What substances can cause fouling of a cation exchange resin?

Fouling of a cation exchange resin primarily occurs due to the buildup of certain substances that can interfere with the resin's ability to exchange ions effectively. In this context, iron and manganese are known to cause significant fouling. These metals can precipitate and create a coating or clog the resin beads, which reduces the resin's capacity to perform its intended function of exchanging cations from the water.

Iron often oxidizes and forms insoluble compounds that can adhere to the resin, while manganese can also precipitate, especially in the presence of oxygen. Over time, the accumulation of these deposits inhibits the resin's ability to regenerate and perform properly, leading to reduced efficiency in water treatment processes.

Other options include substances that do not typically result in the same degree of fouling. For instance, calcium and sodium, though they are cations, generally participate in the ion exchange process without leading to significant resin fouling. Sulfur and chlorine may impact water quality in terms of disinfection or odor but do not typically cause physical fouling of cation exchange resins like iron and manganese do. Carbon and oxygen are not ions that would accumulate on these resins in a harmful manner. Hence, the selection of iron and manganese as the correct answer reflects their