Mining and mineral processing generate a wide range of As-rich minerals, including scorodite (FeAsO4•2H2O), and arsenical ferrihydrite, which are common secondary minerals found in mine tailings. Scorodite and arsenical ferrihydrite are relatively stable under a wide range of physico-chemical conditions which makes them suitable arsenic sinks in mining environments. However, bacteria can reduce these minerals and release arsenic into the aqueous environment. Two dissimilatory iron and arsenic reducing bacteria, Shewanella sp. ANA-3 and Shewanella putrefaciens CN32, were used to investigate their effects on the reductive dissolution of scorodite and arsenical 6-line ferrihydrite in a chemically defined medium containing low phosphate concentrations representative of the natural environment. Analysis of the aqueous phase of all biotic reduced samples found mainly As(III), the more toxic form of As, while very little As(V) was reduced in the abiotic samples. Solid state analysis of the scorodite biotic post-reduction minerals identified scorodite, biogenic Fe(II)-As(III) compounds, parasymplesite and tooeleite, while in the biotic reduced arsenical six-line ferrihydrite, biogenic Fe(II)-As(III) compounds, hematite, akaganeite and unconfirmed magnetite were identified as secondary reduction products. Results from this research add to the body of literature on As and Fe biogeochemistry and provide very useful information for future assessments of the long term stability of As-rich minerals. L’activité minière et la transformation du minerai génèrent divers minéraux riches en arsenic, tels la scorodite (FeAsO4•2H2O) et la ferrihydrite riche en arsenic, lesquels sont des minéraux secondaires communs des résidus miniers. Comme la scorodite et la ferrihydrite riche en arsenic sont relativement stables sous une grande gamme de conditions physico-chimiques, ces minéraux peuvent potentiellement être utilisés pour stocker de façon permanente l’arsenic dans les environnements miniers. Cependant, certaines bactéries peuvent réduire ces minéraux, ce qui entraine la solubilisation de l’arsenic. Deux bactéries capables de réduire l’arsenic et le fer, soit Shewanella sp. ANA-3 et Shewanella putrefaciens CN32, ont été utilisées afin de déterminer leurs effets sur la réduction microbienne de la scorodite et de la ferrihydrite riche en As dans un milieu de culture contenant de faibles concentrations de phosphate. Les analyses de la phase aqueuse ont démontré que dans tous les systèmes biotiques, As(V) a été réduit en As(III), alors que dans les systèmes contrôles abiotiques, peu de As(V) a été réduit. L’analyse des minéraux secondaires présents à la fin réduction dans les systèmes biotiques contenant de la scorodite indique que la scorodite est encore présente, ainsi que des composés organiques riches en Fe(II) et As(III), de la parasymplésite et de la tooéleite, alors que dans les systèmes biotiques contenant de la ferrihydrite riche en As, des composés riches en Fe(II) et en As(III), de l’hématite, de l’akaganéite et de la magnétique ont été identifiés comme minéraux secondaires. Les résultats de cette étude enrichissent la littérature sur le cycle biogéochimique du Fe et de As et fournissent de l’information importante pour l’évaluation de la stabilité à long terme de minéraux riches en As.

Scaling in green liquor handling systems is a persistent problem in many kraft mills. Scaling is commonly believed to be the result of pirssonite (Na2Ca(CO3)2∙2H2O) deposition. In this work, scale characterization was performed by analyzing 12 scale samples obtained from 10 kraft mills. Only 4 samples were identified as pirssonite while the remaining consisted of CaCO3. The predominant presence of CaCO3 in the scale samples was found to be the result of selective dissolution of Na2CO3 from pirssonite scale, leaving CaCO3 behind. Experimental studies were also conducted to study pirssonite solubility under green liquor conditions. Results obtained from these studies were used to create and validate a database for pirssonite in the OLI Systems® software to predict its formation. This database was used to generate a family of pirssonite solubility curves that can be used by the kraft mills as operational guidelines to prevent pirssonite precipitation.

Scaling in green liquor handling systems is a persistent problem in many kraft mills. Scaling is commonly believed to be the result of pirssonite (Na2Ca(CO3)2∙2H2O) deposition. In this work, scale characterization was performed by analyzing 12 scale samples obtained from 10 kraft mills. Only 4 samples were identified as pirssonite while the remaining consisted of CaCO3. The predominant presence of CaCO3 in the scale samples was found to be the result of selective dissolution of Na2CO3 from pirssonite scale, leaving CaCO3 behind. Experimental studies were also conducted to study pirssonite solubility under green liquor conditions. Results obtained from these studies were used to create and validate a database for pirssonite in the OLI Systems® software to predict its formation. This database was used to generate a family of pirssonite solubility curves that can be used by the kraft mills as operational guidelines to prevent pirssonite precipitation.

