Fedmis Pty (Ltd) situated in Palaborwa, South Africa produces phosphoric acid using the wet process production process. For this study, two main areas of concern in the wet process phosphoric acid production were investigated. The first area is the formation of sludge in the system due to impurities that reduces the grade of the acid produced, thereby lowering the selling price. The second area is the crystallisation of the gypsum that influences filtration and thereby affects plant productivity. These two aspects were investigated separately as they occur in different steps of the production process at different acid concentrations. A major component of the acid sludge is known as x-compound, ((Fe,Al)3KH)14 (PO4)8.4H2O). The purpose of the investigation of x-compound is to determine what effects different ionic impurities have on its precipitation and to determine if these effects could be used to decrease the amount of sludge formation. Due to the complexity of the system and the wide variety of impurities only the major impurities were considered in this study. These impurities included potassium (K+), sodium (Na+), magnesium (Mg2+), aluminium (Al3+) and iron (Fe3+). For all the experiments investigating the effect of impurities, analytical reagents were used on laboratory scale. For the silica experiments, commercially available samples were used. For the experiments investigating the impurity effects on the precipitation of x-compound it was found that: <ul> <li> Agitation increases x-compound precipitation and can be used commercially to increase the precipitation rate to a point where sludge can be removed before transportation.</li> <li> Adding x-compound seeding crystals or magnesium ions also increases precipitation.</li> <li> Adding gypsum, sodium, hexafluorosilicates or fluorosilic acid reduces the precipitation, with sodium ions producing the lowest yield. This reduction is however not sufficient to be used commercially.</li> </ul> From the Raman study it became clear why x-compound precipitation is such a slow process. E At low acid concentrations, more H2PO4 - ions are present that form a complex with iron and aluminium. E As the acid concentration increases the concentration of H2PO4- ions decrease as the degree of dissociation of phosphoric acid decreases. The ferric- H2PO4- and aluminium- H2PO4- complexes become less stable and ultimately precipitation of the x-compound is favoured above solvation. E Addition of potassium impurities to the solutions had no visible effect on the Raman spectra and is suspected not to form a complex with the acid. From the silica sources investigated namely Dicalite, Serina Kaolin, Foskor silica and Aerosil 200 it can be concluded that none of the sources will be useful for the removal of potassium through formation of potassium hexafluorosilicates. For the determination of the concentration of impurities present in the production of phosphoric acid, the Fedmis monitoring program was initiated. It included the monitoring of Foskor rock analyses on a daily basis, and the monitoring of the 27%, 39% and 54% P2O5 phosphoric acid and precipitate, from these acid solutions on a weekly basis. From the investigation of the effect of these impurities on the solubility of potassium hexafluorosilicates, it was found that magnesium causes K2SiF6 to be the most soluble and fluoride the least. Unfortunately, the impurities did not help to reduce the potassium concentrations in the acid to below the required amount for sludge formation. For the calcium sulphate dihydrate surfactant experiments, the purpose of the investigation was to determine whether higher crystallisation qualities could be obtained to improve plant productivity. The investigation was limited to using surfactants with sulphate or phosphate functionalities and experiments were done on laboratory scale using analytical reagents. Atphos E3205, Atpol E3202 and Atpol E1231 are polyethoxylated alkyl phenol phosphate esters that had no visible effect on the crystal structure of the precipitated gypsum, but differences in the crystal sizes were observed. Smaller crystal structures with relatively equal masses compared to reference experiments are an indication of a growth inhibitor and a nucleation promoter as seen with Atphos E3205 and Atpol E3202. Increased crystal sizes were obtained using Atpol E1231. The use of Calsoline Oil caused a wider crystal size distribution in the precipitated crystals as thin and broad crystals with approximately the same length are found. The crystal mass obtained is also approximately the same as that of the reference experiment. Thus, it can be concluded that the surfactant affects the growth of the crystals and not the nucleation. Arlatone 1489, calcium gluconate monohydrate, Dowfax Hydrotrope and Tamol NN 8906 had no visible effect on the structure or size of the precipitated gypsum crystals. With the use of Nansa SS30, drastic effects were seen on the crystallisation of the calcium sulphate as small hexagonal rods were found. With an increase in surfactant concentration, there is a clear decrease in the mass of crystals obtained as well as crystal size. An increase in the crystal size distribution and a decrease in crystal size reduced the filtration rate dramatically. Experiments carried out for 24 hours exhibited the same trends where there is a decrease in yield with an increase in surfactant concentration. Higher yields were however obtained proving that mass transfer barriers were overcome. The results from these experiments again indicate that the surfactant affects crystal growth and nucleation. With the use of Dowfax 3B2 there is definite reduction in yield with an increase in surfactant concentration reaching a minimum at approximately 70% yield. Due to the presence of large amounts of smaller crystals and the almost constant yield obtained compared to the reference experiment, it can be concluded that this surfactant is a growth and not a nucleation inhibitor. As with Nansa SS30, experiments where Empicol LZ/D was used show a continuous decrease in the yield obtained with an increase in the surfactant concentration. At higher concentration of Empicol LZ/D, it seems as if this surfactant changed from a growth promoter to a growth inhibitor because although broad longer crystals are present, there are now also much smaller crystals formed. The crystal size distribution also broadens considerably. Overall, very high yields were obtained using Empimin KSN70 and the observed crystal size distributions were very narrow. The only difference was that the crystals appeared to be more porous or fibrous compared to the reference experiment. It is recommended that the experiments showing promise as crystal habit modifiers like Nansa SS30 and Empicol LZ/D be investigated in more detail as well as combinations of surfactants. Both the areas of concern in the process were investigated successfully. For the sludge formation problem, it is now clear what effects the precipitation of x-compound as well as what affect the impurities and operating conditions have. For the crystallisation of gypsum using surfactants, it was proven that surfactants could be used to affect crystal growth, shape and distribution and in this way influence filtration. / Dissertation (MSc(Chemical Engineering))--University of Pretoria, 2005. / Chemical Engineering / unrestricted

