Ind. Eng. Chem. Process Des. Dev., Vol. 17,No. 1, 1978
Literature Cited ~ J, l A,, l "Eval ~ ,a~ tion , of ~l~~~ as a Matrix for Solidification of Savannah River Plant Waste-Nonradioactive and Tracer Studies", USERDA Report DP-1382, E. I. du Pont de Nemours and Co.. Savannah River Laboratory, Aiken, S.C.. 1975. Knoll, K. C., "Removal of Cesium from Redox Alkaline Supernatant Wastes by ion Exchdoge," USAEC ~ ~HW-84105, ~ ~~~~~~l ~ r Electric t c0,, ~ ~ Atomic Products Operation, Richland, Wash., 1964. Nelson. J. L.. Mercer. 6. W.. "Ion Exchanae Seoaration of Cesium from Alkaline Waste Supernatant Solutions," USAEE Report HW-76449, General Electric Co., Hanford Atomic Products Operation, Richland, Wash., 1963. Stone, J. A., "Evaluation of Concrete as a Matrix for Solidification of Savannah River Plant Waste," USERDA Report DP-1448. E. I. du Pont de Nemours and Co., Savannah River Laboratory, Aiken, S.C.. 1977. Van Slyke, W. J.. "Recovery of Ammonium Carbonate from Cesium Ion EXchange Eluates," USAEC Report HW-80814. Hanford Atomic Products Op~
71
eration, Richland, Wash., 1964. Wallace, R. M., Hull. H. L., Bradley, R. F., "Solid Forms for Savannah River Plant co., High-Level Savannah Waste," RiverUSAEC Laboratory, Report Aiken, DP-1335, s,c,,E. 1973, I. du Pont de Nemours and Wiley, J. R., "A Study of Methods for Removing Strontium, Plutonium, and Ruthenium from Savannah River Plant Waste Supernate." USERDA Report and b., Savannah River Laboratory, Aiken. ~ DP-1408, f E. 1.~du Pontde ~ Nemours d S.C., 1976.
Receiued for reuiew February 7,1977 Accepted September 12, 1977 The information contained in this article was developed during the course of work under Contract No. AT(07-21-1 with the U.S. Energy Research and Development Administration.
Free Energy Parameters for Reverse Osmosis Separations of Some Inorganic Ions and Ion Pairs in Aqueous Solutions. 2' Ramamurti Rangarajan, Takeshi Matsuura, E. C. Goodhue, and S. Sourirajan' Division of Chemistry, National Research Council of Canada, Ottawa, Canada, K I A OR9
Reverse osmosis separations of several inorganic salts in aqueous solutions involving monovalent and polyvalent ions have been studied using porous cellulose acetate membranes. From these studies, free energy parameters for the ions Fe2+, AI3+, Ce3+, La3+, Th4+, OH-, HCOO-, HC03-, HS04-, HPhthalate-, &Os2-, S032-, Cr042-, Cr207'-, C032-, Fe(CN)e3-, and Fe(CN)e4- and for the ion pairs KFe(CN)e2- and KFe(CN)e3have been determined. These parameters offer a means of predicting reverse osmosis separations of inorganic salts in aqueous solutions involving the above ions and/or ion pairs, using porous cellulose acetate membranes from data on membrane specifications only, given in terms of a single reference solute such as sodium chloride. The predictive capability of the parameters generated is illustrated.
Introduction The concept of free energy parameters governing reverse osmosis separations of different (ionic or nonionic) solutes has been discussed in earlier papers (Matsuura et al., 1975, 1976a,b; Dickson et al., 1975; Rangarajan et al., 1976) for aqueous feed solution systems where water is preferentially sorbed at the membrane-solution interface. It may be recalled that free energy parameters are represented by the dimensionless symbol -AAG/RT for each ionized or nonionized solute species, where AAG is the energy needed to bring the solute from the bulk solution phase to the membrane-solution interface, and R and T are gas constant and absolute temperature, respectively. Data on -AAG/RT are functions of the chemical nature of the solute species and that of the membrane surface and are independent of the porous structure of the membrane surface. It has been shown (Matsuura et al., l975,1976a,b; Rangarajan et al., 1976) that these data can be built into reverse osmosis transport equations (Sourirajan, 1970) leading to a method of predicting reverse osmosis separations of different solutes in aqueous solutions obtainable with membranes of different surface porosities; this prediction technique requires only data on membrane specifications given in terms of pure water permeability constant A and solute transport parameter DAMIKSfor a reference solute such as sodium chloride, in addition to data on operating conditions for the reverse osmosis process under consideration. Thus data on -AAG/RT for different solute species are of practical imPart 1 of this paper is by Rangarajan et al. (1976).