Nonlinear optics and ferroelectrics have been recognized for several decades as promising fields with important applications in the area of opto-electronics, photonics, memory devices, etc. High performance electro-optical switching elements for telecommunications and optical information processing are based on the material properties. Hence, there is always a continuous search for new and better materials. In this thesis we have investigated the growth and physical properties of four crystals viz. two NLO and two ferroelectric crystals. This thesis consists of eight chapters. The first chapter gives an overview of historical perspectives of nonlinear optical phenomenon, ferroelectricity and materials developed therein. The second chapter gives a brief description of the underlying theories of crystal growth, nonlinear optics and ferroelectricity. A major portion of this chapter consists of gist of the earlier work carried out on compounds of our interest viz. urea L-malic acid, sodium p-nitrophenolate dihydrate, glycine phosphite and lithium niobate. Synthesis, growth, crystal structure details and some physical properties of these materials are briefed. The third chapter describes the experimental techniques needed to grow as well as characterize these crystals. The experiments are performed on single crystals grown in the laboratory using the solution growth setup and Czochralski crystal puller. These growth units are described in detail. Preliminary characterization techniques like powder Xray diffraction, optical transmission, scanning electron microscopy, Vickers and Knoop hardness are described briefly. Various experimental methods viz. dielectric, polarization reversal, photoacoustic spectroscopy and laser induced damage for characterizing the grown crystals are explained. Urea L-malic acid (ULMA) is a new NLO organic material which is reported to exhibit second harmonic efficiency three times that of the widely used inorganic crystal, KDP. Hence, this material is selected for detailed investigation and the results obtained are discussed in chapter 4. This chapter contains details of single crystal growth and characterization of ULMA. The crystals are grown by slow cooling technique. The complete morphology of the crystal is evaluated using optical goniometry. The grown crystals are characterized for their optical and thermal properties. The defect content in the grown crystal is evaluated by chemical etching. As the surface damage of the crystal by high power lasers limits its performance in NLO applications, a detailed laser induced damage studies are performed on ULMA. Both single shot and multiple shot damage threshold values for 1064 nm and 532 nm laser radiation are determined and correlated with the mechanical hardness. In addition, the thermal diffusivity and thermal conductivity of ULMA along various crystallographic orientations are evaluated using laser induced photoacoustic spectroscopy and the results are interpreted in terms of crystal bonding environment. Another NLO crystal taken up for study is sodium p-nitrophenolate dihydrate (NPNa 2H2O), a semiorganic material. This crystal is a very efficient NLO material and has the advantages of both organics and inorganics. Earlier investigations on growth of NPNa.2H2O in various solvents have shown methanol as the most suitable solvent for growth. Growth from aqueous solution was discarded as it did not yield crystals which are stable. In the present investigation, stable, NLO active NPNa.2H2O crystals are obtained using aqueous solution itself by varying the crystallization conditions and exploring the suitable temperature range. The details of growth and characterization form the subject of fifth chapter. The grown crystals are characterized using optical transmission, XRD and thermo gravimetric analysis. Later, laser induced damage threshold is evaluated for both 1064 nm and 532 nm laser radiation and compared wit the methanol grown ones. A possible mechanism of damage is given. The sixth and seventh chapters deal with growth and characterization of ferroelectric materials namely glycine phosphite and lithium niobate respectively. Glycine phosphite is a low temperature ferroelectric crystal which is well studied in terms of its dielectric and ferroelectric properties. But very few radiation damage studies are reported. The effect of ionizing radiation on ferroelectrics is of considerable interest as it significantly modifies the physical properties of these materials. In the present investigation, effects of X-ray irradiation (_ = 1.5418 °A) on the lattice parameters, dielectric constant, loss tangent, polarization switching characteristics and domain dynamics of glycine phosphite are investigated. X-ray irradiation is performed in the non-polar phase of the sample. The effect as a function of duration of exposure is studied. X-ray irradiation in GPI has resulted in drastic reduction in _ values and shift in transition temperature towards lower temperatures. X-ray irradiation on polarization switching properties of the crystal are also investigated. The activation energy and threshold field of switching increase with the irradiation time. The behaviour of domain wall mobility is quite different from that exhibited by other well known ferroelectrics. These results are discussed in chapter 6 and a possible explanation for the unusual behaviour of domain wall mobility is given. The defect generated is identified as PO32− radical by electron paramagnetic measurement. Lithium niobate (LiNbO3) is an extensively studied material in terms of its NLO and ferroelectric properties. This material has high piezoelectric coupling coefficients along certain directions which makes it suitable for wide band surface acoustic wave applications. Hence there is a demand for good quality, single domain YZ-LiNbO3 substrates. Chapter 7 describes the growth of Z-pulled congruent LiNbO3 using Czochralski technique. Large single crystals of diameter 30 mm and length 80 mm are grown from congruent composition employing Czochralski technique. The grown crystals are multidomain and hence electric field poling is performed to get single domain crystals. Their subsequent characterization for SAW devices upto 200 MHz was performed and compared with the imported substrate. The general conclusions are given in chapter 8 along with possible future work that could be performed on these crystals.