One of the first commercial applications of a medium to effect a sink-float separation used a fine silica sand suspension for treating anthracite coal and is known as the “Chance” process. Thus, in a continuous process it becomes necessary to provide means for continually cleaning a portion of the medium to eliminate slime at the same rate at which it is introduced into the medium by the incoming feed.
An accumulation of contaminating fines and slime in the bath would affect its specific gravity and viscosity and reduce its separating efficiency. When materials are separated in such a suspension or medium, they will inevitably contain some contaminating fines or slimes resulting from incomplete washing of the feed material and from abraded fines generated through particle attrition as the material passes through the separating vessel. As a consequence, no rising currents of water are necessary to assist in the separation of sink from float, nor is it necessary to supply strong mechanical agitation to maintain the medium in suspension. If the solid phase of the suspension is ground to suitable fineness and mixed with water in correct proportion, a medium is obtained that is stable or so slow settling that a substantially uniform specific gravity can be maintained from top to bottom of the bath. Many years ago it was discovered that suspensions of finely divided solids in water closely approached the properties of heavy liquids in sink and float practice. The heavy liquids commonly employed are inorganic salt solutions, such as of zinc chloride, or organic liquids, such as halogenated hydrocarbons. The lighter fraction of the two is floated at the surface of the liquid while the heavier product sinks. The Sink and Float separation process is part of what is also known as a Heavy Media Separation Process ( HMS) and are commercial adaptations of the common laboratory procedure used for separating a mixture of two products having differentials in specific gravity by immersing the sample in a heavy liquid having a gravity intermediate to those of the products to be separated. INDUSTRIAL PROCESSES USING HEAVY SUSPENSIONS.INDUSTRIAL PROCESSES USING HEAVY LIQUIDS.The HMS Heavy Media Separation Process Flowsheet.
0 kommentar(er)
