Aqueous waste solutions, cation exchange

The principal reaction with aqueous waste solutions is believed to cation exchange as illustrated in Eq. 2. 

Also, nylon-6 waste may be hydrolyzed in the presence of an aqueous alkali metal hydroxide or acid5 to produce an alkali metal or acid salt of 6-aminocaproic acid (ACA). The reaction of nylon-6 waste with dilute hydrochloric acid is rapid at 90- 100°C. The reaction mixture is poured into water to form a dilute aqueous solution of the ACA salt. Filtration is used to remove undissolved impurities such as pigments, additives, and fillers followed by treatment of the acid solution with a strong cation exchange resin. A sulfonic acid cationic exchanger absorbs ACA salt and pure ACA is eluted with ammonium hydroxide to form a dilute aqueous solution. Pure ACA is obtained by crystallization of die solution. 

Acid-containing wastes are produced in many industries. Thus, in leaching of minerals, in regeneration of cation exchangers, and in metal surface treatment, only a part of the acid is utilized (due to the reduced activity at the lower acid concentration). The acids plus salts comprising aqueous solutions formed in these operations as well as in others (e.g., zinc electrowinning) are neutralized in most cases and disposed of. Efficient separation and recovery of the acid values is more beneficial, as it would save on acid and base consumption, reduce discharge of solution or solids, and enable recovery of other valuable components (e.g., metal values) from the deacidified solutions. 

Anions and cations dissolved in a dilute aqueous waste can be removed from solution through the process of ion exchange. As the... 

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