# Metachrylate-Based Polymeric Sorbents for Recovery of Metals from Aqueous Solutions
## 5 Adsorption of Metal Ions on Polymeric Sorbents--General Remarks
### Desorption of Metals and Reusability of Polymeric Sorbents  
An effective adsorbent should have a high adsorption/desorption capacity. The ability of the adsorbent to regenerate makes the adsorbent desirable and the adsorption process economical. In order to ensure successful adsorbent regeneration and reusability, a suitable stripping agent should be carefully chosen. It has to be cost-effective, highly efficient, and non-damaging to the adsorbent.  
Various stripping agents such as acids hydrochloric, sulphuric, nitric, formic, and acetic acid; bases: sodium and potassium hydroxide, sodium carbonate and bicarbonate, potassium carbonate; salts: sodium and potassium chloride, ammonium sulfate and nitrate, calcium chloride, potassium nitrate, deionized water, chelating agents (ethylene diamine tetraacetic acid, EDTA); and buffer solutions (bicarbonate, phosphate and tris) were used in literature.  
Desorption of heavy metal ions seems to be rapid and higher in acidic than in basic and neutral media [86]. In order to reduce the consumption of acids and bases, the use of other chemicals was investigated. A comprehensive review that summarizes the removal efficiency of various adsorbents, desorption efficiency of various stripping agents, and recovery of heavy metals can be found in the literature [87].  
[PERSON] et al. published a desorption study on Cu(II), Ni(II), and Pb(II) loaded poly(glycidyl methacrylate) and ethylene glycol dimethacrylate (PGME-en) [88]. Regeneration experiments with 2 M H\({}_{2}\)SO\({}_{4}\) as desorption eluent showed that PGME-en could be reused in several sorption/desorption cycles. For example, a capacity loss of 8% after four cycles of Cu(II) sorption was observed.  
[PERSON] et al. performed a desorption study on chromium(VI)-loaded copolymer of glycidyl methacrylate and ethylene glycol dimethacrylate functionalized with hexamethylhene diamine (PGME-HD) [89]. It was concluded that Cr(VI) sorption was reversible. PGME-HD can be easily regenerated with 0.1 M NaOH up to 90% recovery in the fourth sorption/desorption cycle, while in the fifth cycle, a considerable sorption loss of 37% was noted.  
[PERSON] et al. used nitric acid solutions for testing the desorption efficiency of La(III) and Y(III) loaded polyaminophosphonic acid-functionalized polyglycidyl methacrylate (PGMA) [64]. It was concluded that metal-loaded sorbent could be regenerated over six successive sorption/desorption cycles with 0.5 M HNO\({}_{3}\) solutions. The sorption and desorption efficiencies decreased by less than 7% after the sixth cycle.  
[PERSON] et al. tested the desorption ability of vinylbenzyl chloride/divinylbenzene copolymer (VBC/DVB) with attached 2-mercapto-1-methylimidazole and guanylthiourea ligands loaded with silver (Ag(I)) ions [58]. As desorption eluents, solutions of sodium thiosulphate, thiourea, potassium cyanide, potassium cyanide in hydrogen peroxide, sodium hydroxide and ammonium buffer were used. It was observed that Ag(I)-loaded sorbents can be effectively regenerated with 1% potassium cyanide solution in 0.5% hydrogen peroxide solution at 50 \({}^{\circ}\)C. In addition, polymer sorbents with mercapto-1-methylimidazole and guanylthiourea ligands retained their Ag(I) capacity in five consecutive sorption/desorption cycles.