of 30% hydrogen peroxide were added over a period of 1/2 hr. After the mixture had been held for about 1/4-1/2 hr at 6OoC, i t was a straw color. The product solution contained 41.5% solids and was isolated in a yield of 9075 grams. It was used directly in the spray-drying experiments. SPRAYDRYING OF “THIRD-PASS~’ PRODUCT SOLUTION. The product solution from the bleaching step was subjected to standard spray-drier conditions at 375°C with forced hot air. The material was isolated as a finely divided, low-density powder slightly off-white in color. It has the following composition : Component
Wt
Sodium nitrilotriacetate. HzO Sodium nitrilodiacetate HzO Sodium salt of glycine Sodium glycolate Sodium formate Sodium carbonate Sodium hydroxide Sodium cyanide
-
91 0 0 2 1 0 4 Ca. 17
% 6 7 2 5 0 5ppm
Stage I I (Single-Pass Operation). The product solution from the first stage was cooled to 4OoC, and 656 grams (13.4 moles) of sodium cyanide were dissolved in 1100 grams of Later and 1140 grams (14.1 moles) of 37y0 formalin solution mixed with 1000 grams of water added over 1 hr. The temperature was maintained a t 45°C during this addition period. The charge was next heated as rapidly as possible to 100-110°C and held a t this temperature for about 1 hr. Ammonia \vas evolved vigorously during the first half of this hold period. Finally, the light-brown product solution was cooled to 6OoC and treated over a period of 1/4 hr with 41.5 grams (0.37 mole) of 30% hydrogen peroxide. After this mixture had been held a n additional 1/2 hr a t 6OoC, it was straw-colored in appearance.
The product solution weighed 9900 grams, contained 41.5% solids, and had the following composition: Component
Sodium nitrilotriacetate. HzO Sodium nitrilodiacetate. HzO Sodium salt of glycine Sodium glycolate Sodium formate Sodium carbonate Sodium hydroxide Sodium cyanide
Wt
%
87.7 1.7 0 4.3 1.8 0.5 4.0 Ca. 0 . 5 ppm
Acknowledgment
The author expresses his appreciation for the assistance received from I. J. Barna, R.T. Alumkal, J. A. Crane, 0. B. Mathre, IT. J. Sloan, E. L. Mongan, E. F. Chollis, and C. P. Downs, Jr., in carrying out this investigation. Literature Cited
Berdnig, C., Guenthert, P., Koehler, W., Schulz, G. (to Badische Aniline and Soda-Fabrik Aktiengesellschaft ), U.S. Patent 3,607,930 (July 8, 1968). British Patent 1,179,959 (to Standard Oil) (June 22, 1967a). British Patent 1,181,615 (to Monsanto Co.) (-March 20, 1967b). British Patent 1,184,608 (to Hooker Chemical Corp.) (October 20, 1967~). Gaunt, J. A. (to Geigy Chemical Corp.), U.S. Patent 3,415,878 (December 10, 1968). Sibert, J. W. (to Ethyl Corp.), U.S. Patent 3,419,609 (December 31, 1968). Singer, J. J., Singer, J. P. (to Hamsphire Chemical Corp.), U.S. Patent 3,183,262 (hlay 11, 1965). Singer, J. J., Weisberg, h1. (to Hampshire Chemical Corp.), US.Patent 2,855,428 (October 7, 1958). Wollensack, J. C. (to Ethyl Corp.), U.S.Patent 3,337,607 (August 22, 1967). RECEIVED for review June 12, 1972 ACCEPTEDAugust 23, 1972
Removal of Boron and Calcium from Magnesium Chloride Brines by Solvent Extraction Robert R. Grinstead Western Division Research Laboratories, Dow Chemical U S A , Walnut Creek, Calif. 94698
Boron and calcium can b e removed from strong (>30%) MgCI2 brines b y extraction with 4-f-butylcatechol (TBC) dissolved in kerosine containing a higher alcohol. Boron i s extracted as a catechol-borate anion, for which calcium serves as the counter ion. The extracted calcium is solvated by the excess TBC. In the absence of calcium, boron extraction is poor but can b e improved by addition of a kerosine-soluble amine cation. In either case, extraction is pH dependent, and removal of these species from the organic phase is readily accomplished with dilute mineral acid. In the absence of boron, calcium can b e extracted alone as solvated CaClz and removed b y contact with water alone. Selectivities of the solvent for calcium over magnesium close to 1000 are observed.
I n the recovery of magnesium compounds from the sea and the production of magnesium metal from them, certain impurities are quite critical, The successful operation of the electrolytic metal reduction cells depends on the rejection of most of these impurities, two of the principal ones being calcium and boron (Schambra, 1945). Existing practice has been to reject the boron by use of excess lime during the 454
Ind. Eng. Chem. Prod. Res. Develop., Vol. 1 1 , No. 4, 1972
initial precipitation of magnesium hydroxide from sea water. This causes the boron to remain in solution and to be discarded in the filtrate. Calcium is separated subsequently by precipitation with sulfate. The current investigation was undertaken to determine whether the methods of solvent extraction might be used t o improve the purification process. The approach was based
Table 1. Composition of MgClz Brines
MgC12, wt SP gr pH B, g/l. Ca, g/l. Xa, g/l.
%
IV
V
35 8 1 342 5 6 0 006 1 08 4 1
34 6 1 338 5 9 0 012 0 66 4 3
--
1
(3
on the rather unique tendency of boron to form complexes with polyhydroxy organic compounds. The chemistry of borate-polyol complexes has been studied a t great length, and in addition to reviews (Boesecken, 1949) of the older literature, new work continues to appear (-\ntikainen, 1959b; Dale, 1961; Roy et al., 1957). The reaction of boric acid with polyols is given by the following equations: H3BOj
+
PR(OH)2
-
+
2R(OH)?