portance in reverse osmosis process design. This paper extends the earlier work, Part 1 (Rangarajan et al., 1976), concerned with the generation of data on -AAG/RT for different inorganic ions and ion pairs in aqueous solutions for reverse osmosis separations using porous cellulose acetate membranes. Similar data on -AAG/RT are presented in this paper for 5 cations, (Fe2+,A13+,Ce3+,La3+, and Th4+),13 anions (OH-, HCOO-, HC03-, HS04-, HPhthalate-, &Os2-, s0s2-, C Z O ~ ~Cr042-, -, C r ~ 0 7 ~C032-, -, F ~ ( C N ) G ~and -, F~(CN)G~-) ~- KF~(CN)G~-). and 2 ion pairs ( K F ~ ( C N ) Gand
Experimental Section Eighteen inorganic solutes listed in Table I (along with some relevant physicochemical data) a t the concentrations specified therein were used in this work in single-solute aqueous solutions. The apparatus and experimental procedure used were the same as those reported earlier (Rangarajan et al., 1976). Batch 316 (10/30)-type cellulose acetate membranes (Pageau and Sourirajan, 1972) were used a t the operating pressures of 250 or lo00 psig. Membranes 1to 6 and 7 to 12 (Table 11)were subjected to pure water pressures of 300 and 1700 psig, respectively, for 6 h prior to use in reverse osmosis experiments. The initial specifications (Sourirajan, 1970) of membranes used are given in Table I1 in terms of pure water permeability constant A (in g-mol of H20/cm2s atm) and solute transport parameter (DAMIKS,treated as a single quantity (Sourirajan, 1970), in cm/s) for sodium chloride a t different operating pressures. The surface porous structure of the membranes used
0019-7882/78/1117-0071$01.00/0 0 1978 American Chemical Society
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Ind. Eng. Chem. Process Des. Dev., Vol. 17, No. 1, 1978
Table I. List of Solutes Used with Relevant Physicochemical Data
Solute no. 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69
Solute formula FeC12* Al(N03)3 Ce(N03)3* Lac13 Th(N03)4 NaOH
DAB X lo5, (crnZ/s)a 1.255 1.187 1.249 1.293c 0.665 1.06 1.391 1.254 1.358 1.625 1.271 1.224d 0.648 1.555 1.227e 1.161 1.493 1.46gC
Dissociation constant,
Hydrolysis constant,f
K, 0.436 NA NA NA 0.213 NA
KH
*
Solute molality in feed, m
ffH
CUD
atm,
atm,
%
%
Method of analysis
K, = 5.0 x 10-9 K. = 7.14 X
5.4 x 10-3 0.1 99.3 AA 2.96 X 0.05 AA NA 6.71 x 10-3 SPg PT NA 8 . 3 2 ~10-3 2.13 x 10-4 EDTAh NA 8.69 x 10-4 99.8 NA 1.05 x 10-3 AA 9.03 x 10-3 0.008 AA 3.61 x 10-3 0.3 AA 1.81 x 10-3 0.002 AA 2.45 x 10-3 TOC 0.005 99.5 AA 1-25 x 10-3 4.04 x 10-3 0.7 99.7 AA AA 1.76 x 10-3 0.03 1.34 x 10-3 0.5 AA 1.02 x 10-5 AA 8.30 x 10-4 39.0 98.8 AA 3.98 x 10-2 NA 1.38X 99.99 AA 2.63 x 10-3 88.6 AA 71 K4Fe(CN)6* 5.01 x 10-3 NA 0.13 75.9 Calculated unless otherwise stated. b Sillen and Martell (1964). c Robinson and Stokes (1959b). Matejec and Meyer (19651, calculated from equivalent conductance data. e Extrapolated to zero concentration with data from 6holm (1940). f Margolis (1966). g Sandell (1950). Van Nieuwenburg and Van Ligten (1963). NA = not available.
Table 11. Specifications of Cellulose Acetate Membranes Used in Reverse Osmosis Experiments
Film no. 1
2 3 4 5 6 7 8 9 10 11
12
Operating pressure, Psig
Initial or final dataa
A X lo6, g-mol H2O/ cm2 s atm
( D A M I K x~ )105 for NaC1, cm/s
250 250 250 250 250 250 250 250 250 250 250 250 lo00 lo00 lo00 lo00 1000 lo00 lo00 1000 1000 lo00 lo00 1000
Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final Initial Final
11.85 11.51 2.13 2.13 3.63 3.78 6.50 6.82 8.77 8.49 5.53 5.65 1.29 0.86 2.19 1.58 2.85 1.93 2.68 1.89 3.08 2.00 4.07 2.42
484.4 856.6 2.02 3.3 19.7 18.8 105.9 143.0 285.1 416.9 66.9 75.4 5.17 8.61 21.2 22.9 67.6 72.5 45.3 42.6 68.9 52.6 344.8 134.7
-1n
C*NaCI
6.70 6.13 12.18 11.69 9.90 9.95 8.22 7.92 7.23 6.85 8.68 8.56 11.24 10.73 9.83 9.75 8.67 8.60 9.07 9.13 8.65 8.92 7.04 7.98
NaCl sepn, % 25.3 16.7 95.4 91.9 74.7 77.7 46.3 42.1 27.5 24.7 54.9 53.0 93.1 91.6 84.5 83.4 61.0 59.1 69.7 67.7 60.5 61.9 30.2 31.9
a Initial = prior to all reverse osmosis experiments. Final = on completion of all reverse osmosis experiments. Feed: 5000 ppm of NaCl-HZO.
