Dow Water & Process Solutions

DOWEX Resins for Separation of Zinc from Liquid Media

Zinc - Zn Zinc is the 24th most abundant element in the Earth's crust. Zinc is processed into hundreds of useful product from protective galvanized coatings, to high tech batteries, to cold remedies, to diaper rash ointment.

Applications

Brine or HCl: Normally we think of ionic zinc as a di-valent cation that is easily picked up by a standard cation exchange resin. An interesting property of ionic zinc is that in the presence of acid or brine, zinc forms multi-valent anionic complexes (42KB PDF) that can be captured on anion exchange resins. Most other cations remain cationic under these conditions so they are not captured by an anion exchange resin, thus creating the opportunity for a new separation process. Zinc can be eluted from the resin by simply washing with water, reversing the equilibrium of the anionic complex formation.

ZnCl₂+ 2NaCl   is at equilibrium with   Na₂ZnCl₄

DOWEX™ 21K XLT resin has been used by a geothermal power company to commercially mine 30,000 MT of zinc annually from geothermal brine. Classical zinc mining operations are generally very waste intensive, however, this new ion exchange process will enable geothermal power companies to operate the most environmentally benign zinc mining operation in the world.

Only the superior performance inherent to uniform particle technology could provide the processing edge that the process designers needed in order to meet their demanding cost/performance criterion. Very hot geothermal brine at a rate of more than 2.5 million pounds per minute (68,000 MT/hour) pass through DOWEX anion exchange resin, where the zinc is captured and concentrated for further refining. The resin is eluted with plain water, eliminating the need for costly chemicals, storage, and permitting.

Water / Wastewater: Removing zinc from water via ion exchange is common in chemical, petrochemical, oil refining, semiconductor manufacturing and power utility plants. In waters with low levels of dissolved salts, strongly acidic cation exchange resins such as DOWEX G-26 (H) cation exchange resins are employed. Weak acid cation exchange resins such as DOWEX MAC-3 often provide high capacity and good multi-valent ion selectivity. However, in more brackish waters, chelating resins may be required. Chelating resins have reactive units dispersed along their polymer matrix, each of which have multiple metal binding sites. Hence, chelating resins are selective for multi-valent cations, over mono-valent cations, such as sodium and potassium.

DOWEX Ion Exchange Resins

Product	Description	Type	Matrix	Total Exchange Capacity* eq/l (kgr/ft3)	Available Forms
DOWEX 21K XLT	Uniform particle size, high capacity, strong base anion exchange resin for mineral processing applications.	Type I Strong Base Anion	Styrene-DVB, Gel	1.4	Cl-
DOWEX G-26 (H)	Uniform particle size strong acid cation exchange resin for specialty demineralization and catalyst applications.	Strong Acid Cation	Styrene-DVB, Gel	2.0	H+
DOWEX MAC-3	A macroporous weak acid cation exchange resin used for water softening, dealkalization, and demineralization applications.	Weak Acid Cation	Polyacrylic, Macroporous	3.8 (83.0)	H+