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Home , Calcium sulfate

Patented July 13, 1954 2,683,695

. STATES TENT OFFICE 2,683,695 REGENERATION 0F CATION vEXCHANGERS CONTAINING ALKALENE EARTH METALS Russell N. Dwyer, Needham, and Verity C. Smith, West Roxbury, Mass, assignors to Barnstead Still and Sterilizer 00., Jamaica Plain, Mass., v" a corporation of Massachusetts No Drawing. Application June 27, 1952, Serial No. 296,062 6 Claims. ( Cl. 260-22) 1 2 This invention relates to -exchange and in makes use of a pre-treatment of the exhausted particular to the regeneration of cation-exchange exchanger with sodium chloride solution to con materials to the hydrogen form from the alkaline vert the exchanger from the earth metal form. A primary object of this in form to the sodium form. The exchanger is then vention is to utilize a regenerant chemical which in regenerated with with less danger of is chie?y sulfuric acid, without causing the pre the formation of insoluble . A disadvan— cipitation of insoluble alkaline earth sulfates tage of this technique is that it is a two-step proc within the bed of cation exchange material. ss that requires additional regenerant chemical Ion-exchange processes are frequently used to as well as additional regenerant water. It has treat aqueous solutions that contain undesirably 10 also been found that it is diiiicult to remove all high concentrations of alkaline earth metal salts alkaline earth metals by this technique and that to remove the alkaline earth metal cations and insoluble sulfates do tend to form in the bed replace them with other cations, often hydrogen. after prolonged cyclical operation. The mechanism of this process is the exchange of The present invention provides a method of re cations in the ion-exchange material for cations generating a cation exchanger in the alkaline in the water being treated. For the removal of earth metal form by means of regenerating chem alkali earth metals and the replacement of them icals consisting chie?y of sulfuric acid directly in in solution with hydrogen , an ion-exchange a one-step process while greatly reducing the material in the hydrogen form, that is, a solid formation of insoluble sulfates. It has been water-insoluble cation exchange material having 20 found that sulfuric acid may be used in ordinary ?xed negative charges and positive mobile hydro regenerating strength to regenerate a cation ex gen ions associated with the negative charges, changer that has been exhausted in treating would be used. On contacting such a material aqueous solutions containing alkaline earth met with water containing alkaline earth metal ions, als such as , if a small amount of nitric hydrogen ions from the ion-exchange material 25 acid is ?rst mixed with the sulfuric. As little as are replaced by alkaline earth metal ions until the 5% nitric acid (based on total acids present in ion-exchange capacity of the ion-exchange ma the regenerant) in a regenerating solution con terial is substantially exhausted. In order to taining up to about 15 % total acid has been found treat more water with this material and continue effective to regenerate a cation exchanger con the process, it is necessary to regenerate the ion~ taining substantial calcium, without the forma exchanger by treating it with an acid to replace tion of insoluble calcium either in the bed the alkaline earth metal cations on the ion-ex or in the effluent regenerant. Even after pro change material wih hydrogen ions from the acid. longed cyclical operation, there is no apparent It is obviously desirable from an economic point clogging of the bed nor serious loss of its ion of View to use sulfuric acid as the source of hy .1 exchange capacity. drogen ions, but it has been found that in contact The process of this invention is applicable to ing a cation-exchange material in the alkaline the regeneration of all known cation-exchange earth metal form with sulfuric acid, there results materials commonly used industrially for hydro the formation of insoluble alkaline earth metal gen exchange. Included are the sulfonated humic sulfate which coats the granular particles of 40 compounds for instance, such as those described the ion-exchange material, thus impairing its ion in U. S. Patent Numbers 2,191,063; 2,205,635; exchange capacity, and which also clogs the beds 2,1Q1,060; 2,206,007; the condensation polymers of the ionwexchanger to render the passage of of phenols, polyhydric