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 ion-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 alkaline earth metal 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 sulfuric acid with less danger of is chie?y sulfuric acid, without causing the pre the formation of insoluble sulfates. 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 ions, 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 calcium, 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 sulfate 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 calcium sulfate 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 calcium carbonate), 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.