Fluoride ion is an accompanying impurity in a wide variety of chemical gypsum throughout the world. In this study, the Ion Selective Electrode (ISE) method, the Ion Chromatography (IC) method and the standard Willard and Winter method of fluoride analysis were adapted and compared for use in the quantification of fluoride in South African chemical gypsum. During the use of ISE, the pH of sample solutions was found to be a critical parameter for the results to be meaningful. An operating pH of approximately 5 was suitable for consistency of results. It was important to ensure the existence of the ionised form of fluorine in solution, because the detection was based on the sensitivity of the membrane electrode to this species. In the case of the Willard and Winter method, the traditional visual indicator titration was replaced by a more sensitive spectrophotometric detection, because of low fluoride levels in the chemical gypsum. The parameter sensitive reaction rate approach was adapted, and the reaction allowed to go to completion to enable measurement with a bench top spectrophotometer. The IC method required a good separator since fluoride ions usually eluted too early for detection on common ion exchange columns. The data handling of the chromatographic software was thoroughly examined and consistent integration of the chromatograms maintained. Sample preparation of the chemical gypsum involved particle size reduction through grinding. No trend between fluoride impurity and the particle size of the sample was observed. <p. The quantity of fluoride in Kynoch and Omnia phosphogypsum were found to be 0.10% and 0.04% respectively. The Tioxide chemical gypsum, titangypsum, was found to contain in the region of 0.02% fluoride. Generally, the level of fluorine (F) has to be reduced to about 0.2% before phosphogypsum can be used as substitute for natural gypsum in the cement industry. The aim of this study is to critically evaluate three analytical methods, namely, the Willard and Winter standard method of fluoride analysis, the ISE method, and IC as applied in the quantification of fluoride in chemical gypsum. Secondly, the efficiency of treatment of the chemical gypsum with water, lime and sulphuric acid was investigated. The ISE method was found to be faster and relatively simpler versus both Willard and Winter and the IC methods. The IC method was quite superior for indicating general complexity of the sample and it was faster than the Willard and Winter method. The standard Willard and Winter method was generally found to be long and tedious. The three methods validated one another as percentages of fluoride in the chemical gypsum samples were the same. The study indicated that a sulphuric acid pretreatment of the chemical gypsum was the most effective (90%) in the removal of fluoride impurity compared to the lime treatment and water washing (9%). However, the water washing would be inexpensive for practical treatment of chemical gypsum at plant level. / Thesis (PhD(Chemistry))--University of Pretoria, 2006. / Chemistry / unrestricted

