FI67494C - REFERENCE AVAILABLE WITH CHROME FRAME RELEASE CHLORINE - Google Patents

Description

M __ ANNOUNCEMENT, _, Λ Λ jijjjjfc W t ”) utlAggningsskrift 67494 ^ Patent li '· 1 dc lat βΙ) Μ? *» Α3 B 01 J 41/04, B 01 D 15/04 // c 01 G 37 / 14, C 01 B 11/14 FINLAND — FINLAND (21) ** —— * «782748 (22) 07.09.78 '* (23) AHn ^ iMI — GMtighaCsdag 07.09.78 (41) T« tetHMwtai — HMt »tiwtg 14/3/79

Htittl- and register haflita ·. fa | —_ P * tewt- och reglsterstyreiasn '* Aieak — wthei «& edXtew.pJGteral 31.12.84 (32) (33) (31)« VlM-tr s-oita · .- * ^ phertm 13.09.77 USA ) 832866 (71) Pennwalt Corporation, Pennwalt Building, Three Parkway, Philadelphia, Pennsylvania 19102, USA (72) Jesse Gyger Grier, Gilbertsville, Kentucky, Jimmie Ray Hodges, Benton, Kentucky, USA (74) Berggren Oy Ab (54) Removal of chromate ions from aqueous chlorate solutions -

The present invention relates to a process for removing chromate ions from a solution containing a large amount of dissolved alkali metal chlorate and having a dissolved alkali metal.

U.S. Patent No. 3,835,001 discloses a process for removing a substantial portion of chromate ions from an aqueous alkali metal chlorate chloride solution by passing the solution through a layer of a strong base ion exchange resin in chloride form at an initial solution pH of less than 6.5 and preferably about 5. Although the method provides a clear improvement in the removal of chromate ions from such solutions compared to previous methods, the need for further improvement to remove even higher amounts of chromate ions is obvious. In other words, it is commercially desirable to provide a process that can economically remove substantially all chromate ions from solutions containing only 10 ppm by weight, but generally less than about 20 g / L dissolved alkali metal chromate, so that a single solution treatment provides substantial removal of chromate ions. and preferably substantially complete removal from solution without associated formation of hazardous chlorine dioxide.

Accordingly, the present invention relates to a process for removing chromate ions from a solution containing a large amount of dissolved alkali metal chlorate and dissolved alkali metal, the process passing the solution through a layer consisting of a substantially homogeneous mixture of anion exchange resin in chloride form and weak cation exchange resin , wherein the cation exchange resin has at least as many exchange sites as the anion exchange resin and wherein the anion exchange resin is present in such an amount that the number of exchange sites exceeds the number of chromate ions removed from solution, and that the liquid flow is stopped when the pH of the effluent rises above about 2.

In industrial practice, the number of switching points is defined as the "total switching capacity" expressed in milliequivalents / ml or milliequivalents / g. The method of assay for this quantity differs somewhat among resin suppliers. The manufacturer's technical notice (1972) for Amberlite IRC-50 resin states: "Total exchange capacity: The maximum capacity of Amberlite IRC-50 resin can be easily determined by equilibrating a representative sample in hydrogen form with excess 0.1 N sodium hydroxide. with an excess of base for 24 to 48 hours. The amount of neutralized sodium hydroxide is considered to correspond to the maximum capacity of the ion exchanger ".

Both cationic and anion exchange resins useful in this invention may be of either the gel type or the macrogrid type, but the macrogrid type is preferred due to its greater stability in numerous cycles of the ion exchange process. Various types of ion exchange resins are described, for example, in Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition, Part II, pages 871 onwards.

3 67494

The anion exchange resin may be a weak or strong base resin, but for more quantitative recovery during regeneration, a weak base anion exchange resin is recommended. When an anion exchange resin is used during the use or chromate adsorption step of the ion exchange process, it should initially be in the chloride form.

The cation exchange resin of this invention is a substantially weak acid cation exchange resin that must be in a standardized hydrogen form at the beginning of the process operation, i.e., when initiating the removal of chromate from the chlorate-rich solution.

