Equilibrium diagrams, extraction

The present description pertaining to copper refers to solvent extraction of copper at the Bluebird Mine, Miami. When the plant became operational in the first quarter of 1968 it used L1X 64, but L1X 64N was introduced in to its operation from late 1968. The ore consists of the oxidized minerals, chrysocolla and lesser amounts of azurite and malachite. A heap leaching process is adopted for this copper resource. Heap-leached copper solution is subjected to solvent extraction operation, the extractant being a solution of 7-8% L1X 64N incorporated in kerosene diluent. The extraction process flowsheet is shown in Figure 5.20. The extraction equilibrium diagram portrayed in Figure 5.21 (A) shows the condi-... 

The equilibrium diagram in Fig. 7.2 is considerably different from the triangular diagram in Fig. 7.1. It is the same extraction liquid-liquid equilibrium, with water the feed-raffinate, benzene the solvent-extract, and acetic acid the solute. The complete solution has been performed in Microsoft Excel, but other commercial software spreadsheets may also be used. Please notice first, as shown in the boxed area in columns A and B, that the equilibrium curve data have been entered. Next we will see how such a curve is made. 

FIGURE 2 Triangular equilibrium diagram showing extraction of feed F by solvent S to give extract E and raffinate R. Dashed lines are tie-lines. 

Using the phase equilibrium diagram in Figure 11.2, determine the compositions and flow rates of the extract and raffinate. 

Another application of the shortcut column section method is for solving liquid-liquid extraction problems. The fundamentals of extraction were discussed in Chapter 11, and graphical solution methods were described based on ternary liquid-liquid equilibrium diagrams. These methods are limited to three-component extraction systems. 

For liquid-liquid extraction systems, the approach is the same to analyze a single equilibrium-limited contact. A mass balance (operating) line is plotted on a phase equilibrium diagram. In this case, the phase equilibrium diagram is a ternary diagram. 

Extraction, liquid-liquid, 8,10,13 equilibrium diagrams, 103 equipment, 76-84 extract reflux, 415 group method, 475-480 infinite stages, 415 McCabe-Thiele method, 315-318... 

The first phase-equilibrium diagrams discussed are for two-component liquid-vapor systems. Next, three-component diagrams used in extraction, absorption, leaching, and ion exchange are developed. Finally, enthalpy-composition diagrams, which include energy effects, are constructed. 

Step 3. Apply the lever rule to the equilateral triangular phase equilibrium diagram. Letting x, be the mass fraction of species i in the raffinate stream j and y, the mass fraction of species / in extract stream /. 

Countercurrent extraction calculations are readily made on equilateral-triangle phase equilibrium diagrams, no new principles being involved. In Fig. 11.5, we see the solution to Case 1 of Fig. 11.3h. 

The calculation method proceeds as follows. 1) Plot the locations of S and F on the triangular equilibrium diagram 2) Draw a straight line between S and F, and use the lever-arm rule or Eqs. tl3-31i to find the location of the mixed stream M. Now we know that stream M settles into two phases in equilibrium with each other. Therefore, 3) construct a tie line through point M to find the compositions of the extract and raffinate streams. 4) Find the ratio E/R using mass balances. We will follow this method to solve the following exanple. 

The external mass balance and the equilibrium diagram in Figure 13-21B can be used to determine the effect of variation in the feed or solvent concentrations, the raffinate concentration, or the ratio F/S on the resulting separation. For example, if the amount of solvent is increased, the ratio of F/S will decrease. The mixing point M will move toward point S, and the resulting extract will contain less solute. 

A5. If the extract and raffinate phases are totally immiscible, extraction problems can still be solved using triangular diagrams. Explain how and describe what the equilibrium diagram will look like. 

Types of Problems. The principal quantities in the extraction process are F, Xp, Ey Xpy R, Xr, Sy and Xs Of these, F, Xf, and Xs are ordinarily fixed by the process. Only one of the remaining quantities can be arbitrarily fixed, whereupon the remainder are no longer under control but are determined by the characteristics of the equilibrium diagram. 

If the equilibrium data are given or if in the simplest case we even have a constant distribution ratio, we can construct the extract (content of solute in extract phase) versus raffinate (content of solute in raffinate) equilibrium diagram. 

FIGURE 3.3 Extract from the iron carbon equilibrium diagram, including the temperature ranges for certain heat treatment processes... 

By material balance, the concentration of solute in the extract will be 14,1 lb solute per 1,000 lb cumene. We now have established the condition at the top of the extractor that can be located on the equilibrium diagram. The operating line will join the compositions at the top of the tower with the compositions at the bottom of the tower on this diagram,... 

When both components of a binary gas or vapor mixture are separately adsorbed to roughly the same extent, the amount of either one adsorbed from the mixture will be affected by the presence of the other. Since such systems are composed of three components when the adsorbent is included, the equilibrium data are conveniently shown in the maimer used for ternary liquid equilibria in Chap. 10. For this purpose it is convenient to consider the solid adsorbent as being analogous to liquid solvent in extraction operations. However, adsorption is greatly influenced by both temperature and pressure, unlike liquid solubility, which is scarcely affected by pressure under ordinary circumstances. Equilibrium diagrams are consequently best plotted at constant temperature and constant total pressure, and they are therefore simultaneously isotherms and isobars. 

Equation (13,8) permits calculation of the weight of , and Eq. (13.11) that of / [. Modification to allow for the presence of B in the liquid withdrawn, necessitating an equilibrium diagram of the type shown in Fig. 13.24a, is readily made by analogy with the corresponding problem in liquid extraction. 

Figure 6.4.8. (a) Mixer - a well-mixed vessel with one phase dispersed in the other, (b) Settler-the two phases have settled into two separate layers, (c) Equilibrium diagram, operating line and stage efficiencies in solvent extraction, (d) Well-mixed continuous mixer-settler. 

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