Scale formation is one of the persistent problems in mineral processing and related industries. One of the main components of the scale is frequently gypsum or calcium sulphate dihydrate (= CaS04.2H20). Gypsum is formed through the process of crystallisation, and it is well known that crystallisation process is significantly affected by the presence of admixtures. Industrially, scale formation occurs in an environment which is very rarely free from the presence of admixtures. In a typical mineral processing industry, certain types of admixtures are present, which may include metallic ions (e.g. originated from corrosion products) and certain types of the flotation agents used. The effect of admixtures on crystallisation kinetics and cyclical morphology can be very significant, even if they are present in trace amounts. It is important to emphasise that the effects are generally specific, that there is no unified theory that applies to all and every situation. The present study has investigated the effect of certain admixtures on gypsum crystallisation, and was accomplished in three phases of experiments: (1) seeded batch crystallisation; (2) seeded continuous crystallisation, and (3) once through flow system under isothermal condition. The three phases of the work used equimolar solutions of CaC12 and Na2SO4 to produce CaS04 which is the precipitating species. The seeded batch crystallisation experiment explored the effect of two flotation agents commonly used in mineral processing plants: (1) sodium isopropyl xanthate (= SIPX) and, (2) isopropyl thionocarbamate. The experiments were performed at 25, 35, and 45°C, respectively. The initial concentration of the crystallising solution was 2,000 ppm of Ca 21 and it reached the equilibrium concentration values of between 1,000 and 8,00 ppm of Ca 2+ in 90 minutes. / The effect of the two selected admixtures on crystallisation was measured by continuous monitoring of the desupersaturation of the crystallising solution with time, which subsequently resulted in the determination of the crystallisation rate constant. The results arc as follows. Firstly, the admixtures selected (either individually or in combination) were able to retard the growth rate of gypsum. In the absence of any admixture, the second order rate constant was between 1,405 x 10-6 and 1,561 x 10-6 ppm-1 min-1. Addition of SIPX at a typical plant dosing level 0.200 g/L) reduced the rate constant to 475 x 10-6 PPM-1 min', while isopropyl thionocarbamate at a typical plant dosing level (= 0.070 g/L) decreased the rate constant to 254 x 10-6 ppm-1 min-'. However, addition of a combination of the two admixtures, each at a typical plant concentration level, reduced the rate constant to 244 x 10-6 ppm-1 min-1, which was only slightly below that in the presence of isopropyl thionocarbamate. Thus, in these batch crystallisation studies, isopropyl thionocarbamate seemed to be dominant over SIPX. Secondly, the batch crystallisation system in the current work did not show any induction time. It was concluded that the seeds added into the batch system could be capable of eliminating the induction time. Thirdly, the reduced growth rate of the gypsum crystals as affected by the admixtures was probably caused by the adsorption of admixtures onto the crystal surface. The second phase of the project involved a seeded continuous (MSMPR) crystalliser. Some parameters used in this experiment (mean residence time, agitation speed and type of one admixture) were taken from the batch experiment carried out in the first phase of the project. / Three admixtures were chosen for the seeded continuous crystallisation: (1) SIPX, (2) Fe3+, (3) Zn2-, and they were used either individually on in combination with each other. SIPX was chosen as it is one of the most common flotation agents used in mineral processing. Metallic ions: Fe3+ and Zn2+ were selected, since they were found in substantial amounts in both scale samples and process water in certain minerals processing industries. In general, the admixtures tested were found to be able to inhibit the crystal growth rates, but to enhance the nucleation rates. In addition, the growth rate was found to be dependent on crystal size, and hence, a correlation between these two parameters and the admixture concentration was formulated. For a fixed level of concentration (f 700 ppm of Ca z+ at steady state) and crystal surface area, it was proved that for each crystallisation temperature: 25 and 40°C, the correlation function can be represented as G = k Lα (1 +C)β where: G = linear growth rate, micron/hour; k, α, and β = dimensionless constants; L = (sphere equivalent) crystal size, micron; C = concentration of the admixtures used, ppm. For both the crystallisation temperatures used, the correlation function shows that the growth rate is significantly dependent on crystal size, but a weak function of admixture concentrations. The mechanism of crystal growth inhibition was assumed to be that of adsorption of admixtures onto the active growth sites, thereby decreasing or stopping the growth. Similar to the first phase of the present study, this seeded continuous crystallisation also showed no induction time. The third phase of the project investigated the gypsum scale formation in a oncethrough pipe flow system under isothermal condition and in the presence of admixtures. / Four types of pipe materials were tested: PVC, brass, copper and stainless steel. Two admixtures were selected: SIPX and Fe3+. The behaviour of the gypsum scale formation was measured as the mass of the gypsum scale deposited on the substrate per unit area of the pipe surface. Within the range of the experimental conditions applied in this scale formation study, the following results were obtained. Firstly, the mass of the gypsum scale increased with concentration (in the range: 2,000 to 6,000 ppm of Ca t+) and that the correlation between the mass and the concentration can be represented by quadratic functions. Secondly, the mass of the gypsum scale decreased with increasing concentration of the admixtures used. Thirdly, the flow rate of the scaling solutions (in the range: 0.4 to 1.3 cm/sec) did not significantly affect the mass of the gypsum scale. PVC produced the highest mass of gypsum scale, followed by brass, copper, and stainless steel, respectively. Fourthly, the presence of admixtures caused the surface of the scale deposit to become rougher than was the case in a pure system, and longer scaling experimental times resulted in denser scale deposits. In this scale formation project, the induction time was investigated. In contrast with the first and the second phase of the projects, the induction time in the scale gypsum formation experiment was significant. At a concentration of 2,000 ppm of Ca 2+' pure gypsum solutions had induction times of about 105 minutes at 18.3°C and 97 minutes at 20.3°C. In the presence of 10 ppm of SIPX, the scaling solution at 2,000 ppm of Ca2+ and 19.2°C had an induction time of 1,400 minutes. The present study produced three important findings. / Firstly, the presence of Fe 3+ or sodium isopropyl xanthate (SIPX) reduced the growth rate of gypsum crystallised either in a vessel (= a continuous crystalliser) or in a pipe flow system. Secondly, the rate of growth of gypsum crystals was found to be consistently higher in the vessel than in the pipe flow system. The rate of growth of the pure gypsum in the crystalliser at 25°C was 0.0389 kg/ m2 hour while those in the pipe flow system were between 0.0289 and 0.0202 kg/m2 hour, depending on the pipe material and the scaling solution flow rate. Thirdly, with respect to gypsum scaling, PVC was the least favourable material, followed by brass and copper, while the most favourable was stainless steel. It is believed that the present study has significantly contributed to the understanding of the effect of admixtures on crystallisation of gypsum, especially in relation to the scale formation.

