pb minerals into insoluble chloropyromorphite in soils. This transformation was more significant at acidic condition (e.g., pH相似文献   

Characterization of fugitive material within a primary lead smelter.

The primary production of Pb via the sinter plant-blast furnace method resulted in a large number of Pb and other phases, reflecting the complex reactions occurring within each of the processes. Optical microscopy and X-ray diffraction (XRD) techniques have been used to characterize fugitive emissions and dusts generated during sintering, smelting, Cu drossing, refining, and slag fuming at a primary Pb-Zn smelter. The results displayed a complex array of phases, with the mineralogy of the dusts and fume reflecting conditions of the particular metallurgical operation. The principal Pb species followed a transformation from PbS through PbSO4 and PbO to Pb(o) (metal) from raw materials to the refinery. The fugitive emissions generated by the blast furnace were of a finer size with more complex chemistry than fugitive material from other source areas. XRD identified a mixture of PbS, ZnO, and ZnS, associated with one or more of the Cl-bearing phases Pb(OH)Cl, PbCl2, Pb4O3Cl2, Na3Pb2(SO4)3Cl, Pb10(SO4)Cl2O8, Pb4SCl6, and Pb7S2Cl10. The presence of Cl-bearing phases in the fume has possible health implications.     

废铅酸蓄电池铅膏性质分析

为给废旧铅蓄电池铅膏的湿法回收工艺提供理论依据,对湖北金洋冶金股份有限公司破碎分选后的废铅膏进行了XRF、XRD、物理分析及化学分析等,确定了废铅膏的主要成分、理化性质等特性。结果表明,废铅膏粒径细小,碾钵磨细后能过120目的筛下物超过77.4%,这对湿法转化是有利的。废铅膏主要组成为64.5%PbSO4、29.5%PbO2、4.5%PbO、0.8%Pb及其他微量杂质元素,杂质主要包括Fe、Sb和Si等。因此,铅膏湿法处理时应该采取合适的净化工艺。     

Composition and element solubility of magnetic and non-magnetic fly ash fractions

Magnetic and non-magnetic fractions of coal fly ashes from SE US electric power plants were characterized with special emphasis on the potential environmental consequences of their terrestrial disposal. Quartz and mullite were the crystalline minerals dominating the non-magnetic fractions. Magnetic fractions contained magnetite, hematite, and, to a lesser extent, quartz and mullite. Chemical analyses revealed that magnetic fractions had about 10 times higher concentrations of Fe, and 2-4 times higher concentrations of Co, Ni, and Mn. Non-magnetic fractions were enriched in K, Al and Ca. Iron content within fly ash particles was negatively correlated with elements associated with aluminosilicate matrix (Si, Al, K, Na). Solubility of most elements was higher in the non-magnetic than in the magnetic fractions of alkaline fly ashes at comparable pH. Calcium was associated with the non-magnetic fraction of the alkaline fly ashes which resulted in a higher pH buffering capacity of this fraction.     

Study of lead phytoavailability for atmospheric industrial micronic and sub-micronic particles in relation with lead speciation

Particles from channelled emissions of a battery recycling facility were size-segregated and investigated to correlate their speciation and morphology with their transfer towards lettuce. Microculture experiments carried out with various calcareous soils spiked with micronic and sub-micronic particles (1650 ± 20 mg Pb kg⁻¹) highlighted a greater transfer in soils mixed with the finest particles. According to XRD and Raman spectroscopy results, the two fractions presented differences in the amount of minor lead compounds like carbonates, but their speciation was quite similar, in decreasing order of abundance: PbS, PbSO₄, PbSO₄·PbO, α-PbO and Pb⁰. Morphology investigations revealed that PM_2.5 (i.e. Particulate Matter 2.5 composed of particles suspended in air with aerodynamic diameters of 2.5 μm or less) contained many Pb nanoballs and nanocrystals which could influence lead availability. The soil-plant transfer of lead was mainly influenced by size and was very well estimated by 0.01 M CaCl₂ extraction.     

