If inadequate the disposal of mining tailings can cause serious environmental problems. The mining tailings reuse is an alternative solution capable of minimizing the environmental impacts of mining activity and its production process, due to the tailings volume reduction and the financial benefits generated by the sale of these materials as by-product and raw material for different industrial sectors. This research aims the use of copper tailings from Sequeirinho flotation plant, Sossego mine, situated in the Carajás Mineral Province (CMP), southeast of Pará, as starting material on Layered Double Hydroxides (LDHs ) synthesis. LDHs are natural or synthetic anionic clays containing structures formed by the octahedral stacking layers positively charged containing di- and trivalent cations in their interior and hydroxyl inside the vertices, with water and anions occupying the interlayer domain. They are represented by the formula: M2+1-xM3+x(OH)2An-x/n • yH2O where M2+ represents a divalent cation, M3 + a trivalent cation and An- an anion intercalated with n- charge. 24LDHs synthesis experiments were performed by co-precipitation method. As starting material, has been used the Sequeirinho flotation plant tailings. The characterization of LDHs was made by X ray diffraction (XRD), thermal analysis (DTA-TGA), infrared spectroscopy (IR) and scanning electron microscopy (SEM). Initially, 4 syntheses were made with different molar ratios Mg2+/(Mg2++Fe 3+). These experiments had as pre-set variables: 4h dripping time, pH 14, vigorous agitation and hydrothermal treatment period of 5 days at 80°C. As result, there was the formation of Iowaite Mg4Fe(OH)8OCl • xH2O), Nitratine (NaNO3) and Brucite (Mg(OH)2). For the 20 remaining syntheses, magnesium nitrate was replaced by magnesium chloride. The pre-set variables were the same as the previous experiments, except for the hydrothermal treatment period (15 days). It was adopted the 4 molar ratios used in the initial experiments. For each ratio, 5 syntheses were made each one with a different pH value (10, 11, 12, 13 and 14). The result was the formation of Pyroaurite (Mg6Fe2CO3(OH)16 • 4H2O). The majority of the results presented the following paragenesis: Pyroaurite and Calcite. The new compounds X ray diffraction characterization allowed to calculate: the basal spacing values (d003 = 7.62-7.94 Å); a = b (between 3.0797 and 3.1042 Å) and c parameter values (between 22.86 and 23.82 Å); and the thickness of the interlayer spacing (2.82 - 3.14 Å).The synthesis pH is directly proportional to the structural planning. This information was confirmed by SEM micrographs in which was also possible to observe the increase on the crystallites size as the pH becomes more alcaline. The synthesized pyroaurite thermal decomposition occurs in 4 stages: in the first and second stages (25-101° C and 101-197ºC) occur the loss of adsorbed water and the elimination of intercalation of water, respectively. Subsequently, there is the decarbonation (333-357°C), followed by dehydroxylation (378-395°C).The LDHs intercalated anion was determined by IR and it corresponds to carbonate (1363-1377cm-1 and 2339-2362 cm-1).
|
