Distribution and mobility of arsenic and iron in soil profile at Kalinovac-Hrastova Greda, Podravina

Predmet istraživanja ovog diplomskog rada su uzorci tla s profila Kalinovac-Hrastova Greda u Podravini. Uzeto je ukupno 5 uzoraka i to na različitim dubinama profila: K–HG 1 (0–30 cm), K–HG 2 (30–60 cm), K– HG 3 (60–80 cm), K–HG 4 (80–100 cm) i K–HG 5 (100–130 cm). Cilj rada je bio odrediti raspodjelu i mobilnost arsena i željeza u istraživanom profilu tla. U tu svrhu, provedena su laboratorijska istraživanja određivanja kapaciteta kationske zamjene metodom Cu–triena, sekvencijska ekstrakcijska analiza (BCR), otapanje željezovih (oksi)hidroksida pomoću DCB–a, mineraloška analiza primjenom rendgenskog difraktometra (XRD) i određivanje veličine čestica metodom laserske difrakcije. Na temelju granulometrijskog sastava utvrđeno je da u svim uzorcima dominiraju čestice praha i pijeska, osim u zadnjem uzorku gdje dominira pijesak u odnosu na prah. Mineraloškom analizom utvrđene su pojave goethita, koje posebno dominiraju na dubinama od 60-100 cm, što odgovara dosadašnjim istraživanjima. Duž profila tla od svih uzoraka najveću koncentraciju As i Fe ima uzorak K–HG 3 koji se nalazi na dubini od 60 do 80 cm, što je povezano s oscilacijom podzemne vode (Fe2+ se precipitira u Fe3+). Iz dobivenih korelacija, utvrđeno je da je As dominanto vezan za Fe. Usporedbom koncentracija As dobivenih BCR metodom i zlatotopkom netopivog ostatka nakon DCB-a, utvrđeno je da As nije u potpunosti vezan za Fe, već je manjim djelom vezan i za rezidualnu frakciju. Usporedbom koncentracija As i Fe dobivenih ICP-MS metodom iz dosadašnjih istraživanja s BCR metodom, utvrđeno je da su veće koncentracije dobivene ICP-MS metodom. Na temelju rezultata BCR metode, utvrđeno je da nije pouzdana za određivanje distribucije Fe po frakcijama tla u uzorcima bogatim željezovim oksidima. To u ovom slučaju vrijedi i za As jer je dominantno vezan za Fe.

Study subjects of this master’s thesis were soil samples collected at Kalinovac-Hrastova Greda in the Podravina region. The total of five samples were collected at different depths in the following profiles: K–HG 1 (0–30 cm), K–HG 2 (30–60 cm), K–HG 3 (60–80 cm), K–HG 4 (80–100 cm) and K–HG 5 (100–130 cm). The goal of this master’s thesis was to determine the distribution and mobility of arsenic and iron in the soil profile. For that purpose, laboratory research was performed by means of cation exchange capacity using the Cu-trien, BCR sequential extraction procedure, dissolution of iron oxide-hydroxide by DCB, X-ray diffraction (XRD) and determination of grain size by laser diffraction. Based on granulometry composition, the predominant presence of silt and sand particles was confirmed in all the samples except the last, where sand was more dominant than silt. Occurrences of goethite, which are dominant at depths from 60 to 100 cm, were determined through mineralogical analysis and correspond to previous studies. The K–HG 3 sample, positioned 60-80 cm in depth, contains the highest concentrations of As and Fe which are correlated with underground water oscillation, when Fe2+ precipitates into Fe3+. Arsenic is dominantly connected to iron which was determined from conducted correlations. The comparison of As concentrations obtained by BCR to those obtained using the aqua regia on the insoluble residue after the DCB, proved that As is mostly linked to Fe and residual fraction in minority. The comparison of As and Fe concentrations obtained by ICP-MS from previous studies to those obtained by using the BCR method confirmed the higher concentrations of elements when measured by ICPMS. Based on results obtained with the BCR, it was assessed that the method wasn’t reliable for determination of well crystallized Fe-minerals per individual soil fractions. In our case, this also applies for As which is dominantly connected to Fe.