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«In situ transformations of mineral particles in soils Andreas Birkefeld Zurich 2005 Doctoral Thesis ETH No. 16036 In situ transformations of mineral ...»

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Doctoral Thesis ETH No. 16036

In situ transformations

of mineral particles in soils

Andreas Birkefeld

Zurich 2005

Doctoral Thesis ETH No. 16036

In situ transformations of mineral particles in soils

A dissertation submitted to the

SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH

for the degree of

DOCTOR OF NATURAL SCIENCES

presented by

ANDREAS BIRKEFELD

Dipl. Geol., University of Goettingen born 3 November 1967 citizen of Germany accepted on recommendation of Prof. Dr. Rainer Schulin, examiner PD Dr. Bernd Nowack, co-examiner Prof. Dr. Ruben Kretzschmar, co-examiner Table of contents Summary VII Zusammenfassung IX 1 Introduction 1

1.1. Objectives of this study 3 2 In situ methods – Introduction, benefits and general use 9

2.1 What are in situ methods 9

2.2 Experimental in-situ methods 11 2.2.1 Polymer bags 11 2.2.2 Microcosms 11 2.2.3 Mineral into soil mixing 12 2.2.5 Diffusive gradients in thin films (DGT) 12 2.2.6 “Gellyfish” 13 2.2.7 Resin Bags 13 2.2.8 Lysimeters 13 2.2.9 Micro Suction Cups 14

2.3. Analytical in-situ methods 14 2.3.1 Field Based 14 2.3.1.1 Submersible electrochemically micro probe 14 2.3.1.3 Laser atmospheric analysis 15 I 2.3.2 Laboratory Based 15 2.3.2.1 X-ray absorption spectroscopy (XAS) 15 2.3.2.2 Scanning probe microscopy (SPM) 16 2.3.2.3 Fourier transform infrared micro spectrometry (micro-FTIR) 16 2.3.2.4 Raman micro spectrometry 17 2.3.2.5 Environmental scanning electron microscopy (ESEM) 18 2.3.2.6 Desorption Electrospray Ionization (DESI) 19 3 A new in situ method to analyze mineral particle reactions

–  –  –

Transformations of particulate mineral phases are important natural, geological and pedological processes in rock weathering and soil formation. They can also be rate-limiting in the release of toxic metals from anthropogenic particles emissions distributed into the environment. The release of metal contaminants into soil solution caused by weathering of the emitted contaminant particles can seriously damage soil fertility, adversely affect the quality of surface and ground waters and create health risks for the consumers of crops produced on such soils. Several investigations were carried out using different in situ methods to study mineral behavior in the field. The in situ methods applied different technical approaches to study mineral reactions but they all had some drawbacks in common. First of all they disturb the soil matrix in a massive way during incubation and second the test minerals are surrounded by bags or bottles preventing direct particle-soil contact.

The goal of this dissertation project was to develop, validate and apply a new in situ method to analyze mineral particle reactions under field conditions. In a first step a simple in situ method for studying (mineral) particle reactions under field conditions was developed. Fine mineral particles (20 µm – 200 µm Ø) were glued with a thin layer of epoxy resin onto small Plexiglas® plates (2 cm × 2 cm). The technique leaves the majority of the particle surface uncovered and thus provides a reactive surface to the soil system. The coated polymer supports were placed in soils and recorded after different times. After recovery the minerals can be analyzed for phase transformation reactions by non-destructive analysis methods e.g. scanning electron microscopy, Raman spectroscopy, x-ray fluorescence spectroscopy and x-ray diffraction.

In a second step the newly developed technique was applied to investigate the dissolution behavior of selected mineral particles in an acidic forest soil. Lead oxide, copper concentrate and copper smelting slag were used as test particles.

During the incubation time of up to 18 months, the lead oxide particles showed noticeable dissolution whereas the copper concentrate and slag particles did not show any significant dissolution signs. Comparing the field data with simultaneously carried out laboratory experiments showed a faster dissolution rate VII in the field than in the laboratory probably by the high biological activity in the field compared to the pots in the lab.

In a third step the method was used to investigate the phase transformations of lead oxide particles in three different soils. In calcareous soils the lead oxide particles showed significant formation of secondary mineral precipitates. During the complete incubation of 18 months no significant increase of mineral precipitates between the second and the eighteenth months of incubation could be recognized.

Lead oxide particles incubated in the non-calcareous soil did not show significant formation of secondary precipitates. Using electron microscopy, x-ray probe and micro-Raman spectroscopy the newly formed mineral precipitates could be identified as predominately lead-hydroxy-carbonates (hydroxycerussite). Traces of lead phosphates could be identified on the particles buried in non-calcareous soil.

