The effect of hydrofluoric acid (HF) pretreatment on flotation of feldspar and quartz using dodecylamine (DDA) as collector was investigated by micro-flotation, zeta potential, pyrene fluorescence spectroscopy, attenuated total reflection flourier transformed infrared spectroscopy (ATR-FTIR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and bench scale flotation. The micro-flotation tests revealed that there was little difference in the flotation of feldspar and quartz at pH 2, using H₂SO₄ as pH regulator. After HF pretreatment, the floatability of feldspar significantly increased while the floatability of quartz showed no change. HF pretreatment resulted in leaching of SiO₂ and enrichment of Na, K and Al on the feldspar surface. Consequently, the negative surface charge of feldspar increased at pH 2, which allowed for the flotation separation of the feasible minerals. This took place via an increased electrostatic adsorption between DDA and Na, K, Al on the feldspar surface, which effectively increased its hydrophobicity and as a result, improved the floatability of feldspar. An alternative process which exhibited effective separation of quartz and feldspar while recycling the tailwater from the flotation was proposed.

The flotation behaviors of perovskite, titanaugite, and magnesium aluminate spinel (MA-spinel), using octyl hydroxamic acid (OHA) as the collector, were investigated using microflotation experiments, zeta-potential measurements, Fourier transform infrared (FT-IR) analyses, X-ray photoelectron spectroscopy (XPS) analyses, and flotation experiments on artificially mixed minerals. The microflotation experiments show that the floatability of perovskite is clearly better than titanaugite and MA-spinel at around pH 5.5, while titanaugite possesses certain floatability at pH 6.0–6.5, and MA-spinel displays good floatability at pH > 8.0. The results of the FT-IR and XPS analyses show that OHA mainly interacts with Ti, resulting in perovskite flotation, and that the Al on titanaugite, as well as the Mg and Al on the MA-spinel surface, chemically react with OHA under acidic conditions. However, OHA mainly reacts with the Ti and Ca on the perovskite surface, Ca and Mg on the titanaugite surface, and Mg and Al on the MA-spinel surface under alkaline conditions. The results of the artificially mixed mineral flotation experiment show that the concentrate of TiO₂ grade increased from 19.73% to 30.18% at pH 5.4, which indicates that a weakly acidic solution is the appropriate condition for the flotation separation of perovskite from titanaugite and MA-spinel. The results of the modified slag flotation experiments show that the TiO₂ grade of concentrate increased from 18.13% to 23.88% at pH 5.4, through the open circuit test of “one roughing and one cleaning”. OHA displays selectivity toward perovskite in the modified slag flotation, but the consumption of H₂SO₄ is very high. The CaSO₄ precipitate covered on the mineral surfaces results in poor TiO₂ grade and recovery.

Carbon@REC nanocomposite (C@REC) was synthesized by a hydrothermal carbonization process, and characterized by XRD, Fourier transform infrared spectroscopy, thermal gravimetric analysis, SEM, nitrogen adsorption–desorption measurements, and zeta potential analysis. The adsorption property of the C@REC was investigated as a function of pH of solution, adsorbent dosage, contact time, and initial concentration of MB and NR. The results suggest that amorphous carbon supported on the surface of rectorite. The adsorption experiment showed that adsorption kinetics of MB and NR onto the followed the pseudo-second-order kinetic model. The adsorption isotherm data were fitted well to the Langmuir isotherm. The adsorption capacities for the removal of MB and NR on the C@REC determined using the Langmuir equation were 15.68 and 20.30 mg g⁻¹, respectively.

Current research aims to investigate the influence of calcination temperature on the pozzolanic activity of the waste kaolin and the impact of calcination products on Portland cement hydration. The raw material with approximately 85 % kaolinite was calcined to temperatures ranging between 500 and 1000 °C. The clay and its calcined products were characterized by TGA-DTA, SEM-EDS, XRD, FT-IR and BET. The pozzolanic activity of the calcined products was assessed by electrical conductivity test and compressive strength in mortars with 30 % substitution of Portland cement. The effect of calcined products on Portland cement hydration was characterized by XRD and SEM. The results showed that the calcination temperature had an important influence on mineral phase transition and the pozzolanic activity of calcined products. The degree of disorder and pozzolanic activity of calcined products at 800 °C was the highest at temperatures ranging from 500 and 1000 °C. The impact of calcined products on the hydration of blended systems was a combination of a filler effect at early ages and the pozzolanic reaction at later. The experimental results indicated that calcined products of waste kaolin constituted a potential source of high reactivity pozzolanic materials. DOI: http://dx.doi.org/10.5755/j01.ms.24.2.18192