This study focuses on using spodumene flotation tailings (SFT) to prepare phosphoric acid-activated metakaolin geopolymer, in which the replacement of metakaolin (MK) by a high percentage (up to 75 wt.%) of tailings was achieved. The compressive strength of geopolymer mortar was significantly improved with SFT as aggregates. In addition, the mechanical properties could also be enhanced by an increased concentration of phosphoric acid (H3PO4) solution or a decreased aggregate particle size. The optimized geopolymer mortar composite was SFT:MK = 3:1, which was activated by H3PO4 solution with a concentration of 51 vol%, followed by curing at 55 °C for 24 h. On the other hand, properties of the geopolymer mortar could also be affected by the morphology of the aggregates. For example, SFT as aggregates could produce more interconnected pores compared to standard sand. The major chemical structural units of geopolymer mortar were -P-O-Al- and AlPO4, which could be spontaneously generated according to the thermodynamic calculation results. Finally, many aluminum ions and a small amount of silicon ions could be leached from the tailings under acidic conditions.
The aim of the study was to compare the effects and mechanism of tetrasodium pyrophosphate (TSPP) and sodium tripolyphosphate (STPP) as dispersants on the selective flotation of arsenopyrite from muscovite. The results of single-mineral flotation showed that the recovery of arsenopyrite was 81.4% when no dispersant was added. The recovery of arsenopyrite slightly decreased with increasing dosage of TSPP. When the dosage of STPP was 6 × 10−5 mol/L, the recovery of arsenopyrite was only 28.6%. Neither of the dispersants had significant influence on the muscovite flotation (<10%). However, in a mixed-mineral system, the recovery of arsenopyrite dropped significantly, and then under the action of dispersants, its recovery back up. The RPM results showed that the dispersion effect of TSPP was superior to that of STPP. The electrokinetic potential showed that the potential change value of muscovite with TSPP was −17.37 mV, while that of muscovite with STPP was −8.33 mV (pH = 8). The adsorption of TSPP onto muscovite was stronger than that of STPP. FTIR and XPS analysis confirmed that dispersants exhibited chemical adsorption with the Al atoms on muscovite and that dispersant STPP exhibited stonger adsorption than TSPP on arsenopyrite, which was consistent with flotation experiments.
To enhance the sorption efficacy of attapulgite for heavy metals, mercapto-functionalized attapulgite (ATP-SH) was synthesized with mercaptan functional groups. When the mass-to-volume ratio of calcined attapulgite (ATP-C) to 3-Mercapropyltrimethoxysilane (MPTMS) was 1 g:0.5 mL (ATP-SH-0.5) and the pH was set to 8, a strong adsorption capacity for Cd (II) and Pb (II) was demonstrated. This indicates excellent adsorption performance for these heavy metals. ATP-SH-0.5 exhibited a maximum adsorption capacity of 43.81 mg/g and 274.83 mg/g for Cd (II) and Pb (II), respectively, in a single ion system. In a binary ion system, the maximum adsorption capacity was 31.86 mg/L and 254.45 mg/L for Cd (II) and Pb (II), respectively. Various characterizations and experiments showed that the adsorption of Cd (II) and Pb (II) onto ATP-SH-0.5 involves ion exchange reactions involving hydroxyl and thiol functional group complexation reactions. This adsorption process follows a single-molecule layer adsorption mechanism. XPS results indicate that hydroxyl and grafted thiol functional groups on the surface of mercapto-functionalized attapulgite participated in surface complexation reactions with Cd (II) and Pb (II), resulting in the formation of Cd-S and Pb-S species. Overall, this study provides a promising mercapto-functionalized modification material for the remediation of polluted water and soil.
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