Several recent projects in building science have examined the hygric performance of building materials. Most building materials adsorb from and desorb water vapour to their environments. This phenomenon could be used to help control relative humidity fluctuations in buildings, experienced during periods of moisture production such as cooking, washing or bathing. They could also be used to reduce the need for mechanical ventilation and air conditioning to remove excess moisture. To understand how a building material responds to transient changes in relative humidity, testing is required.<p> This thesis outlines the testing performed on gypsum board, a common wall and ceiling finishing material used inside buildings. The effect of paint coatings on the gypsum boards and heat and mass transfer coefficients of the air passing over the gypsum bed was tested. The data produced from these experiments was used to validate several numerical models through an International Energy Agency/Energy Conservation in Buildings and Community Systems (IEA/ECBCS), Annex 41: Whole Building Heat, Air and Moisture Response. The validated models are important for simulating the process of adsorption and desorption in building materials to predict failure in the building envelope and expected indoor air conditions.<p> A sensitivity analysis is also presented which examines the effects of the sorption isotherm and vapour permeability of the gypsum and paints as well as the heat and mass transfer coefficients the boards are exposed to. The sensitivity range used was determined from the tests performed on the gypsum boards and paints which were also performed during the work of Annex 41.<p> The results of this thesis produced a high quality data which can also be used to validate future numerical models. All information required for validation of future models is available such as dimensions of test section, test conditions, material properties and the experimental data.<p> The results show that when designing for passive humidity control in buildings using gypsum boards, the most influential factor is the type of coating or paint applied to the surface. The sensitivity analysis showed that material properties such as vapour permeability and the sorption isotherms, for the expected temperature range, should be well known for increased accuracy of the simulation. The material properties were determined from inter-laboratory testing at 14 different institutions to achieve confident values.<p> The effect of increasing the heat and mass transfer coefficients, over the range of coefficients studied in this thesis, showed negligible differences in the results. The simulated results had very good agreement between the models and were mostly within experimental uncertainty of the measurements.

