Flocculants are usually selected by the results of laboratory-scale experiments. Flocculant mixing and dilution can affect the results and indicated dosage.
A structured testwork program on fresh, representative slurry samples is essential to determining flocculant type and dosage. Changes of flocculant selection will be required if water quality, ore type or mineralogy changes. Guides to flocculant selection and testing have been published irregularly eg Stock and Parker, Selecting the right thickener for each application needs to be based on tailings deposition criteria as well as knowledge of slurry characteristics:.
The balance between tailings pumping or disposal costs against water savings will move system design towards paste applications when water supply available to the processing operation is limited. Stable feed, flocculation and hence discharge flow are essential to maintaining reliable operation of all thickeners. Control systems must allow for steady bed levels which in turn demand reliable high performance flocculation Shoenbrunn, Hale and Bedell, The final delivered density may be dictated by TSF management and beach requirements, or more simply it can be raised to obtain maximum water conservation.
The demands on the rake and the torque required from its drive will rise concomitantly with underflow density and yield stress. Mechanical designs of rakes and drives have taken these extreme forces into account so that the failures of these components that were experienced in early installations are not repeated. The high yield stresses in underflow slurry generally arise from the sum of the viscous interaction of the slurry and the residual action of the flocculant following compression and dewatering of the floccules. Through shearing the slurry at least a fraction of the yield stress may be dissipated to lower the demand for pumping energy Nguyen and Boger, Recirculation of the slurry through the underflow cone or boot of the thickener by pumping can break the floccules and lower slurry yield stress substantially.
Proprietary designs of shearing systems are offered by vendors to provide lower yield stress in delivered slurry. Concha, F, and Burger, R, Thickening in the 20 th Century: A Historical Perspective.
Farrow, J, and Swift, J, A new procedure for assessing the performance of flocculants. International Journal of Mineral Processing Vol. Optimising flocculation and thickener performance for paste disposal Proceedings of Paste , Jewell et. Editors, Aust.
Centre Geomechanics, Perth. Nguyen, Q, and Boger, D, Thixotropic behaviour of concentrated bauxite residue suspensions , Rheologica Acta, Vol 24, No 4, Pearse, M, Historical use and future development of chemicals for solid—liquid separation in the mineral processing industry.
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Minerals Engineering 16, — Strategies For Instrumentation and Control of Thickeners. SME Roebl, A, Stock, P, and Parker, K, Bustos, M, Concha, F. Coe, H, and Clevenger, G, Understanding the Thickening Process.
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Effect of shear on particulate suspension dewatering. Jagger, N, and Arbuthnot I, Paterson, A, Usher, S, Gladman, B. Filtration and Separations Soc. Wilhelm, J, and Naide, Y, Toggle navigation.
Sedimentation - Wikibooks, open books for an open world
Login Trouble signing in? Search here Thickener sizing Comprehensive laboratory or continuous pilot testing will provide confidence in the selection of key parameters if slurry samples are representative. The general steps towards sizing include: conduct a series of bench tests to determine the optimum feedwell solids loading to investigate and confirm flocculant selection, and establish rise rate conduct a series of continuous scale diameter mm or up to 1 m tests at optimum feedwell solids loading to determine relationship between solids flux rate, underflow solids and overflow clarity establish relationship between mud bed volume and underflow density rheology measurements on fresh slurry and paste samples provide information for rake mechanism, underflow discharge pumps and pipes and drive requirements.
Flocculant selection and testing The natural settling properties of finely divided solids are generally slow.
The factors which influence the degree of flocculation are well documented, eg Wills : efficiency or strength of adsorption of the polymer on the particle surface the degree of agitation during flocculation the subsequent degree of feedwell and bed agitation. For this reason we have organized the chapters in such a way that the book can be read in two ways. Engineers and engineering students will find a rigorous formulation of the mathematical model of sedimentation and the exact and approximate solutions for the most important problems encountered in the laboratory and in industry in Chapters 1 to 3, 7 and 8, and 10 to 12, which form a self-contained subject.
They can skip Chapters 4 to 6 and 9, which are most important to applied mathematicians, without losing the main features of sedimentation processes. On the other hand, applied mathematicians will find special interest in Chapters 4 to 6 and 9 which show some known but many recent results in the field of conservation laws of quasilinear hyperbolic and degenerate parabolic equations of great interest today.
Sedimentation and Thickening: Phenomenological Foundation and Mathematical Theory
These two approaches to the theory keep their own styles: the mathematical approach with theorems and proofs, and the phenomenological approach with its deductive technique. The book is an interesting combination of modeling and rigorous mathematics.