+
Mf
P I
W
2
0
2 3.6
4.0
E 44
48
5.2
DH
Figure 1. Effect of pH on calcium extraction Aqueous: 36% MgCI2, containing 4.0 gram Co/l., 0.21 gram B/l. Organic: 0.20M TBC, A70 2-octanol in kerosine Temp: 22'C, phase ratio ( 0 : A ) = 6:l Water and acid strips a t O:A = 1 :1 0 Total Ca extracted A Ca in " 0 3 strip C Total M g extracted V Total M g in HNOa strip
With 1,2 or a-configuration of t'he diol, Reaction 1 is usually observed, whereas with 1,3 or p-diols, Reaction 2 predominates (Dale, 1961). If sufficiently hydrophobic substit'uents \yere present in a n a or p diol molecule, the resulting borate-diol complex should be extract'able into an immiscible solvent. Also, in the case of Reaction 1, to preserve electroneutrality, coestraction of a cation will be required. The proposed reaction for extraction is HJBO,
I
-
where the barred species are in the organic phase. Because of the desire to remore calcium along with boron, only compounds whose behavior conformed to Reaction 1 were studied. Industrial application of this general idea has been reported, involving extraction of boron from alkaline brines (Chem. Eng. Xews, 1963, 1964; Garrett, 1961; Garrett et al., 1963; Havighorst, 1963). I n this case, Reaction 1 is also apparently utilized, and sodium and potassium, which are the only significant cations present, are coextracted. Experimental
Materials. The magnesium chloride solutions were usually production brines of the composition shown in Table I. I n some cases, solutions \vere prepared from reagent materials. Boric acid and calcium chloride were added where higher concentrations of these species were desired. Kerosine was a high-boiling aliphatic hydrocarbon obtained from the Standard Oil Co. It was stated to contain about 1% or less aromatic hydrocarbons and to have a n aniline point of 180. Shell 42 \vas a high-boiling alkylated aromatic hydrocarbon solvent obtained from the Shell Oil Co. and stated to contain 667, aromatics, 25Y0 naphthenes,
and 9% paraffins. (The manufacturer has discontinued this product but has informed us that a nearly identical material is available as C'yclosol 73.) Where alcohol concentrations in these solvents are given, they refer to volume concentrations. The phenolic compounds used k s extractants were all commercial materials and were usually used as received. The 4-t-butyl catechol was usually recrystallized from a mixture of petroleum ether and toluene. The tertiary amine Xlamine 336 is a product of General Mills and is essentially tri-(n-octyl) amine. Solutions of the hydrochlorides were prepared by contacting amine solutions with excess aqueous 1S HC1. Analyses. Boron was determined by the carminic acid procedure ( C a l h o a t and Wolszon, 1959 ; Hatcher and Wilcos, 1950), with the modification that brine samples were usually diluted 1: 1 with water to prevent the precipitation of magnesium sulfate in the mixture. A11 fractions of a n experiment were analyzed for boron to obtain material balances as a check on the method. Precision was believed to be about +5%. Calcium and magnesium were determined in the brine samples by Versene titration. Subsequent calcium determinations were done radiometrically with Ca4j tracer and a Packard Tri-Carb liquid scintillation count'er. These were counted to +2% standard deviation. Slagnesium analyses were done by neutron activation and generally determined to about 1 0 . 0 1 gram Ng/liter, Sodium Tvas determined by flame photometry. p H measurements Fvere made with a standard L&K p H meter directly on the brine systems after standardization with appropriate buffers. All p H values reported here are equilibrium values. Procedure. Where control of p H during a n extraction was desired, the p H elecbrodes were inserted directly in the beaker being stirred with a magnetic stirrer. Experiments a t higher temperatures were carried out with the beaker surrounded by a circulating water bath, maintained to within 1°C of the desired temperature. At the higher pH values it was necessary to provide a nitrogen atmosphere over the solutions to prevent air oxidation of the catechol. I n experiments where boron was extracted, acid was produced arid a drop in pH occurred. To maintain the desired p H , 50% KaOH or solid l I g ( O H ) * was added during the extraction. Phases Ind. Eng. Chem. Prod. Res. Develop., Vel. 1 1 , No. 4, 1972
455
1
;;coo,
I
I
I
Table 111. Effect of Solvents on Boron Extraction b y TBC-Amine Systems
Organic phase: 0.20111 TBC, 0.2031 hlamine 336 hydrochloride 111 designated solvent Ique3us phase: 36y0 JIgCl,, T = 22°C) pH = 5.0, phase ratio (O:-I) = 1:2 Solvent
AQUEOUS -BORON 1 , M G ' L
Figure 2. Effect of amine hydrochlorides on boron extraction Organic: 0.20M TBC in Shell 4 2 Aqueous: 36% MgC12 Temp: 6OoC, pH = 5.0 A 0.20M Alamine 336 hydrochloride in organic 0 No amine hydrochloride
Table 11. Effect of Amine Salt on Cation Coextraction b y TBC
-1queous phase: Brine IV, pH 4.5, T = 22OC, phase ratio(0:X) = 1:3 Organic phase: 0.2031 TRC in 4% 2-octanol in kerosine, plus salt as indicated B
Original brine S o amine salt in oiganic Raffinate Crganic 0.1OJ1 Alamine 336 HC1 Raffiiiate Organic 0 2031 .Ilamine 336 HCl Raffinate Organic
Concentrations, g/l. Ca Mg
No
0 160
0 70
121
1 73
0 004 0 54
0 40 0 92
121 0 22
2 24 0 21
0 008 0 39
0 67 0 084
121 1 76 0 074 0 005
0 70 01
121 1 81 0 027 0 017
0 011 0 51