phenols and‘ sulfonated fluids through them increasingly dimcult. phenols with formaldehyde or other aldehydes, A number of schemes have been proposed to 45 such as those described in U. S. Patent Numbers make it possible to use sulfuric acid to regenerate 2,443,029; 2,204,539; 2,191,853; 2,104,501; 2,230, cation~exchanger in the alkaline earth metal 6‘41; 2,361,754; 2,228,159; 2,228,160; and the sul form. One proposal is to use a very dilute sulfuric fonated copolymers of monovinyl aryl compounds acid in the hope that insoluble sulfate salts will and polyvinyl aryl compounds, for instance, a not precipitate. it has been found, however, that 50 sulionated oopolymer of styrene and divinyl ben even with very dilute solutions of sulfuric acid as zene and similar compounds described in U. S. the regenerant chemical, insoluble sulfates do Patent Numbers 2,366,007 and 2,500,149. form in the bed on prolonged cyclical operation. Preferred utilization of the present invention is Another scheme proposed to regenerate an ion in the treatment of aqueous solutions containing exchanger in the alkaline earth metal form, 55 greater than about 300 parts per million (p. p. m.) 2,683,695 3 4 of calcium (expressed as equivalent calcium car The procedure in each example was ?rst to bonate). At lower concentrations, sulfuric acid form a bed 3 inches in diameter and 20 inches in alone, without the addition of nitric acid, may height of a sulfonated polystyrene type cation be used effectively in ordinary regenerating exchange resin, which was ?rst regenerated with strength (about 5—15% by weight), and the im the regenerant solution to be tested by ?owing provement resulting by adding nitric acid is only the regenerant solution downward through the slight. When greater amounts of calcium are bed. The bed was then drained of residual acid, present in the water being treated, however, a re and the solution to be treated was ?owed upward generant solution containing only sulfuric acid through the bed until the speci?c resistivity of results in appreciable precipita~ 10 the e?iuent after subsequent acid removal by con tion. Under such conditions the addition of nitric ventional anion exchange dropped to 1990 ohm acid to the regenerant in accordance with this cm., at which point the bed was drained and the invention is advantageous. regenerant solution was again ?owed downward The amount of nitric acid that should be in therethrough. In each regeneration about 300 cluded in the regenerant depends generally on 15 per cent of the theoretical amount of acid re "H the concentration of calcium in the solution being quired for complete regeneration was used to treated, and on the ratio of calcium to other assure complete regeneration. In several of the cations in the solution. At a calcium concentra examples cyclical operation was performed by tion of about 300 parts per million (p. p. in.) (ex repeatedly passing the solution to be treated pressed as equivalent ), with 20 through the bed and regenerating it in the man or without additional cations, about 5 per cent ner described above. Table II reports the volume nitric acid, by weight based on total acid in a (in liters) of solution treated to the end point of regenerant of ordinary regenerating strength is 1000 ohm cm. in each pass or" solution through effective to enhance the regenerated capacity of the bed, and whether a precipitation of calcium the bed and prevent precipitation of calcium sul sulfate occurred during regeneration. fate. At 500 parts per million (p. p. m.) of Ca, Table II a de?nite improvement in the regenerated capac ity of the bed is observed with 10 per cent nitric Liters of solution denied to acid, by weight based on total acid, but best re Solution Regener 1000 ohm-cm. end point, sults are attained when 20-25 per cent nitric acid 30 Trcated out 1 is incorporated in a solution containing between Pass 1 Pass 2 Pass 3 Pass lil‘ass '1