The term "standardized hydrogen form" as used herein means a form of cation exchange resin in which a portion of the hydrogen ions in the cation exchange resin, which was originally entirely in hydrogen form, have been replaced with alkali metal (Na +) ions to prevent excessive acidification of the chlorate solution during the process operation. As stated otherwise, to reduce the "salt cleavage" effect of the chromate adsorption (use) step, the hydrogen form of the cationic resin is rinsed (conditioned) with an alkali metal chloride brine, preferably at neutral pH (6-8) to bring the effluent (brine effluent) to pH 1: , 0, preferably up to about 2.

Salt cleavage typically occurs when a solution containing a salt of a strong acid and a strong base is passed through a strong acid ion exchange resin or a strong base ion exchange resin. . The cation of the salt is easily converted to the hydrogen of a strong acid resin. Likewise, the anion of the salt is easily converted to the hydroxide of the strong base resin. The distinguishing feature of weak acid weak base ion exchangers compared to strong acid and strong base types is that this cleavage of the salt does not usually occur to a significant extent. The fact that it actually occurs and must be controlled in the process in question is probably due to the very high salt concentrations involved.

The process of the present invention, which is preferably a cycle process, is broadly described below:

Selected exchange resins are treated either separately or as a mixture with mineral acid brine to give the starting material. The 67494 cationic resin (if separate treatment) or mixture is then treated with neutral brine to obtain the cationic resin in a standardized hydrogen form. Unless the exchange resins have been mixed prior to these treatments, they are mixed in a manner well known in the art, for example by blowing water under water. The adsorption step of the use or chromate is then started by passing a chromate-containing, highly chlorate-containing liquid through the mixed resin layer. When the ion exchange layer is consumed, as indicated by the rise of the pH of the effluent to 2 and its concomitant yellowing, the flow of the chromate-containing solution is stopped and the anion exchange resin is treated to recover chromate ions with or without separation of the exchange resins.

As described below, the resins can be separated, if desired, by passing the saline upward through the bed at a rate sufficient to cause the resins to have somewhat different specific weights to separate.

The chromate is easily and completely stripped by treating the anionic resin or layer with an alkaline solution of an alkali metal chloride, e.g. a 12-15% aqueous solution of sodium chloride containing about 4% sodium hydroxide. After the chromate is removed from the anion exchange resin, the process is repeated according to the steps outlined above for several cycles until the resins are no longer capable of sufficient adsorption to provide a useful process.

In order to facilitate the understanding of the different stages of the process and their impact, the following table describes the theoretical exchange mechanisms in question. process using and without resin separation.

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The flow rates for the chromate-containing solution through the ion exchange resin layer in the process of this invention should not exceed about 40 1 / min, preferably 30 1 / min per square meter due to the widening of the adsorption front.

The process of this invention is suitable for any aqueous solution containing alkali metal chlorate at a concentration sufficient to decompose upon acidification to a pH of about 0.5-1.0. The concentration of the alkali metal chlorate or chlorate and chloride should not be so high as to cause the salt to separate from the solution under the conditions of the ion exchange column or bed. For example, the acceptable upper limit for sodium chloride-rich sodium chloride solution concentrations at 26.7 ° C is about 120 g / L sodium chloride and 550 g / L sodium chlorate.

The following examples are presented to illustrate the process of this invention.

Example I

An equal weight of gel type strong anion exchange resin (Amberlite IRA 400, product of Rohm & Haas Company) and gel type weak acid exchange resin (Amberlite IRC 84 - product of Rohm & Haas Company) was added as a thorough mixture to a glass column with an internal diameter of 1, 25 cm. The height of the mixed resin layer in the column was approximately 80 cm and the volume 100 cm. The conditioning step of passing 25 milliequivalents of hydrochloric acid through the column was performed to ensure that the exchange resins were partially in the chloride and hydrogen forms, respectively. This step was followed by rinsing with deionized water.

An aqueous chlorate feed liquid containing sodium chromate (600 g / l sodium chlorate and 5.9 g / l sodium dichromate) was passed through the column upstream at a rate of 2 cm 2 / min. The upper direction was desirable because the specific gravity of the chlorate solution was higher than that of the resin.

