A new approach to define batch settling curves for analyzing the sedimentation characteristics

The results of batch settling tests (BST) are used to investigate settling behavior of solids suspension, which contribute to sizing thickeners. Conventional methods in analyzing BST on the basis of visual and graphical procedures lead to sub-optimally sized and selected thickeners. A computational approach based on quantitative analysis of BST can be beneficial. About 300 settling experiments were performed by varying conditions, including solids concentration, type and dosage of chemical aids. Solid samples were collected from iron, copper, coal, lead and zinc tailings and feed streams. Settling curves based on experimental data considering extreme limits were generated and analyzed. Therefore, a mathematical model, h(t), is introduced to define batch settling curves. Furthermore, it is shown that, on settling velocity curves a maximum value is likely to occur (except in extreme conditions such as very high or very low solids concentration suspensions or extremely high dosage of flocculant). In addition, to compare batch settling curves quantitatively, an index, Ii, based on parameters which can be obtained from the model h(t), is developed. The proposed model and index can simply be utilized in a computerized approach of settling curves analysis.