Dewatering of clays

Vijh, A. K. Electro-Osmotic Dewatering of Clays, Soils, and Suspensions 32... 

Figure 1. A schematic diagram of dewatering of clay by the combined processes of electro-osmosis and pressure. ...

Additions of new flocculants after conventional thickening produce further dewatering of mineral slimes. A clay flocculated with polyacrylamides and rotated in a dmm can produce a growth of compact kaolin pellets (84), which can easily be wet-screened and dewatered. A device called a Dehydmm, which flocculates and pelletizes thickened sludges into round, 3-mm pellets, was developed for this purpose. Several units reported in commercial operation in Japan thicken fine refuse from coal-preparation plants. The product contains 50% moisture, compared with 3% soflds fed into the Dehydmm from the thickener underflow (85). In Poland, commercial use of the process to treat coal fines has been reported (86), and is said to compare favorably both economically and technically to thickening and vacuum filtration. 

B. J. Schemer and A. G. SmeUey, Dewatering of Thickened Phosphate Clay Wastefrom Disposal Ponds, Paper A81-6, The Metallurgical Society of AIME, Warrendale, Pa., 1981 J. R. Pederson, ed., U.S. Bureau of Mines Research 81, U.S. Government Printing Office, Washington, D.C., 1981, p. 83. 

The process of sedimentation in which the settling of suspended particles results in a dense compaction, or coagulation, of particles in which liquid is squeezed out. Geologically, significant compaction of clay layers caused by lowering of the water table (dewatering). 

The fundamental electrochemical approach of interest in this context is the electro-osmotic dewatering (EOD) of clays, the phenomenology... 

Surface Area. An important characteristic of small particles is the rapid increase in exposed surface area per unit mass as size decreases, which leads to increased chemical reaction rate. Fine powders of organic and inorganic oxidizable materials (such as coal or iron) burn vigorously or explode violently when they are present as aerosols of solid particles. Furthermore, fine sand particles influence the performance of dewatering devices, clay behavior in suspension, and oil sands sludge characterization. 

The chemical and physical properties of clay suspensions produced during oil production from oil sands are described. With a composition of approximately 70 wt% water (with some unrecovered bitumen) and 30 wt%solids (>90% less than 44 gm in size)9 these clay suspensions consolidate very slowly. Clay aggregate or floe morphology has been shown to be a function of the water chemistry and can be manipulated to produce a tailings suspension that is easier to consolidate and dewater. Commercial oil sands processing has been going on in northeastern Alberta since 1967, and in that time approximately 250 million m3 of this difficult to dewater clay suspension has been produced. The reclamation options for this material (mature fine tailings) on a commercial scale are also outlined. 

Similarly, electrophoretic methods are also finding increasing applications in other areas. For instance, electrophoretic processes are established techniques for the dewatering of fine clays and latexes. Electrically enhanced liquid-liquid extraction was reported by Thornton [166]. Adaptation of this method for the extraction of biochemicals was reported [167]. Greater clarification and faster floe formation were claimed using electrocoagulation in comparison with conventional chemical methods [4]. 

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