Tolerance of lead by the fruiting body of Oudemansiella radicata

This study focused on the tolerance responses of the fruiting body of Oudemansiella radicata towards different concentrations of lead (250-1000 mg kg(-1)) for 2-6 d. To know about the lead tolerance and detoxification strategy, the lead content, thiol content and the activities of antioxidant enzymes were investigated. The maximum level for the lead concentration in O. radicata was recorded in the 6 d sample in each treatment, and for thiols, it was recorded in the 500 mg kg(-1) Pb/2d sample, while for superoxide dismutases (SOD) and catalases (CAT) activities, it was reached at 1000 mg kg(-1) Pb after 2 d in the stipe and cap, respectively. Peroxidases (POD) activities showed a more complex trend and glutathione reductases (GR) reached the maximum at 500 mg kg(-1) Pb after 2 d in the stipe. Overall, the results showed that low concentration lead stimulated the fruiting body of O. radicata to produce the thiols and activate the antioxidant enzymes after 2 d/4 d, while high concentration Pb resulted in the decline/decrease of the thiols and the activities of antioxidant enzymes after 4 d/6 d. Benefiting from the metal accumulation, detoxification potential and the short lifetime, mushroom have the potential for bioaccumulation of heavy metal in polluted farmland.     

A systematic review and meta-analysis of lead and cadmium concentrations in cow milk in Iran and human health risk assessment

The aim of the current research was to systematically review and summarize the studies that evaluated the concentration of lead (Pb) and cadmium (Cd) in cow milk in different regions of Iran and to perform a meta-analysis of the findings. Moreover, the non-carcinogenic and carcinogenic risks of Pb and Cd through milk consumption in adult and child consumers were assessed. As a result of a systematic search in the international and national databases between January 2008 and October 2018, 17 reports involving 1874 samples were incorporated in our study for meta-analysis. The pooled concentrations of Pb and Cd were estimated to be 13.95 μg mL−1 (95% CI 9.72–18.11 μg mL−1) and 3.55 μg mL−1 (95% CI − 2.38–9.48 μg mL−1), respectively, which were lower than the WHO/FAO and national standard limits. The estimated weekly intake (EWI) of Pb and Cd through consuming milk was 16.65 and 7 μg day−1 for adults of 70 kg and 45 and 34 μg day−1 for children of 26 kg, respectively, which was well below the risk values set by Joint FAO/WHO Expert Committee on Food Additives (JECFA). The maximum target hazard quotient values (THQs) of Pb and Cd were 5.55E−5 and 5.55E−5 for adults and 5.55E−5 and 5.55E−5 for children, respectively, which were lower than 1 value, suggesting that Iranian consumers are not exposed to non-carcinogenic risk through consuming milk. Moreover, the incremental lifetime cancer risk (ILCR) of Pb estimated to be 2.96E−04 in adults and 1.0E−03 in children, indicating that consumers in Iran are at threshold carcinogenic risk of Pb through consuming milk (ILCR > 10−4). Therefore, planning and policy making for the sustainable reduction of these toxic metals in milk, particularly in industrial regions of Iran, are crucial.     

Influence of metal oxides on PCDD/Fs formation from pentachlorophenol

Chlorophenols (ClPhs) are considered as important precursors for PCDD/Fs formation. The influences of series of metal oxides including MgO, Al2O3, CaO, BaO, TiO2, V2O5, MnO2, Fe2O3, Co3O4, CuO, Ag2O, ZnO, HgO, SnO, PbO, La2O3, CeO2, and Eu2O3 on PCDD/Fs formation from pentachlorophenol (PCP) were investigated in a laboratory-scale reactor. The results indicated that most of the above metal oxides have obvious suppressing effects on the total amount of PCDD/Fs formation from precursor PCP except for CuO, ZnO, MnO2, TiO2 and Co3O4 with promotion effects at 280 degrees C for 2 h. Although MgO, Al2O3, Fe2O3, PbO, La2O3 and Eu2O3 could reduce the amount of octachlorinated dibenzo-p-dioxin (OCDD), they promote the formation of more toxic 1,2,3,4,6,7,8-HpCDD at the same time. The total suppressing efficiencies of several metal oxides including CaO, BaO, PbO, Ag2O, HgO and SnO which have lower Z/r (charge to radius ratio) <2 are all over 90%. The theories of generalized acid-base and atomic parameter (Z/r) were used to speculate the effecting mechanisms. The factors including time and temperature on suppressing efficiencies of CaO, BaO and PbO have also been studied in the present paper. The results showed that the total suppressing efficiencies of CaO, BaO and PbO increase with the increase of heated time and temperature.     

