Ion exchange resin contamination and disposal (1)

Iron pollution and treatment:

Both Yang and Yin resins may be contaminated by iron. The appearance of the contaminated resin is dark brown and can turn black in severe cases. In general, when the iron content in every 100g of resin exceeds 150mg, it should be treated. The presence of iron will accelerate the degradation of Yin resin.

In the use of positive resin, most of the iron ions brought in by raw water exist in Fe2+, and after they are absorbed by the resin, some of them are oxidized to Fe3+, which can not be completely exchanged by H+ during regeneration, and therefore remain in the resin causing iron pollution. When iron salt is used as coagulant, part of the alum flowers are brought into the Yang bed, and the filtration effect causes it to accumulate on the surface of the resin layer. During regeneration, the acid solution dissolves the alum flowers, making it Fe3+, which is partially absorbed by the Yang resin, causing iron pollution. A large amount of Fe3+ in industrial hydrochloric acid will also cause iron pollution to the resin. Positive resins used for sodium ion exchange are more susceptible to iron contamination.

The iron content of negative resin is sometimes many times greater than that of positive resin. The iron of Yin resin mainly comes from the regenerated liquid. The caustic soda produced by the diaphragm method contains 0.01%~0.03% Fe2O3, and at the same time, it also contains 6~7mg/L NaClO3. Such caustic soda will generate ferrate (FeO4) in contact with iron containers and pipelines (without anti-corrosion layer) during storage and transportation. After ferrate enters the Yin bed with lye, it will decompose due to the decrease of pH value, and the reaction formula is as follows:

2FeO42- + 10H+ → 2Fe3+ + 2/3 O2 + 5 H2O

Fe3+ further produces Fe(OH)3, which adheres to the negative resin particles, causing iron pollution.

After the resin is contaminated with iron, it cannot be removed in the general regeneration process and must be cleaned with hydrochloric acid.

The commonly used cleaning method is to use 10%HCl solution, before carrying out this method, the corrosion resistance of the exchanger equipment must be checked, otherwise hydrochloric acid with inhibitor must be used.