This work investigates mercury flux in soil amended by gypsum from flue gas desulphurization (FGD) units of coal-fired power plants. There are two phases of this research, including field and greenhouse studies. Previous studies indicate that FGD gypsum could increase corn yield, but may lead to more mercury uptake by corn. Recent studies have been carried out in greenhouses to investigate mercury transport in FGD gypsum treated soil. Major aspects include uptake of mercury by plants and emission of mercury into the atmosphere based on application rates of FGD gypsum. Additional aspects include rainfall, temperature, soil, and plants types. Higher FGD gypsum application rates generally led to higher mercury concentration in the soil, as well as, increased mercury emission into the atmosphere, and increased mercury levels in plants, especially roots and leaves. Soil properties and plant species also played important roles in mercury transport. In addition, it was also found that increased water and higher temperatures may contribute to mercury emission in the atmosphere. Some plants, such as tall fescue, were able to prevent mercury from atmospheric emission and infiltration within the soil. Mercury concentration in the stem of plants was found to be increased and then plateaued upon increasing FGD gypsum application. However, mercury in roots and leaves was generally increased upon increasing FGD gypsum application rates. Some mercury was likely absorbed by leaves of plants from mercury in the surrounding atmosphere.

Several recent projects in building science have examined the hygric performance of building materials. Most building materials adsorb from and desorb water vapour to their environments. This phenomenon could be used to help control relative humidity fluctuations in buildings, experienced during periods of moisture production such as cooking, washing or bathing. They could also be used to reduce the need for mechanical ventilation and air conditioning to remove excess moisture. To understand how a building material responds to transient changes in relative humidity, testing is required.<p> This thesis outlines the testing performed on gypsum board, a common wall and ceiling finishing material used inside buildings. The effect of paint coatings on the gypsum boards and heat and mass transfer coefficients of the air passing over the gypsum bed was tested. The data produced from these experiments was used to validate several numerical models through an International Energy Agency/Energy Conservation in Buildings and Community Systems (IEA/ECBCS), Annex 41: Whole Building Heat, Air and Moisture Response. The validated models are important for simulating the process of adsorption and desorption in building materials to predict failure in the building envelope and expected indoor air conditions.<p> A sensitivity analysis is also presented which examines the effects of the sorption isotherm and vapour permeability of the gypsum and paints as well as the heat and mass transfer coefficients the boards are exposed to. The sensitivity range used was determined from the tests performed on the gypsum boards and paints which were also performed during the work of Annex 41.<p> The results of this thesis produced a high quality data which can also be used to validate future numerical models. All information required for validation of future models is available such as dimensions of test section, test conditions, material properties and the experimental data.<p> The results show that when designing for passive humidity control in buildings using gypsum boards, the most influential factor is the type of coating or paint applied to the surface. The sensitivity analysis showed that material properties such as vapour permeability and the sorption isotherms, for the expected temperature range, should be well known for increased accuracy of the simulation. The material properties were determined from inter-laboratory testing at 14 different institutions to achieve confident values.<p> The effect of increasing the heat and mass transfer coefficients, over the range of coefficients studied in this thesis, showed negligible differences in the results. The simulated results had very good agreement between the models and were mostly within experimental uncertainty of the measurements.

This research studies 6 eclogites from Qinglongshan Donghai in the Sulu ultrahigh-pressure (UHP) province, eastern China. Petrographic microscope, Ramam spectrometer, scanning electron microscope (SEM) and transmission electron microscope (TEM) are utilized to identify mineral compositions, microstructures and mineral precipitates. Optical observations show the eclogites with the following mineral assemblage: garnet + omphacite + amphibole + epidote + rutile ¡Ó quartz ¡Ó phengite ¡Ó kyanite ¡Ó coesite pseudomorph ¡Ó apatite ¡Ó talc. Oriented mineral precipitates are found within omphacite and within apatites. The parallel precipitates in omphacite are quartz rods confirmed by electron probe microanalysis (EPMA) and TEM diffraction patterns. The direction of the long axes of the quartz rods seem to have relation with the cleavage and with the parting of omphacite. The direction of the long axis of quartz is not necessarily the c axis direction of quartz. Pargasite is intergrown with quartz and the amounts of both minerals seem to have a positive relation. Pargasite contain element K which is not found in omphacite and there is no obvious crystallographic relation between quartz, pargasite, and omphacite. There is amphibole exsolved from the omphacite and the crystallographic axes of tht exsolved amphibole parallel to those of omphacite. The a and c parameters for the two phases are equal while the b parameter of the amphibole is almost twice that of omphacite. A two-stage growth mechanism for quartz and amphibole intergrown within omphacite is proposed: (1) very fine quartz rods exsolved (or aided with infilling fluids) from a supersilicic clinopyroxene during decompression, creating grain boundaries between quartz rods and host, (2) growth of amphibole and quartz along the grain boundaries with fluid participation and an expense of omphacite during retrograde metamorphism. There are two different precipitates within apatites in different eclogites. One of the precipitates is calcium sulfate (anhydrite or gypsum) and the other is ferrous sulfide (pyrrhotite?). There was no report about calcium sulfate within apatite in UHP rocks before. The formation of sulfide (reduced) or sulfate (oxidized) is controlled by the fugacity of oxygen. According to the previous reports and the discoveries of this research, there are many different kinds of precipitates containing silicate incompatible elements in apatites. It can¡¦t be ruled out that the precipitates exsolved from apapites but apatites are more likely to act as sinks of silicate incompatible elements and different minerals precipitated within apatites under different redox conditions rather than exsolution processes.