Levels of Lead in Urban Soils from Selected Cities in a Central Region of the Philippines (7 pp)

Background Aims, and Scope. Lead (Pb) is a naturally occurring element that poses environmental hazards when present at elevated concentration. It is being released into the environment because of industrial uses and from the combustion of fossil fuels. Hence, Pb is ubiquitous throughout global ecosystems. The existence of potentially harmful concentrations of Pb in the environment must be given full attention. Emissions from vehicles are major source of environmental contamination by Pb. Thus, it becomes imperative that concentrations of Pb and other hazardous materials in the environment not only in the Philippines, but elsewhere in the world be adequately examined in order that development of regulations and standards to minimize risk associated with these materials in urban areas is continued. The objectives of this study were: (1) to determine the levels of Pb in soil from selected urbanized cities in central region of the Philippines; (2) to identify areas with soil Pb concentration values that exceed estimated natural concentrations and allowable limits; and (3) to determine the possible sources that contribute to elevated soil Pb concentration (if any) in the study area. Methods This study was limited to the determination of Pb levels in soils of selected urbanized cities located in central region in the Philippines, namely: Site 1 – Tarlac City in Tarlac; Site 2 – Cabanatuan City in Nueva Ecija; Site 3 – Malolos City in Bulacan; Site 4 – San Fernando City in Pampanga; Site 5 – Balanga City in Bataan; and Site 6 – Olongapo City in Zambales. Soil samples were collected from areas along major thoroughfares regularly traversed by tricycles, passenger jeepneys, cars, vans, trucks, buses, and other motor vehicles. Soil samples were collected from five sampling sites in each of the study areas. Samples from the selected sampling sites were obtained approximately 2 to 3 meters from the road. Analysis of the soil samples for Pb content was conducted using an atomic absorption spectrophotometer. This study was conducted from 2003 to 2004. Since this study assumed that vehicular emission is the major source of Pb contamination in urban soil, other information which the researchers deemed to have bearing on the study were obtained such as relative quantity of each gasoline type disposed of in each city within a given period and volume of traffic in each sampling site. A survey questionnaire for gasoline station managers was prepared to determine the relative quantity of each fuel type (diesel, regular gasoline, premium gasoline, and unleaded gasoline) disposed of or sold within a given period in each study area. Results and Discussion Analysis of soil samples for Pb content showed the presence of Pb in all the soil samples collected from the 30 sampling sites in the six cities at varying concentrations ranging from 1.5 to 251 mg kg–1. Elevated levels of Pb in soil (i.e. greater than 25 mg kg–1 Pb) were detected in five out of the six cities investigated. Site 4 recorded the highest Pb concentration (73.9 ± 94.4 mg kg–1), followed by Site 6 (56.3 ± 17.1 mg kg–1), Site 3 (52.0 ± 33.1 mg kg–1), Site 5 (39.3 ± 19.0 mg kg–1), and Site 2 (38.4 ± 33.2 mg kg–1). Soil Pb concentration in Site 1 (16.8 ± 12.2 mg kg–1) was found to be within the estimated natural concentration range of 5 to 25 mg kg–1. Site 1 registered the least Pb concentration. Nonetheless, the average Pb concentration in the soil samples from the six cities studied were all found to be below the maximum tolerable limit according to World Health Organization (WHO) standards. The high Pb concentration in Site 4 may be attributed mainly to vehicular emission. Although Site 4 only ranked 3rd in total volume of vehicles, it has the greatest number of Type B and Type C vehicles combined. Included in these categories are diesel trucks, buses, and jeepneys which are considered the largest contributors of TSP (total suspended particles) and PM10 (particulate matter less than 10 microns) emissions. Conclusion Only one (San Juan in Site 4) of the thirty sampling sites recorded a Pb concentration beyond the WHO permissible limit of 100 mg kg–1. San Juan in Site 4 had a Pb concentration of >250 mg kg–1. On the average, elevated Pb concentration was evident in the soil samples from San Fernando, Olongapo, Malolos, Balanga, and Cabanatuan. The average soil Pb concentrations in these cities exceeded the maximum estimated natural soil Pb concentration of 25 mg kg–1. Average soil Pb concentration in Site 1 (16.8 mg kg–1) was well within the estimated natural concentration range of 5 to 25 mg kg–1. Data gathered from the study areas showed that elevated levels of Pb in soil were due primarily to vehicular emissions and partly to igneous activity. Recommendation and Outlook The findings of this study presented a preliminary survey on the extent of Pb contamination of soils in urban cities in central region of Philippines Island. With this kind of information on hand, government should develop a comprehensive environmental management strategy to address vehicular air pollution in urban areas, which shows as one of the most pressing environmental problems in the country. Basic to this is the continuous monitoring of Pb levels and other pollutants in air, soil, and water. Further studies should be conducted to monitor soil Pb levels in the six cities studied particularly in areas with elevated Pb concentration. The potential for harm from Pb exposure cannot be understated. Of particular concern are children who are more predisposed to Pb toxicity than adults. Phytoremediation of Pb-contaminated sites is strongly recommended to reduce Pb concentration in soil. Several studies have confirmed that plants are capable of absorbing extra Pb from soil and that some plants, grass species in particular, and can naturally absorb far more Pb than others.     

