Using ion exchange to remove heavy metals from industrial waste water.
Ion exchange is an efficient tool for removing objectionable materials from dilute industrial waste waters, especially heavy metals. However, these “dilute wastes” usually contain other materials that do not pose a problem but can interfere with the efficiency of the ion exchange process.
These interfering substances can often be eliminated by softening or deionizing the water before it is used in the process. Recirculating rinse waters through an ion exchange bed back to the rinse process can further enhance efficiency. This prevents interfering substances from entering the waste stream; especially calcium, magnesium, and sodium ions which are present to varying degrees in ordinary tap water. This allows the ion exchange waste treatment step to operate in a more efficient manner, usually with a less expensive resin such as ResinTech CG8. This approach can provide substantial savings over the long term in reduced regenerant and makeup resin expenses.
When it is not practical to change the quality of the water provided for rinsing or washing, and interfering substances such as calcium and magnesium can not be eliminated, then special types of ion exchange resins are used. These selective ion exchange resins have specialized functional groups that form complexes with specific substances. There are several different kinds of these resins. Each type of selective resin offers unique characteristics for, at best, only a few ions, therefore it may sometimes be necessary that more than one kind of resin be used for complete removal of all objectionable substances. The table below is a generalized guide for the most efficient ResinTech product for specific ion removal based on the application and type of feedwater.
*Mercury can form anionic complexes in the presence of chlorides.
**In photo finishing waste, silver is removed as the thiosulfate complex.