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1.
Assessment of alternative adsorption models and global sensitivity analysis to characterize hexavalent chromium loss from soil to surface runoff 下载免费PDF全文
We investigate our ability to assess transfer of hexavalent chromium, Cr(VI), from the soil to surface runoff by considering the effect of coupling diverse adsorption models with a two‐layer solute transfer model. Our analyses are grounded on a set of two experiments associated with soils characterized by diverse particle size distributions. Our study is motivated by the observation that Cr(VI) is receiving much attention for the assessment of environmental risks due to its high solubility, mobility, and toxicological significance. Adsorption of Cr(VI) is considered to be at equilibrium in the mixing layer under our experimental conditions. Four adsorption models, that is, the Langmuir, Freundlich, Temkin, and linear models, constitute our set of alternative (competing) mathematical formulations. Experimental results reveal that the soil samples characterized by the finest grain sizes are associated with the highest release of Cr(VI) to runoff. We compare the relative abilities of the four models to interpret experimental results through maximum likelihood model calibration and four model identification criteria (i.e., the Akaike information criteria [AIC and AICC] and the Bayesian and Kashyap information criteria). Our study results enable us to rank the tested models on the basis of a set of posterior weights assigned to each of them. A classical variance‐based global sensitivity analysis is then performed to assess the relative importance of the uncertain parameters associated with each of the models considered, within subregions of the parameter space. In this context, the modelling strategy resulting from coupling the Langmuir isotherm with a two‐layer solute transfer model is then evaluated as the most skilful for the overall interpretation of both sets of experiments. Our results document that (a) the depth of the mixing layer is the most influential factor for all models tested, with the exception of the Freundlich isotherm, and (b) the total sensitivity of the adsorption parameters varies in time, with a trend to increase as time progresses for all of the models. These results suggest that adsorption has a significant effect on the uncertainty associated with the release of Cr(VI) from the soil to the surface runoff component. 相似文献
2.
Chromium pollution were investigated by sampling the abandoned chromium contaminated sites in Chongqing. Its health risk was assessed following the procedures made by USEPA. The results showed that the most seriously polluted land was found at the former production area (G4) with average Cr(VI) concentration of 3369.2 mg kg-1 on the surface soil. The assessment indicated that there was high risk of non-carcinogens for children. The assessed risk of the first layer of office area (G1) for children, chromium slag transition (G2), drainage pipeline chromium slag transition (G3) and production area (G4) for both children and adults were not acceptable (〉1.00× 106). It was strongly suggested that the accessible measures of remediation should be taken for a portion of contaminated sites before the reuse of abandoned lands. 相似文献
3.
During the manufacturing of chromate salts (1972–1992) large quantities of Chromite Ore Processing Residue (COPR) were released
into a decantation pond east of the former chemical plant of Porto-Romano (Durres, Albania), giving rise to yellow colored
pond sediments. These Cr(VI) bearing sediments were deposited upon Quaternary silty-clay lagoonal sediments rich in iron oxides
and organic matter. The pH values in these lagoonal sediments vary around 6.6, while in the pond sediments, it is mainly acidic
(due to the presence of the sulfur stock piles in the area and the release of the H2SO4 from the activity of the former chemical plant), varying between 1.4 and 3.8. Continuous leaching of the COPR waste resulted
in yellow-colored surface water runoff. The prediction of pH changes in the different types of sediments based upon acid/base
neutralizing capacity (ANC/BNC) jointly with the quantitative data on release of heavy metals and especially Cr is considered
an important advantage of the pHstat leaching test if compared to conventional leaching procedures. Thus, factors controlling the leaching of Cr(VI), Cr(III),
Ca, Al, Fe, Mg from the COPR were investigated by means of pHstat batch leaching tests and mineralogical analysis. Moreover, mathematical and geochemical modeling complemented the study.
The COPR in the area contain very high concentrations of chromium 24,409 mg/kg, which mainly occurs as Cr(III) (75–90%) as
well as Cr(VI) (25–10%). The leaching of Cr(VI) occurs in all the range (2–10) of the tested pH values, however, it decreases
under acidic conditions. Beside some reduction of Cr(VI) to Cr(III), the Cr(VI) content of the leachtes remains relatively
high in the acidic environment, while the limning of Cr(VI) pond sediments will increase the release of the latter specie.
