Evaluation of the natural zeolite as filler in permeable reactive barriers for remediation of groundwater polluted by cadmium and zinc : master thesis

Ispitana je mogućnost primjene prirodnog zeolita klinoptilolita kao punila u propusnim reaktivnim barijerama (PRB) za zaštitu podzemnih voda od onečišćenja teškim metalima. Za simuliranje dinamičkih uvjeta u podzemlju provedeni su eksperimenti u koloni na nepomičnom sloju prirodnog zeolita klinoptilolita propuštanjem binarne vodene otopine kadmija i cinka od vrha prema dnu kolone pri protocima od 1, 2, 3 i 4 mL/min. Iz dobivenih eksperimentalnih rezultata izračunati su koeficijent raspodjele (K d ) i koeficijent zadržavanja (R d ), kako bi se procijenio potencijal zeolita za sorpciju i zadržavanje kadmija i cinka u barijeri. Također su izračunati hidrodinamički koeficijent disperzije (D L ) i hidrodinamički disperzijski koeficijent zadržavanja (D LR ) u svrhu procjene utjecaja hidrodinamičke disperzije na širenje onečišćenja u podzemnoj vodi i zaobilaženje postavljenje barijere. Za sve ispitane protoke dobivene su veće vrijednosti K d i R d za kadmij nego za cink što upućuje na bolju raspodjelu i zadržavanje kadmija u sloju zeolita. Razlog tome je njegov manji hidratizirani ionski radijus u odnosu na cink, što mu omogućuje bolju pokretljivost, a time i vezanje na slobodna aktivna mjesta na zeolitu. Povećanjem protoka manja je razlika između K d i R d za kadmij i cink jer je uslijed kraćeg vremena kontakta kompeticijski efekt između kadmija i cinka manje izražen. Vrijednosti D L i D LR za oba iona rastu porastom protoka, povećavajući njihovo širenje u poroznom mediju uslijed hidrodinamičke disperzije, što u konačnici može dovesti do zaobilaženja postavljene barijere. Najbolja raspodjela i zadržavanje iona u zeolitnoj barijeri uz njihovo minimalno širenje postignuta je za najmanji protok otopine od 1 mL/min (0,01277 m/min) koji je od svih ispitanih protoka najbliži prosječnom protoku podzemne vode (≈ 0,00003 m/min). Dobiveni rezultati ukazuju na mogućnost primjene prirodnog zeolita klinoptilolita kao punila u propusnim reaktivnim barijerama u svrhu zaštite podzemnih voda od onečišćenja teškim metalima.The possible application of natural zeolite clinoptilolite as filler in permeable reactive barriers (PRBs) for protection of groundwater from contamination by heavy metals were investigated. For simulation of underground dynamic conditions for the column experiments on the fixed natural zeolite layer were performed by passing the binary aqueous solution of cadmium and zinc through the column by down-flow mode at flow rates of 1, 2, 3 and 4 mL/min. From the obtained column results the distribution coefficient (K d ) and retardation coefficients (R d ) were calculated in order to estimate the zeolite potential in sorption and retardation of cadmium and zinc in the barrier. The hydrodynamic dispersion coefficient (D L ) and hydrodynamic dispersion retardation coefficient (D LR ) were calculated as well in order to estimate the impact of the hydrodynamic dispersion on the contaminant plume and possible bypassing of the barrier. For all flow rates tested, the highest values of K d and R d were obtained for cadmium compared to zinc, pointing on better distribution and retardation od cadmium in zeolite layer. The reason for that is smaller hydrated ionic radius of cadmium than zinc, making it more mobile, and thus easier to bind on free active zeolite sites. With increasing in flow rate the difference between the K d and R d of cadmium and zinc is lower due to the shorter contact time at which to competition effect is less pronounced. The D L and D LR values for both ions increase with increasing in flow rate, thus increasing their spreading in the porous media caused by hydrodynamic dispersion, which at the end leads to bypassing of the barrier. The best distribution and immobilization of the ions inside the zeolite barrier, alongside their minimum spreading is achieved for the lowest flow rate of 1 mL/min (0.01277 m/min) which, among all tested flow rates, is the closest to the average flow of the groundwater (≈ 0.000003 m/min). The obtained results pointing on possible application of the natural zeolite clinoptilolite as filler in permeable reactive barriers for protection of groundwater from heavy metals pollution