In vitro and in vivo studies of lead immobilization by synthetic hydroxyapatite

Apatite appears a useful compound for removing lead from water, due to its ability to immobilize the metal by precipitation. In dilute solution, dissolved hydroxyapatite [HA, Ca1O(P04)6(OH)2] provided phosphates that were reactive with aqueous lead (molar ratio HA/Pb= 1/10) forming precipitates at around pH 6. These dissolved at a more acidic pH (3). Solid HA in contact with Pb2+ions, led to the formation of pyromorphite [Pblo(P04)6(OH)2], identified by X-ray diffraction and insoluble at pH tested (3-8). The amount of pyromorphite increased with the weight ratio of HA/Pb. When this one increased from 1 to 1000, lead precipitated as pyromorphite rose from 19 to 99%. In vivo experiments on rats confirmed the in vitro results. In fact, lead bioavailability assessed by intestinal perfusion was unchanged in the presence of dissolved HA, whereas it was significantly lower in the presence of solid HA, evaluated by gastric intubation, at a weight ratio equal to 10 (amount of lead absorbed decreased by 60%). Apatite could bean effective means of immobilizing lead in drinking or sewage, since accidental pyromorphite ingestion does not yield bioavailable lead.     

Highly efficient biosorptive removal of lead from industrial effluent

This study has been focused on the efficient removal of Pb (II) from contaminated waters by biosorption using plant derived material. Accordingly an indigenous shrub, Tinospora cordifolia has been identified as the most suitable biosorbent. The plant biomass was subjected to optimization of various parameters such as the pH, equilibrium time, dosage, concentration, temperature and the applicable adsorption models. The optimum pH identified was 4.0 with a contact time of 60 min at room temperature (27 ± 2 °C). The experimental data fitted well to adsorption isotherms and the uptake capacity of Pb (II) was found to be 20.83 and 63.77 mg/g in batch mode and column mode, respectively. The high correlation factors obtained for Langmuir and Freundlich models indicated that both models were obeyed by the system. Kinetic study for adsorption of Pb (II) follow only pseudo second order rate of reaction. The accumulation of lead in biomass was confirmed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. The FTIR analysis indicated the involvement of hydroxyl (−OH), alkenes (=CH) and carbonyl group (C = O) chelates in metal binding. The SEM and EDX analysis showed the structural changes and the filling of voids in the biomass thus, it indicated the metal-binding mechanism. In elution studies, the 0.1 M Na₂CO₃ was found to be the best with about 71% elution of the adsorbed metal. The biomass was then used for the removal of Pb (II) in synthetic and real wastewater samples from a lead-acid battery industry. It is also noteworthy that even at a very high concentration of 450 mg/L, the biomass was showing about 92% removal. The result is to establish the efficacy of T. cordifolia as a very good bioadsorbent for the Pb (II) removal from contaminated water.

     

硫酸铅在柠檬酸钠-酸体系中的浸出转化

硫酸铅可以在柠檬酸钠-乙酸体系中脱硫转化生成柠檬酸铅。考察了柠檬酸钠投加量、反应时间、固液比以及反应温度对PbSO4浸出转化的影响。实验结果表明，PbSO4的转化率随着柠檬酸钠投加量和反应时间的增加而增大，固液比和反应温度对浸出过程影响不大。溶液中溶解的铅含量随着柠檬酸钠投加量的增大而增大，其他条件对其影响不明显。最佳浸出工艺条件是：柠檬酸钠与PbSO。的物质的量之比为2：1，固液比为1／5～1／3，反应温度为25℃，反应时间为2h，此时PbSO4的转化率可达到99％左右，溶液中的铅含量为总铅的3．8％左右。PbSO4浸出得到[Pb，（C。H，O，），]·3H2O，它在350℃左右可完全分解，得到PbO／Pb粉末。     

Effects of lead contamination on soil microbial activity and rice physiological indices in soil-Pb-rice (Oryza sativa L.) system

