Processes of Removing Zinc from Water using Zero-Valent Iron

Zero-valent iron has received considerable attention for its potential application in the removal of heavy metals from water. This paper considers the possibility of removal of zinc ions from water by causing precipitates to form on the surface of iron. The chemical states and the atomic concentrations of solids which have formed on the surface of zero-valent iron as well as the type of the deposited polycrystalline substances have been analyzed with the use of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The BET surface area, the pH at point of zero charge (pH(PZC)), the ORP of the solutions, and the pH and chemical concentrations in the solutions have also been measured. Furthermore, the paper also considers the possibility of release of zinc from the precipitates to demineralised water in changing physicochemical and chemical conditions. In a wide range of pH values, Zn(x)Fe(3 − x)O(4) (where x ≤ 1) was the main compound resulting from the removal of zinc in ionic form from water. In neutral and alkaline conditions, the adsorption occurred as an additional process

Trakun, Politics and the Thai State

Politiske trakun er patrilineære slægtsgrupper der har udmærket sig gennem engagement i politik igennem adskillige generationer ved at udfylde nøglepositioner i staten, såsom i kabinettet og parlamentet. De er endnu ikke blevet viet akademisk opmærksomhed. På trods af at de fleste redegørelser for Thailands politiske historie samtidig er beretninger om kongefamilien og andre elitefamilier, findes der ikke megen forskning der har søgt at forstå hvordan familierne og staten smelter sammen. Litteraturen om Thailand efter 1932 giver endnu mindre indsigt i slægtskabsrelateret politik i Thailand. Hvis de overhovedet nævnes optræder politiske trakun generelt i fodnoter, som anekdoter eller dele af biografier. I denne afhandling vil jeg behandle dette hul i litteraturen. Denne afhandling vil vise hvad politiske trakun er og hvordan de er blevet grundlagt. Ydermere vil deres udvikling gennem historien samt måden hvorpå de har tilpasset sig skiftende politiske omstændigheder blive undersøgt. Der vil blive givet en forklaring på hvordan politiske trakun har været i stand til at smelte sammen med den thailandske stat. Dette vil blive demonstreret gennem analyse af beretningerne om fem politiske trakun set i forhold til den bredere kontekst der udgøres af det thailandske samfund og af politik i Thailand. Specifikke begivenheder fra disse trakuns liv og karrierer, såsom ægteskaber, valgkampagner og begravelser fungerer som linser der skaber en optik som muliggør en kritisk gentænkning af krydsfeltet mellem tilsyneladende separate størrelser: trakun og staten. Dette studie vil argumentere for at politiske trakun har indtaget nøglestillinger i den thailandske stat gennem årtier. På denne måde kontrollerer de staten og samler ressourcer som de kan transformere til økonomisk og symbolsk kapital. Denne kapital bruges til at vinde valg og til at fastehold de politiske trakuns indflydelsesrige positioner. Kapital reproduceres gennem socialisering fra en generation til den næste. Strategiske ægteskabspagter skaber alliancer eller styrker samarbejdet i en trakun. Når et medlem af en trakun dør medierer begravelsen det mulige tab af symbolsk kapital i alle dets fremtrædelsesformer. Herved bliver traditionelle begravelsesritualer benyttet og genfortolket for at tjene til udbredelsen af trakuns symbolske kapital. Den rolle politiske trakun spiller viser at den thailandske stat er en abstrakt forestilling om en institution der udøver sin suverænitet over et givent territorium, og relaterer grundlæggende til opretholdelsen af orden indenfor dens territorium og til regeringsudøvelsen. Dette har frembragt et billede af en organisationsstruktur, der anerkendes som staten. Regeringspraksissen udføres af en sammenfiltret masse af relationer mellem individer og grupper af individer. En af disse typer af relationer, som er en uadskillelig del af en thailandske stat, er slægtskabsrelationer, som er åbenbare i de politiske trakun.Political trakun are patrilineages that have distinguished themselves through engaging in politics over several generations by filling key positions of the state, such as the cabinet and parliament. The study of political trakun though has not yet been given academic attention. Despite most accounts of Thai political history being simultaneously the accounts of the royal and other elite families, little research has aimed to understand the entanglement of families and the state. The literature on Thailand after 1932 offers even less insight into Thai kinship politics. Political trakun, if they are mentioned at all, generally appear in footnotes, as anecdotes or as part of biographies. In this thesis I will address this gap. This thesis will show what political trakun are and how they are established. Their evolvement over the course of history and the way they adapted to changing political circumstances will also be examined. It will be explained how political trakun have been able to become entwined with the Thai state. This will be demonstrated through the analysis of the case studies of five political trakun in the larger context of Thai society and politics. Particular events from these trakun's lives and careers, such as marriages, election campaigns and funerals, will function as lenses through which to critically reassess the intersection of seemingly disparate strands: the trakun and the state. This study will argue that political trakun have taken crucial positions in the Thai state over decades. In this way they have control of the state and amass resources which they can transform into economic and symbolic capital. This capital is used to win elections and to maintain the influential position of political trakun. Capital is reproduced through socialization from one generation to the next. Strategic marriages create alliances or strengthen cooperation in the trakun. Upon the death of one member of the trakun, the funeral mediates the possible loss of symbolic capital in all its forms. Hereby, the traditional funeral rituals are utilized and reinvented for the proliferation of the trakun's symbolic capital. The role of political trakun shows that the Thai state is an abstract concept of an institution exercising sovereignty over a given territory, relating fundamentally to the maintenance of order within its territory and to the business of government. This has given rise to the image of an organizational structure, which is recognized as the state. The praxis of government, however, is performed by an entangled mass of interlocking relationships between individuals and groups of individuals. One type of such relationships that is integral to the Thai state is kinship relationships, which are manifest in the political trakun

