Chromium uptake from tricomponent solution in zeolite fixed bed

Removal of Cr3+, Ca2+, Mg2+ and K+ in equilibrium isotherms and in tricomponent solutions (Cr/Ca/K, Cr/Ca/Mg and Cr/Mg/K) were investigated in NaX and NaY packed beds at 30 degrees C. The equilibrium selectivity was obtained as Cr+3 > Mg2+ > Ca2+ approximate to K+ for zeolite NaY and Ca2+ >> Cr3+ > Mg2+ approximate to K+ for zeolite NaX. The breakthrough curves showed sequential ion exchange where chromium ions are able to replace the competing cations. Some mass transfer parameters, such as length of unused bed and overall mass transfer coefficient, were investigated. Chromium retention was also investigated through a mass balance. Based on the breakthrough results, it was concluded that chromium-uptake mechanism was hardly influenced by the competition and interaction between the entering ions. NaY showed a higher affinity towards Cr3+ for both equilibrium and dynamic systems and its sites were more efficiently used in the ion exchange process. Chromium was less retained in NaX due to the high selectivity towards calcium ions.