Slurry analysis

Although one must be aware of the potential problems posed by particle size effects in slurry and powder analysis, in many cases, the range of particle size and particle composition for a process stream is sufficiently constant that reliable measurements can be made using on-line XRF systems. Successful applications which have been reported include an on-stream XRF measuring system for ore slurry analysis [38] a system for direct XRF analysis of pulverised coal streams [39] and on-stream analysis of cement using XRF [2, 40]. The latter is available as a commercial on-stream cement analyser which it is claimed can measure lime saturation factors (a function of Ca, Si, A1 and Fe concentrations) with a relative standard deviation of better than 1% in 100 s measurement time. Obtaining such results with a sampHng frequency of over 10 measurements per hour can allow effi-... 

Slurry analysis can also be applied to compact samples which are difficult to dissolve after pulverization. Attention must be paid to possible contamination resulting from abrasion in the mill. For mills of very hard materials such as tungsten carbide abrasion in the case of ceramics may amount to serveral percent of the sample mass. Slurry sampling has been reviewed comprehensively in [132],... 

This is used extensively for qualitative analysis, for it is a rapid process and requires simple apparatus. The adsorbent is usually a layer, about 0 23 mni. thick, of silica gel or alumina, with an inactive binder, e.g. calcium sulphate, to increase the strength of the layer.. A. i i slurry of the absorbent and methanol is commonly coated on glass plates (5 20 cm. or 20 x 20 cm.), but microscope... 

Heat Exchangers Using Non-Newtonian Fluids. Most fluids used in the chemical, pharmaceutical, food, and biomedical industries can be classified as non-Newtonian, ie, the viscosity varies with shear rate at a given temperature. In contrast, Newtonian fluids such as water, air, and glycerin have constant viscosities at a given temperature. Examples of non-Newtonian fluids include molten polymer, aqueous polymer solutions, slurries, coal—water mixture, tomato ketchup, soup, mayonnaise, purees, suspension of small particles, blood, etc. Because non-Newtonian fluids ate nonlinear in nature, these ate seldom amenable to analysis by classical mathematical techniques. 

A development in the 1960s was that of on-line elemental analysis of slurries using x-ray fluorescence. These have become the industry standard. Both in-stream probes and centralized analyzers are available. The latter is used in large-scale operations. The success of the analyzer depends on how representative the sample is and how accurate the caUbration standards are. Neutron activation analyzers are also available (45,51). These are especially suitable for light element analysis. On-stream analyzers are used extensively in base metal flotation plants as well as in coal plants for ash analysis. Although elemental analysis provides important data, it does not provide information on mineral composition which is most cmcial for all separation processes. Devices that can give mineral composition are under development. 

Media Si. Media are suppHed in several size grades and the grade used varies at each plant. The finer grades improve media stabiUty, but finer particles are more difficult to recover and the feed rate of these finer-grade slurries should be reduced by a factor of 0.5—0.75 to maintain magnetic recovery. A typical size analysis as used in various heavy-media separation plants treating coal (qv) is given in Table 4. 

Correlations of nucleation rates with crystallizer variables have been developed for a variety of systems. Although the correlations are empirical, a mechanistic hypothesis regarding nucleation can be helpful in selecting operating variables for inclusion in the model. Two examples are (/) the effect of slurry circulation rate on nucleation has been used to develop a correlation for nucleation rate based on the tip speed of the impeller (16) and (2) the scaleup of nucleation kinetics for sodium chloride crystalliza tion provided an analysis of the role of mixing and mixer characteristics in contact nucleation (17). Pubhshed kinetic correlations have been reviewed through about 1979 (18). In a later section on population balances, simple power-law expressions are used to correlate nucleation rate data and describe the effect of nucleation on crystal size distribution. 

Cyanuric acid is sold mainly in coarse granular form, >85% 2—0.15 mm (10 to 100 mesh). It is also available in powdered form. Typical analysis of commercial CA is CA >98.5% ammelide <1% water <0.6% pH of 1% slurry >2.8. Eor the chlorinated derivatives ... 

