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The effect of polyacrylic acid on the surface properties of calcite and fluorite aiming at their selective flotation

Zhang C., Gao Z., Hu Y., Sun W., Tang H., Yin Z., He J., Guan Q., Zhu Y.

Physicochemical Problems of Mineral Processing

2018

Vol. 54, iss. 3

868--877

In this study, the polyacrylic acid (PAA) was studied as a selective depressant for calcite in the selective flotation of fluorite and calcite, and the implications of this process for the separation of fluorite ore were studied using micro-flotation tests, and the results were analyzed with Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses. The flotation tests indicated that the preferential adsorption of PAA onto calcite rather than sodium oleate (NaOl) could selectively depress the flotation of calcite, allowing its separation from fluorite at pH 7. The zeta potential of calcite became more negative with the addition of PAA rather than with NaOl. However, the characteristic features of PAA adsorption were not observed for fluorite, suggesting that NaOl preferentially adsorbed on the surface of fluorite, or that PAA could be replaced by NaOl on the fluorite surface. FT-IR and XPS analysis were utilized to obtain a better understanding of the mechanism by which PAA was more strongly adsorbed on the calcite surface than NaOl. This was revealed to occur through chemical bonding between the carboxyl group of PAA and the hydroxyl groups of the Ca species on the calcite surface, modifying the structure of the adsorbed layer. A possible adsorption mechanism, along with a postulated adsorption mode for the surface interaction between PAA and calcite, is proposed.

Mechanical Spectroscopy of Equal-Channel Angular Pressed Fe-Cr Alloys and Tungsten

Hao T., Tang H., Jiang W., Wang X., Fang Q.

Archives of Metallurgy and Materials

2015

Vol. 60, iss. 3A

2101--2106

nternal friction technique was used to investigate the microstructural stability of equal-channel angular pressed (ECAP) 9Cr1Mo steel (T91), Fe-18wt.%Cr alloy, and pure W. Several non-relaxation internal friction peaks are observed in three ECAP-strained specimens, which are related to the microstructural transition from a severely deformed state to a static recovery state of dislocations, and to recrystallized state. Along with the disappearance of the P1 peak, another relaxation internal friction peak P2 is observed during the second heating run only in Fe-18wt.%Cr alloy, and it does not disappear even during subsequent third heating run. This peak is not observed in T91 steel and W. The P2 peak is likely associated with a process of grain boundary (GB) sliding. Unlike T91, no abundant carbide precipitates distribute on GBs to pin GB and repulse GB sliding, thus, the P2 peak only occurs in Fe-18wt.%Cr alloy. It is concluded that high-temperature internal friction measurements are required to detect the grain boundary peak in pure W.

Technika tarcia wewnętrznego została użyta do zbadania stabilności mikrostruktury poddanych wyciskaniu przez kanał kątowy stali 9Cr1Mo (T91), stopu Fe-18wt%Cr, i czystego W. Zaobserwowano wiele nie-relaksacyjnych pików tarcia wewnętrznego w trzech próbkach odkształconych przez ECAP, które są związane z przejściem ze stanu silnie odkształconego do statycznego stanu zdrowienia dyslokacji, i do stanu zrekrystalizowanego. Wraz z zanikiem piku P1, tylko w przypadku stopu Fe-18wt%Cr obserwowany jest inny pik P2 relaksacji tarcia wewnętrznego podczas drugiego ogrzewania, i nie znika nawet w kolejnym trzecim etapie ogrzewania. Pik ten nie jest obserwowany w stali T91 i W. Pik P2 prawdopodobnie związany jest procesem poślizgu granicy ziaren. W przeciwieństwie do stali T91, brak bogatych w węglik wydzieleń na granicach ziaren, które by unieruchomiły granice i uniemożliwiły poślizg, stąd pik P2 występuje tylko w przypadku stopu Fe-18wt.%Cr. Stwierdzono, że pomiary tarcia wewnętrznego w wysokiej temperaturze są potrzebne, aby wykryć pik granicy ziarna w czystym W.

Enhancement of removal of organic pollutants from coking wastewater through adsorption by modified coal fly ash

Tang H., Liu G.-Z., Yan Y.-B., Gong J.-L.

Environment Protection Engineering

2012

Vol. 38, nr 3

79--95

Potential use of modified coal fly ash (MCFA) has been investigated for adsorption of organic pollutants from coking wastewater (OPs-CW). The surface morpholgy, element profile, BET specific surface area and pore size distributions of MCFA were determined. FT-IR spectrum was used to detect changes of organic functional groups in MCFA after adsorption. The results showed that when the dosage of MCFA was 2.0 g/l at pH of 6.0, 94.2% of COD removal could be achieved after 600 min of agitation at 303 K. The adsorption kinetic of OPs-CW onto MCFA was fit well to the pseudo-second order model. The intraparticle diffusion was identified not to be a sole rate limiting step, and there may also be film diffusion. Freundlich model gave a better fit to all adsorption isotherms than Langmuir. The values of Ea calculated by D-R model are approximately in the range of 8-16 kJ/mol, suggesting that chemical bonding could be more likely to be the main adsorption mechanism. Negative values of ΔG° demonstrate feasibility and spontaneous nature of the adsorptive treatment.