Evaporate minerals were very important raw materials in very different and broad industries for years. Since gypsum became important raw material especially in construction industry as plaster, demand to these minerals rises each following year. The aim of this thesis is to map out these industrial raw materials by using remote sensing techniques. Ankara Bala region has very rich Gypsum sites and this region is showed as one of the best gypsum potential sites of Turkey according to the studies of MTA so that this area is selected for the usage of remotely sensed data. For the remote sensing analyses ASTER images which have high spatial and spectral resolution are used. The analyses are applied using PCI Geomatica software and ARCGIS software is used for mapping purposes. Band ratio, decorrelation stretch, principal component analysis and thermal indices are used in order to map gypsum minerals. For gypsum minerals previously known Crosta method is modified and by the selection of suitable bands and principle components, gypsum minerals are tried to map and it is seen that it has a high success. For TIR indices previously known Quartz index is modified as Sulfate index and used for gypsum mapping. For relative accuracy all the results are add, percentages of the results are estimated. According to results / 288 km2 area is mapped as gypsum with the total of four methods but it is seen that only 8 km2 is found by every methods. According to these percentages modified Crosta method and Sulfate Index methods are showed the highest success.

Thesis (Ph.D.(Chemistry))--University of Pretoria, 2004. / Summaries in English and Afrikaans. Includes bibliographical references (leaves 229-238). Also available online.

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One of the most commonly used boron compounds, boric acid, is produced by dissolving colemanite (2CaO&times / 3B2O3&times / 5H2O) in aqueous sulfuric acid whereby gypsum (CaSO4&times / 2H2O) is formed as a byproduct and must be separated from the main product. This process consists of two steps, dissolution of colemanite and formation of gypsum. The amount of boric acid formed depends on the first step, dissolution of colemanite. In the latter step, gypsum crystals are formed and stay in the reaction mixture to grow up to a size large enough to be filtered out of the solution. Filtration of gypsum crystals is a crucial process in boric acid production because it affects the purity and crystallization of boric acid. In this study it is aimed to investigate the effects of particle size of colemanite, stirring rate and reaction temperature on the dissolution of colemanite, gypsum formation and particle size distribution of gypsum formed in the reaction of boric acid production. Colemanite, sulfuric acid and distilled water were used as reactants for the boric acid production reaction in this study.The colemanite minerals were provided from a region of Emet, Kutahya, Turkey. Three types of colemanite minerals having different chemical composition and particle size were used. The sulfuric acid was supplied by Eti Holding A.S. Hisarcik 1 and Hisarcik 2 colemanites were crushed in a jaw crusher, ground in a hammer mill and then sieved. The sieve analysis was performed to learn the size distribution of Hisarcik 1 and Hisarcik 2 colemanite. Hisarcik 3 colemanite was brought from Emet Boric Acid Plant. The maximum diameter of the colemanite minerals was 150 &amp / #956 / m. The experiments were performed at different particle sizes of colemanite (0-150, 0-250 and 250-1000 &amp / #956 / m), temperatures (70- 90 &amp / #61616 / C) and stirring rates (350-500 rpm). The photographs of gypsum crystals were taken. The boric acid and calcium ion concentrations were determined for each experiment. Also, the solid content of the solution in the reactor were measured. The dissolution of colemanite can be followed by monitoring the boric acid concentration change in the slurry. The crystallization of gypsum from the solution can be found from the calcium ion concentration in the solution. The crystallization kinetics of calcium sulfate dihydrate was studied. The growth of the gypsum crystals were examined under the light microscope and the particle size distribution of gypsum crystals were analyzed by of the laser diffraction instrument.