changed significantly as a result of contact with different salt solutions. The causes of such change and their implications to reverse osmosis process design and development need a separate investigation. Since the data on free energy parameters themselves are independent of the porous structure of the membrane surface, the change in surface pore structure was not a severe problem in this experimental work. In order to generate the above data, it was only necessary to redeter-
mine the specifications of the membranes a t frequent intervals. The specifications closest to each run were used for prediction calculations on membrane performance. Data on membrane specifications were obtained using aqueous sodium chloride feed solutions containing 5000 ppm of NaCl. The data on final specifications given in Table I1 are those obtained at the end of the project. All experiments were of the short run type, and they were
Ind. Eng. Chem. Process Des. Dev., Vol. 17, No. 1, 1978
carried out at the laboratory temperature (23-28 "C) using a feed flow rate of 400 f 10 cm31min. In each experiment, the fraction solute separation f , defined as
f=
(solute molality in feed) - (solute molality in product) (solute molality in feed) (1)
and product rate (PR) and pure water permeation rate (PWP) in g/h per given area of film surface (13.2 cm2 in this work) were determined under the specified experimental conditions. In all experiments, the terms "product" and "product rate" refer to membrane permeated solutions, and the reported permeation rates are those corrected to 25 "C using the relative viscosity and density for pure water. The concentrations of sodium chloride in feed and product solutions were determined using a conductivity bridge; the concentrations of the other solutes were determined by one of the following methods as indicated in Table I: atomic absorption technique (AA), spectrophotometry (SP) in the visible region, EDTA titrations, total organic carbon analysis (TOC), and potentiometric titration (PT) for chloride. Since some of the salts used are oxidizable, their solutions were prepared in distilled water which was boiled to expel dissolved oxygen (and also carbon dioxide), and cooled to room temperature in a nitrogen atmosphere. During the reverse osmosis experiment, nitrogen was bubbled through the stock solution. The solutes involved in experiments conducted under nitrogen atmosphere are indicated with an asterisk (*) in Table I. In the case of salts which are either hydrolyzable a t low concentrations or which tend to form ion pairs at high concentrations, the feed concentration was so chosen to reduce the above effects to the minimum (see discussion below). The values of -AAGIRT were obtained in most cases using reverse osmosis data at 250 psig; the same values were used for predicting membrane performance a t 1000 psig. All data presented in this paper are for 25 "C.
Results and Discussion Feed Concentrations Used in Reverse Osmosis Experiments. All solutes listed in Table I dissociate into ions in aqueous solutions. In addition, some of the solutes hydrolyze or form ion pairs a t very low or relatively high solution concentrations, respectively. The extent of hydrolysis tends to increase with decrease in solute molality (m), whereas increase in m tends to favor ion pair formation. From literature data on hydrolysis constants KH (= K, or Kb) (Margolis, 1966), and/or dissociation constants K, (Sillen and Martell, 1964; Yatsimirskii and Vasil'ev, 1960), together with corresponding data on activity coefficients yi (Robinson and Stokes, 1959a; Parsons, 1959; Bromley, 1973), one can calculate the degree of hydrolysis (CUH)or degree of dissociation (LID) using the following relations
and
Table 111. Data on Free Energy Parameters for Some Ions and Ion Pairs at 25 "C Free energy parameter, -AAGIRT
Ion Cations Fez+
9.33 10.41 10.62 12.89 12.42
~ 1 3 +
Ce3+ La3+ Th4+ Anions OHHCOOHC03HS04HP hthalateSZO~~S032c~04~Cr042Cr2072-
-6.18 -4.78 -5.32 -6.21 -4.63 -14.03 -13.12 -14.06 -13.69 -11.16 -13.22 -20.87 -26.83
co32-
Fe(CN)e3Fe(CN)64Ion pairs KFe(CN)e2KFe(CN)63-
-2.53 -17.18
formation was negligible (