The new in situ method has the potential to be used in other systems e.g. aquatic environments or sediments. The new method was able to provide comprehensive new data concerning the dissolution behavior of fine particles in field and laboratory experiments showing that field dissolution rates can be faster than laboratory dissolution rates.





VIII Zusammenfassung

Die Umwandlung von Mineralphasen ist ein wichtiger natürlicher, geologischer und pedologischer Prozess in der Gesteinsverwitterung und bei der Bodenbildung.

Sie kann ebenfalls die Freisetzungsrate von toxischen Metallen aus anthropogen freigesetzten Partikelemissionen bestimmen. Die verwitterungsbedingte Freisetzung von gefährlichen Spurenmetallen in die Bodenlösung kann ernsthaft die Bodenfruchtbarkeit beeinträchtigen und Oberflächen- und Grundwässer verunreinigen. Eine gesundheitliche Gefahr für Konsumenten von landwirtschaftlichen Produkten die auf solchen belasteten Flächen angebaut wurden, kann nicht ausgeschlossen werden.

Zahlreiche Untersuchungen zur Bestimmung des Verhaltens von Mineralen in Böden wurden mittels in situ Methoden ausgeführt. Diese Methoden haben verschiedene methodische Ansätze verfolgt um Mineralreaktionen in Böden zu untersuchen. Alle verwendeten Methoden hatten substantielle Schwachstellen aufzuweisen. Zum einen wurde die Bodenmatrix während des Probeneinbaus merklich gestört und zum anderen sind die zu untersuchenden Minerale durch kleine Gefässe oder Beutel von einem direkten Bodenkontakt ausgeschlossen.

Das Ziel der vorliegenden Arbeit war es, eine neue in situ Methode zur Analyse von Mineralreaktionen unter Feldbedingungen zu entwickeln, auszutesten und anzuwenden. In einem ersten Schritt wurde eine einfach anzuwendende in situ Methode zur Untersuchung der Reaktionen von Mineralpartikeln unter natürlichen Bedingungen entwickelt. Mit Hilfe eines Epoxydharzfilmes wurden kleine Mineralpartikel (20 µm – 200 µm Ø) auf einer kleinen Plexiglasplatte (2 cm × 2 cm) fixiert. Diese Technik lässt den grössten Teil der Mineralpartikel unberührt von dem Epoxydharz und stellt damit eine relativ grosse reaktive Fläche zur Verfügung um mit dem Bodensystem zu reagieren. Diese beschichteten Plättchen werden dann in Böden eingebracht Nach der Reaktionszeit können die Proben einfach aus dem Boden entfernt werden und mit zerstörungsfreier Analytik, z.B. Elektronenmikroskopie, Mikroramanspektroskopie, RöntgenfluoresenzspekIX troskopie, Röntgendiffraktion auf Umwandlungsreaktionen untersucht werden.

In einem zweiten Schritt wurde die neu entwickelte Methode angewandt um das Lösungsverhalten von ausgesuchten Mineralpartikeln in einem sauren Waldboden zu untersuchen. Bleioxid, Kupferkonzentrat und Kupferschlacke wurden als Testpartikel verwendet. Während der 18 monatigen Versuchszeit zeigten die Bleioxidpartikel merkliche Lösungserscheinungen wohingegen die Kupferkonzentrat- und Kuperschlackepartikel keine wahrnehmbaren Lösungserscheinungen aufwiesen. Ein Vergleich der Feldversuchsdaten mit Daten eines parallel durchgeführten Laborversuchs zeigten eine erhöhte Auflösungsges chwindigkeit der Bleioxidpartikel im Feld. Dies wurde wahrscheinlich durch die stärkere biologische Aktivität im Feld verursacht, welche im Laborversuch nicht aufzeigbar war.

In einem dritten Schritt wurde die Methode zur Untersuchung von Phasenumwandlungen von Bleioxidpartikeln in drei verschiedenen Böden angewandt. In einem Kalksand zeigten die Bleioxidpartikel deutliche Neubildungen von sekundären Mineralausfällungen bereits nach einer zweimonatigen Reaktionszeit. Während der 18 monatigen, gesamten Versuchszeit konnte keine weiter Zunahme der Ausfällungen beobachtet werden. Bleioxidpartikel die in einem kalkfreien Boden eingebracht wurden zeigten keine visuellen Spuren von Sekundärausfällungen. Durch den Einsatz von Elektronenmikroskopie, Röntgenmikrosonde und Ramanmikrospektroskopie konnten die neu gebildeten Sekundärmineralausfällungen als vorwiegend Bleihydroxycarbonate (Hydroxycerusit) identifiziert werden. Spuren von Bleiphosphaten (Pyromorphit) konnten an den Bleioxidproben aus dem kalkfreien Boden festgestellt werden.

