Understanding the Deposition and Surface Interactions of Gypsum

Abstract

Using a surface forces apparatus (SFA) and an atomic force microscope (AFM), we have studied the deposition of gypsum on a silicate mineral (mica) and their surface interactions. An exponential forceÀ distance repulsion relation was obtained for two rough (gypsum) crystal surfaces with root-mean-square (rms) roughness between 4 and 200 nm on approach and separation after the initial contact. The effective surface energies were estimated as γ eff = 32.8 and 7 mJ/m 2 for gypsum surfaces with an rms roughness of ∼8 and ∼100 nm, respectively, which increase with a decrease of the rms roughness, approaching the thermodynamic value ∼48 mJ/m 2 estimated by a three-probe-liquid contact angle measurement. The repulsive force observed for rough gypsum surfaces was found to be a mainly elastic force due to asperity interactions. The surface forces measured between two silicate mineral surfaces (mica) in CaSO 4 solutions were fitted well by the DerjaguinÀLandauÀVerweyÀOverbeek (DLVO) theory at low concentrations (10 À4 À10 À2 M) but deviated at higher concentration. Our results have provided insight into the basic surface interaction mechanisms of gypsum and silicates in many mineral flotation processes and industrial operations.

Fabrication of novel phosphotungstic acid functionalized mesoporous silica composite membrane by alternative gel-casting technique

“…Fig. 10c shows the proton conductivity of MCM-41-HPW65-m membrane fabricated from slurry with solid state loading of 70 vol.% under continuous flow of distilled water on both sides of the membrane at 80 C. The measured proton conductivity of the membrane is 0.076 S cm À1 , which is comparable to the reported results [5,6,12]. The stability of the proton conductivity of PEMs is a very important factor to determine the performance stability of the fuel cells.…”

“…This indicates that the cell performance increases with increasing HPW loading in MCM-41 support. The cell performance of MCM-41-HPW65-m electrolyte fabricated by gel-casting technique is slightly lower than 115 mW cm À2 of that using VIM-67 wt.% HPW/meso-silica electrolyte made by pressing method under the same operating conditions [6]. The difference is attributed to the lower density of the membrane in this case.…”

“…The position of the scattering peaks for HPW/MCM-41 powders remains the same as that of the pristine MCM-41 without any HPW impregnated, indicating that HPW has coalesced well into the mesoporous structure of MCM-41 [5,6]. This is explained by the occurrence of the relative intensities of scattering peaks of the as-assembled HPW/MCM-41 powders, which decreased significantly with the increase of HPW content until the peak disappeared/almost disappeared [6].…”

“…Moreover, the intensity of the MCM-41-HPW powders band at around 802 cm À1 increases gradually with the HPW loading, which is much more than that of HPW band at 796 cm À1 and that of MCM-41 band at 801 cm À1 . The increased intensity of the band at w802 cm À1 with the increase in HPW loading can be attributed to the interaction between the Keggin anions of HPW and the silanols on the silica surface to form (^SiOH 2 þ ) (H 2 PW 12 O 40 À ) species [6,55,56]. Typical thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) profiles for the pristine MCM-41 powders, pure HPW powders, HPW-impregnated MCM-41 powders, and PAA are shown in Fig.…”

Combining air recharging and membrane superhydrophobicity for fouling prevention in membrane distillation

“…crystal surface free energy 47.76 [34,42] crystal-water interfacial energy 45.20 [34] crystal surface free energy due to dispersion forces 47.14 [42] surface free energy of crystals due to acid-base (polar) forces 0.62 [42] 6 (12a)…”