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Immobilization of heavy metals in water and soil by phosphate treatment
No full textHeavy metals such as Pb, Cd, Cu, Zn, Hg, Cr, and Ni are the main contaminants of surface water, groundwater, and soils. The heavy metals are of great concern because of their extreme toxicity even at low concentration and the tendency to accumulate in the food chain. Conventional methods for heavy metal removal from water and soil include chemical precipitation, filtration, solvent extraction, electrochemical technique, ion exchange, and adsorption. In particular, chemical immobilization is one of the most used for reducing the bioavailability of heavy metals. The aim is to immobilize the ions trapping them in minerals with low solubility and stable in the environment in a wide range of conditions. Synthetic or natural apatite and phosphate rock have been proved to immobilize divalent heavy metal ions such as Pb, Zn, Cd, Cu, Co, Cr, Ni, and Sb in contaminated waters and soils. The mechanisms of metal removal include ion exchange, surface complexation and dissolution/precipitation. In this study the removal of Cd, Pb, Zn, and Cu from aqueous solutions by both synthetic hydroxyapatite (HA) and natural phosphate rock (FAP) was investigated in batch conditions at 25 ± 2°C. The metals were applied both as single- or multi-metal (Cd + Pb + Zn + Cu) systems with initial concentrations from 0 to 8 mmol L-1. The removal capacity of phosphate amendments generally ranges between 50 and 99%. In the multi-metal systems competitive internal metal sorption reduced the removal capacity by 13–83% compared to the single-metal systems. The sorption of heavy metals by phosphate amendments follows the Langmuir model. Heavy metal immobilization occurs through a two-step mechanism: rapid surface complexation on the ≡POH sites followed by partial dissolution of phosphates and ion exchange with Ca resulting in the formation of heavy metal-containing phosphates.The sorption of Cu on HA was further investigated by means of the results of a combined structural simulation and EXAFS analysis. The EXAFS results suggest that the heavy metal is present in the Cu+2 form. The structural experimental and theoretical analysis shows that Cu is bond to about four O atoms at a distance of about 1.95Å. In all the studied cases the immobilization site of Cu is the same. The fixation of Cu occurs in the surface sites of hydroxyapatite whereas the sorption in the Ca sites in the inner part of the structure is unlikely.The effectiveness of phosphate treatment for Cd, Pb, Zn, and Cu immobilization in mine waste soils from sulfide mine areas (tailing dumps, ore stocking areas, streams, etc.) in Tuscany and Sardinia (Italy) was examined in batch conditions. Application of HA and FAP effectively reduced the heavy metals water solubility generally by about 84 to 99%. Between the two amendments evaluated, HA was slightly more effective with respect to FAP in immobilizing heavy metals. Although the lower effectiveness of phosphate rock, its application to reduce metal solubility in contaminated soils may minimize soil acidification and potential risk of eutrophication associated with the application of highly soluble phosphate sources
Removal of Lead, Copper, Zinc and Cadmium from Water Using Phosphate Rock
No full textRemoval of Pb(2+), Cu(2+), ZD(2+) and Cd(2+) from aqueous solutions by sorption on a natural phosphate rock (FAP) was investigated. The effects of the contact time and initial metal concentration were examined in the batch method. The percentage sorption of heavy metals from solution ranges generally between 50% and 99%. The amount of sorbed metal ions follows the order Cu>Pb>Cd>Zn. Heavy metal immobilization was attributed to both surface complexation of metal ions on the surface of FAP grains and partial dissolution and precipitation of a heavy metal-containing phosphate. The very low desorption ratio of heavy metals further supports the effectiveness of FAP as an alternative and low-cost material to remove toxic Pb(2+), Cu(2+), ZD(2+) and Cd(2+) from polluted waters
Cadmium removal from single- and multi-metal (Cd + Pb + Zn + Cu) solutions by sorption on hydroxyapatite
No full textHeavy metal contamination of waters and soils is particularly dangerous to the living organisms. Different studies have demonstrated that hydroxyapatite has a high removal capacity for divalent heavy metal ions in contaminated waters and soils. The removal of Cd from aqueous solutions by hydroxyapatite was investigated in batch conditions at 25 ± 2 ° C. Cadmium was applied both as single- or multi-metal (Cd + Pb + Zn + Cu) systems with initial concentrations from 0 to 8 mmol L-1. The adsorption capacity of hydroxyapatite in single-metal system ranged from 0.058 to 1.681 mmol of Cd/g of hydroxyapatite. In the multi-metal system competitive metal sorption reduced the removal capacity by 63-83% compared to the single-metal system. The sorption of Cd by hydroxyapatite follows the Langmuir model. Cadmium immobilization occurs through a two-step mechanism: rapid surface complexation followed by partial dissolution of hydroxyapatite and ion exchange with Ca resulting in the formation of a cadmium-containing hydroxyapatite. © 2007 Elsevier Inc. All rights reserved
Immobilization of heavy metals in soil by phosphate treatment: A review
No full textHeavy metal contamination of soil is an environmental and public health issue of prime interest because metals are non-biodegradable and accumulate throughout the food chain. Conventional heavy metal remediation technologies include chemical precipitation, membrane filtration, ion exchange, electrochemical treatment, etc. Recently adsorption has become an alternative treatment method of contaminated media and a great effort has been devoted to develop new adsorbents. Phosphate treatment is widely considered an effective in situ treatment to reduce metal mobility and bioavailability in soils through the formation of highly insoluble phosphates which are stable in a wide range of environmental conditions. The mechanisms of metal retention are still debated and include: ion exchange, dissolution/precipitation and surface complexation. Various types of phosphate amendments, such as synthetic and natural apatites, phosphate rocks, bone meal and bone char have been tested. Phosphate treatment has been shown to be effective in stabilizing Pb, Cd, Cu, Zn, Co, Ni, Sb, Cr, V in contaminated soils. In soils phosphate stabilization has been applied mainly to remediate Pb contamination although the method can be used to reduce also the mobility and bioavailability of other metals. The main factors determining the removal capacity of phosphate treatment in contaminated soils include type of phosphate source due to their different solubilities, rate of phosphate application, heavy metals speciation, soil pH and Eh and grain size of the amendment. The adverse effects of phosphate stabilization resulting in enhanced leaching of phosphate and availability in the soil of contaminants, such as As, Se and W, have to be addressed for evaluating the environmental impact of phosphate treatment. © 2012 Nova Science Publishers, Inc. All rights reserved
Synthetic phosphates as binding agent of Pb, Zn, Cu and Cd in the environment
No full textThe sorption of Pb, Zn, Cu and Cd from aqueous multiple-species solutions by synthetic hydroxyapatite (HAP) was investigated. HAP was reacted with solutions containing different heavy metals concentrations (10, 100 and 500 mg/L) for four times (2, 4, 24 and 48h). The results showed that HAP was very effective in removal heavy metals from aqueous solutions. Approximately 95-99% of the Pb applied was removed from solutions, with the best sorption capacity of 497 mg of Pb/g of HAP, while 92-99% of Zn, 93-99% of Cu and 88-99% of Cd added were attenuated, with best removal capacity of 498, 485 and 477 mg/g, respectively. Sorption mechanisms other than dissolution/precipitation of crystalline phases could be involved in attenuating heavy metals concentrations such as ion exchange, coprecipitation, surface complexation and formation of amorphous phases. The study results confirm HAP provides a cost effective method for the decontamination of solutions polluted by heavy metals
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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