Ion Exchange Resins Essay

Ion exchange resins are well known and widely used for all kind of applications including the removal of dissolved metal salts from (waste) water.[12] Resins are small plastic beads, which are composed of porous natural or synthetic organic polymer chains, charged with functionalized groups build in the resin beads. The resins are electrically neutral. Each bead contains fixed ions and mobile counter ions, which can move into and out of the resin bead (see figure 3). The cation resins attract and exchange cations, while anion resins attract and exchange anions. Cation resins exchange hydrogen (H+) ions for other (metal) cations from the aqueous phase, with the same charge. Likewise, anion exchange resins exchange hydroxide (OH-) for other anions from aqueous streams with the same charge. When hydrogen (H+) and hydroxyl (OH-) are combined water is formed (see figure 4). When the resins have reached their limit, they need to be regenerated: cation resins are regenerated by hydrochloric acid (as hydrogen is positively charged) and anion resins by sodium hydroxide (as hydroxyl is negatively charged).[13,14]

Adsorption by using activated carbon (from coal) is

water). In the standard osmosis process, a solvent naturally moves from an area of low solute concentration, through a semipermeable membrane, to an area of high solute concentration. By equalizing the solute concentrations on each side of the membrane, an osmotic pressure is created. In order to obtain clean water, a pressure is applied, in order to overcome the osmotic pressure, by pressing water (contaminated with metals) against the surface of a membrane, causing pure water (solvent) to move through the membrane, leaving behind the metal salts (solute).[7,17] However, for heavy metals, this method has not been applied widely