Qingjun Guan

Selective adsorption of tannic acid on calcite and implications for separation of fluorite minerals

Selective adsorption of tannic acid (TA) on calcite surfaces and the implications of this process for the separation of fluorite ore were studied by microflotation tests, surface adsorption experiments, zeta potential measurements, UV-vis analysis, and X-ray photoelectron spectroscopy (XPS) analysis. The microflotation tests indicated that TA, when added before sodium oleate (NaOl), could selectively depress calcite from fluorite at pH 7. Surface adsorption experiments revealed that TA hinders the interaction of NaOl with calcite. The zeta potential of calcite became more negative with TA than with NaOl. However, the characteristic features of TA adsorption were not observed on fluorite, suggesting that the dominant adsorption sites are dissimilar on the fluorite and calcite surfaces in the pulp. UV-vis spectroscopy, XPS, and solution chemistry analysis were utilized to obtain a better understanding of the mechanism for selective adsorption of TA as well as the key factors determined by the Ca2+ and Ca(OH)+ components on the mineral surfaces. A possible adsorption mechanism along with an adsorption mode is proposed for the surface interaction between TA and calcite.

Preparation of α-CaSO4·½H2O with tunable morphology from flue gas desulphurization gypsum using malic acid as modifier: A theoretical and experimental study

Huge amount of flue gas desulphurization (FGD) gypsum not only occupies the farmland but also causes severe pollution to the surrounding environment. The most effective way to achieve a high-value utilization of FGD gypsum is to prepare short columnar α-calcium sulfate hemihydrate (α-HH) since short columnar crystals show better mechanical strength than needle-like ones. Here, malic acid, a prolific, inexpensive and environment-friendly modifier was explored for the first time to effectively tune the crystal morphology of α-HH prepared from FGD gypsum in glycerol-water-NaCl solutions. When the concentration of malic acid reached 18.54 × 10-4 mol/kg, α-HH crystals with an average aspect (length-to-diameter) ratio of 1.9 (compared to 29.4 in the absence of malic acid) were prepared. The selective complexation of malic acid with Ca active sites on different α-HH crystal planes played a dominant role in the α-HH crystal morphology transformation, which was then explained by the surface broken bonds theory for the first time. The broken bond number per active Ca atom (Nbper Ca) and broken bond density of Ca atoms (DbCa) on the (2 0 4) end plane were larger than those on the (0 2 0) or (2 0 0) side planes. Therefore, the (2 0 4) end plane was more reactive with organics, resulting in the preferential adsorption of malic acid on the end planes, which reduced the specific surface energy of (2 0 4) and led to an increased exposure of this plane and a decreased exposure of (0 2 0) or (2 0 0) side planes in the final α-HH crystals. Consequently, using malic acid as modifier, the α-HH crystal gradually transformed from a needle-like shape to a short columnar one. This work provided important insights into and perspectives for the selection of crystal modifiers and explanation of the mechanism during the preparation of calcium-containing crystals with controllable morphology.

Synthesis of α-CaSO4·0.5H2O from flue gas desulfurization gypsum regulated by C4H4O4Na2·6H2O and NaCl in glycerol-water solution

A brand new method to transform flue gas desulfurization gypsum (FGD gypsum) into α-calcium sulfate hemihydrate (α-HH) with short hexagonal prisms mediated by succinic acid disodium salt hexahydrate (C4H4O4Na2·6H2O) and NaCl in glycerol-water solution is studied, in which the appropriate reaction temperature is 90 °C. The addition of NaCl facilitates the dissolution of calcium sulfate dihydrate (DH) and creates much higher supersaturation which is a greater driving force for the phase transformation from DH to α-HH. C4H4O4Na2·6H2O as the crystal modifier effectively suppresses the α-HH crystal growth along the c axis, and the products generally change from needle-like particles to fat and short hexagonal prisms, which is attributed to the preferential adsorption of C4H4O42− on the top facets of the crystals by chelating Ca2+.

Depressing behaviors and mechanism of disodium bis (carboxymethyl) trithiocarbonate on separation of chalcopyrite and molybdenite

Abstract This work focuses on the organic depressant, disodium bis(carboxymethyl) trithiocarbonate (DBT), as a selective depressant in copper-molybdenum sulfide flotation separation. Micro-flotation, Zeta potential, FTIR and XPS measurements were carried out to investigate the selective depression mechanism of DBT on chalcopyrite. Zeta potential and FTIR measurements revealed that DBT had higher affinity for chalcopyrite than molybdenite and the XPS results of chalcopyrite before and after treatment with DBT further proved that DBT adsorbed on chalcopyrite surface. The investigation indicates that the mechanism of DBT adsorbing on chalcopyrite is mainly physical adsorption. Locked circuit experiments were carried out and the results showed that DBT could be considered as a cleaner option in commercial Cu-Mo flotation separation circuits.

Efficient utilisation of flue gas desulfurization gypsum as a potential material for fluoride removal

This study introduces the use of a waste by-product from wet limestone flue gas desulfurization as a potential material for fluoride removal. Systematic laboratory-scale experiments were tested to identify the fluoride removal performance and determine the underlying mechanism. Flue gas desulfurization (FGD) gypsum removes 93.31% of fluoride from 109 mg/L to 7.3 mg/L. Fluoride can be efficiently removed at the optimum pH range of 5-11. Kinetics analysis indicates that the theoretical fluoride capacity at 1 g/L FGD gypsum is 96.9 mg/g. Equilibrium speciation analysis indicates that the decrease of system pH to lower than 5 is unsuitable for the formation of calcium fluoride, and the increase of system pH to higher than 11 opposes calcium release from FGD gypsum. Thermodynamic analysis confirms the feasibility of converting calcium sulphate into calcium fluoride at pH > 5. FGD gypsum and precipitates were characterized to describe their surface morphology, elemental composition and crystalline phase. Results indicate that FGD gypsum removes fluoride through the combination of calcium with fluoride to generate calcium fluoride.

A facile method of transforming FGD gypsum to α-CaSO 4 ·0.5H 2 O whiskers with cetyltrimethylammonium bromide (CTAB) and KCl in glycerol-water solution

A facile method to transform flue gas desulfurization gypsum (FGD gypsum) to α- calcium sulfate hemihydrate (α-HH) whiskers with high aspect ratios mediated by cetyltrimethylammonium bromide (CTAB) and KCl in glycerol-water solutions was studied. Addition of KCl facilitated the dissolution of calcium sulfate dihydrate (DH) and created a much higher supersaturation, which could come into being a larger driving force for the phase transformation from DH to α-HH. CTAB as the crystal modifier can significantly promoted 1-D growth of α-HH whiskers along the c axis and the presence of 0.25% CTAB (by weight of FGD gypsum) resulted in the increase of the average aspect ratio of α-HH whiskers from 28.9 to 188.4, which might be attributed to the preferential adsorption of C16H33(CH3)3N+ on the negative side facets of α-HH crystal.