Methods of Removal of Ions in Ground Water

The common ions removed in groundwater are calcium and magnesium making up water hardness. This process is called softening and may be used in conjunction with well water systems and pond water. Many other ion removal systems are used by industry and military. Some are specific for one metal, such as gold or silver and used to reclaim precious metals in mine tailings. Other ion removal systems are reverse osmosis, electrodialysis, nanofiltration, and aquatic plants. The scope and cost may limit the use to larger projects such as desalination of sea water for irrigation of desert farming.

Ion Specific Resins

• Hardness corrodes and clogs pipes, and increases the amount of detergent for laundry. Softeners are used to remove the hardness ions by ion exchanging with sodium on a back flushing regeneration cycle with a strong brine (salt) solution. The disposal of the brine may pose problems as it is corrosive itself. Therefore, new no salt softeners use electric current to replace brine sodium anion recharge. Many cationic resins remove most metallic positively charges ions like barium, copper and zinc. Anion resins remove negative ions like nitrates and sulphates. Sometimes mixed bed resins are used and water is run through a series of filters. A carbon filter or micro filter is employed ahead of the ion bed to remove small particles and expand the life of the ion removal resins.

Ion Removal by Other Techniques

• Electrodialysis applies a constant voltage across the water stream to affect the separation of calcium and magnesium. Hardness removal can also be directly affected by using a nanofiltration system using commercial membranes. Nitrate is removed by a combination of ion exchange and biological denitrification. Aquatic plants can remove heavy metal contamination in surrounding water. The use of micro alga and aquatic plants remove up to 97 percent of lead concentration. Reverse osmosis units are available for large desalination projects as well as smaller compact systems for providing fresh water from sea water for emergency situations on ships and planes.