Removal of Cd(II) and Zn(II) from binary aqueons solution with concentration ratio Cd/Zn=1.93 onto fixed bed of natural zeolite H=8 cm : bachelor thesis

Ispitano je uklanjanje Cd i Zn iona postupkom u koloni iz binarne vodene otopine ukupne početne koncentracije c o (Cd+Zn) ≈ 1 mmol/L, a koncentracijskog omjera kadmija i cinka Cd/Zn = 1,93. Radni ciklus proveden je propuštanjem otopine s vrha prema dnu kolone kroz nepomičan sloj zeolita visine H = 8 cm pri stalnom protoku od Q = 1 mL/min. Tijek radnog ciklusa pratio se određivanjem koncentracije Cd i Zn iona te pH vrijednosti u efluentu. Nakon radnog ciklusa provedena je regeneracija sloja zeolita otopinom NaNO 3 c = 176,5 mmol/L, uz iste radne uvjete. Rezultati su prikazani krivuljama proboja i krivuljama regeneracije, iz kojih su određene točka proboja, točka iscrpljenja, završetak regeneracije te su izračunati karakteristični parametri: kapacitet u točki proboja, kapacitet u točki iscrpljenja, efikasnost kolone te stupanj regeneracije. Proboj je postignut nakon ≈ 44 h pri čemu je obrađeno ≈ 2,7 L binarne otopine, a do točke proboja Cd i Zn ioni vezali su se istovremeno. Iscrpljenje je postignuto nakon ≈ 65 h do kada je obrađeno ≈ 3,9 L binarne otopine. Koncentracija Cd u efluentu neznatno prelazi njegovu koncentraciju u influentu, dok je koncentracija Zn znatno veća od one u influentu, što ukazuje na efekt istiskivanja već vezanih Zn iona iz strukture zeolita ionima Cd iz otopine. Ovo nije očekivano budući da Cd i Zn ioni imaju slična fizikalna svojstva kao hidratizirani ionski radijus, elektronegativnost i energiju hidratacije. Razlog istiskivanja može se pripisati većoj koncentraciji Cd iona u početnoj otopini, u odnosu na koncentraciju Zn iona, što znači da se promjenom koncentracije iona u influentu može utjecati na količinu vezanih iona u radnom ciklusu. Prema rezultatima ciklusa regeneracije veća je količina eluiranih Cd nego Zn iona, što potrđuje da se u strukturi zeolita vezalo više Cd. Potpuna regeneracija sloja zeolita završena je već nakon ≈ 5 h pri čemu je utrošeno svega 0,31 L otopine NaNO 3 . Visoki stupanj regeneracije α R ukazuje na uspješno provedenu regeneraciju čime je omogućeno ponovno korištenje istog sloja zeolita u novom radnog ciklusu, što je od izuzetne važnosti za primjenu u praksi. The removal of Cd and Zn ions by column method from binary aqueous solution with total initial concentration c o (Cd+Zn) ≈ 1 mmol/L, and with concentration ratio Cd/Zn = 1.93 has been investigated. Service cycle has been performed by passing the feeding solution from the top to the bottom of the column through the fixed zeolite bed of height H = 8 cm at a constant flow rate of Q = 1 mL/min. After service cycle, the regeneration of zeolite bed has been performed at the same experimental conditions with NaNO 3 solution of c = 176.5 mmol/L. The progress of the service and regeneration cycles was tracked by measuring the Cd and Zn concentrations and pH values in the effluents. The results are shown by breakthrough and regeneration curves from which the breakthrough and exhaustion points and the end of regeneration have been determined, as well as the characteristic parameters have been calculated: breakthrough and exhaustion capacities, removal efficiency, and the degree of regeneration. The breakthrough has been obtained after ≈ 44 h when ≈ 2.7 L of binary solution has been treated, and until breakthrough the Cd and Zn ions bound simultaneously. The exhaustion has been achieved after ≈ 65 h when ≈ 3.9 L of binary solution has been treated. The concentration of Cd in the effluent slightly exceeds its influent concentration, while Zn concentration is considerably higher than its influent concentration. This indicates the displacement of already bound Zn in zeolite structure by Cd from the feeding solution. This behaviour has not been expected since Cd and Zn ions have similar physical properties such as hydrated ionic radius, electronegativity and energy of hydration. The reason of displacement can be attributed to the higher inlet Cd concentration, compared to Zn. This means that changing the inlet concentration can affect the amount of bound ions in the service cycle. According to the results of the regeneration cycle the amount of eluted Cd is greater compared to Zn, which confirms that the zeolite structure bound more Cd. The regeneration of zeolite layer has been completed after ≈ 5 h wherein only 0.31 L of NaNO 3 solution was spent. The high degree of regeneration α R indicates a successfully performed regeneration. This enables for reuse the same zeolite layer in a new service cycle, which is extremely important for practical application.