Solid-liquid separation Settling—test

Approximately 10 mL of each coating sample was placed in a glass test tube and centrifuged until the solids began to settle and the first two or more millimeters from the top of the liquid in the tube was clear of solid particles. This took approximately 15-20 minutes. This centrifuging was done in order to separate the liquid fractiou of the coating formulations from solid particles. Talc and silica particles present in the formulations could iuterfere with the Fourier transform infrared spectroscopic analysis. 

The procedure for phase separation follows the schematic in Figure 4-115 [32A]. To prepare the three test phases, a 1 9 ratio by volume of mud to seawater is mixed for 30 min. The pH is adjusted to that near seawater (pH = 7.8-9.0) by the addition of acetic acid. The slurry is allowed to settle for one hour. A portion of the supernatant is filtered through a 0.45- im filter. The filtrate is designated as the liquid phase. The remaining unfiltered supernatant of the slurry is the suspended particulate phase, while the solid phase is the settled solid material at the bottom of the mixing vessel. 

Sulphides and Thio-Salts. Pass hydrogen sulphide into hot dilute solutions of arsenic, antimony, and bismuth trichlorides in separate test tubes. Note that yellow, orange, and black precipitates respectively are formed. Let the precipitates settle to the bottom of the tubes, pour off the liquid, and treat the solid with sodium polysulphide (Na2S solution in which sulphur is dissolved) in each case. The yellow and orange precipitates dissolve the black one does not. To the two solutions add 6AT HC1 in excess and note that yellow and orange precipitates respectively are again thrown out. 

Inclined plate clarification is a traditional separation technology that has been used for decades to remove suspended solids from a liquid stream in various types of systems including traditional precipitation [12]. In the semiconductor industry, the clarifier is commonly used in fluoride waste treatment systems where calcium fluoride precipitate is concentrated prior to dewatering in a press, or in assembly/test operations to separate silicon fines from backgrind operations. The clarifier will concentrate the solid phase of slurry like a UF, but unlike the UF or MF, the clarifier may require the addition of a chemical polymer to facilitate the agglomeration of the suspended solids so that they settle and concentrate. Polymer addition adds another level of complexity to the waste treatment system. The clarifier does not provide a physical barrier to prevent the transport of solids to downstream equipment, so it may be necessary to install a UF or MF downstream of the clarifier to capture extraneous particles or to protect the downstream equipment from clarifier upsets. 

Ovhemical DOSING for improvement of liquid-solid separation is traditionally designed and operated more or less independently of the geometry and hydraulic performance of the actual separation reactor. The widespread use of jar tests in the day-to-day operation of filtration and flotation plants illustrates this fact. Yet it is not difficult to visualize situations in which aggregation processes would furnish floes unsuitable for the subsequent separation unit, such as voluminous floes that do not settle out readily. 

The results from the test procedure are coded as shown in Figure 5.5, using a third set of characteristic letters. For example, a slurry which forms a cake at the rate 0.5 cm min is coded K. Combining this with the settling characteristics gives a total preliminary description of the separation characteristics of the slurry (e.g. BEG, K). If the proposed duty is simply to thicken a slurry then it is not necessary to carry out a filtration test. However, for a total separation of the solid from the liquid (as obtained in a filter, for example) both settling and filtration tests need to be performed. 

There are analogies between the minimum impeller speed Njs for solids suspension and Nmm for drop suspension. Both depend on density difference, continuous phase viscosity, and impeller diameter. However, Njs depends directly on particle size, while Nmin depends instead on interfacial tension and the other physical properties that determine drop size. Skelland and Seksaria (1978) determined the minimum speed to form a liquid-liquid dispersion from two settled (separated) phases of different density and included the sensitivity to impeller location. The vessels used were fully baffled. They determined Nmin for systems of equal volumes of light and heavy phase. Studies included use of single impellers placed midway in the dense phase (C = H/4), at the o/w interface (C = H/2) and midway in the lighter phase (C = 3H/4). They also examined the use of dual impellers located midway in both phases. Several impeller types were tested, including a propeller (Prop), a 45° pitched blade tmbine (PBT), a flat-blade turbine (FBT), and a curved-blade turbine (CBT). Their results are correlated by the following equation, which is dimensionless ... 

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