Made available in DSpace on 2014-12-17T15:01:22Z (GMT). No. of bitstreams: 1 MariaCPAM.pdf: 984936 bytes, checksum: 2ad822e0048cda570ce57a014ed42a7c (MD5) Previous issue date: 2006-05-19 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The tanning industries are those which transform animal hide or skin into leather. Due to the complexity of the transformation process, greater quantities of chemicals are being used which results in the generation of effluents with residual solids. The chromium in the residual waters generated by tanning tend to be a serious problem to the environment, therefore the recovery of this metal could result in the reduction of manufacturing costs. This metal is usually found in a trivalent form which can be converted into a hexavalent compound under acidic conditions and in the presence of organic matter. The present study was carried out with the objective to recover chromium through an extraction/re-extraction process using micro emulsions. Micro emulsions are transparent and thermodynamically stable system composed of two immiscible liquids, one forming the continuous phase and the other dispersed into micro bubbles, established by an interfacial membrane formed by surface active and co-surface active molecules. The process of recovering the chromium was carried out in two stages. The first, an extraction process, where the chromium was extracted in the micro emulsion phase and the aqueous phase in excess was separated. In the second stage, a concentrated acid was added to the micro emulsion phase rich in chromium in order to obtain a Winsor II system, where the water that formed in the micro emulsion phase separates into a new micro emulsion phase with a higher concentration of chromium, due to the lowering of the hydrophiles as well as the ionisation of the system. During the experimental procedure, a study was initiated with a synthetic solution of chromium sulphate passing onto the effluent. A Morris extractor was used in the extraction process. Tests were carried out according to the plan and the results were analysed by statistical methods in order to optimise the main parameters that influence the process: the total rate of flow (Q), stirring speed (w) and solvent rate (r). The results, after optimization, demonstrated that the best percentuals in relation to the chromium extraction (99 %) were obtained in the following operational conditions: Q= 2,0 l/h, w= 425 rpm and r= 0,375. The re-extraction was carried out at room temperature (28 ?C), 40 ?C and 50?C using hydrochloric acid (8 and 10 M) and sulphuric acid (8 M) as re-extracting agents. The results obtained demonstrate that the process was efficient enough in relation to the chromium extraction, reaching to re-extraction percentage higher than 95 %. / Os Curtumes s?o ind?strias que transformam peles em couro. Devido a complexidade do processo de transforma??o s?o utilizadas grandes quantidades de agentes qu?micos e gerados grandes volumes de efluentes e res?duos s?lidos. O cromo presente nas ?guas residu?rias geradas pelos curtumes constitui um s?rio problema ambiental e sua recupera??o poder? representar uma redu??o nos custos do processo. Normalmente encontra-se na forma trivalente podendo ser convertido a cromo hexavalente sob condi??es ?cidas e na presen?a de mat?ria org?nica. Este estudo foi realizado com o objetivo de recuperar o cromo atrav?s de um processo de extra??o/reextra??o utilizando microemuls?es. As microemuls?es s?o sistemas transparentes, termodinamicamente est?veis, constitu?dos por dois l?quidos imisc?veis, um formando a fase cont?nua e o outro disperso na forma de microgot?culas, estabilizadas por uma membrana interfacial formada por mol?culas de tensoativo e cotensoativo. O processo de recupera??o do cromo ocorre em duas etapas. Na primeira, a extra??o, o cromo ? extra?do para a fase microemuls?o e a fase aquosa em excesso ? separada. A segunda etapa, ? realizada adicionando-se a fase microemuls?o, rica em cromo, um ?cido concentrado visando a obten??o de um sistema Winsor II, em que parte da ?gua que formava a fase microemuls?o, devido a diminui??o da hidrofilia e ioniza??o do sistema, se desloca formando uma nova fase aquosa, mais concentrada em cromo. Durante o procedimento experimental, iniciou-se o estudo com uma solu??o sint?tica de sulfato de cromo passando-se, em seguida, ao efluente. No processo de extra??o do cromo em escala semi-piloto utilizou-se o extrator Morris. Os ensaios foram efetuados seguindo um planejamento experimental e os resultados obtidos foram analisados, atrav?s de m?todos estat?sticos, visando a otimiza??o dos principais par?metros que influenciam no processo: vaz?o total (Q), velocidade de agita??o (w) e taxa de solvente (r). Os resultados obtidos, ap?s a otimiza??o, demonstraram que os maiores percentuais de extra??o (99 %) s?o obtidos nas seguintes condi??es operacionais: Q=2,0 l/h, w= 425 rpm e r= 0,375. A reextra??o foi realizada a temperatura ambiente (28 ?C) e a 40?C e 50?C utilizando-se como agente reextratante ?cido clor?drico (8 e 10 M) e ?cido sulf?rico (8 M). Os resultados obtidos demonstraram que o processo foi eficiente com rela??o ao cromo, obtendo-se percentuais de reextra??o acima de 95%