Mineralogical and geochemical properties of bauxite in the Oklaj area

Cilj diplomskog rada je odrediti mineraloški i kemijski sastav boksita te podinskih i krovinskih naslaga s dva lokaliteta na području Oklaja. Poseban naglasak je stavljen na udio elemenata u tragovima u boksitu (uključujući elemente rijetkih zemalja - REE), te mineraloške faze uz koje su navedeni elementi vezani. Prikupljeno je sedam uzoraka boksita i dva uzorka vapnenaca. Uzorci boksita su analizirani u izvornom obliku, te nakon otapanja u zlatotopci. Mineralni sastav analiziranih uzoraka je utvrđen difrakcijom rentgenskih zraka na prahu (XRPD) i polarizacijskom mikroskopijom, a kemijski sastav metodom masene spektrometrije s induktivno spregnutom plazmom (ICP-MS). Struktura uzoraka boksita je glinovita/afanitna osim uzorka TOS-1-G u kojem je oolitična. Glavni minerali boksita su gibbsit, böhmit, hematit, goethit i kvarc. Kao akcesorni mineral se pojavljuje anatas, dok se u uzorku TOS-4 pojavljuje kaolinit (mineral glina). Nakon otapanja uzoraka u zlatotopci, identificirani su gibbsit, böhmit, kvarc, anatas i kaolinit. Udio REE, te pojedinih ostalih elemenata u tragovima (Ti) je značajno povišen u svim istraživanim uzorcima boksita. Rezultati kemijske analize nakon otapanja uzoraka pokazali su da je veći udio REE vezan na hematit i goethit, a manji na gibbsit i böhmit.The aim of this master thesis is to determine the mineralogical and chemical composition of bauxite, hanging wall and footwall deposits from two localities in the Oklaj area. Particular emphasis will be placed on the proportion of trace elements in bauxite (including rare earth elements - REE) and mineralogical phase(s) with which the mentioned elements are bounded with. Seven bauxite samples and two limestone samples were collected. All samples were analyzed untreated and after dissolving in aqua regia. The mineral composition of the analyzed samples was determined by powder X-ray diffraction (XRPD) and polarization microscopy, and chemical composition by inductively coupled plasma mass spectrometry (ICP-MS). The structure of the bauxite samples is clay/afanitic except for the TOS-1-G sample in which it is oolitic. The main bauxite minerals are gibbsite, boehmite, hematite, goethite and quartz. Anatase appears as an accessory mineral, while kaolinite (clay mineral) appears in sample TOS-4. After dissolution of the samples in aqua regia; gibbsite, boehmite, quartz, anatase and kaolinite were identified. The proportion of REE and of other trace elements (Ti) was significantly increased in all bauxite samples studied. The results of the chemical analysis after dissolution of the samples showed that a higher proportion of REE was bound to hematite and goethite and less to gibbsite and boehmite