The control of processes involving the treatment of solids generally requires means for careful samphng and analysis of solids and slurries at various points in an operation. Unlike liquids, particulate solids are not homogeneous. The composition of individual particles will vaiy with particle size and particle density. It follows that care must be... 

A wet-process plant maldug cement from shale and hmestoue has been described by Bergstrom [Roc/c Prod., 64—71 (June 1967)]. There are separate facilities for grinding each type of stone. The ball mill operates in closed circuit with a battery of Dutch State Mines screens. Material passing the screens is 85 percent minus 200 mesh. The entire process is extensively instrumented and controlled by computer. Automatic devices sample crushed rock, slurries, and finished product for chemical analysis by X-rav fluorescence. Mill circuit feed rates and water additions are governed by conventional controllers. 

The flow of slurry within all the agitated erystallizer vessels illustrated is elearly eomplex and mixed to a greater or lesser extent at the mieroseopie level. In order to ease theoretieal analysis a new type of vessel therefore had to be invented This idealized vessel has beeome known as the eontinuous MSMPR erystallizer, after Randolph and Lawson (1988). The MSMPR is the erystal-lization analogue of the CSTR (eontinuous stirred tank reaetor) employed in idealizations of ehemieal reaetion engineering. 

A pilot-scale continuous MSMPR crystallizer of 10 litre capacity is used to crystallize potash alum from aqueous solution, supersaturation. This is being achieved using a 15-min residence time, a 100-ml slurry sample was taken and the crystals contained in this sample subjected to a size analysis. The results of this analysis are given below... 

Theoretical representation of the behaviour of a hydrocyclone requires adequate analysis of three distinct physical phenomenon taking place in these devices, viz. the understanding of fluid flow, its interactions with the dispersed solid phase and the quantification of shear induced attrition of crystals. Simplified analytical solutions to conservation of mass and momentum equations derived from the Navier-Stokes equation can be used to quantify fluid flow in the hydrocyclone. For dilute slurries, once bulk flow has been quantified in terms of spatial components of velocity, crystal motion can then be traced by balancing forces on the crystals themselves to map out their trajectories. The trajectories for different sizes can then be used to develop a separation efficiency curve, which quantifies performance of the vessel (Bloor and Ingham, 1987). In principle, population balances can be included for crystal attrition in the above description for developing a thorough mathematical model. 

Crude methyl 2-bromostearate (33 g, 0 087 mol) is dissolved in 200 mL of acetonitrile containing 0 5 mL of water, and silver(I) fluonde (50 g, 0 393 mol) is added rapidly in one portion The slurry is stirred vigorously for 20 h in an oil bath at 80 C At the end ot this time thin-layer chromatographic analysis (petroleum... 

The reaction is quenched by the addition of 1.28 g (2.94 mmol) of molybdenum pentoxidc/pyridinc/UMPA, and the yellow slurry is stirred initially at OX (30 min), then for 45 min at 25 X. The mixture is added to 1 N sodium hydroxide and extracted with diethyl ether. The ethereal solution is washed with brine, dried over Na,S04 and concentrated in vacuo to give 0.705 g (100%) of an oily, light-yellow solid. Analysis of the crude aldol adduct by 1 C NMR and analytical HPLO (Waters, Radial Pak, 8 mm x 10 cm, silica gel, ethyl acetate/hexane, 15 85) indicates only one. un-diastereomer (2X3S ) accompanied by approximately 10% of the two ethyl acetate/hexane affords fine white needles yield 0.359 g (57%) mp 155.5 156.5X (a]u -92.5 (c = 0.0294, CHCfi). 

Bubble-column slurries have much in common with two-phase bubble columns containing no solid particles, which have also been studied in great detail. Reference will be made in the following to a number of those studies considered to be of relevance with respect to the analysis and design of corresponding three-phase systems containing suspended solids. 

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