Please read the abstract in the section 00front of this document / Dissertation (MSc (Soil Science))--University of Pretoria, 2005. / Plant Production and Soil Science / unrestricted

Made available in DSpace on 2017-06-01T18:20:47Z (GMT). No. of bitstreams: 1 cristina_maria_alves_morais_albuquerque.pdf: 1521157 bytes, checksum: d960407ed7e9ea44fa869c3b4d283641 (MD5) Previous issue date: 2016-12-06 / The plaster projection was developed as a cast material over, to be incorporated into construction systems used in construction.Your application must include interior of the houses and buildings, both commercial and residential, shops, malls,hospitals,etc.These grounds requires is a perfect technique for use in order to have quality and performance to ensure the standards required by the current market, mainly to reduce the consumption of natural resources, ensuring the least possible amount of waste produced during and after the application process. The literature has given very little.scientific information on the production of this type of plaster, due to the essentially commercial nature of this area.In practice it is known that in Plaster Pole of Araripe-Pernambuco, this type of plaster has been made improperly, with inadequate dehydration of the mineral gypsum ore (on conversionreaction), being completed with the incorporation of additives - limited substances, such as the glue plaster; that the high cost adds value.This work, therefore, the objective is to show how the development of a basic projection process of gypsum production, with the aid of totally dehydrated gypsum (anhydrite II). Consisted of hemihydrates and anhydrite II in suitable percentage for fixing setting time required for a better workability.of the mass. This type of plaster has advantages in relation to those produced by current procedures practiced in the Plasterer Polo Araripe, associated with a significant reduction of waste - basic concern that one should have in relation to the duration of deposits. / O gesso de projeção foi desenvolvido como um material a mais, para ser incorporado aos sistemas construtivos. Sua aplicação deve abranger o interior das casas e edifícios, tanto comerciais como residenciais, lojas, shopping centers, hospitais, etc. Nesses recintos exige-se uma técnica perfeita para a sua utilização, de forma a se ter qualidade e desempenho que garantam os padrões exigidos pelo mercado atual, principalmente a redução do consumo das reservas naturais , garantindo a menor quantidade possível de resíduos produzidos durante e após o processo de aplicação. A literatura tem dado pouquíssimas informações científicas sobre a produção desse tipo de gesso, em virtude do caráter essencialmente comercial dessa área. Na prática sabe-se que no Polo Gesseiro do Araripe-Pernambuco, esse tipo de gesso tem sido produzido de forma imprópria, com a desidratação inadequada do minério de gipsita (sobre conversão da reação), complementando-se com a incorporação de aditivos - substâncias limitadas, a exemplo do gesso cola; que pelo alto custo agrega valor. Este trabalho, portanto, objetiva mostrar como ocorre o desenvolvimento de um processo básico de produção de gesso de projeção, com o auxílio de gipsita totalmente desidratada (anidrita II). Constituído de semi-hidrato e anidrita II, em percentuais adequados para a fixação de tempos de pega necessários para uma melhor trabalhabilidade da massa.Esse tipo de gesso apresenta vantagens em relação àqueles produzidos por procedimentos atuais praticados no Polo Gesseiro do Araripe, associado a uma significativa redução de rejeitos - preocupação básica que se deve ter em relação à duração das jazidas.

A indústria de cerâmica branca de objetos decorativos e utilitários, produz diariamente um contingente significativo de resíduo de gesso, oriundo do descarte dos moldes, cuja vida útil é extremamente curta. A deposição desse material via de regra é feita em aterros sanitários, sem qualquer tipo de isolamento em células e sem observar as recomendações da Lei da Política Nacional de Resíduos Sólidos. De acordo com a hierarquia estabelecida pela lei, a supressão da geração dos resíduos sólidos aparece como alternativa prioritária do ponto de vista das boas práticas ambientais. É nessa perspectiva que a tecnologia de produção industrial computadorizada de objetos tridimensionais por deposição de matéria prima, surge como alternativa. A intenção desse trabalho é apresentar conceitos de produtos que potencializem o uso dessa tecnologia através de configurações formais inovadoras para o setor, eliminando a utilização do gesso em seu processo de fabricação além de avaliar os resultados obtidos através da análise dos protótipos fabricados. / White ceramic industry of decorative and utilitarian objects, produces daily a significant contingent of waste gypsum, originated from the disposal of moulds, whose lifespan is extremely short. Deposition of this material usually is made in landfills without any type of isolation cells and without observing the recommendations of the Law of the Brazilian solid waste Policy. According to the ranking established by law, the elimination of solid waste generation appears as a priority alternative in terms of good environmental practices. In this perspective, the technology of computerized industrial production of three-dimensional objects by deposition of raw material, is an alternative. The aim of this paper is to present product concepts that enhance the use of this technology through innovative formal settings for the sector and make an analysis about the results.

