Proučavanje tretmana, fizičko-hemijskih svojstava crvenog mulja i parametara sorpcije na efikasnost uklanjanja jona nikla iz vodenih rastvora

This dissertation investigated possibilities of using red mud from alumina factory “Biraţ” (Zvornik, North-East Bosnia and Herzegovina), for uptake of nickel ions from aqueous solution, in batch conditions. For this purpose, sorption efficiency was examined as a function of red mud treatment conditions and sorption parameters (pH, sorbent dose, contact time, initial sorbate concentration), as well as the presence of coexisting ions. The stability of the loaded sorbents was studied in different leaching solutions. Chemical and instrumental analyses have shown that investigated red mud (BRM) was of heterogeneous composition, with low surface area and high alkalinity. By chemical composition, investigated red mud was a mixture of oxides of iron, aluminum, silicon and titan, where the major component was iron oxide. The main crystalline phases were found to be: hematite (Fe2O3), gibbsite and bayerite (Al(OH)3), sodalite (Na8Si6Al6O24Cl2), quartz (SiO2), anatase and rutile (TiO2), as well as calcite (CaCO3). The presence of hydroxyl, carbonate, Si(Al)–O and Fe–O groups on the surface of the sorbent, play an important role in metal ion binding. In order to obtain more efficient and environmentally benign sorbents, rinsing, thermal and acid treatments were applied. By rinsing the raw red mud, a sorbent (RBRM), with the same mineral compositions, but lower pH and the point of zero charge (pHPZC), was obtained. Thermal and acid treatments, depending on heating temperature and acid concentration, caused physical and chemical changes important for the sorption. The most significant changes provoked by the thermal treatments are: decomposition of gibbsite, bayerite and calcite and structure destruction and transformations of sodalite. pHPZC of rinsed mud heated at 600 °C (RBRM600) is significantly higher than the value of starting RBRM and approaches the value of the raw sample. In acid treatments, the increase of the acid concentration led to a loss of sodalite and calcite, an