Contacting Equipment and Design Calculations

The processing equipment used to conduct soivent extraction of metals is the same as that used in conventional liquid-liquid extraction. The most common choices have been mixer-sutlers, columns with agitated internals, and static mixers. Some advantages and disadvantages of several classes of equipment are summarized in Table 8.5-1. Many of the practical aspects of equipmem sdectkm are discussed by Pratt and Hanson and by Ritcey and Ashbrook.  

An interesting comparative study of six different contactors is summarized in Fig. 8.5-1. An alkaline feed stream containing copper, nickel, zinc, and ammonia was contacted with a Kelex 100 solution in each of the pilot-scale contactors. At a pH above 7 the reaction kinetics of Kelex are probably fast, but it loses some of its intrinsic selectivity for copper because of the tendency of nickel and zinc to tra extracted. Although the various contactors could he made to operate at comparable levels with respect to specific throughput and copper-extraction efficiency, they exhibited quite different selectivities. Detailed liquid-liquid reactor models would help to identify and predict such variations in efficiency and selectivity. 

With both staged equipntent and differential contactors, availability of adequate ph -e piilibrium models and rate expressions would allow application of existing correlations and simulation algorithms. For example, knowledge of metal-extraction kinetics in terms of interfacial species concentrations could be combing with correlations of film mass transfer coefficients in a particular type of equipment to obtain the interfacial flux as a function of bulk concentrations. Correlations or separate measurements of interficial area and an estimate of dispersion characteristics would allow calculation of extraction performance as a 

FIGURE 8..5-1 Conqjarisons of the operating char teristics of several contacting devices for the separation of copper from nickel and zinc by extraction from ammonia (pH 8) solution with Kelex. (a) Comparison of specific throughput at flooding, (h) Comparison of copper extraction efficiency, (c) Comparison of Cu-Zn selectivity, (d) Comparison of Cu-Ni selectivity. From Ref. 9, with petmission. 

Aqueous Copper (g/L) Organic Copper (g/L) Aqueous H2S04 (g/L) Free Reagent (M) 

Data Made) Data Model Data Model Model 

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The hlters must be designed and fastened to allow an easy removal to change the hlter and to keep a perfect peripheral airtightness. They must be provided with differential manometer to check them, (option equipped with maximum contact point). An obturable opening (+/- 100 mm) must be placed before the fan section to inject the DOP. The number of terminal hlters must be calculated to guarantee the same air velocity out of the... 

Basis for Plant Design. The composition of municipal refuse is assumed as shown in Table III. The municipal refuse has the lower calorific value of ca. 1,500 Kcal/Kg. Plant size of 600 T/D is assumed. The capital investment costs, utilities, etc. were calculated using contacts with equipment vendors. Cost for repairs are assumed to be two percent of the plant construction cost per year. Unit costs of utilities and unit prices of recovered energy and material are assumed, based on the actual prices in 1979. Ash and other residues disposal cost is assumed to be 2,450 Yen/T, taking note of the representative cost data of large cities in Japan, The grant available to a municipality is assumed to pay up to fifty percent of the capital investment. The remaining investment cost must be amortized in fifteen years with the interest rate of six percent. 

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