# Prussian Blue: A Safe Pigment with Zeolitic-Like Activity
## 4 Adsorption Properties of PB
### Adsorption of Thallium  
Thallium (TI) is a rare metal with high toxicity. Whereas the elemental form of thallium has essentially no toxicity, its univalent (thallous, TI+1) and trivalent (thallic, TI3+) salts are highly toxic. The human body does not discriminate the uptake of TI+1 over K+ as the ionic radius of TI+ is similar to that of K+, which has fatal consequences because TI disrupts the proper functioning of the K+ involved in many biochemical reactions [63]. In this way, TI could cause acute and chronic poisoning that would imply degenerative changes in the heart, liver, and kidney. The poisoning with TI could be caused by the explosion of a \"dirty bomb\" prepared with radioactive isotopes including cesium and thallium. The presence of nonradioactive TI in the environment is due to the emission of the metal by coal combustion, cement plants, and nonferrous metals metallurgy. The predominant contamination source of TI is wastewater from the mining, beneficiation, and smelting of TI-containing sulfide ores.  
A great number of methods (precipitation, flotation, electrochemical deposition, and solvent extraction) have been developed to remove TI from industrial wastewater [64]. However, adsorption exhibits great potential due to the advantages of high purification efficiency, low energy consumption, and environmental friendliness [65]. In this way, adsorptive technologies based on the use of PB and PBA have been used. The medication Radiogardasse, prescribed for the treatment of known or suspected internal contamination with radioactive Cs+, is also indicated for the treatment of the poisoning by radioactive or nonradioactive TI.  
[PERSON] et al. determined the relationship between physicochemical properties of insoluble PB and its binding capacity [66]. Meanwhile, by using solutions with different pH, they evaluated the effect of pH and storage conditions on the binding to PB. The results indicated that the hydration state of PB influenced the TI uptake. The PB with 17 mol of water had a binding rate constant of 0.52, which was reduced to 0.32 when PB was dehydrated to 2.5 mol of water. Later [67], the same group determined that insoluble and soluble PBA, with similar quality attributes, had nearly identical binding capacities. [PERSON] et al. evaluated the removal of TI+1 by PB and Cu(II)ferrocyanide, a PBA, immobilized on mesoporous silica in varied aqueous systems [68]. Compared to PB, the PBA showed higher capacity of adsorbing TI (28.3 mg/g for PBA and 5.82 mg/g for PB). According to the results, the distribution coefficient of TI on both sorbents increased with the increase of  
Figure 3: Cesium distribution on PB/cellulose aerogel after adsorption. (**A**) SEM image of the cryo-fractured PB composite. (**B**) EDS mapping of iron. (**C**) EDS mapping of cesium. (**D**) EDS mapping of iron-cesium overlay. Reproduced with permission from [39].  
the pH of the solution. Therefore, the cation ion exchange might be the major adsorption mechanism. This mechanism was also postulated by [PERSON] et al. [69]: Tl was exchanged with hydrogen ions in the crystal lattice of PB, or with alkali metal impurities bound to PB during the synthesis process.