Successive portions (samples) of the frying stream from the column were analyzed for pH and chromate content using a colorimetry. The progression of the upwardly moving exchange front in the column was observed from the discoloration of the resin. The findings and the results of the analysis of successive doses are shown in the following table.

67494 Complete chromate recovery was achieved by passing alkaline sodium chloride through the bed at the end of the chromate removal step.

Table I

Sample Chromate of feed liquid Outlet flow Exchange zone layer space-discharge flow pH height x g g / l 1 0.92 0.00 1.96 20 cm 2 1.72 0.00 1.20 36 cm 3 2.57 0.00 1 .35 51 4 3.37 0.00 1.58 63 5 4.16 0.00 1.74 68 6 4.98 0.00 1.96 75 7 5.33 0.02 2.22 78 (peak) 8 5.78 0.20 2.62 9 6.60 1.05 2.88 10 7.45 3.60 2.90 11 8.24 4.80 2.80

Supply - 5.90 5.50 V)

The bed volume of the feed or effluent is a phrase used to compare the capacities of ion exchange columns of different sizes.

One layer volume is the total volume occupied by the resin layer (cross-sectional area times height) including the volume occupied by the exchange resin balls themselves.

Example II

The 1.9 cm diameter column was packed to a height of 132 cm with a thorough mixture of macrogrid type weak cation exchange resin (Rohm & Haas Company's Amberlite IRC 50) and macrogrid type weak anion exchange resin (Rohm & Haas Company's 93 Amberlite I) in a weight ratio of 60:40.

The mixed resin layer was preconditioned by first passing 4% aqueous sodium hydroxide solution through the column and then 4% aqueous hydrochloric acid until the pH dropped below 1.5. Finally, a downward wash was performed with a nearly saturated, aqueous aqueous sodium chloride solution to standardize the hydrogen form of the cation exchange resin until the pH of the effluent rose to 1.5.

67494

The adsorption of the chromate was carried out by passing a chlorate solution (450 g / l of sodium chlorate) containing 1.02 g / l of sodium dichromate (feed liquid) upwards through the resin layer at a rate of 5 craVmin.

3 1850 cm of colorless product was collected before the effluent turned visibly yellow. During this time, the pH of the effluent rose 3 continuously from 1.6 to 2.05. After an additional 150 cm of flow, the effluent contained 24.6 ppm sodium dichromate (^ 20 ^ 0.7) and the pH of the effluent was 2.15.

As in Example I, successive samples were taken from the effluent and analyzed for pH. The color of each sample was determined as a check for chromate content, with the colorless sample showing substantial chromate absence. The following table contains pH and observation data for each sample.

Table II

Sample Feed Fluid Chromate Outlet- Outlet Stream In Alternating Belt Layer Room Stream (Color- pH Zone Indication) Height (cm) 1 1.42 colorless (2.3) * 20 2 1.85 colorless 1.6 41 3 3.57 colorless 1 .67 61 4 4.28 colorless 1.77 91 5 5.00 colorless 1.90 6 5.28 light yellow 2.05 - 7 5.70 clear yellow 2.15 (24.6 ppm) * Initial pH is higher before equilibration of sodium chlorate with resins.

Example III

In a 25 cm diameter column specially tubed to recycle the continuous ion exchange process, a mixed resin layer was prepared by mixing 1 part by weight of a weak cationic resin (Amberlite IRC 84) and 2 parts by weight of a weak anionic resin (Amberlite IRA 94) under water. In a column with a total height of 89 cm.

The bed was treated by passing 4% HCl in NaCl brine downstream until the effluent reached pH 1.5. The conditioning step was then performed by passing saturated NaCl brine 67494 (pH 9.5) down. After initially dropping to 0.4 due to salt cleavage, the pH rose above 1.0 after which the brine rinse was stopped.

