Gypsum is produced as a waste product by various industries, e.g. the fertilizer industry, the mining industry and power stations. Gypsum waste disposal sites are responsible for the leaching of saline water into surface and underground water and create airborne dust. Gypsum waste is not only an environmental problem but has measurable economic value as well. However, all these environmental and economical concerns can be avoided should valuable/saleable by-products like sulphur and calcium carbonate be recovered from the low quality gypsum. The aim of this project was to evaluate a process for converting waste gypsum into sulphur. The process evaluated consists of the following stages: reduction of gypsum to calcium sulphide; stripping of the sulphide with CO2 gas and the production of sulphur. Thermal reduction study showed that gypsum can be reduced to CaS with activated carbon in a tube furnace operating at 1100º C. The CaS yield was 96%. The CaS formed was slurried in water. The reaction of gaseous CO2 with the CaS slurry leads to the stripping of sulphide to form H2S gas and the precipitation of CaCO3. The H2S generated was then reacted in the iron (IIII) and PIPco processes to form elemental sulphur. Sulphur with the purity between 96% and 99% was recovered from waste gypsum in this study. / Thesis (PhD)--University of Pretoria, 2009. / Chemistry / unrestricted

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O desperdÃcio à o principal responsÃvel pela geraÃÃo de resÃduos sÃlidos no ramo da construÃÃo civil, mais notadamente aquele relacionado com a aplicaÃÃo do gesso como revestimento de paredes e tetos. Neste trabalho, buscou-se quantificar a taxa de desperdÃcio de gesso em quatro obras localizadas na cidade de Fortaleza, por meio da utilizaÃÃo de duas metodologias, as quais relacionam a quantidade de massa de gesso demandada com a quantidade de resÃduos gerados. A quantificaÃÃo de resÃduos gerados foi possÃvel devido Ãs empresas construtoras estudadas possuÃrem sistema de coleta segregada desse tipo de material. Foram pesquisados dois mÃtodos. No primeiro tem-se como parÃmetro a Massa de Gesso Demandada (MGD), calculada levando em consideraÃÃo a quantidade de gesso adquirida para a realizaÃÃo do serviÃo. No segundo, a MGD à confrontada com a Quantidade TeÃrica NecessÃria (QTN), sendo esta determinada a partir de parÃmetros como a Ãrea total a ser revestida e o Ãndice de Massa Consumida (IMC), que representa o consumo ideal sem perdas. Foi possÃvel concluir que a tÃcnica da pasta de gesso à aquela que apresenta maior taxa de desperdÃcio, sendo nÃo recomendada, do ponto de vista ambiental, para ser utilizada como revestimento de paredes e, particularmente, tetos. Verificou-se, ainda, que a taxa de desperdÃcio para essas obras à muito grande, sendo maior que os valores encontrados na literatura / The waste is primarily responsible for the generation of solid waste in the construction industry, most notably those related to the application of gypsum as a coating for walls and ceilings. In this work, we tried to quantify the rate of waste gypsum in four works located in the city of Fortaleza, by using two methods, which relate the quantity of mass of gypsum defendant with the amount of waste generated. The amount of waste generated could be due to the construction companies have studied segregated system of collection of such material. We studied two methods. The first parameter has been like a Mass of Gypsum Defendant (MGD), calculated taking into account the amount of gypsum obtained for the completion of service. In the second, the MGD is faced with the Quantity Theory Needed (QTN), which is determined from parameters such as the total area to be coated and Consumed Mass Index (CMI), which represents the ideal consumption without loss. It could be concluded that the technique of plaster folder is one that shows higher rates of waste and is not recommended, from an environmental standpoint, to be used as lining of walls and particularly roofs. There was also that the rate of waste to such works is very large, being larger than the values found in literature