The diploma thesis is concerned with study of preparation and properties of historic mortars. In theoretical part, there is summarized the historic progress of mortars and their material composition. The experimental part is focused on proposition of mortar mixes. The diploma thesis referring to actual research on Institute of Technology of Building Materials and Components, FCE VUT in Brno. The base mixe of historical mortar came from this research. In experiment, there is the base mixe of historical mortar modified with gypsum. In the first phase of the experimental part the basic technological and aplication properties are assessed. The second phase of the experimental part is focused on the course of hydration of the binder in different environments and subseqeunt determination of the phase composition by X-ray diffraction analysis. The aim of the thesis is to determine the optimal amount of gypsum and to optimize the recipe of historical mortar.

The topic of this dissertation was the preparation of a high-quality sulphate binder based on secondary raw materials. For this purpose, the work was primarily focused on the laboratory preparation of beta gypsum from the selected industrial gypsum, the design of the technological process of production and its verification by pilot tests. In the next step, the thesis dealt with the modification of beta gypsum by a selected set of liquefiers. In addition to commercial dehumidifiers, the possible beta casting of beta gypsum was tested by increasing the zeta potential of the gypsum suspension. At the end, a complete complex of construction products was developed based on laboratory and semi-prepared beta plasters, consisting of gypsum plasters, mastics, gypsum premix and small plaster casts.

This diploma thesis deals with the preparation of modified tricalcium aluminate phases using sodium ions, and the study of their hydration processes and products. The X-ray diffraction analysis, isothermal calorimetry, laser diffraction, and scanning electron microscopy with energy dispersion analysis were used to solve this task. The preparation of modified tricalcium aluminate phases using high temperature methods has been described in the experimental section. Furthermore, the X-ray diffraction analysis was used to determine the purity of the prepared phases and the scanning electron microscopy with energy dispersion analysis was used to define the volume of sodium. Laser diffraction was used to measure a particle size distribution in the individual phases. Subsequently, hydration of the pure phases was performed in an isothermal calorimeter. It was followed by hydration of phases in the presence of different gypsum content and then in the presence of saturated portlandite solution. Hydration of some samples was stopped in order to better understand the hydration process. Hydration products were studied by X-ray diffraction analysis. The obtained results were compared with each other and the influence of sodium ions on both the structure of the prepared phases and the course of hydration and its products has been discussed. The effect of adding different volumes of gypsum and portlandite on the course of hydration of the individual phases was also compared.

This work is oriented on the preparation of high-voluable sulphate binder based on gypsum waste. One of the potential mineral resources in Moravia is Pregips chemical gypsum, produced by Precheza. This is the raw material, which is characterized by high purity, high quality and is economically acceptable. Beta burned gypsum plaster from this, however, need to modify due to suppression of the high needs of water mixing, which is determined by its morphology. The need for mixing water has a large impact on the strength of gypsum binders. Therefore it is necessary to find a suitable additive, which would reduce the coefficient of water in the preparation of porridge normal consistency.

This Diploma Thesis deals with the research and advancements in the field of sulphate binders, especially the anhydrite binder. The theoretical part of the thesis is dedicated to the fundamentals of sulphate binders and anhydrite binders. Its second part also introduces standard requirements for screed coatings together with technological methods of their application. Practical part of the thesis looks at the research and production of anhydrite binder with special emphasis on self-levelling compounds. Various types of plasticizers were used in these compounds and their effectiveness and final product quality are compared.