Entfernen von gelösten Metallen aus Regenwasserabfluss durch Eisen

In dieser Studie wurde eine neuartige Methode zur Aufbereitung von schwermetallbelasteten Oberflächenabflüssen untersucht. Dabei kam nullwertiges Eisen (Fe0) als Barrieresystem zum Einsatz. In Batch- und Säulenversuchen wurden die Mechanismen und der Einfluss der Wasser-qualität auf die Schwermetallentfernung in dem Fe0-Barrierensystem untersucht. Die Untersuchungen haben gezeigt, dass mit Fe0 eine vergleichbare Beladungskapazität erzielt wird wie mit granuliertem Eisenhydroxid (GEH). Die Entfernung von gelöstem Kupfer und Zink durch Fe0 ist auf mehrere geschwindigkeitsbestimmende Schritte zurückzuführen, wobei die Eisenoxidation, die Eisenhydroxidbildung, die Metalladsorption und die Mitfällung von Be-deutung sind. Das gelöste Kupfer wird direkt oder indirekt durch Fe0 reduziert. Als Reaktions-produkte wurden Cu0 und Cu2O festgestellt. Die Zinkentfernung ist hauptsächlich auf die Adsorption und auf die Mitfällung zurückzuführen. Die kinetischen Batchversuche haben gezeigt, dass die Zinkentfernung durch geringe Sauerstoffgehalte, niedrige Temperaturen und niedrige pH-Werte sowie hohe DOC- und Metallgehalte verringert wird. Die Säulenversuche mit Fe0 zeigten, dass das gelöste Kupfer besser zurückgehalten wird als das gelöste Zink. Dabei wurde eine mittlere Beladung des Fe0 in Höhe von 76 mg g-1 (mit min.: 55 und max.: 96 mg g-1) für Kupfer und von 55 mg g-1 (mit min.: 22 und max.: 69 mg g-1) für Zink ermittelt. Es zeigte sich ein besserer Rückhalt bei erhöhten pH-Werten sowie bei einer erhöhten Wassertemperatur. Demgegenüber verringerte sich der Kupfer- und Zinkrückhalt bei einer Zunahme der Gelöstsauerstoffkonzentration bzw. der Leitfähigkeit. Von den untersuchten Einflussgrößen auf den Metallrückhalt wurde der NOM-Gehalt im Oberflächenabfluss als wichtigster Einflussparameter identifiziert, der zu einer drastischen Verringerung der Metallrückhaltes. Die festgestellte Inhibierung des Metallrückhaltes in Gegenwart von NOM kann auf die konkurrierende Adsorption, auf die Bildung von metallorganischen Komplexen sowie auf die Hemmung der Eisenkorrosion zurück¬geführt werden. Die im Rahmen der Versuche ergab sich, dass vorzugsweise die höher molekularen, hydrophoben NOM-Fraktionen mit der Eisenoberfläche reagieren. Zur Simulation der Durchbruchskurven unter verschiedenen Randbedingungen wurden Modell-rechnungen mit einem Poren-Diffusionsmodell durchgeführt. Dabei konnten die experimentell ermittelten Durchbruchskurven durch geeignete Wahl der Modellparameter hinreichend abgebildet werden. Im Falle erhöhter NOM-Gehalte im Oberflächenabfluss war zur Modellierung der Durchbruchskurven allerdings eine weitere Anpassung der Modellparameter erforderlich. Mit dem Ziel der Verbesserung der Ausfällung und der Metalladsorption an der Eisenoxidoberfläche wurden Untersuchungen mit karbonatischen Materialien (Calcit, Dolomit, Magnesit) durchgeführt. Die Versuche haben gezeigt, dass bei mittleren Verweilzeiten von 1 bzw. 5 Minuten ca. 30 bis 80 % bzw. ca. 60 bis 100 % der Metallkonzentrationen entfernt werden können. Mit einer Erhöhung der Verweilzeit kann dabei ein verbesserter Rückhalt erzielt werden. Das zur on-site Behandlung von schwermetallhaltigen Oberflächenabflüssen empfohlene Reinigungssystem besteht aus einer mit spiralförmigen Eisenspänen gefüllten Säule gefolgt von einer Belüftungseinheit und einer nachgeschalteten Filtereinheit aus Bimsstein / Dolomitstein. Für die praktische Anwendung ist zu beachten, dass die karbonatischen Materialien durch Ausbildung von Biofilmen und Deckschichten passiviert werden. Zum Erhalt der hydraulischen Leitfähigkeit sowie zur Reaktivierung der Oberflächen ist deshalb eine gelegentliche Rückspülung des Systems erforderlich. Die Kostenanalyse ergab, dass Fe0 ein geeignetes Medium für Aufbereitung von schwermetallbelasteten Oberflächenabflüssen ist.This study investigates the novel treatment method for heavy metals from contaminated runoff by employing Fe0. Batch kinetic, equilibrium and flow-through configurations were thoroughly studied. Based on the investigation, it was found that Fe0 achieves a comparable capacity to a commercial adsorbent like granular ferric hydroxide (GFH). The removal of Cu2+ and Zn2+ by Fe0 takes place through an array of rate-limiting steps including iron oxidation, iron (oxy)hydroxide precipitation and metal adsorption/co-precipitation. Cu2+ is directly or indirectly reduced by Fe0 and/or dissolved, structured Fe2+, and forms Cu0 and Cu2O as reduction products. The removal of Zn2+ is mainly due to the adsorption and co-precipitation processes. Results of batch kinetic tests using showed that when the solution is low in DO, T, pH, IS or reactions take place under high metal and DOC concentrations, the removal rate of Zn2+ dramatically decreases. The breakthrough column tests showed that the exhaustion of zinc occurred more rapidly than copper; yielding a metal loading capacity of an average 76 mg g-1 Fe0 for copper (with min: 55 and max: 96 mg g-1) and 55 mg g-1 Fe0 for zinc (min: 22, max: 69 mg g-1). Increased pH and temperature generally favor faster retention rates of copper and zinc, whereas increases in DO and conductivity of the solution hinder the removal of copper in the column system. Among parameters studied, NOM shows to be the most influent compound that results in a dramatically decreased metal uptake rate. Inhibition of NOM on the removal of metals by Fe0 was due to competitive adsorption, metal-ligand complexes and the inhibition that was caused by surface coverage of iron corrosion products. The NOM fraction that mainly interacts with metals is a larger size hydrophobic fraction with high aromaticity. With aims to upscale the treatment process and to be able to simulate the breakthrough curves at various scenarios, a pore-surface diffusion model (PSDM) was attempted. Generally, the PSDM can adequately capture most of the determined curves but at increased NOM concentration, an over prediction of the curve was observed. Following the test and modeling at various scenarios, optimization of the processes was carried out by incorporating Fe0 with calcite, dolomite and magnesite media. The recommended system for on-site treatment of metal-contaminated runoffs consisted of columns filled with spiral shaped irons followed by an aeration unit and post filtration of pumice/dolomite. According to the test, about 60-100 and 30-80 % of metal concentrations could be removed at an EBCT of 5 and 1 min EBCT, respectively. A longer EBCT will yield a better performance. For practical operations, carbonate materials tend to be passivated by various minerals and biofilms. An occasional backwash in order to reactivate the surface of materials inside and to maintain the hydraulic conductivity of the system is required. Finally, cost analysis showed that Fe0 is a suitable medium for stormwater runoff treatmen

