The oxidation kinetics of a blend of zinc sulphide concentrates in a bench-scale fluidised bed reactor operated in batch regime was studied. The fractional conversion was determined by measuring the SO2 concentration in the exit gas using a chromatograph. The effects of the initial mass of the blend, airflow rate and temperature on fractional conversion were studied. The initial mass of the blend varied from 45 to 75 g, the airflow rate from 6 to 9 L/min and the temperature from 883 to 1213 K. The time for complete conversion was affected by the molar ratio of O2 to S fed into the reactor and by temperature. The oxidation reaction was controlled by surface chemical reaction of the unreacted core of the particles. The value of the activation energy, 87 kJ/mole, supports the contention that the reaction was chemically controlled.

The oxidation kinetics of a blend of zinc sulphide concentrates in a bench-scale fluidised bed reactor operated in batch regime was studied. This work involves the fluid dynamics characterisation of the bed during the reaction. Its purpose is to determine bed behaviour and to assess the experimental conditions used in the roasting experiments. The characterisation is derived from both fluid dynamics maps and an analysis based on the dynamics of gas bubble growth in the bed. Bed behaviour under any experimental condition is evaluated with the fluid dynamics maps. The transitions fixed/fluidised bed, fluidised bed/pneumatic transport and between several fluidisation regimes are obtained from curves of dimensionless gas velocity versus dimensionless particle diameters. The possibility of fluidisation in the slugging regime is verified by the dynamics of gas bubble growth in the bed.

Independentemente da capacidade da enxurrada em transportar as partículas minerais e orgânicas do solo, a avaliação da ação erosiva da chuva, em sua fase inicial, não será completa, se os mecanismos de desagregação e salpico do solo pelo impacto das gotas de chuva não forem avaliados. Considerando a ausência de dados sobre esses mecanismos em solos do Ceará, os objetivos deste trabalho foram: comparar métodos para a coleta do solo desagregado e salpicado e avaliar as correlações entre a erosividade das chuvas e o salpico em solo descoberto e com cobertura para reduzir a erosão em sua fase inicial. O estudo foi realizado sob condições de campo, em Fortaleza (CE), em um Argissolo Vermelho-Amarelo eutrófico, durante a estação chuvosa de 21/3 a 9/7/1994, ocasião em que a erosividade da chuva foi de 6.003 MJ mm (ha h)-1. Para quantificar as massas de partículas de solo desagregadas e salpicadas, foram empregados os métodos da bandeja coletora de Morgan (1982) e o do funil de Sreenivas et al. (1947). Intervalos de confiança a 95 %, para a diferença entre as médias do salpico coletado pelos dois aparelhos, foram calculados pelo teste t em dados emparelhados. Para ambos os tratamentos, solo descoberto e com uma cobertura de 50 % de colmos de capim-elefante, não houve diferença estatística significativa entre os dois métodos. Foram encontradas correlações significativas entre o parâmetro de erosividade EI30 e a massa de solo salpicado para equações de regressão da forma de potência. A média dos salpicos totais coletados nos dois métodos apresentou uma redução de 52 % quando foi comparado o tratamento com cobertura (2,31 kg m-2) com o solo descoberto (4,81 kg m-2). Esse resultado vem confirmar a eficiência da cobertura do solo na redução da erosão por salpico, estádio inicial e de grande importância do processo erosivo.

Independent of the runoff capacity to transport mineral and organic particles of soil, the assessment of rainfall erosive action, during its initial phase, would not be complete if the mechanisms of soil detachment and splash by raindrop impact were not appraised. Considering the lack of data on these mechanisms in soils of Ceará State, Brazil, the objectives of this work were: to compare collection methods of detached and splashed soil and to evaluate the correlations between rainfall erosivity and splash on bare and covered soil to reduce erosion in its initial phase. The study was conducted under field conditions in Fortaleza, Ceará State, Brazil, on an eutrophic Red-Yellow Podzolic during the rainy season from 3/21 to 7/9/1994, with a rain erosivity of 6,003 MJ mm (ha h)-1. In order to quantify the mass of detached and splashed soil particles, the splash cup method of Morgan (1982) and the funnel method of Sreenivas et al. (1947) were used. Confidence intervals at a level of 95 % were calculated by the t-test in paired data for the difference between means of the splash collected by the two devices. There was no statistically significant difference between both methods in the two treatments,'bare soil' as well as 'soil with a 50 % cover of napier grass stems'. Significant correlations between the EI30 erosivity parameter and the splashed soil mass for regression equations in a potency form were found.The mean of total splash collected in both methods showed a reduction of 52 % in the treatment with cover (2.31 kg m-2) when compared to that collected on bare soil (4.81 kg m-2). This result confirmed once more the effectiveness of soil cover in reducing splash erosion, which is of great importance as it is the initial stage of the erosive process.