The effect of lead (Pb) treatment on the soil microbial activities (soil microbial biomass and soil basal respiration) and rice physiological indices were studied by greenhouse pot experiment. Pb was applied as lead acetate at six different levels in two different paddy soils, namely 0 (control), 100, 300, 500, 700, 900 mg kg-1 soil. The results showed that the application of Pb at lower level (<300 mg kg-1) as lead acetate resulted in a slight increase in soil microbial activities compared with the control, and had an inhibitory influence at high concentration (>500 mg Pb kg-1 soil), which might be the critical concentration of Pb causing a significant decline in the soil microbial activities. However, the degree of influence on soil microbial activities by Pb was related to the clay and organic matter contents of the soils. On the other hand, when the level of Pb treatments increased to 500 mg kg-1, there was ecological risk for both soil microbial activities and plants. The results also revealed that there was a consistent trend that the chlorophyll contents increased initially, and then decreased gradually with increase in Pb concentration. Pb was effective in inducing proline accumulation and its toxicity causes oxidative stress in rice plants. In a word, soil microbial activities and rice physiological indices, therefore, may be sensitive indicators reflecting environmental stress in soil-Pb-rice system.     

Multivariate analysis of mineral constituents of edible Parasol Mushroom (Macrolepiota procera) and soils beneath fruiting bodies collected from Northern Poland

Caps and stipes of 141 fruiting bodies of Parasol Mushroom (Macrolepiota procera) and surface layer of soils collected from 11 spatially distant and background (pristine) areas in Northern Poland were analyzed for Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, P, Pb, Rb, Sr, and Zn by inductively coupled plasma optical emission spectroscopy and cold vapor atomic absorption spectroscopy. In terms of bioconcentration and bioexclusion concept, K, Ag, Cu, Rb, and P were highly bioconcentrated in caps, and their bioconcentration factor values varied for the 11 sites between 120 and 500—67–420, 70–220, 10–170, and 45–100, respectively. Cd, Zn, Mg, and Na showed bioconcentration factors (BCFs) between 3.3 and 36, 3.7–15, 0.92–6.3, and 1.4–44 while Al, Ba, Ca, Co, Cr, Mn, Ni, Pb, and Sr were excluded (BCF < 1). The Parasol Mushroom is a species harvested in the wild, and its caps are of unique taste and can contain a spectrum of essential and hazardous mineral compounds accumulated at elevated concentrations, even if collected at the background (pristine) areas. These elevated mineral concentrations of the caps are due to the efficient bioconcentration potential of the species (K, Ag, Cu, Rb, P, Cd, Zn, Mg, and Na) and abundance in the soil substrates (Al, Ca, Fe, Mn). The estimated intake rates of Cd, Hg, and Pb contained in Parasol Mushroom’s caps show a cause for concern associated with these metals resulting from the consumption of between 300- and 500-g caps daily, on a frequent basis in the mushrooming season.     

Current State of the Altai Glaciers (Russia) and Trends Over the Period of Instrumental Observations 1952–2008

Results of research into climate and glacier dynamics in the Altai Mountains (Russia) over the period of instrumental observations (1952–2008) are presented in this article. About 1030 glaciers with a total area of 805 km² and volume of 42.5 km³ have been recorded in the Altai Region. The average summer air temperature in different regions of the Altai has increased during the study period from about 0.2°C (Aktru) to 1.1°C (Akkem). The annual atmospheric precipitation rate has also increased, by 8–10%. Since 1952, the glacier area in different regions of the Altai has decreased by 9–27%, and volume by 12–24%. By 2008, as a result of degradation, the total number of glaciers was 953 with an area of 724 km² and volume of 38 km³.     

Thermal Immobilization of Lead Contaminants in Soils Treated in a Fixed- and Fluidized-Bed Incinerator at Moderate Temperatures

Abstract

Artificially lead-contaminated soils with different lead contents (200, 450, 600, and 900 ppm) were thermally immobilized in both fixed-bed and fluidized-bed modes at moderate treating temperatures (less than 500 °C) for various retention times. Cement powder and brick powder were added to the artificially contaminated soils to enhance lead immobilization. Results indicate that increasing treating temperature and time increases the extent of lead immobilization, as determined by the U.S. Environmental Protection Agency's (U.S. EPA) Toxicity Characteristics Leachability Procedure (TCLP). The percentage of lead leached from the soil/ cement mixtures was in the range of less than 0.251%, compared with the range between 13.6% and 40.7% for the corresponding soil/brick mixtures. As the amount of brick dust added to the Pb-doped soil was increased, the specific Pb immobilization effectiveness increased from 0.0675 to 0.149 mg Pb/g brick (for the 20- and 50-gram brick addition, respectively). An increase in air flow rate from 2 to 40 L/min caused a slight decrease in the Pb leaching percentage from 14.96% to 11.59%. Both the Freundlich and Langmuir isotherms give a satisfactory fit (r = 0.945 ~ 0.998) for the data derived from a TCLP test of the thermally-treated soil samples (105 °C and 500 °C) that contained lead contaminants. Sorption of lead contaminants in soil and sorbent matrices was the primary type of chemisorption. The kinetic results indicated that the Pb-doped soil system was too complicated to be described by a simple calculation.     