Removal of dissolved metals by zero-valent iron (ZVI): Kinetics, equilibria, processes and implications for stormwater runoff treatment. Water Res. 39 4153-4163. Available on website http://www.wrc.org.za ISSN 0378-4738 (Print

Abstract Infiltration of stormwater runoff contaminated with metals is often questionable in several cases due to its long-term potential to cause deterioration of groundwater quality. To ensure the quality of filtrate, a pre-treatment of contaminated runoff is required. This study investigates the processes of copper and zinc ion removal from stormwater runoff using zero-valent iron (ZVI, Fe 0 ). Kinetic and equilibrium tests were performed with laboratory-prepared and in situ stormwater runoff samples collected from roof, street and highway catchments. Based on the results, a substantial portion of Cu 2+ is reduced and transformed to insoluble forms of Cu 0 and Cu 2 O. Unlike copper, the adsorption and co-precipitation associated with freshly precipitated iron oxides play important roles for the removal of Zn 2+ . Investigations under various water quality conditions demonstrated a relatively minor impact on Cu 2+ uptake rates. However, the different conditions apparently altered the removal stoichiometry and phases of the copper deposits. The removal rates of Zn 2+ increase with higher dissolved oxygen (DO), ionic strength (IS), temperature (T) and pH. Dissolved organic carbon (DOC) in runoff samples forms complexes with metals and Fe 2+ , thereby kinetically decreasing the metal uptake rates. Furthermore, depending on its composition, a larger molecular weight organic fraction was found to preferentially compete for the adsorption sites. The study demonstrates that ZVI is a promising medium for achieving comparable capacity to a commercial adsorbent like granular ferric hydroxide (GFH). Longterm performance of ZVI, however, may be limited and governed by the formation of non-conductive layers of iron and cuprous oxides.