The leaching of the Cr(III) occurs strictly under acidic conditions, whereby limning of these sediments will give rise to
the lower solubility of Cr(III). The key mineral phases responsible for the fast release of the Cr(VI) are: the chromate salts
(i.e. sodium chromate and sodium dichromate), while sparingly soluble chromatite (CaCrO4) and hashemite (BaCrO4) release Cr(VI) very slowly. Thus, pH and mineral solubility have been identified as key factors in the retention and the
release of the hexavalent CrO4
2− and Cr2O7
− from the COPR-rich pond sediments. 相似文献
4.
膨润土负载纳米铁去除地下水中六价铬研究 总被引:4,自引:1,他引:3
随着人民生活水平的提高和城市化进程的加快,有机污染物及重金属高强度场地污染对人类健康、生态环境及社会安全构成了严重威胁。地下水中的重金属Cr(Ⅵ)污染逐渐受到重视,纳米零价铁可以有效地将六价铬还原成三价铬,使其沉淀固定下来,从而将污染源区的污染物消减固定,防止其向周围扩散。然而由于纳米铁颗粒微小,易被氧化,极易团聚,自身活性受到限制,因此,纳米铁的分散性、稳定性、良好活性研究至关重要。采用低成本环境友好型粘土矿膨润土作为负载材料制备膨润土负载纳米铁(B-NZVI),批实验和柱实验研究B NZVI去除模拟地下水中Cr(Ⅵ)。结果表明:(1)自制的膨润土负载纳米铁个体呈球形,呈分散状负载于膨润土;(2)相同铁含量的B-NZVI处理Cr(Ⅵ)的效率远大于纳米铁,还原反应符合伪一级反应动力学模型,表观速率常数K随着B NZVI初始浓度的减小而减小;(3)B NZVI在石英砂柱中基本无迁移,适用于点源污染,Cr(Ⅵ)穿透曲线为B-NZVI的实际应用提供了理论和实验基础。 相似文献
5.
The adsorption behaviors of Cr(VI) on laterite from Guizhou Province were studied in this paper, and the adsorption mechanism
was discussed as well. Results showed that different mineral compositions in the laterite would cause differences in the capacity
of laterite to absorb Cr(VI). Gibbsite, iron oxide minerals and non-crystalloids are the main contributors to enhancing the
capacity of laterite to absorb Cr(VI). The pH of the solution is an important factor affecting the adsorption of Cr(VI) on
laterite. Acidic environment (pH=2–5) is favorable to the adsorption of Cr(VI). The amount of adsorbed Cr(VI) decreases with
increasing pH of the solution. With increasing initial concentrations of Cr(VI), the amount of adsorbed Cr(VI) increases first,
and then decreases. The optimal adsorption concentration of Cr(VI) on laterite is 250 μg/mL. The adsorption of Cr(VI) on laterite
is a rapid process, about 80% Cr(VI) will be adsorbed within 2 hours. And the adsorption of Cr(VI) on kaolinite is a slow
process. 相似文献
6.
Alfredo Alberto Muxel Sonia Maria Nobre Gimenez Flaveli Aparecida de Souza Almeida Rení Ventura da Silva Alfaya Antonio Alberto da Silva Alfaya 《洁净——土壤、空气、水》2011,39(3):289-295
The natural cotton fiber was used to synthesize an anion exchange, containing ZrO2 film on its surface, NCFZC (natural cotton fiber/ZrO2 composite). This anion exchanger was produced by the reaction of the zirconium oxychloride and hydroxyl groups on surface of the natural cotton fiber. The material was used for Cr(VI) ions adsorption studies. Adsorption equilibrium time and optimum pH for Cr(VI) adsorption were found to be 6 h and 4.0, respectively. The Langmuir and Temkin isotherms were used to models adsorption equilibrium data. The adsorption capacity of NCFZC was found to be 1.33 mmol/g. Kinetic studies showed that the rate of adsorption of Cr(VI) on NCFZC obeyed a pseudo‐second‐order kinetic model. 相似文献
7.
The rates of the reduction of Cr(VI) with S(IV) were measured in deaerated NaCl solution as a function of pH, temperature and ionic strength. The rates of the reaction were found to be first order with respect to Cr(VI) and second order with respect to S(IV), in agreement with previous results obtained at concentrations two order higher than the present study. The reaction also showed a first-order dependence of the rates on the concentration of the proton and a small influence of temperature with an apparent energy of activation ΔHapp of 22.8 ± 3.4 kJ/mol. The rates were independent of ionic strength from 0.01 to 1 M. The rate of Cr(VI) reduction is described by the general expression
−d[Cr(VI)]/dt=k[Cr(VI)][S(IV)]2