1985 Directory of Governmental Air Pollution Control Agencies

Abstract

Clay that contains kaolinite has been used extensively as a raw material for manufacturing of bricks and china at 900–1100 °C. This study used clay to stabilize the contaminant chromium(VI) [Cr(VI)] through a heating process at 500–1100 °C. X-ray absorption spectroscopic results indicated that the 500–900 °C heating process transformed hazardous Cr(VI) to nontoxic Cr(III); Cr₂O₃ was the species detected as most abundant. The 1100 °C heating process caused the formation of Cr₂SiO₅, which was not detected in the samples heated at 500–900 °C. Fourier transformed extended X-ray absorption fine structure spectra were fitted by use of WinXAS software. Phase shifts and backscatter(ing) amplitudes for specific atom pairs, based on the crystallographic data for CrO₃ and Cr₂O₃, were theoretically calculated with the FEFF software. The processed XAS data show that the first shell coordination numbers were similar to each other as the temperature was increased from 500 to 900 °C and 1100 °C, implying that their Cr(III) crystallite size was relatively similar. The interatomic distance between the target center element and the first shell for the 500– 1100 °C samples was 1.98Å. The Debye-Waller factor for the 1100 °C sample was increased compared with the 500 and 900 °C samples and probably indicates the formation of Cr₂SiO₅.     

Factors influencing lead sorption-desorption at variable added metal concentrations in Rhodoxeralfs

The response of ten soils of the lithic Rhodoxeralf type to the supply of lead at concentrations of 500, 1000, 2000, 3000, 4000, 5000 and 6000 mg kg-1 was examined in batch sorption-desorption tests. Lead availability in the soils was found to depend on its partitioning between the soil solution and the solid phase as reflected in adsorption isotherms. The isotherms, of the H type, were consistent with a high affinity of the sorbent for the metal, with which it forms stable inner-sphere complexes on the soil surface. Sorption-desorption tests revealed that some properties of the soils such as their pH (mean=8) and high contents in clays (particularly in kaolinite) and crystalline iron oxides significantly influence Pb sorption, the effect being especially marked at high added metal concentrations. Added lead is largely retained by crystalline iron oxides and the soil clay fraction; the pH of the soil favours the release of variably-charged sites from both. The extent of Pb desorption was small, particularly at the lowest added levels (500 and 1000 mg kg-1). Desorption increased with increasing added Pb concentration and exceeded 50% at 5000 and 6000 mg kg-1; this suggests that Pb is present not only as inner-sphere complexes, but also as outer-sphere complexes and, partly, as precipitates. The desorption isotherms consist of three segments that exhibit significant differences depending on the added Pb concentration, namely: 500-1000, 2000-4000 and 5000-6000 mg kg-1.     

Effects of organic acids on adsorption of lead onto montmorillonite,goethite and humic acid

Adsorption isotherms for Pb onto six soil components (quartz, feldspar, kaolinite, montmorillonite, goethite and humic acid) were studied. The influence of pH, EDTA and citric acid on the adsorption of Pb onto montmorillonite, goethite and humic acid were considered. Results indicate that the experimental data fit the Langmuir Adsorption Isotherm. The adsorption capacity for Pb at pH 6 was found to be in the order: humic acid (22.7 mg g(-1)) > goethite (11.04 mg g(-1)) > montmorillonite (10.4 mg g(-1)) > kaolinite (0.91 mg g(-1)) > feldspar (0.503 mg g(-1)) > quartz (0.148 mg g(-1)). Generally, the amount of Pb adsorbed onto montmorillonite, goethite and humic acid decreased with increasing concentrations of EDTA and citric acid and with increases in alkality. However, there were two exceptions: (1) addition of citric acid increased the amount of Pb adsorbed onto humic acid; and (2) the amount of Pb adsorbed onto goethite decreased with increasing pH in the presence of EDTA. Some mechanisms involved in the adsorption reactions are discussed.