Die von uns neu entwickelte in situ Methode hat die Möglichkeit ihr Anwendungsgebiet von Böden auf Sedimente oder sogar aquatische Systeme auszuweiten. Die neue Methode konnte umfangreiche neue Daten bezüglich des Auflösungsverhaltens von feinen mineralischen Partikeln in Feld- und Laborversuchen liefern und dabei zeigen, dass Auflösungsraten im Feld schneller sein können als im Labor.

X 1 Introduction

“Human health and environmental quality are undergoing continuous degradation by the increasing amount of hazardous wastes being produced” (United Nations, 1992). This statement from the Earth Summit held 1992 in Rio de Janeiro shows the concern of society about environmental pollution as a major threat to ecosystems and global population. Worldwide economic growth and increasing global population are key factors for the environmental damage (Nriagu, 1990).

Metal pollution of water, air and soils threatens human, animal and plant health.

Already thirty years ago contamination was perceived as a predominant problem (Alloway and Ayres, 1997). This awareness led to environmental and pollution control regulations in industrial countries and recently also started to raise concern in Third World countries (United Nations, 1992). Regulations created an economic pressure on the industry and resulted in the development of efficient pollution control techniques (Sparks, 2003). They also spawned intensive environmental research and risk assessment activities (Pierzynski et al., 2000a). One area of particular concern is the increasing contamination of soils and sediments by heavy metals (Adriano, 2001). Although some metals are essential micronutrients for organisms in trace concentrations (Marschner, 1995), all metals become toxic at high concentrations (Alloway, 1995). The critical sources of soil-polluting heavy

metals are (Alloway, 1995; Wild, 1993):

• Metalliferous mining and smelting

• Agricultural and horticultural materials

• Fossil fuel combustion

• Metallurgical industries

• Electronics

• Chemical and other manufacturing industries

• Waste disposal

• Sports shooting and fishing

• Military operations and training

• Sewage sludge applications

Chapter 1

While soils often have a high capacity to bind and inactivate toxic metals, unfavorable conditions, e.g. with respect to pH, Corg, Eh, clay content, Fe oxides, colloids (Alloway and Ayres, 1997) result in high solubility, mobility and bioavailability. Moreover, if such soils are used for agriculture, metals may enter the food chain and pose a threat for human nutrition (McBride, 1994; Rieuwerts et al., 1998).

The mobility and bioavailability of metals does not just depend on their total concentration but on their chemical speciation (Ure and Davidson, 1995). It is then essential to know in which form metals are present in soil. The uptake of metals by plants for example primarly depends on the free ion concentration in soil solution and how this pool is replenished from the solid phase (Wild, 1993).

Figure 2.1 visualizes input, transformation and output paths of metals in soils.

Figure 2.1 Input and output paths of minerals and their behavior in soils.

(Figure adopted from Pierzynski et al., 2000) The composition of the soil solution depends on exchange reactions with adjacent mineral and organic phases and organisms, as well as on inputs and outputs through transport processes such as the migration of soluble species into the ground water.

Primary minerals are dissolved in the course of in soil-forming processes. They can

Introduction

form secondary minerals which again can undergo dissolution and precipitation reactions. Mineral particles entering the soil through anthropogenic processes are transformed in similar ways. If the weathering of such particles leads to the release of toxic metals, this can play an important role for soil fertility and crop quality.

The determination of the metal species is an important task in environmental analysis. An important factor for the concentration of available metals is the potential of the soil to maintain their actual concentration. This depends on the phase transformation potential (dissolution) of minerals in the soil matrix (Zhang et al., 1998). To get more insight in the behavior of heavy metal contaminated soils and sediments, methods are available or under development, which have the ability to analyze mineral-soil interactions in situ in the laboratory (Chapter 2 will introduce some of them).

Table 2.1 gives a brief overview of modern molecular techniques applied in the environmental sciences.

The synchrotron based techniques are limited to special facilities, whereas the other techniques can be seen as “standard” equipment in earth and environmental laboratories.

Table 2.1 Molecular techniques applied in environmental sciences [Source adapted from Sparks, 2003].

–  –  –



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