The chromate adsorption step was then started by passing upwards at a rate of 10 l / min / m a liquid flow containing 450 g / l sodium chlorate and 3.1 g / l ^ 2 ^ 2 () 7. The effluent remained colorless until 24.2 L was treated. The pH of the effluent was between 2.05 and 2.2 when the first yellow effluent appeared. Stripping to desorb the chromate from the exchange resin was performed by passing a 4% NaOH solution in half-saturated (12%) NaCl brine as a downward flow.

Table III

Sample Feed Chromate Outlet Stream

layer volume (color indication) pH

1 1/47 colorless 2.0 2 1.90 colorless 1.8 3 3.50 colorless 1.8 4 5.08 colorless 1.95 5 5.93 colorless 2.05 6 6.44 faint yellow 2.2 7 6.87 clear yellow 2.3

The above examples illustrate the process of this invention with respect to the chromate adsorption step. In Examples 2 and 3, after the chromate adsorption step, the chromate is easily stripped from the weak base anion resin by passing a 4% sodium hydroxide solution in half-saturated (12-15% NaCl) brine through the bed. The layer is then regenerated by passing a hydrochloric acid solution through it and then stabilized to a pH of 1-2 with a slightly alkaline or neutral (NaCl) solution. The chromate adsorption step can then be repeated.

The following is a general description of another embodiment of the invention: A mixed layer of a particular ion exchange resin is prepared by blowing underwater on an ion exchange column from about 35 to 65 parts by weight of an anion exchange resin in chloride form and from about 65 to 35 parts by weight of a weak cation exchange resin.

10 67494

After the water is drained from the column, the bed is treated with an alkali metal chloride mineral acid solution and then the cationic resin is conditioned by passing a neutral solution of the alkali metal chloride through the bed to adjust the pH of the effluent as described above. An aqueous solution of alkali metal chloride rich in alkali metal chlorate, containing less than about 20 g / l and preferably less than 10 g / l of alkali metal chromate, is passed up through the mixed ion exchange bed at a rate of about 20 per minute per square meter of bed while monitoring the pH of the effluent. When the pH rises above about 2 and the effluent turns yellow, the chlorate liquid flow is stopped.

The chlorate liquid is discharged from the ion exchange resin layer and half-saturated (12-15%) sodium chloride brine, preferably pH neutral (7-8) is passed up through the layer at a rate sufficient to separate the two exchange resins into an upper (anionic resin) and lower (cationic resin) layer. The brine flow is stopped and 4% sodium hydroxide in 12-15% sodium chloride brine is passed down through the anion exchange resin until the effluent becomes alkaline, indicating the removal of adsorbed chromate from the resin. For regeneration, 4% hydrochloric acid in half-saturated sodium chloride brine is then passed through exchange resins until the pH of the effluent drops to 1.0. The conditioning of the cationic resin is carried out by passing semi-saturated sodium chloride brine up or down through the resin until the pH of the effluent is between 1.5 and 2. The chromate adsorption step is then repeated.

Claims (7)

11 67494 A process for removing chromate ions from a solution containing a large amount of dissolved alkali metal chlorate and having a dissolved alkali metal, characterized in that the solution is passed through a layer consisting of a substantially homogeneous mixture of an anion exchange resin in chloride form and a weak cation exchange resin there are at least as many exchange sites as in the anion exchange resin, and the anion exchange resin is present in such an amount that the number of exchange sites exceeds the number of chromate ions removed from solution, and that the liquid flow is stopped when the pH of the effluent has risen above about 2. A method according to claim 1, characterized in that the solution is passed through the bed at a rate not exceeding about 30 in 1 minute per square meter of the bed. Process according to Claim 1, characterized in that the anion exchange resin is a weak base resin. Process according to Claim 3, characterized in that the ion exchange resins are both macrogrid-like. Process according to Claim 4, characterized in that the cation exchange resin is present in an amount of at least 0.5 but not more than 2.0 parts by weight per part of the anion exchange resin. A method according to claim 1, characterized in that the pH of the effluent of the solution passed through the mixed ion exchange resin layer varies from at least about 1 to at most about 2. Process according to Claim 5, characterized in that the solution contains large amounts of dissolved sodium chlorate and sodium chloride.