Journal of Environmental Analytical Chemistry

In this study, optimization and modeling of leaching parameters affecting nickel dissolution from lateritic ore in Eskişehir (Mihalıççık-Yunusemre) were investigated using Box-Behnken design. Stirring speed (100-400 rpm, temperature (40-80°C), acid concentration (0.1-2 M) and dissolution time (30-180 min) were selected as experimental design parameters. 27 experiments were carried out by Box-Behnken experimental design in Minitab 16.0 program. After leaching experiments, the highest Ni dissolution percentages were obtained as 87.85%. The effective parameters and their interactions in nickel dissolution are described with a mathematical model. The results obtained from the experiments were subjected to ANOVA and multiple regression analysis. The R2 value of the model for nickel dissolution was calculated as 0.980. This showed that the predicted values are in good agreement with the observed values. In addition, three-dimensional response surface and contour graphs of the parameters affecting nickel dissolution efficiency were created and the results were examined.

Information on reservoirs is important as it forms a vital baseline for among others the detection of undesirable changes in water quality. Variations in the physicochemical characteristics of water were investigated in five peri-urban reservoirs Uhuru reservoir located in Nairobi City County and Ruiru, Ngewa, Comte and Kianjjibbe in Kiambu County between February 2014 and January 2015. The aim of the study was to establish the quality of water. Mean Secchi depth recorded in cm was 0.7 ± 0.9 in Uhuru, 0.9 ± 0.43 in Ruiru, 0.1 ± 0.04 in Ngewa, 0.1 ± 0.6 in Comte and 0.3 ± 1.3 in Kianjjibbe. Mean temperatures in °C were 23.8 ± 1.8 in Uhuru, 21.6 ± 2.2 in Ruiru, 24.3 ± 2.9 in Ngewa, 23.4 ± 1.6 in Comte and 24.0 ± 1.9 in Kianjjibbe. Electrical conductivity in μS cm^-1 was 90.4 ± 23.81 in Uhuru, 45.8 ± 5.7 in Ruiru, 195.5 ± 37.3 in Ngewa, 113.3 ± 20.5 in Comte and 298.94 ± 41.5 in Kianjjibbe. pH was 7.4 in Uhuru and Ruiru and 7.2, 7.3 and 7.7 in Ngewa, Comte and Kianjjibbe respectively. Dissolved oxygen in mgL^-1 was 7.1 ± 0.7 in Uhuru, 7.1 ± 0.26 in Ruiru, 6.2 ± 1.1 in Ngewa, 7.6 ± 1.1 in Comte and 9.0 ± 0.8 in Kianjjibbe. Total alkalinity in mgL^-1 CaCO₃ was 35.5 ± 8.8 in Uhuru, 18.0 ± 0.24 in Ruiru, 83.9 ± 7.9 in Ngewa, 41.1 ± 8.9 in Comte and 110.2 ± 15.9 in Kianjjibbe. Nitrate nitrogen μg L^-1 was 9.8 ± 1.37 μg L^-1 in Uhuru, 9.0 ± 12.5 in Ruiru 4.2 ± 0.43 in Ngewa, 7.1 ± 5.56 in Comte and 13.6 ± 1.14 in Kianjjibbe. Total nitrogen in μg L^-1 was 33.1 ± 22.7 in Uhuru, 39.8 ± 3.0 in Ruiru, 34.1 ± 22.5 in Ngewa, 40.5 ± 36.9 and 32.5 ± 28.7 in Comte and Kianjjibbe reservoir respectively. Total phosphorus in μg L^-1 in the reservoirs was 0.8 ± 0.14 in Uhuru, 1.0 ± 0.02 in Ruiru, 1.0 ± 0.77 in Ngewa, 1.0 ± 0.82 in Comte and 2.7 ± 0.25 in Kianjjibbe. Soluble reactive silica in mgL^-1 was 3.4 ± 0.47 in Uhuru, 4.0 ± 0.64 in Ruiru, 7.3 ± 0.7 in Ngewa, 5.9 ± 0.15 in Comte and 7.0 ± 199 in Kianjjibe. Peak values of total nitrogen and total phosphorus were recorded during the wet season while high soluble reactive silica was recorded during the dry season. There was a significant difference in all measured physcio-chemical parameters between the reservoirs (p<0.001, df=59). The study concludes that the reservoirs investigated varied in levels of physico-chemical properties. The variation was attributed to differences in rainfall, volume of outflow and use dynamics of the water of the reservoir.