about 5 and 15 per cent by weight of total acid. l The effect of the presence of other cations, e. g. A I 142. 5 1 101 141. l A II 145. 7 156. 6 143. alkali metal cations, in the water being treated B I 1 133 1 G1 1 for calcium removal is to reduce the amount of B III 1 128 1 (30 13 IV 1 115 1 59 1 ‘ ' nitric acid necessary to prevent calcium sulfate B V 1 130 1 63 1 precipitation. For instance, in treating a natural B VI 1 108 86 O I 1 70 ______.. water containing about 500 p. p. m. of calcium, 580 C II 80 ...... _ p. p. m. of sodium and 50 p. p. m. of magnesium C III 80 ______._ (all expressed as equivalent calcium carbonate), markedly improved results were obtained with a 1 Precipitatc formed during subsequent regeneration. regenerant solution containing only 5 per cent It will be observed from the foregoing data nitric acid (by weight based on total acid) in a that in the treatment of water containing 300 regenerant solution of ordinary regenerating p. p. m. of calcium (Examples 1 and 2) there was strength. 45 some tendency for calcium sulfate to precipitate The following examples describe representative when sulfuric acid alone was used for regenera embodiments of this invention for purposes of tion, and that this tendency was avoided when 5% illustration. The aqueous solutions treated for nitric acid was included with sulfuric. When calcium removal were: treating water containing 500 p. p. m. of calcium 50 A. 300 p. p. m. (expressed as (Examples 3-7 incl), a marked reduction in cal equivalent calcium carbonate) cium sulfate precipitation was found when 15% B. Calcium chloride 500 p. p. m. (expressed as nitric acid was included with the sulfuric, but equivalent calcium carbonate) best results were obtained with nitric acid. With natural brackish water containing 500 C. A natural brackish water containing: 55 Calcium-500 p. p. m. (expressed as equiva' p. p. in. of calcium and other dissolved cations lent calcium carbonate) (Examples 8-10 incl.) as little as 5 per cent nitric Sodium-577 p. p. m. (expressed as equiva acid was found to be entirely effective to prevent lent calcium carbonate) the precipitation of calcium sulfate. Moreover, it will be seen that the process of this invention Magnesium—50 p. p. m. (expressed as equiva 60 lent calcium carbonate) increases the amount of water that may be treated in each pass through the cation ex The aqueous regenerating solutions shown in changer. Table I were used and compared: Having thus disclosed our invention and de Table I.—Regenerating solutions scribed in detail illustrative embodiments thereof, 65 we __claim and desire to secure by Letters Patent: 1. The method of regenerating a water-insol Total H2504 HNOz Designation Acid, wt. Pe‘g‘imgnby Pe‘?ergtnby uble cation exchange material containing an in Percent ' . - . soluble-sulfate-forming alkaline earth metal to Total Acid Total Acid the hydrogen form comprising contacting said 70 cation exchange material with a regenerating 10 100 0 10 95 5 solution containing between about 5 and 15 per 10 9O 10 cent by weight of total acid, of which between 10 85 15 10 80 20 about 75 and 95 per cent by weight is sulfuric 10 75 25 acid and between about 5 and 25 per cent by 75 weight is nitric acid. 2,683,695 5 6 2. The method de?ned by claim 1 wherein the ant solution containing between about 5 and 15 alkaline earth metal is calcium. per cent by weight of total acid of which a minor 3. In a process of treating water containing proportion in excess of 5% of the total acid is not less than about 300 p. p. m. of an insoluble nitric acid and a major proportion of the total sulfate-i‘orming alkaline earth metal (expressed 5 acid is sulfuric acid. as equivalent calcium carbonate) wherein the 6. The method of regenerating a cation ex— water is passed through a bed of a water insoluble change resin in the calcium form to convert it cation exchange material in the hydrogen form, to the hydrogen form comprising contacting the to replace cations in the Water with hydrogen, resin with a regenerant solution containing be the step oi regenerating the cation exchange tween about 5 and 15 per cent by weight of total material to the hydrogen form comprising con acid of which a minor proportion in excess of tacting the cation exchange material with a re 5 per cent of the total acid is nitric acid and generating solution containing between about a major proportion of the total acid is sulfuric 5 and 15 per cent by weight of total acid, of acid. which between about '75 and 95 per cent by weight 15 is sulfuric acid and between about 5 and 25 per References Cited in the ?le of this patent cent by weight is nitric acid. UNITED STATES PATENTS at. The process de?ned in claim 3 wherein the alkaline earth metal is calcium. Number Name Date 5. The method of regenerating a cation ex 2 2,356,651 Rawlings ______Jan. 2, 1945 change resin in the alkaline earth metal form 0 2,413,784 Rawlings et al. ____ Jan. 7, 1947 comprising contacting said resin with a regener